Analytical Land–Atmosphere Radiometer Model

Abstract

Conversion of radiometric land surface temperature (?r) to an equivalent isothermal (aerodynamic) surface temperature (?i) is important in balancing the land surface energy budget with satellite-based ?r measurements. An analytical land?atmosphere radiometer model (ALARM) has been developed to convert ?r taken at any zenith view angle to ?i at a specified scalar roughness length z0h,i. Field data from 1987 and 1989 at the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) were used to evaluate the performance of ALARM. It was possible to find an optimal foliage temperature profile such that ALARM is consistent with these radiometric and atmospheric field data. The errors were significantly less when radiometer zenith angles were less than 40°. The foliage temperature at the canopy top ?fh and the foliage temperature profile curvature parameter b were parameterized as functions of air temperature and leaf area index, respectively. Using these parameterizations, ALARM predicted ?i from a single ?r measurement with a root-mean-square difference between predicted and measured values of 2.0 K or less, for view angles up to 40°. Using these ?i, ALARM estimated the sensible heat flux H into the atmosphere. Predictions of H were better (r2 > 0.5) with the 1989 data than with the 1987 data (r2 near 0).