Exploiting Dense Coherent Reflection Track Areas in the Indonesian Seas to Investigate the Performance of Spire GNSS-R Ocean Altimetry

Spaceborne GNSS reflectometry (GNSS-R) precision ocean altimetry has been demonstrated to decimeter levels using carrier-phase observations from grazing-angle ocean reflections received on several low-Earth orbit (LEO) platforms including the Cyclone GNSS and Spire Global constellations in areas of high coherence such as quiet waters. In the open ocean, calm surface conditions are mainly found in the Gulf of Mexico and Indonesian Seas. Our study in the Gulf of Mexico showed that the grazing-angle Spire phase data can detect the large sea-level signature of the strong Loop-Current for moderate specular point elevations. However, almost half of these coherent Spire tracks provided retrievals inconsistent with the gridded sea level anomaly (SLA) derived from multi-mission nadir radar altimeters. We suspect that instrumental, atmospheric and/or geophysical correction errors either mismodelled or unaccounted for in our Spire's altimetry retrievals are the cause of the mismatch.