Effect of High Resolution Altimetric Gravity Anomalies on the North America Geoid Computations

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Effect of High Resolution Altimetric Gravity
Anomalies on the North America Geoid Computations

• Yan M. Wang and D. Roman
• National Geodetic Survey
• NOAA
• Montreal, Canada, May 17-21, 2004

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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.

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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

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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)

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Altimetry Gravity Models

Model Resolution Method
GSFC00.1 2x2 2D Fourier Series/Inv. Stokes Integral
KMS99 2x2 LSC/FFT
Sandwell/ Smith10.1 1x1 SSH slope/FFT
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RMS Values of Gravity Differences(mgal)

GSFC00.1 KMS99 Sandwell/Smith10.1
GSFC00.1 7.35 3.77
KMS99 7.61
Sandwell/Smith10.1
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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
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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
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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
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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
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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

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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)

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Web Information

• http//www.ngs.noaa.gov/GEOID/PRESENTATIONS/