NOAA’s National Geodetic Survey encourages anyone with survey-grade Global Positioning System (GPS) receivers to join the 2014 GPS on Bench Marks Campaign, a National Surveyors Week (March 16-22, 2014) event to raise awareness about professional surveying while improving the National Spatial Reference System (NSRS).
The nation’s height system, the North American Datum of 1988 (NAVD 88), is founded on historic geodetic leveling surveys on thousands of bench marks. These bench marks are often difficult and expensive to access. By adding GPS coordinates to these marks, the height system can be modeled in GPS survey systems for easier access. The latest hybrid geoid model, GEOID12A, includes many “GPS on bench mark” observations, but would benefit from additional data collection in many areas.
Find local bench marks. Visit Geodesy. noaa.gov for a priority listing of stations to occupy and maps for your reference. Contact your NGS geodetic advisor for more details, or email the National Height Modernization Program at ngs.htmod@noaa.gov.
Collect GPS on your selected bench mark following careful field procedures.
• If time permits, complete reconnaissance at your selected mark to ensure its usability and/or to identify alternative marks.
• Collect a 4+ hour GPS data file.
• Verify antenna type, height, and plumb.
• Use a fixed height tripod (recommended), and brace the legs with sandbags or chain.
• Take two photos of the mark, and note any changes to the existing mark description. (Optional: use observer field log with this step.)
Share your data by uploading to our Online Positioning User Service (OPUS) on the NGS website Geodesy.noaa.gov.
NGS will use your data to improve the next hybrid geoid model, increasing access to NAVD 88 and enabling conversions to the new vertical datum in 2022.