Seasonal change of heat budget in Ikoma mountain forest estimated from satellite-derived data

摘要

The seasonal and spatial changes in heat budget terms in the forest in Mt. Ikoma area, located at the boundary of Osaka and Nara Prefectures, were estimated using LANDSAT/TM data, sensed in April, June, August and December. Sensible and latent heat fluxes were calculated using the bulk transfer equation for heat and for moisture, respectively. In the bulk equation for sensible heat transfer at each pixel, surface temperature (from TM band 6), air temperature (interpolated according to elevation) and wind speed (interpolated distribution using a variational method with consideration of complexity of the terrain) were used as variables. In the bulk equation for latent heat transfer, the moisture availability, wind speed, specific humidity of the air and saturation specific humidity at the surface temperature were used. The bulk transfer coefficient was corrected for diabatic conditions for each pixel. The moisture availability for each day was calculated, considering the normalized difference vegetation index (NDVI). The distribution pattern of estimated sensible heat flux showed a strong contrast between the east and west sides of the ridge line. This contrast became stronger under strong wind conditions. In summer, the value of sensible heat flux was estimated as 160W m~(-2) under a calm condition, while it exceeded 200 W m~(-2) in the case with more than 3 m s~(-1) of mean wind speed. The estimations of latent heat flux fell within the range of 350 (summer)- 100 W m~(-2) (winter). The moisture availability varied in the range of 0.15-0.53, according to wind speed and humidity. It was clear from this analysis that accurate interpolations of meteorological variables such as wind speed and air temperature distributions are important for deducing each heat flux, even with satellite-derived data.