How is the wind direction calculated in Ocean Wind Field (OWI) product?

“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
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.

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