Examination of Snow Mapping Methods over the Weber River Basin, Utah, Using MODIS Observations

The MODIS instruments on the NASA Terra and Aqua spacecraft provide snow cover observations on a daily basis when cloud cover permits over the globe as well as for regional and local areas. This study reports progress on some work using Terra MODIS snow cover observations centered on the Weber River Basin. The Weber Basin covers 2500 square miles/6400 square kilometers within the Great Salt Lake Basin in Utah. The study is presently focused on comparing various snow mapping methods in mapping snow cover in this basin using primarily the first six months (January to June) for the 2001, 2002, and 2003 years. The snow-mapping methods compared are the standard SNOWMAP (daily and 8-day) products and the fractional snow cover product provided operationally by MODIS (designated MOD10 A1 and MOD10 A2) on lists of MODIS products), and a spectral end-member approach employing atmospherically-corrected surface reflectance (the MOD09GHK product). The spectral end-member approach used three end-members—snow, soil/rock, and vegetation. The estimates of snow cover obtained by each of products noted above are compared for each of the 3 years studied. ASTER data are analyzed and used for ground-truth/comparison purposes. Most results are obtained using ENVI/IDL and ArcMAP. The results indicate that the spectral endmember approach consistently obtains lower values of snow cover than the other methods and the results seem to compare more favorably with the higher resolution ASTER snow cover observations. In addition the results show differences in the rate of snow cover depletion in each of the years with 2003 distinctly showing less snow cover than the other two years. Future efforts are going to be placed on relating temporal snow cover observations to observed runoff statistics to with the ultimate objective of assessing the utility of these satellite observations in runoff prediction