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
Feb 25, 2016
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/