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GPS on Bench Marks Webinar

GPS on Bench Marks Webinar. March 15, 2017. Why?. There are ~430,000 published First and Second Order Bench Marks United States and Territories. ~27,000 GPS on bench marks used to create GEOID12B ~40,000 at a distance more than 30 km from a BM used in 12B

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GPS on Bench Marks Webinar

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  1. GPS on Bench Marks Webinar March 15, 2017

  2. Why? There are ~430,000 published First and Second Order Bench Marks United States and Territories ~27,000 GPS on bench marks used to create GEOID12B ~40,000 at a distance more than 30 km from a BM used in 12B ~300,000 bench marks with SCALED positions ~200,000 bench marks not recovered in 30 years

  3. Who and How? • Surveyors • OPUS-Share • OPUS-Projects • Surveyors and Geocachers • Mark Recovery • RTK • Handheld • Cell phone

  4. Different Heights H - Orthometric Height (elevation) h - Ellipsoid Height N – Geoid Height/Undulation

  5. What is a residual and how is it calculated? H ≈ h - N residual = H + N - h Causes can be from: Old/bad leveled height, bad ellipsoid height Time between heights, stability/movement Limited data in area

  6. GEOID12B GPS on BM dataset Rejection Codes (flag) Code S – The State Advisor (now called Regional Geodetic Advisors) recommended it be dropped (subsidence, stability, etc.) Code h – The residual ellipsoid height errors from the NAD 83 (2011) project indicated that the point was too noisy Code H – The orthometric height was suspect Code N – The residual errors during geoid modeling were too high S h H N

  7. Dave Zilkoski GPS World article Analyzing NGS’ GPS on benchmark dataset Used to make GEOID12B Discusses evaluating residuals http://gpsworld.com/analyzing-ngs-gps-on-bench-mark-dataset-used-to-make-geoid12b/

  8. Zilkoski, GPS World http://gpsworld.com/analyzing-ngs-gps-on-bench-mark-dataset-used-to-make-geoid12b/

  9. 28.5 cm difference 30km apart Zilkoski, GPS World http://gpsworld.com/analyzing-ngs-gps-on-bench-mark-dataset-used-to-make-geoid12b/

  10. Questions? GPS on Bench Marks team ngs.gpsonbm@noaa.gov March 15, 2017

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