Sun Glint evaluation (*)

Sun glint normalized reflectance is calculated in SaVoir according to the Cox-Munk model, in simplified conditions of constant wind speed (7 m/s average) and disregard for wind direction, and normalized according to the NASA definition.

The probability of a spatial sample being contaminated by sun glint is given by:

where

is the sun zenith angle (SZA) at the viewed spatial sample.

is the observation zenith angle (OZA) at the viewed spatial sample.

is the relative azimuth angle at the viewed spatial sample

is the mean square surface slope which is function of wind speed Ws (m/s)

Sun glint is evaluated at a wind speed of Ws = 7 m/sec

The glint reflectance is given by

where

r = 0.02 (Fresnel water reflection coefficient)

is the angle formed by the reflecting facet normal and the local normal defined by

where

is the specular reflection angle defined by

The "sun glint normalized radiance" is further evaluated as

which is how it is defined by NASA. This will tend to reduce the size of the glint region.

(*) This algorithm is derived from ESA's GMES Sentinel-3 System Requirements Document S3-RS-ESA-SY-0010 Issue 2.1, 15/02/2007