A methodology for mapping forest latent heat flux densities using remote sensing

Abstract

Basin-scale forest evapotranspiration is strongly influenced by the allocation of net radiation on the watershed. Forested watersheds typically have a wide variety of slopes, aspects, cover types, and other variables which affect the allocation of net radiation. Remote sensing can provide a means to analyze the distribution of solar energy on forested watersheds because of its synoptic coverage. A pilot study was conducted in which surface temperatures and reflectances of an upper elevation Sierran Mixed Conifer Forest were monitored using the Thematic Mapper Simulator (TMS) sensor during the summer of 1985. TMS Bands 3, 5, 7, and 11 (TM Bands 2, 3, 4, and 6) were combined with surface meteorological data and input into an energy budget model designed to generate images which describe the available evaporative energy within the watershed. The results of this initial validation indicate that the model responds well in quantifying relative energy allocation relationships between the two cover types defined in this study. In addition, this methodology has the potential to map forest latent heat flux densities provided that some of the model parameters can be assessed more accurately. It is anticipated that this technique can prove useful in helping to make more efficient decisions concerning water yield from forested environments.