NODC Standard Product: US Navy Geosat altimeter Crossover Differences (XDRs) for the Geodetic Mission (8 disc set) (NCEI Accession 0054498)
This dataset contains a copy of the NODC eight CD-ROMs product set of the Geosat altimeter Crossover Differences data Records (XDRs) for altimeter data obtained between March 30, 1985 and September 30, 1986, the period known as Geosat's Geodetic Mission (GM). These data are in binary format.
The U.S. Navy Geosat altimeter mission lasted for nearly 5 years, from April 1985 to January 1990. Geophysical data records (GDRs) from the final 3 years, when the satellite was performing the exact repeat mission (ERM), were produced by NOAA's National Ocean Service and have been widely distributed. In contrast, GDRs from Geosat's first 18 months (April 1985 to September 1986), known as the geodetic mission, are classified because of military applications related to knowledge of the marine geoid. Only the altimetric heights are considered secret, however, and unclassified subsets of these data have been released. Another unclassified data type is the crossover difference. A crossover is defined as the intersection of the satellite ground track with itself. At this location, the two crossing passes (one ascending and one descending) provide independent sea level measurements at the same place but at different times. The difference of these two sea level measurements (a crossover difference) is not considered classified because the geopotential component of sea level is the same at the intersection of the two tracks and thus cancels. Crossover differences contain information about uncertainties in the satellite ephemeris and therefore enable correction of radial orbit error.
The Geosat altimeter crossover difference records (XDRs) contained on these CD-ROMs are documented in a NOAA handbook (Cheney et al. 1991b); see reference listing in the supplementary information field below. Although only the 18-month GM data are classified, XDRs have been constructed for the first 2.5 years of the Geosat mission, e.g., data from the GM plus the first year of the ERM. This was done to minimize the effect of the 5-week data gap (October 1 to November 8, 1986) between the two missions when the altimeter was off during orbit maneuvers. By computing crossovers for the entire 2.5-year period, continuous sea level time series can be derived.
The U.S. Navy Geosat altimeter mission lasted for nearly 5 years, from April 1985 to January 1990. Geophysical data records (GDRs) from the final 3 years, when the satellite was performing the exact repeat mission (ERM), were produced by NOAA's National Ocean Service and have been widely distributed. In contrast, GDRs from Geosat's first 18 months (April 1985 to September 1986), known as the geodetic mission, are classified because of military applications related to knowledge of the marine geoid. Only the altimetric heights are considered secret, however, and unclassified subsets of these data have been released. Another unclassified data type is the crossover difference. A crossover is defined as the intersection of the satellite ground track with itself. At this location, the two crossing passes (one ascending and one descending) provide independent sea level measurements at the same place but at different times. The difference of these two sea level measurements (a crossover difference) is not considered classified because the geopotential component of sea level is the same at the intersection of the two tracks and thus cancels. Crossover differences contain information about uncertainties in the satellite ephemeris and therefore enable correction of radial orbit error.
The Geosat altimeter crossover difference records (XDRs) contained on these CD-ROMs are documented in a NOAA handbook (Cheney et al. 1991b); see reference listing in the supplementary information field below. Although only the 18-month GM data are classified, XDRs have been constructed for the first 2.5 years of the Geosat mission, e.g., data from the GM plus the first year of the ERM. This was done to minimize the effect of the 5-week data gap (October 1 to November 8, 1986) between the two missions when the altimeter was off during orbit maneuvers. By computing crossovers for the entire 2.5-year period, continuous sea level time series can be derived.
Dataset Citation
- Cite as: Cheney, Robert E.; NOAA National Ocean Service (2009). NODC Standard Product: US Navy Geosat altimeter Crossover Differences (XDRs) for the Geodetic Mission (8 disc set) (NCEI Accession 0054498). [indicate subset used]. NOAA National Centers for Environmental Information. Dataset. https://www.ncei.noaa.gov/archive/accession/0054498. Accessed [date].
Dataset Identifiers
ISO 19115-2 Metadata
gov.noaa.nodc:0054498
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| Time Period | 1985-03-30 to 1986-09-30 |
| Spatial Bounding Box Coordinates |
West: -180
East: 180
South: -72
North: 72
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| Supplemental Information | REFERENCES Cheney, R.E., W.J. Emery, B.J. Haines, and F. Wentz, 1991a: Recent improvements in Geosat altimeter data, EOS, 72 (51), 577-580. Cheney, R.E., Doyle, N.S., Douglas, B.C., Agreen, R.W.,Miller, L., Timmerman, E.L. and D.C. McAdoo, 1991b: The complete Geosat altimeter GDR handbook, NOAA Manual NOS NGS-7, Rockville, MD, 79 pp. Cheney, R.E., Douglas, B.C., and Miller, L., 1989: Evaluation of GEOSAT altimeter data with application to tropical Pacific sea level variability, J. Geophys. Res., 94, 4737-4747. Cheney, R.E., Douglas, B.C., Agreen, R.W., Miller, L., Porter, D., and Doyle, N.S., 1987: GEOSAT altimeter geophysical data record user handbook, NOAA Tech. Memo. NOS NGS-46, Rockville, MD, 32 pp. Cheney, R.E., Douglas, B.C., Agreen, R.W., Miller, L., Milbert, D., and Porter, D., 1986: The GEOSAT altimeter mission: A milestone in satellite oceanography, EOS, 67, 1354-1355. Cheney, R.E. and Marsh, J.G., 1981: Oceanic eddy variability as measured by Geos 3 altimeter crossover differences, EOS, 62, 743-752. Dobson, E.B., Wilkerson, J., Agreen, R., and Douglas, B., 1988: GEOSAT altimeter wind and wave data record user handbook, Johns Hopkins University Applied Physics Laboratory Tech. Report S1R88U-009, Laurel, MD, 28 pp. Emery, W.J., G.H. Born, D.C. Baldwin, and C.L. Norris, 1990: Satellite-derived water vapor corrections for Geosat altimetry, J. Geophys. Res., 95 (C3), 2953-2964. Fu, L.-L. and Chelton, D.B., 1985: Observing large-scale temporal variability of ocean currents by satellite altimetry: With application to the Antarctic Circumpolar Current, J. Geophys. Res., 90, 4721-4739. Marsh, J.G. and Williamson, R.G., 1980: Precision orbit analyses in support of the Seasat altimeter experiment, J. Astron. Sci., 28, 345-369. Milbert, D., Douglas, B.C., Cheney, R.E., and Miller, L., 1989: Calculation of sea level time series from non-collinear GEOSAT altimeter data, Mar. Geod., 12, 287-302. Miller, L., Cheney, R.E., and Milbert, D., 1986: Sea level time series in the equatorial Pacific from satellite altimetry, Geophys. Res. Lett., 13, 475-478. Minster J-F., D. Jourdan, E. Normant, C. Brossier, and M.C. Gennero, 1992: An improved SSMI water vapor correction for Geosat altimeter data, J. Geophys. Res., 97, 17859-17872. Sandwell, D.T., Milbert, D.G., and Douglas, B.C., 1986: Global nondynamic orbit improvement for altimetric satellites, J. Geophys. Res., 91, 9447-9451. Tai, C.-K., 1991: How to observe the gyre to global scale variability in satellite altimetry: Signal attenuation by orbit error removal, J. Atmos. Ocean. Tech., 8, 271-288. Tai, C.-K., 1989: Accuracy assessment of widely used orbit error approximations in satellite altimetry, J. Atmos. and Ocean. Technol., 6, 147-150. Wentz, F., 1989: User's manual for the collocated Geosat SSM/I tape, Tech. Rep. 083189, Remote Sensing Systems, Santa Rosa, CA. |
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Last Modified: 2024-03-02T15:22:34Z
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