Remote Sensing of the Radiation Balance during the Growing Season at the Niwot Ridge Long-Term Ecological Research Site, Front Range, Colorado, U.S.A.

This paper examines the use of Landsat Thematic Mapper and digital terrain data combined with a radiative transfer model to map the spatial patterns of the radiation balance at the Niwot Ridge Long-Term Ecological Research (LTER) site during the 1986 growing season. The analysis of maps and profiles of the components of the radiation balance for this alpine tundra site show particularly important contrasts in solar radiation receipts and longwave exitance between north-and south-facing slopes on a given day at the time of the satellite overflights. However, 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. Leeward (east-facing) slopes that accumulate a deep snowpack during the winter experience the largest decrease in surface albedo. Albedo for these slopes decreased from about 0.55 to 0.15 while remaining nearly the same for west-facing (windward) slopes. Finally, the good agreement between estimates of the radiation balance and its components, and surface measurements acquired during three summer field seasons on Niwot Ridge suggest that the approach is suitable for mapping incoming and outgoing fluxes over mountainous areas at the spatial resolution of Landsat TM, and potentially at that of higher or lower resolution satellite sensors.