Radiometric corrections

Convert relative digital-number to at-sensor radiance

Raw spectral signature (digital numbers)

Physical unit of measurement spectral signature (spectral radiance [watts/m².μm])

Conversion to at-sensor radiance is needed in pre-processing if the image is to be used for:

Calculation of biophysical variable is required (e.g. temperature, absorption)
Multi-date mapping of biophysical variables
Using field measured spectral-signature libraries to process data

Converts relative sensor measurement (digital-numbers) to an absolute physical unit of measurement AT THE SENSOR: (e.g. spectral radiance [watts/m².μm] ).

Conversion equation is established for each band(λ) pre-launch and in some cases updated post-launch: At-sensor spectral radiance _λ = [gain _λ * DN _λ] + offset _λ

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correction types