Submitted to: Proceedings Water Environment Ecology Socio-Economics and Health Engineeri
Publication Type: Book / Chapter
Publication Acceptance Date: July 23, 1999
Publication Date: N/A
Interpretive Summary: Research was conducted to develop a new method for analyzing AVHRR (Advanced Very High Resolution Radiometer) satellite imagery to determine snow covered area using a geographic information system (GIS). A GIS is a computer-based information system that is used to store, manipulate, and display geographically referenced information. A series of programs written for the ARC/INFO GIS were used to analyze five years of AVHRR images. These programs, in addition to graphical analysis, were used to determine the numerical values that differentiate snow-covered from snow-free land, and to reclassify each AVHRR scene into snow-covered or snow-free areas. The success of the reclassification was determined by inspection of the agreement between the scenes identified as snow covered and the actual snowfall data. The results showed that the reclassification scheme correctly predicted the presence or absence of snow cover 72 - 78 percent of the time. The advantages of this method are the ease of acquisition of the required data (AVHRR and climate data), and that no additional satellite data such as Landsat TM are required. The low resolution of the AVHRR data (1-km pixel size) and the small area of analysis probably reduced the accuracy of the results.
Technical Abstract: A procedure is developed that links a geographic information system (GIS) and remotely sensed data to determine the extent of snow cover in a complex mountainous watershed. Snow cover extent is used in a hydrologic model to predict snowmelt and rainfall produced runoff. A series of programs (AMLs) are used in the GIS to reclassify AVHRR satellite data for snow cover extent & to delineate the watershed boundary and elevation zones. Four GIS data layers (obtained from AVHRR channels 1, 3, NDVI and derived channel 6) were used in the reclassification scheme, which identified thresholds for the detection of snow-covered or snow-free areas. The scheme correctly predicted the presence or absence of snow cover 72% of the time using one evaluation method, and 78% of the time using a different evaluation method. The low resolution of the AVHRR data (1-km pixel size) and the small area of analysis probably reduced the accuracy of the results. Other possible inaccuracies in this method may be due to temperature variations that woul cause snow to either remain or melt sooner or later than expected, low or ice clouds mistaken for snow cover, snow cover under clouds mistaken for clouds, or errors in the climate data. The use of subpixel analysis, further validation of the spectral differences between snow, cloud and land in AVHRR data using higher resolution satellite images, or ground truthing could refine this procedure.