4 open review comments to “Remote sensing of sea ice”
Introduction, line 8, insert:
“Satellite observation of ice thickness is under development using altimeter, but need to be combined with non-satellite methods to obtain reliable estimates of the thickness variability and trend.”
Section Ice Concentration, fifth last line, insert:
“It is also important to improve and validate the retrieval methods used to estimate sea ice extent. Presently, there is significant discrepancy between existing algorithms, resulting in up to 10 % (≈ 1 mill sq. km) deviation in the Arctic ice extent (Ivanova and Johannessen, 2009). Another reason for improving the algorithms is that thinning of the ice cover may lead to increased errors in the retrievals”
Section Ice type and age: Proxies of ice thickness, line 15, insert: “The thickness of thin ice can be retrieved from passive microwave data, as demonstrated by Naoki et al., 2008 and Martin et al., 2004.”
Section Ice drift at moderate resolution, 10th last line, insert new paragraphs:
“Estimation of ice drift through the Fram Strait is a major issue since this strait is the main exit gate for ice export from the Arctic basin to the Sub-Arctic seas. Ice drift through the strait has been estimated using passive microwave data since 1978 [Kwok, 2004]. Since 2004 wideswath SAR data from ENVISAT have been used to estimate ice drift with improved spatial resolution, about 20 km, with three day interval at 79 N (Sandven, 2008). SAR-derived ice drift vectors can be retrieved year-round while ice drift from passive microwave and scatterometer are only available from October to May. The SAR vectors are also capable of resolving the cross-strait velocity profile. At present, studies are conducted to assess the accuracy of ice drift retrievals in the Fram Strait from passive microwave and scatterometer data (http://cersat.ifremer.fr) using SAR data and buoy data.
By combining ice concentration profile from passive microwave data with drift profile from SAR, the area flux across 79 N can be estimated. Time series of ice area flux is now available for 3 decades from passive microwave data, and by adding SAR-derived ice fluxes for the last five years, it is possible to validate the accuracy of the passive microwave retrievals. The final goal is to estimate the ice volume flux through the strait on seasonal and interannual scale, and this can be done by combining area flux data with thickness data. With satellite-based ice thickness from IceSat (Spreen et al., 2006) and upcoming thickness data from CryoSat, it will be possible to monitor ice volume fluxes through the strait. Furthermore, Upward-Looking Sonar have collected ice thickness data for several years (Vinje et al., 1998, Kwok, 2004) and these data will be important for validating the ice volume fluxes derived from the satellite data.”
In Conclusion, insert new bullet point no. 4: “Improve existing algorithms and develop new algorithms for retrieval of ice parameters through a coordinated programme. Algorithms should be compared and validated against independent data”
- and a last bullet point: “Establish validation procedures for the satellite retrievals using data from independent observing system. The validation should include both regular operational validation carried out on daily, weekly or monthly basis, and hindcast validation carried out with data available in delayed mode”
Additions to the reference list:
Ivanova N. and Ola M. Johannessen, 2009: Arctic Science Summit, March 2009, abstract.
Kwok, R., G. F. Cunningham and S. S. Pang (2004). Fram Strait sea ice outflow. J. Geophys. Res., 109, C01009.
Martin, S., R. Drucker, R. Kwok, and B. Holt (2004), Estimation of the thin
ice thickness and heat flux for the Chukchi Sea Alaskan coast polynya
from Special Sensor Microwave/Imager data, 1990–2001, J. Geophys.
Res., 109, C10012, doi:10.1029/2004JC002428.
Naoki, K., J. Ukita, F. Nishio, M. Nakayama, J. C. Comiso, and A. Gasiewski (2008), Thin sea ice thickness as inferred from passive microwave and in situ observations, J. Geophys. Res., 113, C02S16, doi:10.1029/2007JC004270.
Sandven, S. Sea ice monitoring in European Arctic Seas using a multisensor approach. Chapter in the book “Remote Sensing of the European Seas” (Eds. Barale and Gade) Springer Science and Business Media B. V., 2008, pp. 487 – 498.
The paper will be updated with the input from Stein Sandven.