Abstract's details
The Harvest Experiment: Updates from the Platform and Regional Campaigns
CoAuthors
Event: 2018 Ocean Surface Topography Science Team Meeting
Session: Regional and Global CAL/VAL for Assembling a Climate Data Record
Presentation type: Type Oral
Contribution: PDF file
Abstract:
We describe the latest satellite radar altimeter calibration/validation (CALVAL) results from data collected at the Harvest offshore platform. Located 10 km off the coast of central California near Point Conception, the Harvest oil platform has hosted a dedicated CAL/VAL facility for over 25 years, dating to the launch of TOPEX/POSEIDON (T/P) in August 1992. The T/P repeat ground track was designed to take the satellite directly over Harvest every ten days, enabling the development of a continuous calibration 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 through the platform.
Proper interpretation of the tide gauge data from Harvest requires careful monitoring of the non-linear land (seafloor) motion using observations from platform GPS systems. We have developed a new model of the complex vertical land motion at Harvest based on continuous GPS data from 1992–2018. This new land-motion model provides the basis for updated estimates of the sea-surface (SSH) bias and drift for the entire series of reference (T/P and Jason) altimeter missions dating back to 1992.
Based on data collected during 59 overflights of the latest (Jason-3) mission, we estimate the sea-surface height (SSH) bias is –14 mm. In contrast, results for Jason-1 and -2 yield a consistent SSH bias of +10 mm. Updated results for the legacy T/P mission yield SSH bias estimates of +4 and +3 mm respectively for TOPEX Sides A and B respectively and –15 mm for Poseidon-1. For the first time, the SSH bias estimates for all systems are in the range of ±15 mm, and none are statistically distinguishable from zero when systematic errors sources—such as the platform geocentric position error—are properly considered. In contrast, the relative Jason SSH biases are considered significant. In particular, the fact that Jason-3 measures lower (by 24 mm at Harvest) than both its predecessors is consistent with results from other calibration sites and global analyses.
We also report on new regional campaigns from the Harvest vicinity. Tide gauges have been installed provisionally on Santa Catalina and San Clemente Islands along the ascending track (No. 119) adjacent to and south of Harvest. Following successful deployments of our precise GPS buoy in 2016 at Daisy Bank (Oregon) and 2017 at Monterey Bay (California), a dual-buoy campaign is planned for the Harvest platform in 2018. Combined results from these campaigns testify to the potential of similar techniques for expanding the calibration footprint of Harvest in order to support other altimeter missions such as SWOT.
Proper interpretation of the tide gauge data from Harvest requires careful monitoring of the non-linear land (seafloor) motion using observations from platform GPS systems. We have developed a new model of the complex vertical land motion at Harvest based on continuous GPS data from 1992–2018. This new land-motion model provides the basis for updated estimates of the sea-surface (SSH) bias and drift for the entire series of reference (T/P and Jason) altimeter missions dating back to 1992.
Based on data collected during 59 overflights of the latest (Jason-3) mission, we estimate the sea-surface height (SSH) bias is –14 mm. In contrast, results for Jason-1 and -2 yield a consistent SSH bias of +10 mm. Updated results for the legacy T/P mission yield SSH bias estimates of +4 and +3 mm respectively for TOPEX Sides A and B respectively and –15 mm for Poseidon-1. For the first time, the SSH bias estimates for all systems are in the range of ±15 mm, and none are statistically distinguishable from zero when systematic errors sources—such as the platform geocentric position error—are properly considered. In contrast, the relative Jason SSH biases are considered significant. In particular, the fact that Jason-3 measures lower (by 24 mm at Harvest) than both its predecessors is consistent with results from other calibration sites and global analyses.
We also report on new regional campaigns from the Harvest vicinity. Tide gauges have been installed provisionally on Santa Catalina and San Clemente Islands along the ascending track (No. 119) adjacent to and south of Harvest. Following successful deployments of our precise GPS buoy in 2016 at Daisy Bank (Oregon) and 2017 at Monterey Bay (California), a dual-buoy campaign is planned for the Harvest platform in 2018. Combined results from these campaigns testify to the potential of similar techniques for expanding the calibration footprint of Harvest in order to support other altimeter missions such as SWOT.