Assessment of Spire GNSS-R Winds and Mean Squared Slope

On December 11, 2019, Spire Global launched two satellites with Global Navigation Satellite Service Reflectometry (GNSS-R) sensors to provide ocean wind and mean squared slope (MSS) estimates. These data have been acquired through NASAs Commercial Smallsat Data Acquisition (CSDA) Program and are available for scientific investigations. These data add a commercial source of ocean sea state estimates to a constellation of government operated assets. With this presentation, we will provide an assessment of the wind speed and MSS retrievals from Spire via co-locations with model based wind (ERA5) and MSS (IFREMER WAVEWATCH III) as well as Cyclone Global Navigation Satellite System (CYGNSS) estimates. ERA5 and WAVEWATCH III are often used for satellite validation, providing reliable estimates with high spatio-temporal resolution, and CYGNSS uses a constellation of 8 small satellites and validated algorithms to provide estimates using a similar GNSS-R technique as the Spire sensors. Together they provide frequent coincident measurements over a wide range of geophysical and remote sensing conditions from which to provide a meaningful assessment of Spire data. Assessment of the Spire product spatial and temporal sampling characteristics together with relative retrieval bias and variability (offset and random component statistical summary) with respect to reference observations will be presented as well as an assessment of retrieval stability (temporal variability) and geospatial consistency with respect to the reference observations.