| Bidirectional Reflectance Distribution Function (BRDF)
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- BRDF ( f ) is the most fundamental property describing the complete reflectance characteristics of a surface and is given by the following equation:
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- In the above equation, unprimed angles describe location of radiation source, primed angles refer to location of sensor. ω and ω' are generally small enough in practical RS geometric arrangement so that the property of the quantity in question does not vary appreciably as a function of these solid angles.
- BRDF is a function of incident and reflected radiation expressed by θ, Φ ; θ', Φ'. In literature, f is also sometimes referred as ρ ( θ, Φ ; θ', Φ' ).
- BRDF describes bidirectional reflectance values for all combinations of input-output angles and provides reflectance as a function of illumination geometry and viewing geometry.
- It is function of wavelength and cumbersome to determine but can be measured in field and laboratory.
- Values available only for a limited number of materials and land cover types.
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| In the adjacent figure, consider a small element solid angle dω which can be expressed as dω = sinθ dθ dΦ. Taking L( θ,Φ ) as incident radiance from direction ( θ,Φ ) through a solid angle dω, the irradiance from the same direction is given as
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| Measurement of BRDF is complex since accurate measurement of dE( θ,Φ ) at the target surface is generally inconvenient.
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