Reflectance to Radiance Algorithm Specification |

### Reflectance to Radiance

Reflectance is the proportion of the radiation striking a surface to the radiation reflected off of it.
Radiance is the amount of radiation coming from an area.
Top-of-atmosphere reflectance (or TOA reflectance) is the reflectance measured by a space-based sensor flying higher than the earth's atmosphere.
These reflectance values will include contributions from clouds and atmospheric aerosols and gases.

The Reflectance to Radiance results from the following formula:

radiance = pixelValue * cosinus(radians(incidenceAngle)) * solarIrradiance * scale / (pi * d2)

, where:
d2 = 1.0 / U (the sun-earth distance)
solarIrradiance = the mean solar exoatmospheric irradiances for each band
scale = 1 / (0.001 * 1000) = 1 (default)

For Sentinel-2 the incidence angle is replaced with the values from the sun_zenith band.