REMOTE-SENSING OF THE RADIATION BALANCE DURING THE GROWING-SEASON AT THE NIWOT RIDGE LONG-TERM ECOLOGICAL RESEARCH SITE, FRONT-RANGE, COLORADO, USA

This paper examines the use of Landsat Thematic Mapper and digital ter rain data combined with a radiative transfer model to map the spatial patterns of the radiation balance at the Niwot Ridge Long-Term Ecologi cal Research (LTER) site during the 1986 growing season. The analysis of maps and profiles of the components of the radiation balance for th is alpine tundra site show particularly important contrasts in solar r adiation receipts and longwave exitance between north- and south-facin g slopes on a given day at the time of the satellite overflights. Howe ver, the presence of snow and consequently higher albedo in the early part of the growing season is the most important factor that explains the difference in the radiation balances between June and August. Leew ard (east-facing) slopes that accumulate a deep snowpack during the wi nter experience the largest decrease in surface albedo. Albedo for the se slopes decreased from about 0.55 to 0.15 while remaining nearly the same for west-facing (windward) slopes. Finally, the good agreement b etween estimates of the radiation balance and its components, and surf ace measurements acquired during three summer field seasons on Niwot R idge suggest that the approach is suitable for mapping incoming and ou tgoing fluxes over mountainous areas at the spatial resolution of Land sat TM, and potentially at that of higher or lower resolution satellit e sensors.