Abstract
The paper discusses application of active and passive microwave data for assessment of time and space variations of first-year ice cover. The Caspian and Aral seas are chosen as main study areas. The Caspian Sea evolution is primarily climate driven, while for the Aral Sea there is a mix of anthropic and climate factors. We analyze ice cover conditions using a novel method that combines active and passive satellite measurements for ice discrimination. This method uses the synergy of simultaneous data from active (radar altimeter) and passive (radiometer) microwave instruments onboard the TOPEX/Poseidon (T/P) satellite, launched in 1992. The benefits, drawbacks, and potential of ice cover studies using the proposed method are discussed. We analyze in detail how this method is influenced by the difference in footprints of the T/P sensors and by the radiometric properties of ice and snow at different stages of ice cover evolution. In order to link the T/P-derived results to historical observations that end in the mid-1980s, long time series of passive microwave data from SMMR and SSM/I sensors have also been analyzed. Satellite time series of ice cover extent and duration of ice period have been obtained for the Caspian and Aral seas since 1978. A good agreement is obtained between historical and satellite data, with significant spatial and temporal variability of ice conditions. There is a marked decrease of both duration of ice season and ice extent during the winters 1998/1999-2001/2002. These satellite-derived time series of sea ice parameters are very valuable in view of the heterogeneous and mostly unpublished data on ice conditions over the Caspian and Aral seas since the mid-1980s.
Highlights
T HE PRESENCE of ice cover influences human activities in many parts of the world
Applying the methods described above to the T/P and SMMR-Sensor Microwave/Imager (SSM/I) data for the northern Caspian and Aral Seas, time series of beginning and end dates of ice season, of ice season duration and of ice cover extent were obtained
This satellite-derived dataset provides for the first time continuous time series of ice cover variability since the mid-1980s for the Caspian and Aral Seas
Summary
T HE PRESENCE of ice cover influences human activities in many parts of the world. Studies and monitoring of ice conditions is important for maritime safety and sustainable. The ice processes in the Caspian and Aral Seas have significant temporal and spatial variability, influenced by climate conditions, wind fields, and water currents, as well as sea morphology. Both seas are located on the far southern boundary of sea ice cover development in the Northern Hemisphere. The satellite time series of ice cover parameters show significant changes in the ice conditions in the last two decades These results are probably the first attempt to fill in this important information gap in the ice cover information for the Caspian and Aral Seas since the mid-1980s
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