“The inversion unit derives the wind speed and direction from the NRCS, incidence
and track angles obtained from L1 product and a priori information from ancillary
data”
source: Sentinel-1 Ocean Wind Fields (OWI) Algorithm Definition.
Can someone explain to me if the wind direction from the OWI algorithm from Sentinel 1 OCN is being calculated with the geophysical model function or its using priori data from a weather forecast model?
As cited, the OWI algorithm is described in the Sentinel-1 Ocean Wind Fields (OWI) Algorithm Theoretical Baseline Definition Document available here: Sentinel-1 - Sentinel Online
This documents describes the wind inversion methodology.
In short, the algorithm is based both on inversion of a geophysical model function (providing relationship between wind speed, wind direction and incidence angle on one side and normalised radar cross section on other side) and a priori wind information from a weather forecast (for wind direction).
The output of the inversion process is a wind field with higher resolution than the weather forecast used as a priori, and with wind speed and direction that can be different. The provided wind speed and direction correspond to the most likely values considering the conditions of observations and the a priori wind directions.