Infrared remote temperature measurements: Its physics with reference to complexities, approximations and limitations involved. I - Conceptual considerations and surface temperature estimation

A critical review of spaceborne IR remote temperature measurements is presented, with particular reference to the spectroscopic aspect of the radiative transfer problem in order to reveal the intricacies and uncertainties in the formulation of the radiative transfer equation. Attention is given to the concept of local thermodynamic equilibrium and to the determination of surface temperature, especially over oceans where it is difficult to get data by conventional methods. Estimation of sea-surface temperature using 3.7- and 11-micron channels as well as the use of a statistical technique in obtaining clear column radiance from cloudy areas are discussed.