OceanObs'09 - Additional Contributions

 
Session: Satellite (04B)


Sentinel-3 Surface Topography Mission System Performance Simulator and Ground Prototype Processor and Expertise
Amarouche, Laiba1; Dumont, Jean-Paul1; Obligis, Estelle1; Valette, Jean-Jacques1; Philippe, Sicart1; Blusson, Annick1; Soulat, Francois1; Thibaut, Pierre1; Tran, Ngan1; Denneulin, Marie-Laure1; Jourdain, Sylvain1; Houpert, Alexandre2; Mavrocordatos, Constantin3; Seitz, Bernd3; Zanifé, Ouan Zan1
1CLS, FRANCE;
2Thales Alenia Space, FRANCE;
3ESA/ESTEC, NETHERLANDS

Sentinel-3 is an Earth Observation Mission in the frame of GMES which launch is expected for the end of 2012. Its payload includes the following instruments:

  • A Ocean and Land Colour (OLCI) instrument,
  • A Sea and Land Surface Temperature (SLSTR) instrument,
  • A SAR Radar Altimeter (SRAL) instrument,
  • A Microwave Radiometer (MWR) instrument,
  • A Global Navigation Satellite System (GNSS) receiver.

    The set of the 3 instruments, SRAL, MWR and GNSS constitute the so-called Surface Topography payload.

    In the frame of the development of the first Sentinel-3 satellite, System Performance Simulator (SPS) and Ground Processors Prototype (GPP) are to be built for each instrument of the topography mission. This activity is performed by CLS under Thales Alenia Space contract for ESA (end customer). The objectives of these simulators/processors are the following:

  • Support the development and the validation of the operational level 0, level 1b processor;
  • Support the development of the instruments.
  • Evaluate along the development program the end-to-end mission performances
  • Support during the In Orbit Commissioning phase To reach these objectives, the two simulators/processors are identified as follows:
  • The Ground Prototype Processors (GPP) which will include the level 0, level 1b processing and will help satisfying the above first objective
  • The System Performance Simulators (SPS) which include the GPP as well as other modules. It will help satisfying the last two objectives by generating geophysical representative Mission data products. It will require a simplified level 2 processing.

    The usage of the STM SPS and GPP will evolve in time. At the beginning of their life, they will be used to establish the performances baseline. Then along the development of the instruments they will be used to check the instruments conformance to the expected products performances. In parallel they will be used to support the ground processing development. Once the instruments integrated to the platform, they will be used to check the correctness of the integration. Finally once the satellite in orbit, they will be used as a support for the performance assessment.

    The SPS aims at simulating the end to end Surface Topography Mission , from scene simulation, through satellite and instruments behavior , and up to the ground processing system. It will be used for checking the Satellite or Instrument parameters (monitoring the instrument design and effect of characterisation data), and for analysing the overall Satellite and Sentinel-3 Surface Topography Mission Instruments compliance to the products performance requirements, at L1b level and simplified Level 2 processors.

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    Sentinel-3 Surface Topography Mission Products and Algorithms Definition
    Amarouche, Laiba1; Soulat, Francois1; Sicart, Philippe1; Labroue, Sylvie1; Baker, Steve2; Zelli, Carlo3; Femenias, Pierre4; Picot, Nicolas5; Dumont, Jean-Paul1
    1CLS, FRANCE;
    2UCL/MSSL, UNITED KINGDOM;
    3ACS, ITALY;
    4ESA/ESRIN, ITALY;
    5CNES, FRANCE

    GMES is an ambitious program developed by ESA and European Union which will allow Europe to get autonomous and independent access to geo-spatial information services.

    It will be composed of satellites and in situ measurement facilities, core services and downstream services. In this framework the Sentinel-3 mission is devoted to provide ocean information products.

    For that, the payload has been designed to fulfill three objectives:

  • the topography mission through combination of altimeter, radiometer and POD measurement,
  • the ocean color and land cover mission,
  • the sea surface temperature mission.

    This payload takes benefit from the heritage of past and on-going ESA missions, namely ERS1-2 and ENVISAT. As far as the topography mission is concerned it will also take benefit from the CRYOSAT development allowing to enhance the altimeter performances through use of delay Doppler technique. The payload will also benefit from new features, a GPS POD receiver will be used, the POD system will be coupled to the altimeter to get a better tracking of all surfaces and the radiometer will also include new developments.

    The purpose of the project presented here is to define and develop the mission level 2 products and associated processing algorithms for the Topography Mission. Thanks to the orbit selection and topography payload design the Sentinel-3 mission will provide valuable information over multiple areas:

  • Open and coastal ocean,
  • Sea ice and glaciers,
  • Inland waters.

    This will give to these measurements a key role to fulfill various GMES objectives. Three types of products will be processed and distributed to meet the requirements all users operational requirements:

  • The Near Real Time product will be mainly dedicated to meteorological analysis and forecast centers needs.
  • The Slow Time Critical product will be mainly dedicated to ocean analysis and forecast centers needs.
  • The Non Time Critical product will be mainly dedicated to off line analysis and climatology.

    These products will meet specifications defining error budget, latency, etc. and CalVal processes will monitor their quality.

    The main tasks that are performed in the framework of the project are:

  • Level 2 products design to fulfill users needs.
  • Algorithms design necessary to process these products from level 1b products, satisfying error budgets.
  • Reference processor development that will implement these algorithms and will be used to verify the performances and provide TDS, this processor will also be used to support the ground system development.

    To realize this work our consortium gathers key actors, CLS, MSSL, ACS and CNES having recognized experience in this area and which cover all the expertise needed. More precisely:

  • CLS provides its expertise in altimetry processing over open ocean, coastal zone and hydrology and its expertise in CalVal and level 3/4 processing.
  • MSSL provides its expertise in altimetry processing over ice, sea ice, its expertise in SAR altimeter processing and CalVal.
  • ACS provides its experience in the development of CRYOSAT processing and its knowledge of GAMME environment.
  • CNES provides its global experience in altimetry and its expertise in POD processing using multiple techniques, DORIS, GPS, laser through its involvement in TOPEX/POSEIDON, ENVISAT, Jason among other missions.
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    THE LUCINDA JETTY COASTAL OBSERVATORY’S ROLE IN OCEAN COLOUR CALIBRATION AND VALIDATION FOR COASTAL WATERS
    Brando, Vittorio1; Dekker, AG1; Daniel, P1; Keen, R1; Hawdon, A1; Allen, S2; Steven, A1; Schroeder, T1; Park, YJ1; Clementson, L2; Mitchell, R2
    1CSIRO Land & Water, AUSTRALIA;
    2CSIRO Marine & Atmospheric Research, AUSTRALIA

    As part of the Australian National Mooring Network 9ANMN) of the Integrated Marine Observing System (IMOS), the Facility Satellite Ocean Colour calibration and validation aims to provide valuable data in coastal waters to unravel the inaccuracies in remotely-sensed satellite ocean colour products due to the optical complexity in coastal waters and the overlying atmosphere. The Lucinda Jetty Coastal Observatory (LJCO) is the first of the site of the Satellite Ocean Colour calibration and validation IMOS-ANMN Facility. LJCO aims to become a major source of measurements in the Great Barrier Reef for the validation of coastal-ocean colour radiometric products by increasing the number of satellite vs. in situ match-ups assessment of normalized water-leaving radiances, water inherent optical properties and aerosol optical properties. LJCO will merge two different data streams: above water measurements of the water radiance and in water measurement of the optical properties. An autonomous above-water radiometer (CIMEL-SeaPRISM) will perform marine radiometric measurements for determining water leaving radiance in addition to the regular atmospheric data for retrieving aerosol optical properties. An in situ instrument package representing the state-of the art of underwater optical instruments will be deployed to characterize the optical properties of these complex coastal waters. The instruments will be commissioned in May June 2009. Preliminary results for LJCO will be presented.

     
    The Wavemill Concept for Direct Measurement of 2D Ocean Surface Currents
    Buck, Christopher1; Marquez, José2; Lancashire, David3; Richards, Byron3; Caparrini, M2
    1ESA/ESTEC, NETHERLANDS;
    2Starlab, SPAIN;
    3EADS Astrium, UNITED KINGDOM

    Wavemill is a variation on the Wide-Swath Ocean Altimetry concept. As such, tt uses pairs of antennas separated in the across-track direction to form interferogrammes and hence derive the sea-surface topography to both the left and right of the sub-satellite track. However, there the similarity with WSOA ends since the beams of Wavemill are squinted fore and aft by up to 45 degrees, the incidence angle is around 20-30 degrees and in addition to the across-track baseline, there is also an along-track baseline between the antennas. In this way it is possible to measure directly, by means of along-track interferometry, the current velocities on the surface of the ocean in orthogonal directions (line-of-sight of the antenna beams) so that a 2D map of these currents can be formed. Furthermore, the Wavemill concept includes the capability for self-calibration with respect to attitude and baseline errors which in the past have been seen as a major obstacle to the conventional WSOA-type instrument.

    This paper looks at the properties and possibilities of the Wavemill concept and reports on on-going work to determine its performance in terms of accuracy - resolution, height, current velocity and current direction. It also looks at the possible applications such as separating surface from geostrophic currents and its suitability for monitoring coastal waters.

     
    CTOH REGIONAL ALTIMETRY PRODUCTS: EXAMPLES OF APPLICATIONS
    Cancet, M.1; Birol, F.1; Roblou, L.1; Langlais, C.2; Guihou, K.2; Bouffard, J.3; Dussurget, R.4; Morrow, R.1; Lyard, F.4
    1LEGOS/CTOH, FRANCE;
    2CSIRO/UTAS, AUSTRALIA;
    3IMEDEA, SPAIN;
    4LEGOS, FRANCE

    The Centre for Topographic studies of the Oceans and Hydrosphere (CTOH) is a French Observation Service dedicated to satellite altimetry studies. Its objectives are to 1) maintain and distribute homogeneous altimetric databases for applications over the oceans, the hydrosphere and cryosphere, 2) help scientific users develop new altimetry derived products and 3) contribute to the development and validation of new processing approaches of the altimetric data in emerging research domains. For some years, a dedicated data processing system has been developed by the MAP (Margins Altimetry Project) community to recover information from altimetry over marginal seas: the X-Track software. Starting from classical Geophysical Data Records (GDR) products, it incorporates the latest corrections available in the CTOH database, the editing strategy has been re-defined to recover a maximum of useful information, a variable sampling rate processing is available (1Hz to 20 Hz), inversion algorithms have then been added for estimating a high resolution mean sea surface directly from the improved altimeter data and the post processing step is based on user defined criteria. When available, regional high-frequency models of tides and atmospheric loading are also applied. The result is a processing tool which can be easily tuned to respond to particular applications. After a validation stage in different experimental regions, the X-Track software is now routinely operated by the CTOH for coastal applications. 1Hz or higher frequency along-track data from different altimetric missions are reprocessed on a regional basis. Once they are validated, these data are made freely available through the CTOH website: http://www.legos.obs-mip.fr/en/observations/ctoh/. They have already been used for various scientific applications (eg coastal and shelf ocean dynamics, model validation, data assimilation, regional variations of long term trend, ) in different areas: in the Mediterranean Sea, the southwest and southeast Pacific, northern Indian Ocean, Gulf of Biscay, Great Australian Bight. Besides technical difficulties in recovering the oceanic signal near the coasts, the question of how to interpret sea level anomalies observations in terms of coastal processes is still open. Here, we start to address this issue through examples of different applications.

     
    Performance Estimation of Recent Tide Models Using Altimetry and Tide Gauges Measurements
    Carrere, L.1; Legeais, JF.1; Bronner, E.2
    1CLS, FRANCE;
    2CNES, FRANCE

    Thanks to its current accuracy and maturity, altimetry is considered as a fully operational observing system dedicated to various applications such as climate studies. Altimeter measurements are corrected from several geophysical parameters in order to isolate the oceanic variability and the tide correction is one of the most important.

    Global tide models GOT00v2 and FES 2004 are commonly used as a reference for tide correction in the altimetry products (GDR). GOT00v2 is an empirical model based on altimeter data, while FES 2004 is a finite elements hydrodynamic model which assimilates altimeter and in situ data. The accuracy of both models in open ocean is centimetric but significant errors remains in shallow waters and in polar regions, due to the omission of compound tides and to sea ice effects on data respectively.

    New global models are now available (GOT4.7, EOT08a). We use multi-mission (Topex-Poseidon, Jason-1 and EnviSat) altimetric analysis of Sea Surface Height (SSH) differences at crossovers, sea level anomalies (SLA) and in-situ measurements (tide gauges from several databases) to determine and compare their performances. First analysis shows that GOT4.7 improves GOT00v2 in polar and coastal areas but is worse in Hudson Bay and Bering Strait due to seasonal ice coverage. Tide gauge time series constitute local references and comparison to altimetric SSH reveals a decrease of the SSH variance of 4 cm2 when using GOT4.7 model instead of GOT00v2. EOT08a model also allows reducing the variability in shallow water regions if compared to the reference model, even though some problems due to aliasing of S2 signal are detected in deep ocean. In the future, assimilation of data is essential to maintain good performances of models in open ocean and still improve the transition to coastal zones. In these areas, more observations are needed to improve the modelling of non linear tides and secondary waves which are characterised by respectively short wavelengths and weak amplitudes, and are thus not well resolved by actual altimetric systems. A better bathymetry is also essential to refine local modelling of tides. Moreover, the performances of global models will be improved in coastal areas thanks to the coupling with high resolution local models: nested models are being developed by several international research groups (Laboratoire dEtudes en Geophysique et Oceanographie Spatiales, Bedford Institute of Oceanography).

     
    EXPERIMENTAL COASTAL ALTIMETRY DATA FROM THE COASTALT PROJECT
    Cipollini, P.1; Coelho, H.2; Fernandes, J3; Gomez-Enri, J.4; Martin-Puig, C.5; Snaith, H. M.1; Vignudelli, S.6; Woodworth, P.7; Dinardo, S.8; Benveniste, J.9; Gommenginger, C1
    1National Oceanography Centre, Southampton, UNITED KINGDOM;
    2Hidromod, Lisbon, PORTUGAL;
    3Faculdade de Ciências, Universidade do Porto, PORTUGAL;
    4Universidad de Cádiz, SPAIN;
    5Starlab Barcelona S.L, SPAIN;
    6Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Pisa, ITALY;
    7Proudman Oceanographic Laboratory, Liverpool, UNITED KINGDOM;
    8Serco/ESRIN, Frascati, ITALY;
    9European Space Agency/ESRIN, ITALY

    Satellite altimetry over the open ocean is a mature discipline, and data are routinely assimilated for operational applications. In contrast, global altimetry data collected over the coastal ocean remain largely unexploited in the data archives, simply because intrinsic difficulties in the corrections (especially the wet tropospheric component, the high-frequency atmospheric signal and the tides) and issues of land contamination in the footprint have so far resulted in systematic flagging and rejection of these data. In the last couple of years, significant research has been carried out into overcoming these problems and extending the capabilities of current and future altimeters to the coastal zone, with the aim to integrate the altimeter-derived measurements of sea level, wind speed and significant wave height into coastal ocean observing systems. At the same time the major Space Agencies have recognized the importance of the topic and are sustaining coastal altimetry research through projects such as COASTALT (ESA), PISTACH (CNES) and some OSTST (NASA/CNES) initiatives. A number of crucial improvements to the processing of the altimetric waveforms in the coastal zone and to the correction of the measurements for path delay and geophysical effects (tides and atmospheric) are being implemented and tested. The first custom-processed coastal altimetry data are now available, and many more data from Jason-1, Jason-2 and Envisat will become available during 2009. This new coastal altimetry community, inherently interdisciplinary, has already had two well-attended international workshops (see http://www.coastalt.eu/pisaworkshop08/) and the third one is scheduled for the week before OceanObs09 (http://www.congrex.nl/09C32/ )

    In the poster we will illustrate the new experimental Envisat radar altimeter products in the coastal zone generated within the COASTALT Project, funded by the European Space Agency. COASTALT aims at defining, developing and testing a prototype software processor over a few pilot areas surrounding Europe, including the Northwestern Mediterranean, the West Britain coast and the West Coast of the Iberian Peninsula. Ultimately, the plans are for ESA to routinely generate and distribute these new Envisat coastal altimetry products globally, also in preparation for exploitation of data from the future altimetry missions, CryoSat and Sentinel-3. These missions will have inherently improved coastal zone capabilities by virtue of the adoption of a Delay-Doppler instrument.

    First we will show the architectural design and operation of the COASTALT prototype software retracker, i.e. the software processor that generates the improved coastal altimetry data. This consists of two functional units, which are both run as stand-alone applications:

  • the baseline COASTALT Processor. The processing options of the baseline processor are controlled by the user at run-time through an editable Configuration file. The baseline processor components, interfaces and data flow are shown in Figure 1. The basic functions of all the significant blocks are described below in more detail.
  • the User-defined Coastal Geophysical Corrections (UCGC) module. The UCGC module is an optional add-on for users interested in ingesting their own user-defined geophysical corrections into the COASTALT product

    Then we will briefly describe the COASTALT Envisat product generated for the coastal domain by the above processor. The product will be based on the data from the Envisat level 2 Sensor data record, as defined in the Envisat product handbook and product specification documents. Not all records from the Envisat SDR data are included in the COASTALT product instead only those data considered necessary for processing of the output data, or useful for direct comparison with the new fields, are included. The COASTALT data product uses the NetCDF (network Common Data Form) data format. The format was chosen as it is extremely flexible, self describing, platform independent and has been adopted as a de-facto standard for many operational oceanography systems. Although the latest version of NetCDF (v 4) has advantages in terms of data compression, COASTALT data will be produced in NetCDF v 3 format, to retain maximum compatibility with existing software and for simplicity of installation, as it does not require the additional HDF 5 and compression libraries.

    Finally, we will briefly recall some possible applications of the new product which are covered in a more extensive way in a OceanObs09 Community White Paper on Coastal Altimetry.

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    Ephemeral mesoscale niches of phytoplankton taxa in the global oceans
    De Monte, S.1; d'Ovidio, F.2; Alvain, S.3; Dandonneau, Y.4; Levy, M.4
    1ENS, Paris, FRANCE;
    2LOCEAN-IPSL and ISC-PIF, Paris, FRANCE;
    3LOG, Univ. de Littoral, FRANCE;
    4LOCEAN-IPSL, Paris, FRANCE

    The biogeochemical role of phytoplankton organism varies considerably from one taxon to another and the presence in an oceanic region of a specific dominant phytoplankton group can greatly affect water properties like CO2 uptake and the sustainability of zooplankton or larger predator populations. Monitoring plankton communities and understanding the mechanisms shaping their distributions is therefore crucial for issues ranging from the ocean response to climate change to fisheries management. Although the emergence of dominant planktonic groups is qualitatively explained with the paradigm 'everything is everywhere but the environment selects', understanding the spatiotemporal structure of plankton communities in any specific region is currently a challenge. Focusing on the mesoscale and submesoscale domains, here we propose to combine multisatellite data re-analysed by recently proposed techniques. This approach extracts from ocean color and altimetry high-resolution data the location of dominant groups and of transport barriers induced by mesoscale eddies. We argue that mesoscale turbulence organizes surface waters into filamentary patches of contrasted physical properties that may constitute relatively isolated 'natural mesocosms' able to support specific planktonic types. Through stirring, fluid dynamics can hence affect key ecological and evolutionary features, such as the localization of the bloom, the scales of dispersal and of competition. This mechanism may suggest how to combine future remote and in situ observational networks for better understanding the coupling between the surface turbulence and the biotic component of the global oceans.

     
    Comparing And Combining Argo Data With Altimeter And SST Data To Reconstruct 3D Thermohaline Fields
    Dhomps, A.-L.1; Guinehut, S.1; Larnicol, G.1; Le Traon, P.-Y.2
    1CLS / Space Oceanography Division, FRANCE;
    2Ifremer, Technopole de Brest-Iroise, FRANCE

    Studying the oceans vertical structure greatly depends upon the availability of ocean observations. On one hand, temperature (T) and salinity (S) profile measurements from Argo profiling floats provide sparse in-situ data, but give precise estimations of the oceans steric vertical structure every 10 days and for large part of the world ocean. On the other hand, satellite altimetry (Sea Level Anomaly, SLA) and sea surface temperature (SST) measurements provide steric and non-steric synoptic observations of the sea level every 7 days, all over the world. Both types of data are needed for climate and operational oceanography and it is necessary to distinguish steric and non-steric components in order to merge correctly altimeter and in-situ data through data assimilation techniques. The aim of the study is to merge these three dataset in order to reconstruct global instantaneous 3D thermohaline fields (ARMOR-3D) from the surface, down to a depth of 1500-m according to the method develop by Guinehut et al. (2004). The first step consists in using a linear regression method to reconstruct temperature and salinity fields from satellite altimeter and SST measurements. The accuracy of the merging is highly sensitive to the extraction of the steric component from the altimetry signal, to the climatology data used as the first guess, to the resolution of the SST and of course to the estimated errors covariances between different signals. In the second step, these reconstructed fields are combined with in-situ data using an optimal interpolation method.

    Compared to previous estimates, this study shows large improvements thanks to the Argo data set and the use of high resolution SST fields. In particular, the mesoscale structures and the deep fields are much better constrained. Relative impact of the three observing systems (SLA, SST, T/S profiles) has been quantified at global scale and shows their complementarities. ARMOR-3D fields have been used to analyse the ocean variability over the past 16 years, and keep being improved.

     
    Global maps of altimetry-derived submesoscale fronts and filaments from Lyapunov exponent calculation
    d'Ovidio, F.1; Levy, M.2; Morrow, R.3; Dussurget, R.3
    1LOCEAN-IPSL and ISC-PIF, Paris, FRANCE;
    2LOCEAN-IPSL, Paris, FRANCE;
    3LEGOS, Toulouse, FRANCE

    Submesoscale filaments are ubiquitous in high resolution observations of the ocean surface. By stirring water masses with contrasted properties, they affect a large number of biophysical processes, ranging from the vertical circulation to the structure of phytoplankton communities. Filaments are characterized by very high horizontal aspect ratio (~km for the width, ~100 km for the length) and temporal variability of the order of the day. Due to the presence of clouds obscuring remote optical sensors and to the cost of in situ surveys, filament direct observation is very sparse, and the filament dynamics at the global or even regional scale mostly unknown. In order to circumvent this observational problem, some diagnostics have been developed that try to reconstruct synoptic submesoscale information indirectly. This is achieved by identifying a mechanism able to create filaments from a resolved, global component of the ocean dynamics. The Lyapunov exponent technique exploits the mechanism of horizontal stirring, that create submesoscale tracer filament from mesoscale turbulent structures. By applying this technique to altimetry data, this technique is able to produce maps of filament location and stirring intensity at submesoscale resolution for the global oceans. In a joint collaboration between the CTOH-LEGOS in Toulouse, LOCEAN-IPSL and the Institute of Complex Systems (ISC) in Paris, we are constructing maps of Lyapunov exponents from satellite based surface velocity fields, producing filament-resolving (4-10km), daily maps. These will be obtained using AVISO altimetry-derived geostrophic velocities, and using the CTOH geostrophic and Ekman near-surface currents. This product (available for both near-real time and historical applications) will provide the first systematic, uninterrupted, global survey of the submesoscale ocean structure. Its intended applications are the design of next generation filament resolving platforms, the near real time support to campaign studies, and the study of the submesoscale ocean climate variability.

     
    Investigating Bay of Biscay mesoscale and coastal ocean dynamics from a combination of satellite and in-situ observations
    DUSSURGET, R; BIROL, F; MORROW, R
    LEGOS, FRANCE

    The dynamics of the Bay of Biscay have been intensively investigated, from both hydrographic data and numerical studies. In parallel, satellite data also give very important informations about the ocean dynamics. Optical and infrared sensors provide high spatial and temporal resolution data,but their use is significantly limited by the atmospheric conditions prevailing in the Bay of Biscay. On the other hand, satellite altimetry, which is substantially less affected by meteorological conditions, has been relatively scarcely used within the Bay of Biscay compared to other oceanic regions. One of the reasons is the aliasing of unresolved high-frequency tidal and wind induced signals corrupting measurements over shallow waters parts of the basin. Recent studies have shown that the use of state-of-the-art dealiasing models significantly improve the quality of the data in these highly dynamic regions and enable access to their dynamics.

    In this study we analyze the potential of altimetry (from both standard gridded altimetric data, and a regional altimetric product including the latest available dealiasing corrections and a specific coastal oriented processing) in conjunction with other data sets (in-situ and remote sensing data) to investigate the dynamics of the Bay of Biscay. We will focus on the ability of these different data (used in combination or separately) to detect mesoscale processes and to document their main characteristics. We will also examine closely the associated year-to-year modulation and its possible relationships with coastal dynamics and climatic conditions.

     
    Exploitation of GlobColour dataset: global characterisation of Chlorophyll, aCDM and bbp uncertainties at pixel level
    Fanton d'Andon, Odile1; Maritorena, Stephane2; Lavender, Samantha3; Antoine, David4; Morel, Andre4; Pinnock, Simon5; Mangin, Antoine1
    1ACRI-ST, FRANCE;
    2ICESS / UCSB, UNITED STATES;
    3University of Plymouth / ARGANS, UNITED KINGDOM;
    4LOV, FRANCE;
    5ESA, ITALY

    The GlobColour project has been initiated and funded by the ESA Data User Element Programme to develop a satellite based ocean colour data service to support global carbon-cycle research and operational oceanography. It aims to satisfy the scientific requirement for a long (10+ year) time-series of consistently calibrated global ocean colour information with the best possible spatial coverage. In order to cover the long time span necessary for climate monitoring purposes, the required ocean colour data set can only be built by merging together observations made with different satellite systems. To that purpose, MERIS products are merged with MODIS and SeaWiFS and a Full Data Set (FPS) covering more than 10 years of observation has been built and made available to the scientific community (www.globcolour.info ) and in particular to the key users of the project: IOCCP, IOCCG and UKMO. The GlobColour service distributes global daily, 8-day and monthly data sets at 4.6 km resolution for, chlorophyll-a concentration, normalised water-leaving radiances (412, 443, 490, 510, 531, 555 and 620 nm, 670, 681 and 709 nm), diffuse attenuation coefficient, coloured dissolved and detrital organic materials, total suspended matter or particulate backscattering coefficient, turbidity index, cloud fraction and quality indicators. New demonstration products are available online too: Photosynthetic Available Radiation, Depth of the Heated Layer, Secchi Disk Depth. Error statistics from the initial sensor characterisation are used as an input to the merging methods and propagate through the merging process to provide error estimates on the output merged products. These error estimates are a key component of GlobColour as they are invaluable to the users; particularly the modellers who need them in order to assimilate the ocean colour data into ocean simulations. The NRT service was started mid-2008, with a global daily delivery of merged MERIS and MODIS ocean colour data to primarily support operational oceanography. The GlobColour service has begun to feed in the European Community funded Marine Core Service, MyOcean, which starts to provide, in 2009, a suite of services to support Europe's decision makers. GlobColour's merged ocean colour dataset are provided by the Global Ocean Colour Thematic Assembly Centre (http://www.myocean.eu.org/repository/full_catalogue_v0.pdf) whose main objective is to bridge the gap between space agencies providing ocean colour data and Global Monitoring for Environment and Safety (GMES) marine applications. The exploitation of the GlobColour dataset gives access to the spatial and temporal variability of the Chlorophyll, aCDM and bbp uncertainties at global and regional scales. Results of this characterisation will be presented and discussed.

     
    The SLOOP Project: Preparing the Next Generation of Altimetry Products for Open Ocean
    Faugere, Yannice1; Lux, Muriel2; Bronner, Emilie3; Picot, Nicolas3; Rio, Marie-Helene1
    1CLS, FRANCE;
    2Noveltis, FRANCE;
    3CNES, FRANCE

    Since the launch of the first altimeters the accuracy of the altimetry data has continuously increased thanks to the improvement of both the technology of the instruments and the on-ground processing. These improvements allowed the apparition of various applications. About a thousand teams (in 2007) now use the altimetry products around the world for geodesy, oceanic circulation, model, wind/waves applications...

    The SLOOP project, initiated by CNES in 2008, intends to prepare the next generation of altimetry products for open ocean. This project consists in two phases. The first phase is the analysis of the users needs and the subsequent redefinition of the product content in terms of resolution way of data distribution to the final user. Secondly all the potential improvements of the altimetry processing chains will be analysed. This includes the development of new retracking algorithms, the update of geophysical corrections based on recent models and algorithms, and the computation of new reference surfaces (Mean Sea Surface, Mean Dynamic topography). A specific study will also be dedicated on the quantification of the errors of altimetry measurements.

    Improving the altimetry products requires several fields of expertise. A consortium gathering experts in most of these fields will be in charge of this project on behalf of CNES. This project is a good opportunity to have a consistent approach for the general improvement of the current altimetry processing. It is also a good opportunity to reinforce the collaboration between the altimetry product development teams and the final users, which is essential to have optimal products, suitable for all kind of applications.

     
    CP34: A Spanish Infrastructure to Provide Global Salinity and Soil Moisture Maps From SMOS Satellite Observations
    Font, J.1; Torres, F.2; Monerris, A.3
    1ICM-CSIC, SPAIN;
    2UPC, SPAIN;
    3SMOS-BEC, SPAIN

    The European Space Agencys Water Mission, the Soil Moisture and Ocean Salinity mission (SMOS) was selected in 1999 as the second Earth Explorer opportunity mission to be implemented and is expected for launch in July 2009. SMOS single payload, an interferometric microwave (L-band) radiometer, shall provide for the first time global observations of soil moisture and ocean salinity to improve our understanding of the Earths hydrological cycle.

    The SMOS Data Processing Ground Segment (DPGS) is organised to generate reconstructed images of brightness temperature from the multiple (69 elements) antenna correlations measured on board and transmitted to the ESA ground stations (primarily ESAC, near Madrid, Spain). Then these snapshot brightness temperatures are accumulated along an orbit, and the multi-angular measurements used to retrieve both geophysical variables, through an iterative adjustment based on modelling the L-band emissivity of the observed surfaces with the knowledge of auxiliary information on the environmental characteristics of both soil and ocean. The result will be strips, approximately 1000 km wide, of the spatial distribution at a resolution of 30-50 km of moisture over the continents and surface salinity over the oceans with an expected accuracy of 4% and 1 psu respectively.

    The ESA mandate is to compute and distribute these level 2 products. However, many users interested in performing large scale and climate studies are expecting global gridded maps at an improved geophysical resolution. This can be achieved by temporal and spatial averaging of the SMOS L2 products to reduce noise, and that in the case of ocean salinity can result e.g. in monthly maps at 1º spatial resolution and accuracy of the order of 0.1 psu.

    The Spanish Delegation to ESA and the National Program on Space decided to fund and implement a specific facility, the SMOS Level 3 and Level 4 Processing Centre (CP34), to offer these high level products to the international research community. CP34 has been designed and developed since 2004 and will be ready for operation at the SMOS launch. It is formed by a Production and Distribution Centre, located at ESAC close to the SMOS DPGS, and an Expert Centre in charge of the definition, algorithm development and testing, and further validation of the CP34 products. The latter is part of the SMOS Barcelona Expert Centre on Radiometric Calibration and Ocean Salinity (SMOS-BEC) installed at the Institute of Marine Sciences (Spanish Research Council, Barcelona) in cooperation with the Universitat Politècnica de Catalunya.

    This presentation is describing the different products that will be generated and openly distributed by CP34, as well as providing an overview of the SMOS-BEC activities in support of several aspects of the SMOS mission.

     
    The EUMETSAT Ocean & Sea Ice SAF (OSI SAF): Overview of the Project and its Products
    Guevel, Guenole
    Météo-France, FRANCE

    The two previous phases of the OSI SAF, the Development phase (1997-2002) and the IOP (initial Operations Phase, 2002-2007) met the main target which was to develop, validate and then produce operationally quality controlled satellite-derived products related to four key parameters (Sea Surface Temperature, Radiative Fluxes, Sea Ice, Wind) over various geographical coverage from regional to global.

    These products are currently available in near real time both through EUMETCAST and local FTP servers, and off line from local archive. Archiving at EUMETSAT central Archive (UMARF) is being implemented.

    The current phase of the OSI SAF, the CDOP (Continuous Development and Operations Phase) has taken into account new requirement sources, in particular from GODAE, GHRSST and GCOS at international level, and GMES (through MyOcean) at European level, with a strong need for increasing the temporal and geographical resolution of the products and for extending the coverage range from coastal to global.

    In terms of access to the products a new approach has been defined that can be summarized as following:

    The products are (or will be soon) accessible both:

  • via EUMETCAST and UMARF, in particular at the intention of meteorological institutional users, in GRIB (ed 2) or BUFR, over predefined areas and projections,
  • via INTERNET FTP servers, in particular at the intention of the oceanographic community, with increasing use of NETCDF, at full resolution and satellite projection, and with specific interface allowing geographical extraction, re-projection and re-gridding, etc.

    The objective of the poster is to offer an overview on the OSI SAF project and its current and future production in the time frame of the CDOP.

  •  
    The Aquarius Salinity Satellite/ In-situ Data Comparison Processing System – A Demonstration
    Gunn, John; Lagerloef, Gary
    Earth & Space Research, UNITED STATES

    The Aquarius/SAC-D satellite mission, scheduled to launch in 2010, will utilize various types of near-real time in situ data to validate the satellite remote sensing sea surface salinity (SSS) measurements. The validation data will include SSS data from Argo floats, moored buoys, ship thermosalinographs, CTDs and surface drifting buoys. Each data type will require data-specific processing to optimize the comparison with the surface-focused satellite measurement. The objectives of the Aquarius Validation Data System (AVDS) are to collect appropriate in situ surface salinity data for comparison with Aquarius/SAC-D satellite surface salinity measurements and to make this data available to the user community at large. The AVDS data will be matched up with associated satellite data by the Aquarius Data Processing System at Goddard Space Flight Center which will be incorporated back into the AVDS for processing and evaluation. An operational model of the Aquarius/SAC-D data exchange will be running during the year prior to launch to resolve conflicts and to fine-tune the data exchange process before real-time satellite data are available. As part of the AVDS, a web-based data base management system will allow the user community to review and evaluate the data and validation processing utilizing user selectable parameters. We will present an overview of the AVDS system as well as provide an example of the prototype web database access with simulated satellite data and in situ data.

     
    Physical Oceanographic Data Sets Available at PO.DAAC
    Hausman, Jessica; Armstrong, E.; Moroni, D.; Foti, G.
    JPL/NASA, UNITED STATES

    What is PO.DAAC
    PO.DAAC (Physical Oceanographic Distributed Active Archive Center) is the archive for NASA's physical oceanographic data and related information. It manages and distributes satellite data for Ocean Surface Topography (OST), Ocean Vector Winds (OVW), Sea Surface Temperature (SST), Ocean Circulation & Currents, and Gravity.

    Operational Products
    PO.DAAC has several data products that are available within 6-hours or less from time of data collection. These products are ideal for meteorological use, plotting courses for shipping routes and fisheries management.

    OST
    OST includes sea surface height (SSH), sea surface height anomalies (SSHA), and significant wave height (SWH). Jason-1 OSDRs are available within a 3-5 hour time lag and contain significant wave height and wind speed. PO.DAAC also has a GPS orbit derived SSHA product from OSTM/Jason-2. It is available within a 5-7 hour time lag and includes all the same parameters as the OSTM/Jason-2 OGDR plus a highly accurate GPS orbit and derived SSHA.

    OVW
    OVW products provide ocean surface wind speed, direction, and individual wind components referenced at the 10 meter height level. QuikSCAT data are available within a 2 hour time latency and has 25 km spatial resolution.

    GHRSST
    PO.DAAC, in conjunction with NOAA NODC, is also distributing the complete catalog of sea surface temperature products from the Group for High Resolution SST (GHRSST) Project. This is an international effort to produce SST products in common file and metadata formats for nearly every SST measuring instrument in space. They provide real time data from microwave instruments such as AMSRE and TMI, and from IR instruments such as MODIS, AATSR, GOES, SEVIRI and AHVRR. Resolutions vary from 25 km to 1 km.

    Science Quality Products
    PO.DAAC's primary mission is to provide Level-2, 3 and 4 data products that can be used for ocean and climate research. These products have typically undergone rigorous calibration and validation processes to ensure the highest quality product possible. Moreover, as algorithms improve these products are often superseded with more accurate ones.

    OST
    OST data can be used for analysis and/or prediction of sea level rise, hydrology and geostrophic currents. PO.DAAC archives the entire suite of products for TOPEX/Poseidon and Jason-1, which together span16 years of data collection. In collaboration with Ray et al, PO.DAAC will soon distribute a consistent 16+ years climate data record. This will be followed by a gridded level 3 version of this product from Leben et al. This year PO.DAAC will also distribute a coastal SSH and near surface alongshore current product available for the USAs west coast from Strub et al.

    GRACE measures the Earth's gravity field and can be used for sea level variations, ice mass variations and changes in ocean bottom pressure. It was launched in 2002. It has a spatial resolution of 500 km to 1 degree.

    OVW
    PO.DAAC's OVW data holdings collectively account for nearly 28 years of data starting in July of 1978 and discontinuously extend until present day. These products are primarily acquired through satellite-based scatterometer instruments such as: SeaWinds on QuikSCAT, SeaWinds on ADEOS-II, NSCAT, and Seasat SASS. Satellite radiometer ocean surface wind speeds are also available from SSM/I, TMI, AMSR-E, and Nimbus-7.

    The Cross-Calibrated Multi-Platform (CCMP) multi-instrument ocean surface wind velocity product is an analysis of satellite, in situ, and NWP-derived quantities. It offers a consistent gap-free climate data record at a grid resolution of 25 km with temporal sampling every six hours extending from January 1, 1987 until June 30, 2008.

    SST
    SST is useful for detecting currents, ocean circulation, predicting locations of sea life and for helping determine long-term climate change. PO.DAAC provides over a dozen SST data sets including the Pathfinder Version 5 dating back to 1985. The primary instruments used in detecting SST are the Advanced Very High Resolution Radiometer (AVHRR), the MODerate Resolution Imaging Spectroradiometer (MODIS) and the Imager used on the Geostationary Operational Environmental Satellites (GOES).

    PO.DAAC will be producing sea surface temperature frontal probabilities (fig. 1) and average SST gradient fields derived from the 1985-2008 version 5 AVHRR Pathfinder SST time series. These products will be produced in 10 day and monthly intervals for the entire Pathfinder record as a retrospective product. These products are useful for identifying persistent regions of high mesoscale SST variability and gradients due to upwelling, eddies, and strong western boundary currents and current shear. Many of these ocean dynamics have been linked to phytoplankton growth, food web dependencies, and fisheries and marine mammal management. These products will become available summer 2009.

     
    Operational Wind Field Retrieval from Synthetic Aperture Radar
    Horstmann, Jochen1; Koch, Wolfgang2
    1NATO Undersea Research Center, ITALY;
    2GKSS Research Center, GERMANY

    Satellite borne synthetic aperture radar (SAR) instruments enable image the ocean surface at a very high resolution, typically below 100 m. Since the launch of the European remote sensing satellites ERS-l, ERS-2 and ENVISAT, as well as the Canadian satellites RADARSAT-1 and RADARSAT-2, SAR images have been acquired on a continuous basis over the oceans for the last 18 years. Their high resolution and large spatial coverage make them a valuable tool for measuring ocean surface winds. The above mentioned SARs operate at C-band and at moderate incidence angles. For this electromagnetic wavelength and range of incidence angles the backscatter of the ocean surface is primarily caused by the small scale surface roughness, which is strongly influenced by the local wind field and therefore allows the backscatter to be empirically related to the wind.

    In this paper, we introduce WiSAR a methodology that enables retrieval of high resolution ocean surface wind fields from C-band SAR data on a fully automated and operational basis. Wind directions are extracted from wind-induced phenomena that are aligned in the wind direction. The orientations of these features are derived by determining local gradients of the normalized radar cross section (NRCS) from the SAR data. In this approach, a SAR image is sequentially smoothed and reduced to resolutions of 100, 200, and 400 m. From each of these images, local directions defined by the normal to the local gradient (to within a 180° ambiguity) are computed. Pixels associated with land, surface slicks, and sea ice, are masked and excluded from the analysis by considering land masks and several parameters retrieved from the SAR data. From all of the retrieved directions, only the most frequent directions in a predefined grid cell are selected. For better results this process can be assisted by consideration of results of an atmospheric numerical forecast model. The 180° directional ambiguity is removed by considering external a priori information, e.g., weather charts, atmospheric models or in situ measurements. Wind speeds are retrieved utilizing a geophysical model function (GMF) that describes the dependency of the NRCS on the local near-surface wind and imaging geometry. For C-band, VV-polarization, there are a number of popular model functions. The most commonly used is Cmod5. Each of these GMFs is directly applicable for wind speed retrieval from C-band VV polarized SAR images. For wind speed retrieval from C-band SAR images acquired at HH-polarization, no similar well- developed GMF exists. To meet this deficiency a hybrid model function is used that consists of one of the prior mentioned GMF and a C-band polarization ratio (PR).

    WiSAR is validated on a data set consisting of over 600 ENVISAT ASAR images acquired in European waters and co-located to in situ wind measurements from buoys. For the validation WiSAR was run with and without assistance of the numerical atmospheric model NOGAP. The comparison to buoy winds also includes the comparison of the C-band models Cmod_Ifr2, Cmod4, and Cmod5.

    Within a demonstration project, WiSAR has been running since September 2005 at the GKSS Research Center on an operational basis. In this project wind field maps of the North and Baltic Sea are generated on a daily basis and made available via the internet. Therefore, WiSAR was setup to process ENVISAT ASAR data of the North and Baltic Sea into ocean surface wind fields fully automated and in near real time.

     
    Use of satellite measurements to reconstruct the three-dimensional dynamics of the oceanic upper layers
    Isern-Fontanet, Jordi1; Chapron, Bertrand2; KLEIN, Patrice3; Lapeyre, Guillaume4
    1Institut Catala de Ciencies del Clima, SPAIN;
    2Ifremer, FRANCE;
    3IFREMER/CNRS, FRANCE;
    4LMD/IPSL, FRANCE

    We examine the emerging potential offered by satellite microwave measurements to derive the three-dimensional dynamics of the upper ocean. The proposed approach exploits the properties of a theoretical framework based on Surface Quasi-Geostrophic (SQG) equations. Within this framework, Sea Surface Heights (SSH) and Sea Surface Temperatures (SST) are closely related. This provides a way to combine SSH and SST measurements and allows to recover surface currents from a single SST image. On the other side, this framework allows to reconstruct subsurface fields, such as horizontal velocities and density anomaly, in the upper 500m of the ocean from SSH and/or SST measurements. Furthermore, within this framework vertical velocities can also be diagnosed from a single SST and/or SSH snapshot. To demonstrate the feasibility of this approach, first, we have explored the ability to reconstruct the three-dimensional dynamics of the oceanic upper layers using numerical simulation. Then, these results have been applied to existing altimetric measurements and microwave SST data from AMSR-E instrument. Our results confirm the validity of this framework and unveil some limitations in the existing microwave measurements that should be improved in future missions.

     
    Ocean Modelling using GOCE geoid products
    Knudsen, P.1; Benveniste, J.2; Andersen, O.B.1; Rio, M.H.3; Johannessen, J.4; Bertino, L.4; Haines, K.5; Snaith, H.6; Balmino, G.7; Bingham, R.8; Rummel, R.9; Gruber, T.9; Schröter, J.10; Tscherning, C.C.11; Stammer, D.12; Jeansou, E.13; Hernandez, F.14; Dobricic, S.15; Lea, D.16; Drinkwater, M.17
    1DTU Space, DENMARK;
    2ESA, ITALY;
    3CLS, FRANCE;
    4NERSC, NORWAY;
    5UREADES, UNITED KINGDOM;
    6NOC, UNITED KINGDOM;
    7Privat, FRANCE;
    8Newcastle, UNITED KINGDOM;
    9TUM, GERMANY;
    10AWI, GERMANY;
    11UCPH, DENMARK;
    12UH, GERMANY;
    13Noveltis, FRANCE;
    14MERCATOR, FRANCE;
    15MFS, ITALY;
    16Met office, UNITED KINGDOM;
    17ESA, NETHERLANDS

    With the availability of satellite altimeter data since the mid eighties, both globally andover longer periods of time a huge effort were made in the scientific communities to process those global data sets in joint analyses of geoid and ocean dynamic topography. The quality of the available data was not sufficient to recover the details of the general ocean circulation. However, the very large scales (>5000 km) of the dynamic topography could be recovered and compared with the early oceanographic results obtained from hydrographic data. Already at this time the importance of consistency between the reference ellipsoids as well as the role of the permanent tidal correction were identified. The release of satellite gravity data from the GRACE mission and the launch of the ESA GOCE satellite on 16 March 2009 are starting to provide a more accurate and higher resolution global picture of the Earths gravity field than ever before. The basic definition of the ocean dynamic topography is simply the difference between the sea surface height and the geopotential reference surface called the geoid. Hence, the topography is a geometrically surface that describes the shape of the Earth. Simultaneously the dynamic topography may be considered as a reference surface for the ocean circulation at the ocean surface. The key application of oceanography will benefit because the sea level slopes relative to the geopotential surface allow calculation of surface ocean currents on a global scale. Oceanographers have become familiar with the uses of satellite altimeter data over the last 15 years, but are less familiar with the geodetic information, that gravity satellite will provide. The EU FP5 project GOCINA brought together a small consortium of geodesists and oceanographers in order to develop a common understanding of the geodetic and oceanographic needs, in order to prepare to maximize the information available with the new satellite data from GOCE. One of the most interesting opportunities with the GOCE mission is that it will pprovide error covariance information on the gravity field down to spatial scales of 100 km for the first time. The purpose of this white paper is to further advance mutual understanding between the geodesy and oceanography communities and to identify issues related to methods for producing a mean dynamic topography from the gravity and altimeter data. It will furthermore identify issues on how the geoid or the mean dynamic topography (MDT) will be used by the oceanography community and how the errors in the MDT can be estimated and used.. The purpose is to fill a gap by describing the final uses of satellite gravity data within oceanography, and should inform the geodesy community about the subtleties encountered for ocean circulation studies. The experiences from the EU GOCINA and GOCINO projects and the ESA GOCE User Toolbox (GUT) consortium seeks to highlight the major use cases that have been developed over the last few years in preparation for the GOCE mission. Further cross-disciplinary research in geodesy and oceanography is needed to meet and trigger the interests in the oceanographic community to contribute to the challenging task of validation of the GOCE derived geoid and MDT, both on global and regional scales.

     
    COASTAL HIGH RESOLUTION ALTIMETRIC DATA : Application of the Regional CTOH product in South-West Australia
    Langlais, C1; GUIHOU, K.1; OKE, P.1; COLEMAN, R.2; BIROL, F.3
    1CSIRO Marine and Atmospheric Research, AUSTRALIA;
    2UTAS, AUSTRALIA;
    3LEGOS CTOH, FRANCE

    The coastal zone is an actual important challenge. In term of ocean forecasts, shelf modelling is necessary if we want to extend the predictability of the global operational systems towards coastal and regional sub-systems. And on another hand, climatic shelf reanalysis are also crucial to understand the actual global climatic change because the exchanges at the shelf breaks are important source terms which need to be taken into account at a global scale. Satellite altimetry data have been distributed to the scientific community since 1992 and are routinely assimilated for operational forecasting system. Altimetry data over the coastal ocean remain largely unexploited because of difficulties of corrections and land contamination problems. Using the X-TRACK processing tool and the post-processing technique adapted specifically for coastal regions, the Centre de Topographie des Océans et de l'Hydrosphère (CTOH) (LEGOS, FRANCE) provides along track Sea Surface Height regional products, with a resolution of 300m (http://www.legos.obs-mip.fr/soa/altimetrie/ctoh/COTIER/). In this poster, the regional high resolution CTOH product is analyzed and compared with the AVISO along track product (6km of resolution, http://www.aviso.oceanobs.com/ ) along the South-Western Australian coast. The main oceanographic feature in this area is the Leeuwin Current (LC) an eastern boundary current flowing towards the South Pole. As the LC is a warm and narrow current with a lower density than the Indian Ocean waters, SSH map allows us to follow the LC along the Australian coastline. Moreover, the LC exhibits a high mesoscale activity, which can be tracked with altimetry products. After smoothing, the CTOH product exhibits a usable resolution of 2 km with a better coverage near the coast (up to 10km close to the coast). Compared to AVISO, we obtain a better representation of the LC on the shelf. Even offshore, the high resolution product highlights mesoscale details unrevealed by AVISO. A comparison with the Bluelink Ocean ReAnalysis (BRAN) (a global short-range operational forecasting system (http://www.bom.gov.au/oceanography/projects/BLUElink/index.html)) lets us expect an improvement of the eddy resolving simulation, in case of assimilation of the high resolution CTOH product.

     
    Validation of the Updated Envisat ASAR Ocean Surface Wave Spectra with Buoy and Altimeter Data
    Li, Jian-Guo; Saulter, Andrew
    Met Office UK, UNITED KINGDOM

    Ocean surface wave forecasting is an important tool for aiding various marine activities and coastal defence decision making. The state of art wave forecast is based on an ocean surface wave spectral model, which plays an increasingly important role in a coupled atmospheric and ocean system. Developing and validating wave spectral models result in a direct demand for global ocean surface wave spectral observation. Traditional buoy observations cannot not meet this demand alone because of a limited space coverage and restriction on direction information. Remote sensing instruments, like altimeter and synthetic aperture radar onboard satellites, have greatly enhanced the possibility to achieve global monitoring of the ocean surface wave condition. The advanced synthetic aperture radar (ASAR) on board the Envisat satellite (launched in March 2002) is a good example of global ocean surface wave spectral observation (ESA 2002). However, assessment of this valuable data set is not straightforward, due to a lack of other independent ocean wave spectral observations. The radar altimeter (RA2) on board the same satellite measures ocean wave height at the same time as the ASAR but at a different location about 200 km distant. A small number of moored buoys produce 1-D ocean wave spectra operationally but few ASAR spectra fall on the buoy positions in a given time period. An indirect comparison method by pairing the three independent observations with a common media (an ocean wave model output) is proposed by Li and Holt (2009) to bridge the spatial and temporary gaps among these observations and gain an objective validation of the ASAR wave spectra. This study over the period from July 2004 to February 2006 revealed that the Envisat ASAR ocean surface wave spectra are generally in good agreement with the other two observations though some spurious long waves are present in the ASAR spectra. The Envisat ASAR fast delivery ocean surface wave spectral data have undergone an important upgrade in late October 2007 (Johnsen and Collard 2006) and preliminary study has showed that the updated spectra are better than those before the upgrade. This paper presents the result of a validation study of the updated Envisat ASAR ocean surface wave spectra using the above indirect comparison technique over a 14-month period from November 2007 to December 2008. One conclusion is that the update has removed the spurious long waves in the old ASAR spectra, leading to enhanced agreement of the ASAR and spectral buoy data in the long wave range. In addition, the updated ASAR spectra have tidied up noise beyond the azimuthal cutoff, resulting in improvement in the short wave range. A parameter equivalent to the widely used significant wave height (SWH) but integrated over a finite spectral sub-range, and hence called sub-range wave height (SRWH), is used to show the spectral performance of these observations. The SRWH provides a practical solution to tackle the varied spectral resolutions among the different observations and wave models. It is also an efficient alternative for ocean model spectral output as most model 2-D wave spectra are too large (typical 600 elements for each grid point) to be saved for full grid. A proposed set of sub-ranges (>16 s, 16-10 s, 10-5 s, and < 5 s in periods) is used for this study and is recommended for other weather centres to facilitate cross-model comparison in the future. References: ESA, 2002: ASAR Product Handbook. ESA web page: http://envisat.esa.int/dataproducts/, 539 pp. Johnsen, H., and F. Collard, 2006: ASAR wave mode - validation of reprocessing upgrade. Report IT, 26pp. Li, J. G. and M. Holt, 2009: Comparison of ENVISAT ASAR ocean wave spectra with buoys and altimeter data via a wave model. J. Atmos. Oceanic Techno., 26, 593-614.

     
    The PARIS Ocean Altimeter In-orbit Demonstrator
    Martin-Neira, M; D'Addio, S; Buck, C; Floury, N; Prieto-Cerdeira, R
    ESA-ESTEC, NETHERLANDS

    Mesoscale ocean altimetry remains a challenge in satellite remote sensing. Conventional nadir looking radar altimeters can make observations only along the satellite ground track and many of them are needed to sample the sea surface at the required spatial and temporal resolutions. The Passive Reflectometry and Interferometry System (PARIS) using GNSS reflected signals was proposed as a means to perform ocean altimetry along several tracks simultaneously over a very wide swath. The bandwidth limitation of the GNSS signals and the large ionospheric delay at L-band are however issues which deserve careful attention in the design and performance of a PARIS ocean altimeter. This presentation describes such an instrument specially conceived to fully exploit the GNSS signals and to provide multi-frequency observations to correct for the ionospheric delay. Furthermore an in-orbit demonstration mission is proposed that would prove the expected altimetric accuracy suited for mesoscale ocean science.

     
    SMOS Payload In-Orbit Performance
    Martin-Neira, M1; Corbella, I2; Torres, F2; Duffo, N2; Gonzalez, V2; Closa, J3; Benito, J3; Borges, A3; Rautiainen, K4; Kainulainen, J4; Gutierrez, A5; Barbosa, J5; Catarino, N5; Candeias, H5; Castro, R5; Freitas, S5; Freitas, J6; Cabot, F7; Caprolicchio, R8; Zundo, M1; Brown, M1; McMullan, K1
    1ESA-ESTEC, NETHERLANDS;
    2Polytechnic University of Catalonia, SPAIN;
    3EADS-CASA Espacio, SPAIN;
    4Helsinki University of Technology, FINLAND;
    5Deimos Engenharia, PORTUGAL;
    6Critical Software, PORTUGAL;
    7CESBIO, FRANCE;
    8ESA-ESRIN, ITALY

    SMOS is ESA's second Earth Explorer mission with the objective of producing global maps of Soil Moisture and Ocean Salinity over the Earth. It will fly a single payload, MIRAS, the first-ever spaceborne L-band Microwave Imaging Radiometer with Aperture Synthesis in two dimensions. The performance requirements of MIRAS are demanding in terms of spatial resolution, accuracy, stability and precision, all critical to fulfil its scientific objectives.

    During the ground test campaigns both at payload and satellite levels the performance of the instrument was checked against the original system requirements. The verification of the requirements, written in terms of brightness temperatures (Level-1 data), included some image processing of the raw correlations (Level-0 data) acquired inside an empty anechoic chamber. All requirements are satisfied with some margin. The launch of SMOS has been recently confirmed for July 2009. If this calendar is fulfilled, we should have the first in-orbit data available by the time of the OceansObs-09 conference. In such a case, this presentation will include, in addition to the pre-launch performance of SMOS, a description of the Level-1 mission requirements, the in-orbit measurement configurations used to verify them, and the preliminary results of the processing of the first flight data. An extrapolation of this in-orbit learning into the case of a possible SMOSops follow-on mission will also be included.

     
    New models for deriving and partitioning absorption coefficients of colored dissolved organic matter in the global ocean
    Palanisamy, Shanmugam
    Indian Institute of Technology Madras, INDIA

    Colored dissolved organic matter (CDOM) is a strong absorber of ultraviolet and blue light and a key factor in the light-induced biogeochemical cycling of many components in surface waters. Despite the importance of CDOM to such upper ocean processes and optics, our current understanding of its spatial and temporal distributions and the factors controlling these distributions is very limited. This eventually prevents our understanding of its relationship to the pool of dissolved organic carbon in coastal and open oceans. Here we present a new model for deriving absorption coefficients of CDOM (aCDOM) and portioning its terrestrial and marine pools in the global waters. The robustness of this new model was evaluated on the in-situ bio-optical data sets collected in a variety of waters and also tested on the SeaWiFS images acquired over the Northwest Pacific and global ocean waters. The accuracy of the estimates of absorption coefficients of CDOM is generally excellent, although it deviates from the detrital absorption coefficients generally observed in many coastal waters. Applying the model to SeaWiFS images reveals the highest surface abundances of CDOM within the subpolar gyres and along the continental shelves dominated by terrestrial inputs of colored dissolved materials and the lowest surface abundances of CDOM in the central subtropical gyres and the open waters presumably regulated by photobleaching phenomenon, biological activity and local oceanic processes. Large interseasonal changes in CDOM absorption/distribution are also apparently consistent with recent satellite-based assessments at global scale and significant interannual seasonal changes in (terrestrially-derived) CDOM distribution closely correspond with increase of the global mean runoff and river discharge induced by climate change/warming scenarios.

     
    A MULTI-SENSOR APPROACH TOWARDS COASTAL OCEAN PROCESSES MONITORING
    Pascual, A.1; Bouffard, J.1; Ruiz, S.1; Garau, B.1; Martínez-Ledesma, M.1; Vidal, E.1; Faugere, Y.2; Larnicol, G.2; Vizoso, G.1; Tintore, J.1; Escudier, R.3
    1IMEDEA(CSIC-UIB), SPAIN;
    2CLS Space Oceanography Division, FRANCE;
    3IMEDEA, SPAIN

    The coastal ocean is of crucial societal importance. A quantitative understanding of the physical processes impacting the coastal region is necessary to determine how the sea level and current variability will affect coastal systems. Dynamics along the continental slopes are difficult to observe given the wide spectrum of temporal and spatial variability of physical processes which occur. Thus, studying such complex dynamics requires the development of synergic approaches through the combined use of modeling and observing systems at several spatial/temporal sampling level requirements. The objective of this work is to develop coastal operational oceanography on the basis of adequate observing systems which can be integrated into coastal circulation models. Specifically, it is intended: (1) to process, validate and intercalibrate multi-sensor datasets dedicated to coastal ocean studies. In this context, we will implement the technological existent advances in satellite altimetry in the coastal area, that up to now it has not been possible to be used for coastal applications due to relatively poor sampling and inaccuracy of corrections. An ongoing work consists in applying improved altimeter corrections (tidal model, mean profile, MOG2D HR, troposphere correction), high frequency sampling data and reviewing the data recovery near coast. In the meantime the so far unexploited possibilities from the merging of existing in situ data sources with remote sensing data to monitor coastal dynamics will be investigated. The developed system will be implemented initially in the coastal area of the Balearic Islands where the scientific knowledge and the necessary data exist. A second (2) objective consists in scientific applications i.e. to exploit multi-sensor data (in situ and remote sensing) in the context of regional hydrodynamic modelling of shelves and coastal circulation, with focus in the North Western Mediterranean (NWMED). These activities are in line with the new OceanBIT Coastal Observing and Forecasting System, a new facility that will address scientific and technological coastal ocean international priorities. The System will be based in the Balearic Islands but will have a more general Mediterranean / Global Ocean interest (the Mediterranean as an ideal, small scale ocean).

     
    SSALTO/DUACS: Three-Satellite Quality Level Restored in Near Real Time
    PUJOL, M.-I.1; DIBARBOURE, G.1; BRONNER, E.2
    1CLS, FRANCE;
    2CNES, FRANCE


    Near Real Time (NRT): Daily Operational Products

    DUACS-NRT provides GODAE, climate forecasting centers, the MyOcean EU FP7 project, and real time oceanographic research (e.g.: in-situ campaigns) with directly usable, high quality near real time altimeter data. Regional products (European Shelves, Mediterranean Sea, and Black Sea) are delivered to operational projects. Commercial applications are also developed for the fishery and offshore drilling industries. All DUACS near real time products are generated and distributed on a daily basis to reduce the NRT delay, and to smooth the operational procedures of NRT users.
    DUACS features a systematic quality control of the input data, the system itself, and its products with detailed reports put online twice per week. The system also carries out on-the-fly editing and reprocessing of erroneous datasets, as well as a long term monitoring of NRT data it has used, to quickly detect anomalies, drifts and discontinuities in incoming altimeter data.

    Delayed Time (DT): A consistent data set from built upon all altimeters

    The second generation of DUACS-DT products is composed of global data sets of along track and gridded Sea Level Anomaly, Absolute Dynamic Topography, and geostrophic currents, but also of regional-specific products (higher resolution, optimized parameters). DUACS reprocessed all past altimeter data: Jason-1, T/P, ENVISAT, GFO, ERS1/2 and GEOSAT. These delayed time products are regularly updated when new Level2 data are released and fully validated. The system operationally integrates the state-of-the-art corrections, models and references recommended by the altimeter community, as well as the best Cal/Val and cross-calibration and merging algorithms.
    To that extent, the standards of the ongoing GDR-C reprocessing (Jason1, Envisat) and the standards recommended for the upcoming Topex/Poseidon reprocessing will be taken into account for an update of the DUACS DT data set that should be available by late 2009.

    Ongoing Improvements to secure multi-mission products

    The DUACS system was significantly modified to integrate Jason-2. After a successful experimental phase done during the temporary absence of Jason-1 in August 2008, Jason-2 definitively became the reference mission of the system since January 21, 2009, few days before Jason-1 has been moved on its new orbit. Data from the latter have been reintegrated in the DUACS since Mars 2009. The performances of the multi-satellite system were greatly improved with the tandem Jason-2/Jason-1. The tandem thus allowed a reduction of the formal mapping error from 20 to 60% of the variance of the signal and assuring an improved restitution of mesoscale structures especially in high energetic areas. Thanks to the excellent consistency of the Jason tandem data, this upgrade was made operational only 10 days after Jason-1 reached its interleaved orbit.
    In compliancy with the objectives of the SL-TAC from EU project MyOcean, the Black Sea regional product already available in Delayed Time has been added to the NRT product generation in March 2009.
    More DUACS upgrades are also being worked on: Cryosat is scheduled for launch in November 2009. Initially aimed at ice observation, the mission may provide opportunity data on ocean as well. System and algorithm upgrades are being worked on to use this additional dataset in the multi-satellite system by mid-2010 (pending green light from the CalVal phase). Lastly, in order to minimize the impact of an anomaly on the reference mission used in DUACS (especially in NRT), a new orbit error reduction scheme based on multiple reference missions (e.g.: Jason-2 and Jason1, or Jason-2 and AltiKa/Saral) is being developed.

     
    Intercomparisons among Global Daily SST Analyses
    Reynolds, Richard1; Chelton, D.B.2
    1National Climatic Data Center/NOAA, UNITED STATES;
    2Oregon State University, UNITED STATES

    Six global daily SST analyses were compared. These analyses were the Remote Sensing System (RSS) analysis on a ~1/11° degree grid, the NCEP Real Time Global High Definition (RTG-HD) analysis on a 1/12° grid, the UK Met Office 1/20° Operational SST and Sea Ice Analysis (OSTIA) analysis on a 1/20° gird, the NCDC Daily OI analyses using AMSR+AVHRR and AVHRR-only on a 1/4° grid and the Fleet Numerical Meteorology and Oceanography Center (FNMOC) analysis on a 1/9° grid on the equator. Qualitative comparisons of maps of SST from the various products show areas with large differences (exceeding several °C) over the time period. The regions of the large differences tend to occur near the coast, in strong gradient regions such as western boundary currents and in the far north and south where SST measurements (both in situ and satellite) tend to be sparse and simulated SSTs from sea-ice concentrations may have a large impact if used. To try and quantify these results, comparisons were carried out with moored buoys. Average differences were computed between the analyses and the buoys. In general differences were higher with respect to the RSS and RTG-HR analyses than with respect to the others. Spectra and cospectra (with respect to the buoys) were computed at each buoy location from the buoy data and from each analysis interpolated to the buoy locations. The results show that FNMOC and to a lesser extent OSTIA were strongly tuned locally to the buoy data. SST wavenumber spectra were computed for several regions which show that RSS is noisy, RTG_HR has lower resolution than the others analyses and FNMOC appears to have the highest resolution.

     
    BASIC RADAR ALTIMETRY TOOLBOX & TUTORIAL
    Rosmorduc, V1; Benveniste, J2; Bronner, E3; Niejmeier, S4; Picot, N3
    1CLS, FRANCE;
    2ESA, ITALY;
    3CNES, FRANCE;
    4Science and Technology, NETHERLANDS

    The Basic Radar Altimetry Toolbox is an "all-altimeter" collection of tools, tutorials and documents designed to facilitate the use of radar altimetry data. Such an integrated approach and view is vital not only for assessing the current status of what altimeter products offers, but also to show the system and consistency with the past.

    It has been available (http://www.altimetry.info) from April 2007, and had been demonstrated since about six months before that, including during training courses and scientific meetings. Quite a large number of people downloaded it. Users feedbacks, developments in altimetry, and practice, show that some new interesting features could be added.

    It is able
    - to read most distributed radar altimetry data, from ERS-1 & 2, Topex/Poseidon, Geosat Follow-on, Jason-1, Envisat, Jason- 2, and the future Cryosat mission,
    - to perform some processing, data editing and statistic,
    - and to visualize the results.

    Version 2 has just been developed, with, among other things, improved easiness-of-use of the graphical user interface, pre-selection of data files before computation (to speed it), additional visualization features such as waveform viewing or geo-localized output images. A release for MacOS is also made.

    As part of the Toolbox, a Radar Altimetry Tutorial gives general information about altimetry, the technique involved and its applications, as well as an overview of pas present and future missions, including information on how to access data and additional software and documentation. It also presents a series of data use cases, covering all uses of altimetry over ocean, cryosphere and land, showing the basic methods for some of the most frequent manners of using altimetry data.

    BRAT is developed under contract with ESA and CNES. It is available at http://www.altimetry.info

     
    Annual sea surface height variation and dynamic topography on the Caspian Sea from Jason-1 altimetry data
    Shojaee, Kamyar
    KITO Enterprises, UNITED ARAB EMIRATES

    The recent unseasonably overflow of the Caspian Sea and onrushing to the coastal region is the predominant motivation of this study on the sea surface height anomaly in order to find the climatic and environmental changes impact on the last decade. For this propose the data gathered by Jet Propulsion Library (JPL) from Jason-1 (2002 to present) and Topex/ Poseidon (1995-2002) have been utilized. In addition to the altimetry data, the sea level observation data by Caspian Water Research Institute (CWRI) in Iran has been also used to compare the results. Due to non-stationary habit of sea surface dynamic topography (SSDT) time series in this region, SSDT can be divided into the periodical part and fluctuation around the mean. This fluctuation shows the trend of sea level changes clearly. Since the fluctuations inherit the very low frequency constituents of sea level, the satellite orbit errors came into concentration and the optimal interpolation method has been employed to reduce the orbit errors. The results confirm that the SSDT derived from altimetry data can be used as a forecast module to detect the monthly trends precisely, in order to determine the source of environmental changes before long.

     
    Combined AATSR/MERIS Algorithm for Aerosol Optical Depth Retrieval Over Ocean
    Sogacheva, L.1; de Leeuw, G.1; Kolmonen, P.1; Curier, L.1; Kokhanovsky, A.2
    1Finnish Meteorological Institute, Climate Change Unit, FINLAND;
    2University of Bremen, Institute of Environmental Physics, GERMANY

    The combined AATSR/MERIS algorithm for aerosol optical depth (AOD) retrieval over ocean has been developed at the Finnish Meteorological Institute and tested for more accurate retrieval of the aerosol properties and surface correction. The AOD retrieval algorithm, which is applied to cloud-free pixels over ocean, is based on the comparison of the measured and modeled reflectance at the top of the atmosphere (TOA). The algorithm uses look-up-tables (LUTs) to compute the modeled TOA reflectance. For LUTs generation the SCIATRAN radiative transfer module developed at the University of Bremen has been used. LUTs are generated for different aerosol types as derived for MODIS.

    For AOD retrieval, the atmospheric aerosol is assumed to be an external mixture of fine and coarse mode particles. The two aerosol types are mixed such that the spectral behavior of the reflectance due to aerosol best fits the measurements. The algorithm consists of three parts. The first part of the algorithm includes the AOD retrieval over ocean using AATSR top of the atmosphere reflectance measurements for 555nm, 685nm, 875nm and 1600nm, and chlorophyll concentration data base. The TOA reflectance is the contribution of a path reflectance due to scattering in the atmosphere by aerosols and molecules and reflection by the ocean surface. Contribution of ocean white caps and sun glint are accounted for.

    In the second part of the algorithm, we use LUTs and the aerosol mixture which is chosen in the first part of the algorithm, for determining the reflectance at the TOA for MERIS wavelengths (412-900nm). Using this result for the atmospheric correction, the actual chlorophyll concentration is determined using the MERIS radiance data. In the third part of the algorithm, the MERIS chlorophyll concentration is used in the AATSR algorithm instead of the database. The use of real chlorophyll concentration results in more accurate aerosol optical depth retrieval.

    The combined AATSR/MERIS algorithm has been tested by the comparison with AERONET and MAN ground-based measurements of the retrieved AOD for about 100 collocations of AATSR and MERIS. The work is done in the framework of the ESA sponsored AMARSI project

     
    CLS as Expert Support Laboratory for the Envisat Altimetry Mission
    Soussi, Batoula1; Faugere, Yannice1; Femenias, Pierre2
    1CLS, FRANCE;
    2ESRIN, ITALY

    CLS, as Expert Support Laboratory (ESL), was in charge of the development of the EnviSat RA2/MWR prototype for the level2 processing chain, which became the reference processor for the L2 IPF (Near real time processing). Since 2007, CLS was also designed by ESA to become the MWR ESL which is responsible of the L1B MWR reference processor CLS is not only responsible of the definition, the specification, the development and the maintenance of the ground processing chain, but is also responsible of long term monitoring and validation of the MWR data and of the comparisons of altimeter data against tide gauge measurements. One of the ESA strength requests is that CLS should propose the up to date algorithms, models, corrections in order to have the best EnviSat RA2/MWR data product. The main evolutions since the EnviSat Launch will be described as well as some major studies results (MWR Drift, Ice and Rain Flags..).

     
    Directional wave spectrum estimation by SWIM instrument on CFOSAT
    Amiot, Thierry1; Tison, Céline1; Enjolras, Vivien2; Hauser, Danièle3; Rey, Laurent2; Lambin, Juliette1; Castillan, Patrick1
    1CNES, FRANCE;
    2Thalès Alenia Space, FRANCE;
    3CNRS-LATMOS, FRANCE

    T. Amiot (1), C. Tison(1), V. Enjolras (3), D. Hauser(2), L. Rey (3), J. Lambin, P. Castillan (1) (1): CNES, 18 avenue Edouard Belin, 31400 Toulouse, France (2): LATMOS/CNRS, 10-12 avenue de lEurope, 78140 Vélizy, France (3) : Thales Alenia Space, 26 avenue Jean-François Champollion BP 33787, 31037 Toulouse Cedex 1, France Oceanography greatly benefits from remote sensing satellites for global monitoring and forecast of the sea surface. The CFOSAT (China France Oceanography SATellite) mission, whose launch is planned for 2013, should embark two radar payloads to monitor both wind and waves over the ocean. One of this two radar instruments is called SWIM (Surface Waves Investigation and Monitoring). It is a Ku-band scatterometer designed to measure ocean waves. Actually, this SWIM concept is based on the Jackson et al. proposals [1,2,3], which describe the design and processing of a scatterometer dedicated to the wave field estimation. SWIM is currently in Phase B (concept and design phase). In [6,7], the preliminary design and associated performance analysis have been published taking into account the end of Phase A design. This poster is focused on the performance assessment of the SWIM instrument based on the new developments which occur during Phase B. We aim here at up-dating the first results obtained during Phase A by taking into account the last developments of the instrument. In addition, major reviews have been carried out on the performance analysis. [1] Jackson, F. (1981). An analysis of short pulse and dual frequency radar techniques for measuring ocean wave spectra from satellites. Radio Science, 16(6) :13851400. [2] Jackson F. C., Walton W.T., and Peng C.Y.. A comparison of in situ and airborne radar observations of ocean wave directionality, J. Geophys. Res. , 90 (C1), 1005-1018, ,1985 [3] Jackson F. C., and Walton T.W., Baker P. L., Aircraft and satellite measurement of ocean wave directional spectra using scanning-beam microwave radars, J. Geophys. Res., 90, (C1), 987-1004, 1985 [4] Soussi, E. (1997). Contribution à la spécification et à lanalyse des performances du système VAGSAT pour la mesure spatiale des vagues à partir dun radar à ouverture réelle. PhD thesis, Université de Paris VI. [5] Hauser, D., Soussi, E., Thouvenot, E., et Rey, L. (2001). SWIMSAT : a real aperture radar to measure directional spectra of ocean waves from space - main characteristics and performance simulation. AMS, 18. [6] C. Tison, D. Hauser, G. Carayon, J. Lambin, P. Castillan, A spaceborne radar for directional wave spectrum estimation: first performance simulations, IGARSS08, July 2008 [7] Enjolras V., Caubet E., Richard J., Lorenzo J., Carayon G., Castillan P., SWIM: a multi-incidence beams Ku-band real aperture radar for the observation of the ocean wave field spectra, IGARSS08, July 2008.

     
    High Resolution SST fields: the Medspiration project, analysis of 3 years of data
    Tournadre, J; Piolle, JF; Autret, E
    IFREMER, FRANCE

    In 2002, GODAE (Global Ocean Data Assimilation Experiment) initiated the GODAE High Resolution SST Pilot Project, GHRSST-PP to address an emerging need for accurate high resolution sea surface temperature (SST) products (1). SST is required by operational ocean and atmospheric forecasting systems to constrain the modeled upper ocean circulation thermal structure and for exchange of energy between the ocean and atmosphere. The goal is to combine all the available SST data from across the globe to form a high resolution, high accuracy and high availability SST product. It is organized as a partnership between regional groups responsible for generating SST products, to a common specification, within a limited geographical area. The primary task of the Regional Data Assembly Centers is to collate all level 2 satellite SST measurements within their region, perform quality assessment and reissue the data in a common format (GHRSST L2P data) including a measure of the quality of every measurement. Some centers also use the L2P data to produce global or regional analyzed SST products (called GHRSST L4 data), using well defined procedures. Medspiration has been created by ESA in 2004 to serve as a European DAC for GHRSST-PP, generating L2P and MDB products for the Atlantic Ocean and its adjoining seas (2). Medspiration has also the task of producing an ultra-high resolution (2 km) analyzed SST product for the Mediterranean Sea. The Medspiration system is operational for the European Seas since 2005 and after a test period the processing chain has been stabilized beginning of 2006. Two years of data (2006-2007) have been produced with only minors processing changes. This archive provides a good opportunity to evaluate and to analyzed the interest of ultra high resolution analyzed SST fields.

     
    Uncertainties in the Global Oceanic Precipitation Observed by the Current Generation Merged Satellite Products

    Xie, Pingping; Yoo, Soo-Hyun
    NOAA Climate Prediction Center, UNITED STATES

    Oceanic precipitation is an essential component of the global water cycle and plays an important role in the air-sea interactions. However, its mean state, short-term variability and long-term changes are poorly monitored and documented due to the lack of an appropriate observing system. Direct measurements of precipitation are made by a very sparse network of in situ instruments including atoll gauges and buoys located primarily over tropical oceans. Estimates of precipitation are derived from satellite observations of infrared (IR), passive microwave (PMW) and space radar that are calibrated against some sort of in situ observations one way or another. Several sets of oceanic precipitation data sets (e.g. the GPCP, CMAP, and TRMM) have been constructed through combining satellite estimates from different platforms to generate analyzed fields with quasi complete spatial coverage for an extended period. While these data sets are widely utilized in climate and oceanic studies, accuracy of their quantitative magnitude is uncertain.

    In this work, we will examine the uncertainties in the oceanic precipitation as documented by several widely used data sets and explore possible ways to improve the quantitative accuracy of oceanic precipitation analyses. First, uncertainties of the current generation merged satellite precipitation products are investigated by inter-comparisons among the satellite products and comparisons against concurrent in situ measurements. While merged satellite products present similar patterns of spatial distribution and temporal variations, the magnitude of oceanic precipitation from different products differ by ~10% over most of the oceanic areas. Most of the magnitude differences (biases) among the various merged satellite products are attributable to the differences in the individual input satellite estimates and in the way if / how the in situ data are utilized in the merging process. Even precipitation estimates derived from the same SSM/I satellite observations may differ significantly when different retrieval algorithms and / or calibration schemes are applied. With estimates of uncertainties for the merged satellite estimates, we were able to examine the oceanic precipitation fields generated by various reanalyses and climate models in a quantitative manner.

    Due to the complicated nature of the relationship between precipitation and the radiances measured by satellite observations, precipitation estimates derived from satellite observations alone will present regionally dependent and seasonally changing biases. An effective way to remove the biases is to combine the satellite estimates with in situ measurements. Experiments for precipitation over land demonstrated that bias inherent in the satellite estimates can be removed almost completely over regions with appropriate gauge networks. As the second part of this work, we are performing a series of experiments to examine to what extent bias in the satellite estimates of oceanic precipitation can be reduced using the current network of in situ measurements (atolls and tropical buoys) and how the configuration of the in situ network has to be to provide appropriate reference of ground truth of precipitation over various parts of the global oceans. Detailed results will be reported at the conference.