effect of high resolution altimetric gravity anomalies on the north america geoid computations yan...
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Effect of High Resolution Altimetric Gravity Anomalies on the North America Geoid Computations
Yan M. Wang and D. RomanNational Geodetic Survey
NOAA
Montreal, Canada, May 17-21, 2004
Recent geoid computations at NGS
1. Milbert, D. G., 1991b: GEOID90: A high-resolution geoid for the United States. Eos, 72(49), pp. 545-554.
2. Smith, D.A. and D.G. Milbert, 1999: The GEOID96 high resolution geoid height model for the United States, Journal of Geodesy, V. 73, N. 5, pp. 219-236.
3. Roman, D.R. and D.A. Smith, 2000, Recent investigations toward achieving a one centimeter geoid, presented at GGG2000 session 9 of the IAG Symposium in Banff, Alberta, Canada from July 31 - August 4, 2000.
4. Roman, et al., Assessment of the New National Geoid Height Model, GEOID03 , ACSM Meeting, 4/19, 2004.
Gravimetric geoid computation
Stokes integral /1DFFT
• Topographic reduction: terrain correction at 1/3/30 arc seconds
• EGM96 remove/restore: gravity anomaly of the reference model is removed, reference geoid is added back to residual geoid
• Indirect effect
Data Used for USGG2003
• NGS gravity database: 1,264,372
• NIMA gravity data: 2,064,898
• Altimetric gravity anomaly: 688,876
• GTOPO30 and NGSDEM99
• EGM96 global gravity model up to degree and order 360
• Ellipsoidal correction from Sideris et al. (2003)
Altimetry Gravity Models
Model Resolution Method
GSFC00.1 2’x2’ 2D Fourier Series/Inv.
Stokes Integral
KMS99 2’x2’ LSC/FFT
Sandwell/
Smith10.1
1’x1’ SSH slope/FFT
RMS Values of Gravity Differences(mgal)
GSFC00.1 KMS99 Sandwell/
Smith10.1
GSFC00.1 — 7.35 3.77
KMS99 — 7.61
Sandwell/Smith10.1
—
Geoid Differences (Mean/RMS values in cm)
GSFC00.1 KMS99 Sandwell/
Smith10.1
GSFC00.1 — -0.6/5.3 -0.7/5.2
KMS99 — -0.1/3.4
Sandwell/Smith10.1
—
GPS/leveling Differences (cm)
GSFC00.1 KMS99 Sandwell/Smith10.1
No. of Pts 6169 6169 6169
Slope/
Azimuth
0.12/333 0.15/331 0.16/333
Mean 51.1 51.2 51.0
STD 20.0 21.8 22.0
GPS/leveling Differencesin Florida (cm)
GSFC00.1 KMS99 Sandwell/
Smith10.1
No. of Pts. 372 372 372
Mean -8.7 -17.1 -18.7
RMS 13.6 21.0 22.4
GPS/leveling DifferencesBy Region (Mean/ RMS values in cm)
Longitude GSFC00.1 KMS99 Sandwell/
Smith10.1
West(230-250)
-1.7/19.7 0.0/19.1 0.7/19.2
Central(250-275)
7.0/16.7 9.0/17.9 8.6/18.4
East(275-300)
-13.3/19.8 -16.7/22.8 -16.7/22.6
Conclusions
• Altimetry gravity models differ at ±3 mgal RMS values (excluding few outliers in KMS99)
• Geoid differences can reach 10 cm in coastal regions (land area), few cm in areas thousand miles away from the ocean
• Geoid changes caused by GSFC00.1 improve the US gravimetric geoid
Conclusions (cont.)
• Sea surface topography implied by GSFC00.1 MSS and USGG03 closely emulate the POCM4b
• Ocean/land interface problems (diff. reference systems, lack gravity data)
Web Information
• http://www.ngs.noaa.gov/GEOID/PRESENTATIONS/
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