Ice cover and sea level of the Aral Sea from satellite altimetry and radiometry (1992-2006)

We discuss recent seasonal and interannual variations of ice cover and lake surface level in the Aral Sea from satellite data for 1992-2006. First, we provide an overview of the evolution of the Aral Sea's environmental conditions, hydrological and ice regime, existing observations and current state of the scientific research. Desiccation of the Aral Sea led to disappearance of the infrastructure in the coastal zone, including meteorological and sea level gauge stations. The current lack of reliable in-situ measurements and time series for sea level and ice cover parameters since mid-1980s can be partly overcome with radar altimeter and microwave satellite observations that provide reliable, frequent, regular and weather-independent data. In our study, we use radar altimeter data from TOPEX/Poseidon, Jason-1, ENVISAT and GFO satellites, as well as the Special Sensor Microwave/Imager (SSM/I) radiometer. An ice discrimination method, based on the synergy of active and passive data from the four altimetric missions and SSM/I, is proposed and applied to the entire satellite dataset to define the specific dates of ice events for 1992-2006. We then analyse the evolution of the sea level in the Large and Small Aral sea and Sarykamysh lake. For this purpose, we compare time series from several sources (Hydroweb, USDA Reservoir Database, Integrated Satellite Altimetry Data Base and others), perform an intercomparison of the available observations and discuss the reasons for potential differences. Using the data from the four altimetric retrackers for ENVISAT we also estimate how the presence of ice could affect the altimeter range measures. We estimate the associated uncertainties and provide recommendations for adjusting sea level time series for altimeters where only ocean retracker (T/P, Jason-1, GFO) is present. (C) 2008 Elsevier B.V. All rights reserved.