Oct 15, 2026
NASA’s Physical Oceanography Distributed Active Archive Center (PO.DAAC) is publicly releasing a value-added SWOT Level 2 Near Real Time GPS Nadir Altimeter Operational Geophysical Data Record (NRT GPS OGDR). The dataset produced by the Surface Water and Ocean Topography (SWOT) mission, provides sea surface height, significant wave height and wind speed measurements from the Poseidon-3C nadir altimeter, a Jason-class dual frequency (Ku/C) altimeter. SWOT is a joint mission between NASA and CNES that launched on December 16, 2022. It aims to measure ocean surface topography with unprecedented resolution and accuracy, as well as map inland water bodies globally.
This value-added, best efforts product supplements the standard SWOT Nadir Altimeter OGDR dataset, another near real time product at NADIR from the SWOT mission. Latency for the NRT GPS OGDR dataset is slightly longer (3-5 hours vs 1-3 hours for the standard OGDR), but provides higher accuracy, similar in quality to those provided on the next-day SWOT Nadir Altimeter Interim Geophysical Data Record (IGDR). The higher accuracy is achieved by utilizing a GPS-based orbit ephemeris instead of the onboard DORIS orbit ephemeris, and accounting for radiometer beam pointing and spacecraft attitude when computing the radiometer wet troposphere correction.
Other than the latency and accuracy differences, the data file structures between the standard OGDR and this dataset are otherwise identical. Both consist of discrete measurements along the nadir track with posting intervals of approximately 6-km and 300-m at 1Hz and 20Hz, respectively. The data are distributed as one file per data downlink in netCDF-4 file format. Additionally, this NRT GPS OGDR collection also has no sub-collections, unlike the standard OGDR collection.
The dataset is described and discoverable via Earthdata Search and the following DOI:
If you have questions, please contact podaac@podaac.jpl.nasa.gov or visit PO.DAAC on Earthdata Forum.
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User Services Office
NASA JPL Physical Oceanography DAAC
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