Estimating Regional Distribution of Sensible Heat Flux over Vegetation using Satellite Infrared Temperature with Viewing Angle Correction

Abstract

The spatial distribution of sensible heat flux over rice paddies is estimated on a several tens kilometer scale, together with possible error estimation using satellite infrared data. It is found that three types of correction of satellite infrared temperature (correction for atmospheric absorption, satellite viewing angle, and the surface emissivity) over rice paddy yield estimation errors of 25Wm^-2 for sensible heat flux on a half-hourly basis as root mean squares errors (RMSEs). These errors are sufficiently small compared with general observational errors. In particular, the viewing angle correction is so significant that the RMSE is 46Wm^-2 without the correction. Atmospheric and emissivity corrections using the LOWTRAN7 with radio sounding data yield a good estimation of surface infrared temperature, with RMSE being 1.0°C. An empirical and linear parameterization proposed by Troufleau et al. (1997) is applied for the viewing angle correction. In the approach, parameters are refitted based on the surface infrared temperature data. The Troufleau et al. (1997) parameterization is applied over a wide range of leaf area index (LAI) from 0.01 through 5. This parameterization efficiently corrects the temperature deficit by the viewing angle effect caused by canopy geometry. However, this parameterization is insufficient when the sensible heat flux is large because the temperature deficit is essentially nonlinear with regards to the difference between surface infrared temperature and air temperature.