A 2DVAR Mapping Method of CYGNSS Wind Speed Observations

The Cyclone Global Navigation Satellite System (CYGNSS) mission, launched in December 2016, provides ocean surface wind speed measurements from an eight satellite constellation using GPS reflectometry observations. The wind speed observations obtained provides unprecedented spatial and temporal coverage of the tropics, and is available even in regions of high precipitation. To fully use the CYGNSS winds, we plan to construct a gridded surface wind product based on CYGNSS observations. In the present research, a two-dimensional variational method (2DVAR) is developed to map the along track CYGNSS wind speed observations to a regular spatial grid. Due to the irregular but frequent nature of CYGNSS samples, the creation of surface wind products for science using CYGNSS data requires careful consideration in order to achieve the full benefit of CYGNSS measurements. The difficulty in using 2DVAR is that CYGNSS provides wind speed and not direction measurements, while the relationship between wind components and wind speed is nonlinear. To address this limitation, it is assumed initially that wind direction information from the background field applies to CYGNSS observations. The 2DVAR method is tested for the Indian Ocean region and some early results will be presented.