Category: Optical and atmosphere
Reflectance
Reflectance is the fraction of incoming light that a surface reflects, commonly used for analysis and comparison.
Also known as: surface reflectance (general)
Expanded definition
Reflectance expresses how much of the sun’s light is reflected by the surface relative to how much arrives. It is typically scaled so values fall between 0 and 1 (or 0 and 10,000 in integer-scaled products).
Reflectance is more comparable than radiance because it normalizes for illumination. However, the atmosphere and viewing geometry still affect reflectance unless further corrections are applied.
Many vegetation and water indices assume reflectance-like inputs. Using radiance or mixed products can lead to unstable index values and false change signals.
Related terms
Radiance
Radiance is the raw physical quantity measured by optical sensors, representing energy reaching the sensor.
TOA (Top-of-Atmosphere)
TOA reflectance is reflectance at the top of the atmosphere, before full atmospheric correction to the surface.
Surface Reflectance (BOA)
Surface reflectance estimates what reflectance would be at the ground after removing atmospheric effects.
NDVI
NDVI is a vegetation index that uses red and near-infrared reflectance to approximate vegetation greenness and vigor.