Near Real-time Altimetry from ERS-2 and Topex/Poseidon

Bob Cheney, John Lillibridge, John Kuhn, Nancy Doyle

NOAA Laboratory for Satellite Altimetry

1315 East-West Hwy

Silver Spring, MD 20910

John Blaha

Naval Oceanographic Office

Stennis Space Center, MS 39522

NOAA and Navy are working together with the international space agencies (NASA, ESA, CNES) to acquire and process satellite altimeter sea surface height data fast enough to be of value for operational ocean programs. Near real-time data are presently being generated for both ERS-2 and Topex/Poseidon (T/P). Delay times and accuracies are determined primarily by the way in which the satellite orbit is derived. In the case of NOAA's ERS-2 and the Navy's T/P processing systems, operational orbit predictions made by Delft University and the Jet Propulsion Lab, respectively, are used to achieve fast turnaround times (12-24 hours), but the sea heights have uncertainties of several decimeters. These data are therefore useful primarily for mesoscale applications (e.g. Gulf of Mexico, Gulf Stream). A second, more accurate T/P data stream has recently been implemented which takes advantage of an automated, near real-time GPS tracking system operated at JPL. The resulting T/P data are available with a delay of about 2 days and will be used for operational assimilation in global ocean circulation models of the type used at NOAA to predict El Nino.