Analysis of GNSS-R Altimetry for Mapping Ocean Mesoscale Sea Surface Heights Using High-Resolution Model Simulations

The capability of global navigation satellite system reflectometry (GNSS-R) altimetry to map mesoscale sea surface height (SSH) fields is analyzed using synthetic measurements derived from a high-resolution (1/10°) numerical model of the North Pacific. As an example, we consider the GPS and GLONASS constellation transmitters and assume six reflection-capable receivers onboard the Constellation Observing System for Meteorology, Ionosphere, and Climate satellites in high-inclination (720 km, 72°) orbits. An individual GNSS-R measurement has a ~10-km footprint. The SSH measurement error is simulated as a function of the incidence angle and the error in the delay measurement between the transmitter and receiver. The delay measurement error is assumed to have Gaussian white noise distribution with a root-mean-square error (RMSE) of 1.0 or 2.0 m. Two days of synthetic measurements are used to reconstruct SSH fields using a two-dimensional variational algorithm. For the 1.0-m delay error, the basin-wide RMSE of the mapped field is 2.3 cm and the spatial correlation between the mapped and true mesoscale fields is larger than 0.9. For the 2.0-m delay error, the basin-wide RMSE is 3.8 cm and the spatial correlation is larger than 0.8. Spectral and synoptic analyses suggest that two days of measurements can reproduce mesoscale features down to 100 km. The result demonstrates the ability of GNSS-R altimetry to suppress large measurement errors due to the high density of measurements and the potential to constrain mesoscale features down to scales beyond what the constellation of existing nadir-altimeters allows.