CoAuthors

Eric Leuliette (NOAA Lab. for Satellite Altimetry, USA); Frank Lemoine (NASA/GSFC, USA); Nikita Zelensky (SGT, USA); Brian Beckley (SGT, USA); Remko Scharroo (EUMETSAT, Germany); Walter Smith (NOAA Lab. for Satellite Altimetry, USA)

The U.S. Navy's Geosat mission yielded the first multi-year high-precision radar altimetry data set, and provides the only global sea surface height measurements from the late 1980s. NOAA has produced several versions of the Geophysical Data Records (GDRs) for the mission, with the most recent data release in 1997. This was the first set of GDRs that spanned both the Geodetic Mission (GM: March, 1985 to September, 1986) and Exact Repeat Mission (ERM: November, 1986 to December, 1989).

In April, 2009 we concluded a major data archaeology effort to recover the original Sensor Data Records (SDRs) for the ERM from 9-track tapes. After the SDRs are combined with their companion Waveform Data Records (WDRs) it is possible to retrack the original radar echoes, yielding an improved level-2 data set. This had previously been done for the GM in 2004, and has now been completed for the ERM as well.

This poster describes the steps involved in assembling the full GM+ERM retracked altimetry data set. A major enhancement involves the calculation of precise orbits based on the latest gravity models, terrestrial reference frames, and Doppler station coordinates, with improved Vienna Mapping Function atmospheric refractions. The best possible geophysical corrections are provided, along with the retracked sea surface heights, including GOT4.8 tide models, ECMWF tropospheric corrections, NIC09 climatological ionospheric corrections, and a new sea state bias model.

Ultimately our hope is to extend the altimetric sea level climate data record back to 1985, with the inclusion of these retracked Geosat measurements. Validation via the global tide gauge network from the late 1980s will allow us to assess the accuracy of the sea level trends observed by Geosat.