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Comparing GEOID99 to the GSD95 Canadian geoid model

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.

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Comparing GEOID99 to the GSD95 Canadian geoid model

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  1. 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

  2. Topics of Discussion • Models: NGS (USA) and GSD (Canada) • Comparison and discussion • Future plans

  3. 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)

  4. 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

  5. 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

  6. Ellipsoidal Corrections used in G99SSS (cm)

  7. 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

  8. Basic Statistics of TC Differences using overlapping 2-D FFT regions

  9. 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

  10. PICTURE OF 6169 GPSBMS

  11. PICTURE OF GEOID99

  12. G99BM: NGS geocentric hybrid model • Need a geocentric hybrid model to compare to GSD95 (geocentric) • G99BM = geocentric GEOID99 • Transformed NAD 83 into ITRF96

  13. G99SSS/G99BM vs GSD95 • Re-grid GSD95 from 5’ to 1’ • G99BM valid only inside USA

  14. 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

  15. G99BM - GSD95 • Valid in USA only • Ave: -78 cm +/- 49 cm • New issues: • WA/OR tilt • New England rise

  16. 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

  17. 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)

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