CoAuthors

Shailen Desai (Jet Propulsion Laboratory, California Institute of Technology, United States); Jean-Damien Desjonquères (Jet Propulsion Laboratory, California Institute of Technology, United States); Bob Leben (University of Colorado, Boulder, United States); Christian Meinig (NOAA Pacific Marine Environmental Laboratory, United States); Scott Stalin (NOAA Pacific Marine Environmental Laboratory, United States); Andy Wu (Jet Propulsion Laboratory, California Institute of Technology, United States)

We describe the latest satellite radar altimeter calibration/validation (CALVAL) results from the Harvest offshore platform and vicinity. Located 10 km off the coast of central California near Point Conception, Harvest has served as the NASA prime verification site for the TOPEX/POSEIDON (T/P) and Jason series of altimeter reference missions for three decades. The T/P repeat ground track was designed to take the satellite directly over Harvest every ten days, enabling the development of a continuous verification record based on direct, overhead passes of the platform. The crucial role of T/P in developing a climate-quality record of sea level and ocean circulation has been inherited by the Jason series of reference missions, which have traced out the same 10-d repeat ground track passing by the platform. With the beginning of the routine operations phase in November 2021, the Sentinel-6 Michael Freilich (S-6 MF) mission will assume the mantle of extending this valuable scientific observation record.

With the completion of the year-long S-6 MF commissioning phase, we estimate the sea-surface height (SSH) bias is +13 ± 3 mm (one standard error with N = 29) for the low-resolution mode (LRM) altimeter data. In terms of this bias, the current non-time critical (NTC) and short-time critical (STC) products are indistinguishable, as are the A and B sides of the Poseidon-4 altimeter. The corresponding Jason-3 (J-3) SSH bias is very consistent (+11 ± 2 mm with N = 174). Data from legacy Jason mission also yield slightly positive SSH biases: +6 ± 2 mm (N = 206) and +5 ± 2 mm (N = 249) for J-1 and J-2 respectively. Accounting for systematic errors, none of these SSH bias estimates are statistically different from zero. However, the relative (inter-mission) SSH biases carry greater statistical significance. If the comparison between J-3 and S-6 MF is restricted to common cycles, the result at Harvest indicates the new mission is measuring SSH higher than its predecessor by +5 ± 3 mm (N = 29), in keeping with preliminary results from global analysis.

We also provide preliminary results for reprocessed data from the legacy T/P mission, and describe developments from GPS buoy campaigns at Harvest. Results from a 2018–19 tandem GPS buoy campaign suggest RMS accuracies of <2 cm and <1 cm were achieved for absolute and relative SSH respectively. Following this successful campaign, we deployed in October 2020 a GPS buoy to start permanent occupation of the site (with yearly servicing trips). We report early results from this year-long deployment.