Ocean Topography images are derived from data collected by the TOPEX/POSEIDON and Jason-1 satellite altimetry missions. These are joint missions between CNES, the French space agency, and NASA, the U.S. space agency. TOPEX/POSEIDON has been operating since August, 1992. On board the satellite is a dual-frequency radar altimeter (TOPEX), a single-frequency solid-state altimeter (POSEIDON), the TOPEX Microwave Radiometer (TMR), a DORIS tracking system receiver, a laser retroreflector array, and a Global Positioning System (GPS) receiver. Jason-1 is the TOPEX/POSEIDON follow-on mission, which has been operating since December, 2001. This satellite carries the dual-frequency radar altimeter (POSEIDON-2), the Jason Microwave Radiometer (JMR), a DORIS tracking system receiver, a laser retroreflector array, and a GPS receiver. In addition to extending the measurements made by TOPEX/POSEIDON, the Jason-1 mission has an improved overall measurement accuracy of 2.5 cm.
Global Images are created from the near-real-time data products delivered to PO.DAAC by the TOPEX/Jason Ground System and JPL Global Positioning Group. We provide browse images for: Sea Surface Height Anomaly (SSH - mean SSH). These images are binned and averaged on a 0.5 degree global grid for different time periods; they are also smoothed and interpolated using a Gaussian-type filter. SSH images will be available soon.
Jason-1 Along Track Images show along track values for several parameters contained within the Operational Sensor Data Record (OSDR) and Interim Geophysical Data Record (IGDR) data products. OSDR files are provided every 2 hours and within 3 hours of data collection. They contain wave height, wind speed and water vapor measurements computed using real-time on-board DORIS/DIODE orbits (expected accuracy 30 cm) and other rapidly available corrections. IGDR files contain full accuracy altimeter data, with the exception of an interim orbit (expected accuracy <4 cm), provided within 3 days of data collection. The instruments on Jason-1 make direct observations of the following quantities: altimeter range, significant wave height, ocean radar backscatter cross-section (a measure of wind speed), ionospheric electron content (derived by a simple formula), tropospheric water content, and position relative to the GPS satellite constellation. The IGDR contain all relevant corrections needed to calculate the sea surface height. Sea surface height anomalies are derived from the 1/second IGDRs and are based on the recommended data edit criteria specified in the Jason-1 I/GDR User Handbook. |
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