Abstract
Are the National Geodetic Survey’s surface gravity data sufficient for supporting the computation of a 1 cm-accurate geoid? This paper attempts to answer this question by deriving a few measures of accuracy for this data and estimating their effects on the US geoid. We use a data set which comprises \({\sim }1.4\) million gravity observations collected in 1,489 surveys. Comparisons to GRACE-derived gravity and geoid are made to estimate the long-wavelength errors. Crossover analysis and \(K\)-nearest neighbor predictions are used for estimating local gravity biases and high-frequency gravity errors, and the corresponding geoid biases and high-frequency geoid errors are evaluated. Results indicate that 244 of all 1,489 surface gravity surveys have significant biases \({>}2\) mGal, with geoid implications that reach 20 cm. Some of the biased surveys are large enough in horizontal extent to be reliably corrected by satellite-derived gravity models, but many others are not. In addition, the results suggest that the data are contaminated by high-frequency errors with an RMS of \({\sim }2.2\) mGal. This causes high-frequency geoid errors of a few centimeters in and to the west of the Rocky Mountains and in the Appalachians and a few millimeters or less everywhere else. Finally, long-wavelength (\({>}3^{\circ }\)) surface gravity errors on the sub-mGal level but with large horizontal extent are found. All of the south and southeast of the USA is biased by +0.3 to +0.8 mGal and the Rocky Mountains by \(-0.1\) to \(-0.3\) mGal. These small but extensive gravity errors lead to long-wavelength geoid errors that reach 60 cm in the interior of the USA.
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Abbreviations
- 1-D FFT:
-
1 Dimensional fast Fourier transform
- CO:
-
Crossover
- COE:
-
Crossover error
- CONUS:
-
The conterminous USA
- DEM:
-
Digital elevation model
- DMA:
-
Defense Mapping Agency; now called National Geospatial-Intelligence Agency
- DNSC:
-
Danish National Space Center
- DTED:
-
Digital Terrain Elevation Data
- ECO:
-
External crossover
- ECOE:
-
External crossover error
- EGM2008:
-
Earth Gravitational Model of 2008
- GOCE:
-
Gravity and Ocean Circulation Explorer
- GPS:
-
Global Positioning System
- GRACE:
-
Gravity Recovery and Climate Experiment
- GRAV-D:
-
Gravity for the Redefinition of the American Vertical Datum
- ICO:
-
Internal crossover
- ICOE:
-
Internal crossover error
- IGSN71:
-
International Gravity Standardization Net of 1971
- KNN:
-
\(K\)-nearest-neighbors
- mGal:
-
Milli-Gals
- MSL:
-
Mean sea level
- NAD:
-
North American Datum
- NGS:
-
National Geodetic Survey
- NGVD:
-
National Geodetic Vertical Datum
- RTM:
-
Residual Terrain Model
- SRTM:
-
Shuttle Radar Topography Mission
- USGS:
-
US Geological Survey
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We thank J. Geod. editors and reviewers and colleagues who reviewed this paper before its publication.
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Saleh, J., Li, X., Wang, Y.M. et al. Error analysis of the NGS’ surface gravity database. J Geod 87, 203–221 (2013). https://doi.org/10.1007/s00190-012-0589-9
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DOI: https://doi.org/10.1007/s00190-012-0589-9