Monitoring snow-covered areas using NOAA-AVHRR data in the eastern part of Turkey

Abstract

Monitoring snow-covered areas and estimating the snow water equivalent play an important role in predicting discharges during spring months, especially in regions where snow is an important resource. This study has been conducted in the Upper Euphrates River basin, of 10 200 km2 area, and elevation range of 1125–3500 m. In estimating snow-covered areas, besides semi-supervised multispectral classification of NOAA-AVHRR data, a theta algorithm, developed by the US National Weather Service, has been used. The two classification techniques were applied to the Advanced Very High Resolution Radiometer (AVHRR) data obtained directly from the satellite receiver located at the university campus in Ankara, Turkey. The corrected images were rectified according to the UTM coordinate system. Snow-covered areas were obtained for cloud-free and partial cloudy images for April 1998 within the project area located in the eastern part of Turkey. Furthermore, the threshold to separate clouds from cloud-free areas is determined. The effects of elevation, aspect, slope and prevailing winds in determining the snow-covered areas for April 1998 are explained and the changes in the snow line are determined considering the effects of these topographic and meteorological factors. Snow depletion curves were obtained by using the proper classification technique for all the other cloud-free and partial cloudy images for 1998. These curves were used with other meteorological parameters as input to a snowmelt runoff model in order to predict the daily discharges, which were compared with the records at the streamgauge of the basin. The effects of aspect and slope on the snow depletion curves for different elevation zones are also shown and, considering this effect, the depletion curves are improved.