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Assessment of different topographic corrections in MODIS data for mapping effective snow covered areas in mountainous terrain

Akyürek, Sevda Zuhal
Sorman, A. U.
Topography and its derivatives (altitude, slope and aspect) have an effect on satellite-measured radiances. For mountainous areas the sun zenith and azimuth angles, as well as direction of observation relative to these are more limiting factors. In this paper four topographic normalization methods were used to correct the reflectance values of medium spatial resolution satellite data, namely MODIS. The performance of the topographic normalization methods is examined for snow covered areas of the study area located in the eastern part of Turkey. Modeling of snow-covered area in the mountainous regions of Eastern Turkey has significant importance in order to forecast snowmelt discharge especially for optimum use of water in energy production, flood control, irrigation and reservoir operation optimization. MOD09GKM data, which have the land surface reflectance having atmospheric correction, digital elevation model (DEM) and the geo-location files (MOD03) were used. It is obtained that statistical empirical correction method worked better compared to the other methods in removing the terrain effects for snow covered areas. The importance of topographic normalization in mapping the effective snow covered area in snowmelt modeling is also discussed and the early findings of Satellite Application Facilities on Hydrology (H-SAF) project, which is financially supported by EUMETSAT, is presented. Turkey is a part of the H-SAF project, both in product generation (e. g. snow recognition, fractional snow cover and snow water equivalent) for mountainous regions for whole Europe, cal/val of satellite-derived snow products with ground observations (synoptic, automated weather stations and snow courses) and impact studies with hydrological modeling in the mountainous terrain of Europe.