Satellite radar altimetry plays a crucial role in monitoring the topography and sea state of the world's oceans. NASA's TOPEX/Poseidon and Jason-1 missions have delivered nearly a half-million global sea level measurements every 10 days, with either or both TOPEX/Poseidon and Jason operating continuously since 1992.
NASA's Earth Sciences Senior Review (2005) recognized the criticality of ocean radar altimetry by rating Jason as the mission with the highest scientific value and highest relevancy to NASA's Earth Science Strategy of the 12 missions which had entered into their extended mission phase. The Review noted that: "Extending observations of sea surface topography to decadal scales is essential to implementation of NASA's 10-year goals in addressing the fundamental questions: 'How is the Earth changing and what are the consequences for life on Earth?' and 'How can predictions of climate variability be improved?'"
A continuous record of global sea surface height requires an exacting effort to provide these data free from instrument-dependent biases and from algorithm and model inconsistencies. Many altimeters in assemblage, with different characteristics and processing histories, are required to provide this multi-decadal record. Today there are three active radar altimeter missions (Jason, Geosat Follow On (GFO), and Environmental Satellite (Envisat)). Extending the observations to latitudes greater than 66°requires incorporation of radar altimeter data obtained from other missions (ERS-1, ERS-2, Envisat) which have less inherent accuracy than that of TOPEX/Poseidon and Jason.
Extending the series backward in time requires evaluating data from many earlier missions that have temporal gaps in coverage. For this proposed work we will start by improving the quality of the Climate Data Records produced from TOPEX/Poseidon and Jason based on concurrent progress made in a wide variety of areas including the Gravity Recovery and Climate Experiment (GRACE) gravity field modeling and resulting improvements in orbits and the geoid, the ocean response to atmospheric pressure loading, the sea-state bias, and in the definition of the International Terrestrial Reference Frame (ITRF). We will leverage these improvements by suitably applying them to increase the value of historical altimeter holdings for climate research.
Our proposal is based on work started in the mid-1990s under the auspices of the NASA Earth System Science Pathfinder Program. Our team undertook the reprocessing of data from both older and then-current radar altimeter missions to increase their accuracy and consistency. Despite having over 300 regular users and providing a key data base for monitoring ocean circulation, sea-level rise, and other ocean variability, this Ocean Altimeter Pathfinder Project was discontinued in 2002. Herein we propose building on our previous work with the Ocean Altimeter Pathfinder Project -- by availing ourselves of the recent remarkable progress made in improving (a) gravity fields for geoid and orbit applications, (b) ocean tide models, (c) calibrations of radiometers needed to remove long-period trends in the wet troposphere corrections, (d) sea-state algorithms, and (e) in the International Terrestrial Reference Frame. All of these improvements are well-documented in the literature, are within the capabilities of our proposed team, and will be well-coordinated within the physical oceanography community through our continued participation within NASA's Ocean Surface Topography Science Team.
These data will be made available to the outside community through the nearly total reuse of the robust Ice, Cloud, and land Elevation Satellite Science Investigator-led Processing System (ICESat SIPS).
Distributed by NASA's Physical Oceanography Distributed Active Archive Center (PO.DAAC).