Category: Optical and atmosphere
Radiance
Radiance is the raw physical quantity measured by optical sensors, representing energy reaching the sensor.
Also known as: top-of-sensor radiance
Expanded definition
Radiance is the amount of electromagnetic energy recorded by a sensor from a direction. It is influenced by the surface, the atmosphere, the sun angle, and sensor calibration.
Radiance is not directly comparable across dates or locations unless you correct for factors like illumination and atmosphere. That is why many analysis-ready products convert radiance to reflectance.
Radiance can still be useful when you want to apply your own calibration or correction methods, or when you need the most direct representation of what the sensor observed.
Related terms
Reflectance
Reflectance is the fraction of incoming light that a surface reflects, commonly used for analysis and comparison.
TOA (Top-of-Atmosphere)
TOA reflectance is reflectance at the top of the atmosphere, before full atmospheric correction to the surface.
Atmospheric Correction
Atmospheric correction removes or reduces atmospheric effects so scenes are more comparable across time and space.