INFRARED REMOTE TEMPERATURE MEASUREMENTS: ITS PHYSICS WITH REFERENCE TO COMPLEXITIES, APPROXIMATIONS AND LIMITATIONS INVOLVED. 1-CONCEPTUAL CONSIDERATIONS AND SURFACE TEMPERATURE ESTIMATION

Abstract

A nondetailing account of limitations and approximations involved in the formulation of the theo ry of temperature measurements by satellite exploiting the use of infrared terrestrial emission spectra is presented. Starting from spectroscopic considerations the concept of Local Thermodynamic Equilibrium (LTE), which poses altitude limitation in remote temperature measurements, is introduced towards equating the self-emission function to Planck's black body function. Slirveying the emission spectra of various at nonspheric gases the reasons in favour of choice for 4.3 um and 15 um CO2, bands are discussed. Theoretical and experimental attempts, citing the main uncertainities and limitations, for computing absorption in band/sub-bands demanded for solution of radiative transfer equation including the validity of various line shapes, the effect of time variation of CO 2 concentration and the contribution of averaging over  radiometer/spectrometer filter-transmittance function/slit function towards Proximations have been discussed. Estimation of sea surface texparature usiag 3.7 and 11 um channels towards its estimation in cloudy conditions and the effects of e-type absorption arising due to dimeric Water molecule formations cn window region measurements and the recently reported classical  statistical technique to get clear column radiance from cloudy areas have been discussed.