A customer reported an elevation discrepancy on PAHG between existing NGS benchmarks and the coordinates derived from the use of PAHG. This discrepancy was outside the normal tolerances we would expect.
Upon investigation, it was discovered that a vertical discrepancy of ~ 7 cm existed on the published vs derived coordinates on the control check shots. In looking at the history of the site is was determined that there was a leveling mast adapter with a height of 7.71 cm added to the site on January 26, 2012 as a part of an antenna and receiver update. The appropriate changes were applied to the station coordinates at this time, as the ellipsoid height was changed from 89.32 m to 89.3921 m.
As part of our North American adjustment the coordinates of all stations where recomputed using data that pre-dated the January 26 hardware upgrades on PAHG. When the new NAD83(2011) Epoch 2010.00 coordinates were imported on October 1, 2012 for PAHG the 7.71 cm height offset was not accounted for. Thereby causing the discrepancy that has been reported.
To find a short term solution to this issue, we have recomputed the position of the station using a limited data set to be able to account for the 7.71 cm height offset. This recomputed position will be an interim position until a new position is calculated as part of our bi-annual adjustment that will be completed in the next 30-60 days. Once the larger adjustment has been completed, we will publish a new "permanent" coordinate set for the station, overall change in coordinates should be in millimeter range.
You can find updates to this stations in the SmartNet Site Database - LINK
January 26, 2012 - Hardware and antenna upgrade required a leveling mast adapter to be added, incurring a 7.71 cm height increase
March 16, 2012 - Processing run for the North American Adjustment was begun using data that pre-dated the January 26 additional of the leveling mast adapter
October 1, 2012 - New coordinates were put into service for PAHG that did not account for 7.71 cm height increase
January 29, 2014 - Initial report of discrepancy with local control was made
January 29, 2014 - Investigation of issue was opened
March 3, 2014 - New position for PAHG was calculated using 2 weeks of data and precise ephemeris information (additional 2 week delay required)
March 4, 2014 - Comparison of new and old coordinates, review of site history, etc completed
March 4, 2014 - New coordinates put into production at 3:00 PM ET