REVIEW AND IMPROVEMENT OF AN ALGORITHM FOR DETERMINING EMISSIVITY OF A HETEROGENEOUS CAVITY IN THERMAL INFRARED REMOTE-SENSING

The algorithm for determination of effective emissivity of a cavity de veloped by Caselles and Sobrino (Remote Sensing of Environment, 29, 13 5-146) has been proved to violate Kirchhoff's law, and to give low val ues of emissivity. In this paper a Kirchhoff's law-observing algorithm is developed, and comparison of the two algorithms is performed. Emis sivity retrieved by our algorithm can be 1.5 times larger than emissiv ity calculated with the algorithm of Caselles and Sobrino. Although no significant difference is found between them for almost blackbodies ( vegetated surfaces with large values of ground and vegetation emissivi ty), for other kind of terrestrial surfaces (bare soils and rocks) dif ference between the two algorithms can be up to 0.05 for a typical cav ity.