The Harvest Experiment: Toward a Seamless Multidecadal Altimeter Calibration Record

Bruce Haines (Jet Propulsion Laboratory, California Institute of Technology, United States)

CoAuthors

George Born (University of Colorado, USA); Shailen Desai (Jet Propulsion Laboratory, California Institute of Technology, USA); Rashmi Shah (Jet Propulsion Laboratory, California Institute of Technology, USA)

Event: 2014 Ocean Surface Topography Science Team Meeting

Session: Regional and Global CAL/VAL for Assembling a Climate Data Record

Presentation type: Type Poster

Located about 10 km off the coast of central California, Harvest is a fixed oil platform sitting in about 200-m of water near the western entrance to the Santa Barbara Channel. In addition to its primary and ongoing role as an oil and gas production facility, Harvest has hosted a dedicated altimeter calibration experiment since 1992. Ascending pass No. 43 of the repeat ground track for the primary reference (Jason-class) altimeter missions passes through Harvest by design. This has enabling the development of a continuous, 22-yr altimeter calibration time series spanning the TOPEX/POSEIDON, Jason-1 and OSTM/Jason-2 missions and their combined climate record.

The current reference mission, Jason-2, has passed directly over the platform nearly 220 times, providing the basis for long-term monitoring of both bias and drift in the sea-surface height (SSH) measurements on the latest (D) version of Geophysical Data Records (GDR). The current Harvest calibration record for Jason-2 yields estimates of +18 ± 2 mm and +3 ± 2 mm/yr for bias and drift respectively (one standard error with N = 166). In view of systematic errors, such as uncertainty in the platform position and subsidence rate, neither estimate is considered statistically distinguishable from zero. We provide updates to these estimates based on the latest overflights, and also discuss any enhancements to the overall calibration record that bear on the interpretation of data from the legacy T/P and Jason-1 missions. In particular, we will report on results from the new (E) version of the Jason-1 GDR and describe the impact of this new product on reducing the significant observed SSH bias (currently +96 ± 2 mm with N = 208 using GDR-C).

We also describe preliminary results from the recently launched Indian/French SARAL mission, which carries a Ka-band altimeter (AltiKa). While this mission is on a different (35-d) repeat ground track, regional calibration methods (e.g., Cancet et al., this abstract volume) can be used to relate the satellite geophysical record to the Harvest site. Based on data from a descending pass 18 km from the platform, we obtain a bias of -26 ± 16 mm (N = 9) for the current SARAL data product.
 
Bruce Haines
Jet Propulsion Laboratory, California Institute of Technology
United States
Bruce.J.Haines@jpl.nasa.gov