HR: 1340h
AN: SF43A-0786    [Abstracts]
TI: The Geosat Geodetic Mission Twentieth Anniversary Edition Data Product
AU: * Lillibridge, J L
EM: John.Lillibridge@noaa.gov
AF: NOAA Lab for Satellite Altimetry code E/RA-31, 1335 East-West Hwy, Silver Spring, MD 20910 United States
AU: Smith, W H
EM: Walter.HF.Smith@noaa.gov
AF: NOAA Lab for Satellite Altimetry code E/RA-31, 1335 East-West Hwy, Silver Spring, MD 20910 United States
AU: Scharroo, R
EM: Remko.Scharroo@noaa.gov
AF: NOAA Lab for Satellite Altimetry code E/RA-31, 1335 East-West Hwy, Silver Spring, MD 20910 United States
AU: Sandwell, D T
EM: dsandwell@ucsd.edu
AF: University of California San Diego code 0225, 9500 Gilman Dr, La Jolla, CA 92093-0225 United States
AB: The Geodetic Mission (GM) of the U.S Navy's Geosat remains unique among all ocean radar altimeter satellite missions, yielding the most detailed resolution of the marine gravity field and offering the potential to extend the altimetric observation of global sea level rise back nearly a decade before the era of Topex and ERS-1. Geosat's Geophysical Data Records (GDR) structure is limited to centimeter-level precision in sea surface height, lacks the radar waveform reflected from the ocean surface, and has uncertain pedigree for some of the instrumental corrections. We are now reprocessing Waveform Data Records (WDRs) and Sensor Data Records (SDRs) from the GM and merging these into a new structure with millimeter-scale resolution of instrumental corrections wherever possible. Our new product will be available to the science community through NOAA. The ascii SDR and binary WDR were separated at birth and archived in different agencies. The only item common to both which allows their collation and merger is an oscillator tick counter, a proxy for time. We have repaired glitches in both data streams and merged them. Analysis and modeling of the oscillator counter time tags permits us to convert counts to time and obtain a model of the oscillator drift at the part-per-billion level, required for a range-dilation correction at the 1 mm level. The Doppler shift correction to range is large (13 cm) in Geosat and Topex compared to ERS1 (2.5 cm) due to their longer chirp duration. We have obtained a new Doppler correction at the 1 mm level, much smoother than that available on the SDR and used in the GDR. Retracking of the reflected waveforms [Smith and Sandwell, this meeting] improves the height precision and eliminates phase-shift errors, while also reducing correlation between errors in sea surface height and significant wave height, thereby reducing sea state bias. We will present an overall error budget and explore the possibility that this Geosat product may contribute to the resolution of late 20th-century sea level rise. Sandwell and Smith [this meeting] present seamount abundance and distribution results obtained from a new gravity field made with this new Geosat data product.
DE: 4203 Analytical modeling
DE: 4556 Sea level variations
DE: 4594 Instruments and techniques
DE: 3094 Instruments and techniques
DE: 1640 Remote sensing
SC: Special Focus: Advances in Data Acquisition, Management, Analysis and Display [SF]
MN: 2004 AGU Fall Meeting