1	Texas Spatial Reference Center (proposed) TXCC CORS Survey and other THM goals
2	Challenge Determining valid NAVD 88 heights for Texas CORS Antenna Reference Points.
3	Texas CORS Stations
4	Texas CORS with NAVD 88
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8	GPS Observations Two independent sessions were observed at first-order benchmarks located within 250 meters of the TXCC CORS site. All stations observed with Zephyr antennae.
9	GPS Session Characteristics Five (5) second epoch interval Ten (10) degree elevation mask Session duration minimum of four (4) hours Two independent sessions separated by minimum of four hours.
10	GPS Vector Reduction Used NGS PAGE-NT (version 0601.25) . Fifteen-degree (15) elevation mask Thirty-second (30) observation interval IGR (rapid orbit) ephemeris used (5cm level) ITRF coordinates of TXCC (from file: sitecors.bin) used as reference station Tropospheric unknowns not determined due to proximity of sites to reference station L1 fixed integer solution
11	Processing results Good solutions were obtained for both sessions. Overall rms for solutions were 0.0081m and 0.0057 meters for days 213 and 214 respectively. Final solutions are fixed-integer L-1 only
12	GPS verification of NAVD 88 values for bench marks Published NAVD 88 heights for CORC A and CORC B differ by 0.248 meters. Minimally constrained adjustment yields a height difference of 0.252 meters (NAVD 88 comparison). Digital leveling difference of 0.2513 meters. Our GPS-derived values provide a check of 0.004 meters with published values. Geoid 03 values for all three points vary from -26.357 to -26.361 (range of 0.004 m)
13	Corpus Christi CORS ARP 17.33 m NAVD 88 ARP (old 2002) 17.317 m NAVD 88 ARP (new 2006) (to be published as 17.32 m) Antenna hardware changed 2003
14	Conclusion For 2cm Orthometric TM59 1) We have verified that GPS can yield NGS acceptable differences in height over short distances (less that 1 kilometer). 2) First order digital leveling between control benchmarks validates vertical relationship. This also quality checks the GPS solution for bad integer determinations or other processing defects.
15	Other Texas Height Modernization Project Goals
16	GPS on NAVD 88 Benchmarks
17	Software Development
18	Hurricane Evacuation Route Elevation Profiling
19	CORS on NOS Tide Gauge
20	Texas Height Modernization Forum November 15-16, 2006 JJ Pickle Research Center Austin, Texas http://tsrc.tamucc.edu
21	Thank you for your attention.