抄録
A number of investigators have conducted experiments that used radiative surface temperatures to evaluate the evapotranspiration (ET) on spatial scales from a field plot (using hand-held radiation thermometers) to a regional size (using certain satellite sensors). The purpose of this paper is to review those studies and to present some of the author's recent results, employing a simple estimation model of ET above vegetation.
Studies concerning estimation of ET using remotely sensed thermal measurments were classified into two categories according to platforms of measurements. The first group includes studies which used ground-based measurements to develop models for estimating ET or monitoring the moisture condition of plants or soil. The other group includes studies which used data obtained by air- or spacecraft to estimate soil moisture or ET on a regional scale.
The authors tested the modified equilibrium evaporation model to estimate ET above crops and forests. This model uses surface temperatures of plant canopies to evaluate equilibrium evaporation rather than using air temperatures that have been a convention. The ET estimation is calculated by multiplying the surface-dependent parameter by the equilibrium evaporation, which is a function of surface temperature, net radiation and soil heat flux. Field experiments were conducted to obtain model parameters for a wheat field, a rice paddy and a broad-leaf forest on fine days under drought-less condition. Equilibrium evaporation values cal-culated using canopy surface temperatures were compared with measured ET values using the energy budget with Bowen ratio method. The results indicated model parameters of 1.03 and 1.06 for both kinds of fields and for the broad-leaf forest, respectively.
This model was applied to satellite data (NOAA/ AVHRR data) for estimating ET of the broad-leaf forest under droughtless conditions. The estimated values agreed well with measured values, and thus the model was proved effective.
