Alexei V. Kouraev1,2,4, Fabrice Papa3, Nelly M. Mognard1, Petr I. Buharizin5,
Anny Cazenave3, Jean-Francois Cretaux3, Julia Dozortseva6, Frederique Remy3.
(1) Centre d’Etudes Spatiales de la Biosphère (CESBIO), Toulouse, France, (2) State Oceanography Institute, St. Petersburg branch, St. Petersburg, Russia, (3) Laboratoire d’Etudes en Géophysique et Océanographie Spatiales (LEGOS), Toulouse, France, (4) Nansen International and Remote Sensing Centre (NIERSC), St. Petersburg, Russia, (5) Water Problems Institute (WPI) of Russian Academy of Sciences, Astrakhan division of the WPI RAS, Astrakhan, Russia, (6) Hydrometeorological Centre of the Caspian Fleet, Astrakhan, Russia.
Satellite microwave observations offer reliable, consistent, weather-independent, and easily accessible data on the ice cover. We use the synergy of simultaneous active and passive microwave observations for the study of ice conditions.
Our main source of information is data from the TOPEX/Poseidon satellite, operating since 1992 and followed by Jason-1 in 2002. These platforms have two nadir-looking instruments – a dual-frequency radar altimeter and a passive microwave radiometer. The combination of both active (backscatter coefficient at 13 GHz) and passive (brightness temperature at 18 and 37 GHz) microwave measurements provides information to estimate ice concentration, roughness and height of snow cover on ice. This information on ice cover is further complemented by passive microwave data from the SMMR (Scanning Multichannel Microwave Radiometer) instrument onboard the satellite NIMBUS-7 (since 1979) and the SSMI (Special Sensor Microwave Imager) instrument on board the DMSP (Defense Meteorological Satellite Program) series (since 1987).
To avoid ambiguity when discriminating between first-year and multi-year ice, we have chosen water bodies that are seasonally ice-covered (i.e. where multi-year ice is never or very rarely observed) for development, testing and application of ice algorithms. One of these regions is Hudson bay, where detailed comparison of ice charts provided by the Canadian Ice Service and our data was made, making it possible to assess radiometric characteristics of different types of ice.
Two other regions are Caspian and Aral seas, located on the far southern boundary of sea ice cover development in the Northern Hemisphere. Every winter stable ice cover forms there for several months, negatively affecting conditions for navigation and fisheries, and creating danger for industrial constructions located in the coastal zone, such as Russian and Kazakh oil rigs operating in the Northern Caspian shelf. Our results show significant variability of ice extent and duration of ice season, with strong warming signal in recent time (1998-2002). We discuss the reasons for these changes and their impact on industrial activity, navigation and marine environment.