comparisons of gnss and leveling- derived orthometric heights using gis kevin m. kelly, esri jay...
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Comparisons of GNSS and Leveling-Derived Orthometric Heights Using GIS
Kevin M. Kelly, Esri
Jay Satalich, Caltrans
Kelly, K. M. and J. Satalich (2012). Comparisons of GNSS and leveling-derived orthometric heights using geographic information system software, AGU Fall Meeting, San Francisco, December 3-7, 2012, Abstract G13A-0940.
Outline
• NGS geoids
• Problem statement
• Data and results
• Conclusions
NGS Geoids
• Six models since 1990- GEOIDYY: YY = [90], [93], 96, 99, 03, {06}, 09,
12A
• Hybrid geoids 96 through12A- intended to recover NAVD88 H from specific
realizations of NAD83(YY) h- Corrector surface to the corresponding gravimetric
geoid, USGGYYYY- This surface biases gravimetric geoid to fit
NAD83(YY) ellipsoidal heights, h surveyed on NAVD88 benchmarks (GPSBM)
Problem Statement
How well do NGS hybrid geoids
perform locally?
Problem?In the Palos Verdes Peninsula of Southern California,
discrepancies of up to 8 cm persist between published NAVD88 heights and those derived
from GPS on benchmarks using the last four geoid models: GEOID99, GEOID03, GEOID09 and GEOID12A.
So What?Local accuracy is the
workhorse of the geoid model; local projects
exact high demands from geoid model performance.
SolutionResearch and test potential causes
Collect new gravity data to help verify existing holdings – GRAV-D
Densify GPSBM data?
Improve data screening and quality control
Benefits?NAVD88 usage will continue even
after the new datums.
Geoid modeling and data quality implications/improvements for
forthcoming models.
Solutions for other problematic local areas.
Environmental Setting
Key geophysical features influencing benchmark heights near the Palos Verdes Peninsula, California.
• Palos Verdes Peninsulao Made of sandstone and
basalto Active landslideso Historic landslide areas
• Los Angeles Basino Made of alluviumo Wilmington Anticlineo Wilmington/Torrance oil
fields
The Data Story
• Steady improvement from GEOID99 to GEOID12A but ~8 cm discrepancies persist• Hybrid geoid surface lies consistently above the surface defined by NAVD88• REDONDO – monument disturbance from construction• T1217, T1053 – 4 cm elevation differences between 1960 and 1994• T1217 – ellipsoid height stable to 1 cm between 1997 and 2012• The main purpose of this study is to show that these disagreements are not due to
shortcomings in the control data – that is, the leveling and GPS.
Benchmark stability over time (1)
L25468/14 (1994) minus L17850 (1960)(±1.17 ⁄ ±2.31)
New - Old: ±2.59 mm
New-minus-old comparison of geodetic leveling shown as a component of error propagation± numbers are a posteriori standard error for 1 km of single-run leveling in mm
2 2New Old New Old
Error propagation:
Error propagation:
Benchmark stability over time (2)
L25468/14 (1994) minus L24301/1 (1978)(±1.17 ⁄ ±0.93)
New - Old: ±1.49 mm
New-minus-old comparison of geodetic leveling shown as a component of error propagation± numbers are a posteriori standard error for 1 km of single-run leveling in mm
2 2New Old New Old
Error propagation:
Benchmark stability over time (3)
L25468/14 (1994) minus L25180 (1989)(±1.17 ⁄ ±0.99)
New - Old: ±1.53 mm
New-minus-old comparison of geodetic leveling shown as a component of error propagation± numbers are a posteriori standard error for 1 km of single-run leveling in mm
2 2New Old New Old
Error propagation:
Benchmark Stability - Tabular
New-minus-old comparison of orthometric heights in meters. Benchmarks shown with an asterisk indicate historic vertical
movement beyond 2 cm between 1994 and 1960.
BENCHMARK PIDRUNNING DISTANCE
(km)
1994 minus 1989
1994 minus 1978
1994 minus 1960
941 0660 TIDAL 8 DY1083 0.00 FIXED FIXED FIXEDZ 1217 DY1118 8.95 0.00358 0.00138 noneT 1053* DY0994 13.30 0.01375 0.00814 0.04157Y 1312 DY2499 18.38 0.00912 0.00541 noneS 1053 DY1017 19.89 0.00432 0.00495 0.00038U 1217 DY1227 21.94 0.00208 -0.00321 noneE 169 DY1230 23.97 0.00421 -0.01158 0.00857T 1217* DY1231 24.66 -0.00595 -0.02714 none34 33 A DY9050 24.77 0.00115 -0.00636 noneT 1313 DY2498 24.97 0.00330 -0.01071 noneF 788 DY1233 25.54 -0.00270 -0.00917 -0.00741S 1217 DY1237 27.01 0.00368 -0.00131 none34 39 DY9045 29.08 -0.00103 -0.01846 noneTORRANCE F 10 RM 1* DY1217 30.12 -0.00447 -0.03458 -0.05578REDONDO* DY1212 31.04 -0.00178 -0.11205 -0.19149
GPS Ellipsoidal Height Repeatability
New-minus-old comparison of ellipsoidal heights in meters
GNSS STATION2012
minus 2011
2012 minus 1997
2012 minus 1994
2012 minus 1992
PALOS VERDES ARIES 7268 FIXED FIXED FIXED FIXED941 0660 TIDAL 8 0.007 none 0.014 0.012Y 1312 none none -0.003 noneS 1053 none 0.000 none noneU 1217 none 0.004 none noneT 1217 none 0.010 none noneT 1313 none 0.004 0.008 noneF 788 none -0.006 none none34 39 none 0.009 none noneTORRANCE F 10 RM 1 none -0.002 0.003 noneREDONDO* none 0.036 none none
Conclusions
• Discrepancies of up to -8 cm persist between published NAVD88 heights and GPSBM for all NGS hybrid geoids from 1999 to 2012
• Ellipsoidal heights exhibit repeatability at the 1 cm level over four epochs spanning 20 years
• Differential leveling over four epochs spanning 34 years reveals that benchmarks are stable at ±2 cm or better level
• The data support an apparent shortcoming in NGS geoid models in the Palos Verdes area
A Real Possibility
Fig. 12 The effect of significant gravity biases on the geoid
Saleh, J., X. Li, Y.M. Wang, D.R. Roman and D.A. Smith. (2013). Error analysis of the NGS’ surface gravity database, J Geod 87:203-221.