Heat Budget Estimation of a Forest Area Using LANDSAT-TM Data

Abstract

Distributions of heat budget terms of the forest in Mt. Ikoma area, located at the boundary of Osaka and Nara Prefectures, are analyzed using LANDSAT TM (Thematic Mapper) data. Sensible and latent heat fluxes are derived independently by the use of the bulk equations. In the bulk equation for sensible heat transfer at each pixel, surface temperature (provided by TM band 6 data), air temperature (interpolated according to elevation) and wind speed are used as variables. The bulk transfer coefficient is corrected using the bulk-Richardson number calculated from air and surface temperatures for each pixel. The moisture availability, wind speed, specific humidity of air and saturation specific humidity at surface temperature are used as variables in the bulk equation for latent heat transfer. The normalized difference vegetation index (NDVI) is used to estimate the moisture availability for each pixel. The bulk transfer coefficient for water vapor is assumed to be equal to that for heat.
TM data, sensed on August 6, 1990 is used to estimate distributions of heat budget terms in this study. The heat fluxes, averaged over the forest area, are estimated as 269Wm^-2 for sensible and 256Wm^-2 for latent heat, whereas mean estimations for net radiation and ground heat flux are 529Wm^-2 and 42Wm^-2 respectively. The mean value of moisture availability in the bulk equation for latent heat transfer is derived as 0.08. The distributions of sensible and latent heat flux in the forest area show that each flux on east side of mountain is greater than that on west side, because surface temperatures on east side are higher than those on west side approximately 2-3°C, due to the azimuth angle of the sun.