Concise formulae for the atmospheric correction of hemispherical thermal radiation measured near the ground surface

Abstract

This paper presents the analysis of the atmospheric effects on the measurement of the thermal radiation near the ground surface. The difference of the thermal radiation L at surface and L at some height z was evaluated for various atmospheric conditions and for different sensor heights with the LOWTRAN 7 radiation transfer code. It was found that in many cases the effects of transmission of radiation primarily due to the presence of water vapor and secondarily to other minor gases and aerosols are not negligible for the upward component of thermal radiation, whereas they can be neglected for downward component. Based on the results of LOWTRAN 7 calculations, a simple regression equation of atmospheric path transmissivity ra in terms of the total water vapor w within the air layer between the surface and the sensor height and that of emittance from the air layer between the ground and the sensor height La in terms of w and temperature were obtained; these will then allow the practical estimation of ra and La from measurements of air temperature and humidity near the ground for the atmospheric correction of the upward thermal radiation measured at a certain height. This procedure can be applied to derive net radiation at the ground surface from a four-component radiometer measurement above the ground and also to derive surface radiative temperature from pyrgeometer measurements of the upward long-wave radiation. © 2009 by the American Geophysical Union.