نوع مقاله : مقاله پژوهشی
1 کارشناس ارشد/ سنجش از دور و GIS، شرکت آب منطقه ای تهران
2 استادیار /گروه سنجش از دور و GIS، دانشگاه شهید بهشتی
3 استادیار/ گروه مهندسی ژئوماتیک، دانشگاه خواجه نصیرالدین طوسی
4 کارشناس ارشد /سنجش از دور و GIS، دانشگاه شهید بهشتی
عنوان مقاله [English]
Iran is a drought region which is located in middle meridian of earth. Especially in mountains, precipitations fall as snowfall and provide water supply for warm season. Therefore, it is so important for hydrologists and water resource engineers to determinate boundary of snow cover to be able to estimate water supply. In this study, snow cover area in Central Alborz mountains were detected using NOAA-AVHRR and TERRA-MODIS data using threshold determination in near infrared band.
Discrimination between snow and clouds is one of the important problems in snow mapping using satellite data. Clouds are very diverse and have high reflection in visible and NIR band but snow shows low reflectance in this band. In MODIS snow mapping algorithm, first using NDSI, snow pack detected but for discrimination between snow and other wet lands we utilized threshold in 1, 2, 4 and 6 bands. In NOAA-AVHRR algorithm were also used threshold for Albedo of band 1 and 3 and brightness temperature 3 and 4. Snow areas in AVHRR is 5303 square kilometers in March 27th 2004 and full snow, fractal snow and clouds areas in MODIS data were 994, 2570 and 2505 square kilometers in March 25th 2003, respectively.
Finally, using interrelation between hydro-climatology parameters 2.9°C were calculated as minimum temperature of snowfall and height of corresponding 0° C were calculated for snow permanence height in Central Alborz.