Author(s): Kjetil Melvold; Anund Sigurd Kvambekk; Nils Kristian Orthe; Zelalem Mengistu
Linked Author(s): Zelalem Mengistu
Keywords: No keywords
Abstract: The principal aim of the study is to establish an operational processing chain in order to monitor Open Water Surface (OWS) for lakes larger then about 10 km2 and hopefully some of the largest rivers (i. e. more than 100 m wide), during winter time. We will apply three key operational satellite sensors: NOAA AVHRR, Terra MODIS and Radarsat (1/2) ScanSAR. Most lakes in Norway have an area of less than 100 km2. Thus passive microwave images can not be used due to the relatively low satellite resolution. Multi-temporal information will be used to merge radar data into time gaps in optical acquisition. For validation we will use ground observations and higher resolution satellites (Landsat ETM+, Terra ASTER/MODIS, Radarsat-1 S7) if data is available. OWS presently needs pixel to sub-pixel information, due to the relatively small features that should be mapped. Due to significant differences in surface roughness of various type of land (land, snow on frozen lakes, glaciers, forest etc) the spectral signature or backscatter coefficient will responds differently in time and space. The images will therefore be masked for various land types. For OWS study the mask should remove all the pixels that do not belong to the water classes. Results from spring 2007 and 2008 have shown that OWS maps can be very useful for discriminating ice-free and ice-covered lakes during break-up situations. OWS maps can be used in an overlay analysis with maps of lakes to create maps of ice covered lakes. Lake ice has a strong influence on local energy budget. Lake-ice freeze-up and break-up dates are also good indicators of regional climatic variability and change and important knowledge in real time to calculate ice strength for safe traffic on the ice. The images will improve our Internet based ice information system “ice warning” by increasing spatial cover in regions with sparse data.
Year: 2008