MONITORING WATER LEVEL SEASONAL VARIATIONS OF LARGE NATURAL LAKE EXPLOITING ENVISAT ASAR LOW RESOLUTION TIME SERIES: APPLICATION TO THE POYANG LAKE (P.R. CHINA) DURING THE 2004 - 2005 HYDROLOGICAL PERIOD

摘要

Within the framework of the Flood DRAGON project, an assessment of ASAR Global Monitoring (GMM) data has been carried out over the Poyang Lake, Jiangxi province, P.R. China. This study consists of one of the first assessment of low resolution ASAR data, ENVISAT low rate mode, for land applications. Sixteen ASAR GMM images, which give a good overview of an on going situation over very large area with a high temporal revisit, was analysed, and GMM's potential for flood risk management has been assessed. A new processing chain was created including preprocessing steps (calibration, import and geo-referencing), radiometric enhancement and water bodies extraction. GMM analysis allowed the distinguishing over the very sensitive Poyang lake ecosystem, three major land cover types: permanent water bodies between February 2004 and April 2005, areas of seasonal water level variations, and wet lowlands mostly consisting of marshes. These are in very good concordance with results obtained from reference optical high resolution data. Water body extraction was performed on ASAR GMM images and a map of the annual dynamic of the Poyang Lake was elaborated. In the near future, more GMM data will be integrated within the database in order to improve the revisit frequency at critical period. Hence these first results will be compared with optical (MERIS) and radar (Envisat Wide Swath mode and Precision mode) data and, in parallel with hydrological and meteorological data over the Poyang Lake area and Changjiang catchment.