RADIOMETRICALLY DETERMINED SKIN TEMPERATURE AND SCALAR ROUGHNESS TO ESTIMATE SURFACE HEAT-FLUX .1. PARAMETERIZATION OF RADIOMETRIC SCALAR ROUGHNESS

A series of experiments carried out in a pasture field during a growing season, allowed a radiometric determination of the scalar roughness for sensible heat z(oh,r). The values of z(oh,r) are shown to vary over the range of 10(-1)-10(-7) M both diurnally and seasonally, and an existing theoretical model for the estimation of scalar roughness for sensible heat is found to be inappropriate for the precise estimation of z(oh,r). To parameterize z(oh,r) better, a multiple regression analysis was performed, with predictor candidates such as solar elevation, solar radiation R(s), leaf area index LAI, canopy height, the ratio of the solar radiation and the extraterrestrial radiation R(s)/R(e) the ratio of the direct and the total solar radiation R(d)/R(s), and the roughness Reynolds number among others. The best regression equation which uses R(s), LAI, R(s)/R(e), and R(d)/R(s), is derived with r = 0.75; with smaller numbers of predictors, values of r tend to deteriorate gradually down to r = 0.52 when only one predictor, LAI, was incorporated into the equation.