comparing geoid99 to the gsd95 canadian geoid model
DESCRIPTION
Comparing GEOID99 to the GSD95 Canadian geoid model. Dru A. Smith Daniel R. Roman National Geodetic Survey, U.S.A. Presented at the 2000 Meeting of the CGU Banff, Alberta, Canada. Topics of Discussion. Models: NGS (USA) and GSD (Canada) Comparison and discussion Future plans. - PowerPoint PPT PresentationTRANSCRIPT
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Comparing GEOID99 to the GSD95 Canadian geoid model
Dru A. SmithDaniel R. RomanNational Geodetic Survey, U.S.A.
Presented at the 2000 Meeting of the CGUBanff, Alberta, Canada
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Topics of Discussion
Models: NGS (USA) and GSD (Canada)
Comparison and discussion
Future plans
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G99SSS: NGS gravimetric model
2.6 Million gravity points 30 arcsecond DEM 1 arcsecond DEM for PNW USA EGM96 underlying structure Faye anomalies (not Helmert) 1-D FFT Geocentric (ITRF96/GRS-80)
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New for G99SSS (vs. G96SSS)
KMS98 altimetry Ellipsoidal solution to the Stokes
Integral (Fei and Sideris) Multi-band 2-D FFT TCs 3 arcsecond TCs for PNW USA 1 arcminute resolution North to 58 degrees
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New for G99SSS: Ellipsoidal solution to the Stokes Integral
Fei, Z.L. and M.G. Sideris, 2000: A new method for computing the ellipsoidal correction for Stokes’s formula, Journal of Geodesy, in review.
Significant reduction in N/S tilts
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Ellipsoidal Corrections used in G99SSS (cm)
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New for G99SSS: Multi-band 2-D FFT TCs Lowers N/S errors in TCs; Not as good as 1-D FFT In PNW (3 arcsecond):
10 areas (5 x 2) 18 x 18 degrees (keep 6 x 6) Overlap: 2 degrees E/W and N/S
In CONUS (30 arcsecond) 3 areas (1 x 3)
164 x 46 deg (keep 76 x 17) Overlap: 8.5 degrees N/S
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PNWOverlap
TC DiffRMS
(mGals)
TC DiffMax
(mGals)
E/W 0.054 0.310
N/S 0.508 31.275
Basic Statistics of TC Differences using overlapping 2-D FFT regions
CONUSOverlap
TC DiffRMS
(mGals)
TC DiffMax
(mGals)
N/S 0.837 74.6
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GEOID99: NGS hybrid model
Begin with G99SSS
6169 (NAD 83) GPS heights on (NAVD 88) leveled benchmarks inside USA
Collocation and transformations
Non-geocentric: NAD 83 <--> NAVD 88
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PICTURE OF 6169 GPSBMS
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PICTURE OF GEOID99
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G99BM: NGS geocentric hybrid model
Need a geocentric hybrid model to compare to GSD95 (geocentric)
G99BM = geocentric GEOID99
Transformed NAD 83 into ITRF96
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G99SSS/G99BM vs GSD95 Re-grid GSD95 from 5’ to 1’
G99BM valid only inside USA
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G99SSS - GSD95 Ave = -63 cm +/- 33 cm
Trend: 0.15 ppm (72 cm E/W)
Detrended: Ave = 0 cm +/- 19 cm
PNW, BC, Hudson Bay remain outliers
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G99BM - GSD95
Valid in USA only
Ave: -78 cm +/- 49 cm
New issues: WA/OR tilt New England rise
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Conclusions E/W tilt remains, but reduced from 150 cm to 72 cm
GPS on BM do not significantly help the NGS/GSD disagreement
Data differences in altimetry, and DEM yield systematics that cause tilts NGSDEM99 in PNW Quebec DEM
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FUTURE PLANS Helmert Anomalies, not Faye
GPS on BM through all of North America Re-adjustment in 2003(?)
Density anomalies
1 arcsecond DEM over all of CONUS (USGS) Possibly NA (SRTM)