《The definition of effective emissivity of land surface at the scale of RS pixels》.pdf

NOTES The definition of effective emissivity of land surface at the scale of remote sensing pixels LI ~iaowen* * and WANG ~indi 1 . Research Center for Remote Sensing and C I S , Retjing N ~ Uniirrvity,I ~ Retjing 100875, C h m ; 2 . Centcr for Xemote Semihg. Boston U r u i . , MA022 15, USA Abstract Remote sensing (RS) of land surface temperature (LST) is a very challenging prob- lem at the present development stage of RS science. Tremendous efforts have been devoted to atmosphere correction and temperature emissivity separation (TES) of new LST product algo- rithms. However, the mechanism of directionality of thermal emission from land surface remains unknown, and even worse, there are confusions on the definition of the effective emisswi of land surface at the scale of RS pixels. The mechanism of directionality of thermal emission for isothermal pixels and non-isothermal pixels is different. For non-isothermal pixels (case in most canopy/soil structures), the directionality of their thermal emission is determined by both bidi- rectional reflectance distribution function (BRDF) derived emissivity and distribution patterns of temperature differences. A new definition is suggested to take into account material mixture, multiple scattering, and temperature variation within thermal infrared (TIR) RS pixels. Keywords : non-isothermal pixel, effective emissivity ,directionality of thermal emission. THERS of LST is very difficult partly because there are more unknowns, for example, in visible and near i n f d (VNIR) bands, ( e .g. spectral emissivity in addition to LST, atmospheric emission in addition to scattering), and more variability of these unknowns than in the RS of sea surface temperature. Fortu- nately, in the past decades, a number of algorithms have been developed to overcome these difficul- ties-31 . They in