HIGH ACCURACY REFERENCE NETWORK
FOR WEST VIRGINIA
David R. Doyle
Observation and Analysis Division
National Geodetic Survey
The National Geodetic Survey (NGS) has recently completed the final adjustment of the Federal Base Network (FBN) for West Virginia. Consisting of 31 stations, 8 new, and 23 existing horizontal and vertical control stations spaced at approximately 100 kilometer (60 mile) intervals, the network was observed to A and B-Order accuracy standards (5 mm + 1:10,000,000 and 8 mm + 1:1,000,000) as defined by the Federal Geodetic Control Subcommittee. This network is often referred to as the West Virginia High Accuracy Reference Network (HARN).
Field operations were conducted between July and August, 1995, by NGS surveyors using Trimble 4000SSE dual frequency GPS receivers. Additional assistance for GPS observations was also provided by the Ohio Department of Transportation, Franklin County, Ohio, Engineers Office, and ADR Geodetic Services of Pittsburg, Pennsylvania. Most observations far exceeded the 1:1,000,000 proportional accuracy required for the B-Order adjustment.
In addition to adjusting the GPS data to fiducial stations of the International GPS and Geodynamics Service (IGS), and existing FBN/CBN stations in Kentucky, Maryland, Ohio, Pennsylvania, and Virginia, all existing horizontal control in the State will be readjusted to provide consistency between the HARN and the existing horizontal network. The readjustment will extend into the bordering states to the extent required to maintain consistency of the National Spatial Reference System (NSRS). Until the completion of the state-wide readjustment, HARN stations will be designated as "SPECIAL STATUS" on NGS data sheets to indicate their positional differences with the existing lower order NSRS stations. Given the current back log of other HARN state-wide readjustments, the West Virginia readjustment could require as much as 2 years to complete. The new coordinate values are referred to as North American Datum of 1983 (NAD 83), Adjustment of 1995, and are designated NAD 83 (1995). This designation is necessary to distinguish between the original NAD 83 Adjustment of 1986, or NAD 83 (1986). Coordinate values should be properly labeled to eliminate confusion. Positional changes due to the network improvement vary across the State, but are generally less than 0.6 meter (2.0 feet). Positions and velocities relative to the International Earth Rotation Service (IERS) Terresterial Reference Frame (ITRF) will also be published.
Orthometric heights for FBN stations were determined by occupying 11 published bench marks referenced to the North American Vertical Datum of 1988 (NAVD 88). NAD 83 ellipsoidal heights were determined by holding the values published for 6 existing
A-Order quality stations in and around the State. Accuracy of ellipsoidal heights determined by
these observations vary, and are sometimes less than third-order. Orthometric heights are
considered to be equivalent to those obtained by conventional vertical angle observations (0.1
All GPS surveys performed prior to the HARN, and not submitted to NGS ("Blue Booked") for inclusion in the NSRS, should be readjusted from original observations to maintain consistency with NSRS. Lower order coordinate information (e.g. cadastral survey, photogrammetry,) can be transformed from NAD 83 (1986) to
NAD 83 (1995) using version 2.10 of the NADCON software supplied by NGS, with special transformation grids for the West Virginia adjustment (WVHPGN.LAS and WVHPGN.LOS). The transformation grids will be developed by NGS following the state-wide readjustment, and should provide transformation values accurate to an average of 0.06 meter +/- 0.02 meter (0.20 +/- 0.06 feet) across the State. Updated coordinate information, and the NADCON software can be obtained from the NGS Information Services Section at (301) 713-3242, the NGS Electronic Bulletin Board Service at (301) 713-4181/4182, or the NGS World Wide Web site at http://www.ngs.noaa.gov.
Questions concerning the HARN and state-wide readjustment, or coordinate transformations should be directed to Dave Doyle, NGS Observation and Analysis Division at (301) 713-3178, or email email@example.com.