Mesoscale Ocean Surface Height Retrieval with CYGNSS

CyGNSS is a constellation of 8 small satellites launched in December 2016 that carries the Surrey Satellite Technologies (SSTL) SGR-ReSI GNSS Reflections (GNSS-R) receiver. Developed as the primary science instrument for CyGNSS, the SGR-ReSI receiver performs real time onboard navigation and generates delay-Doppler correlation maps for Earth reflected GPS L1 C/A ranging signals. While these functions were designed primarily to facilitate the retrieval of ocean surface wind speeds, this research explores ocean surface altimetry retrievals using the CyGNSS data sets. The data sets analyzed here span March 18 – June 3, 2017 at +/- 38 deg latitude.

This early analysis includes consideration of the transmitter and receiver orbits, models for ionospheric and tropospheric delays, and mean sea surface topography in the reflection model. In comparison with this reflection model, a statistical analysis of the individual measurement surface height residuals is presented. We further explore the use of a two-dimensional variational algorithm to smooth the altimetric retrievals thereby improving upon the individual measurement errors. We compare retrieved sea surface maps to high resolution regional ocean models in the Pacific to determine the achievable level of performance with the CyGNSS configuration.