Advanced Remote Sensing, 2nd Edition

7.3. LSE estimation methods

For most land surface types in the natural world, emissivity is directional. Indirect measurement methods can measure emissivities at a zenith angle of 10°. Direct measurement methods can theoretically measure emissivities at zenith angles of 0–90° because of their greater flexibility. In LSE remote sensing retrievals, land surfaces are generally assumed as Lambertian, and directionality is neglected.

7.3.1. Emissivity measurement methods

There are two categories of emissivity measurement methods: indirect and direct measurement methods. Indirect measurement methods (Salisbury et al., 1994), based on Kirchhoff's law (for opaque objects, ε λ = 1 − ρ λ , where ρ λ is the directional hemispheric ...