REJUVENATING PRE-GPS ERA GEOPHYSICAL SURVEYS USING THE NATIONAL MAP

Old geophysical surveys (pre-GPS) stand as a valuable, largely un-tapped source of scientific data. If these data were in a format that had reasonable accuracy, availability and ease-of-use, they could enjoy a much wider usage. In this paper we look at integrating old survey coordinates into a modern geographic database, in this case, The National Map. We have a relatively unique set of data for this investigation that includes a pre-GPS survey’s positional coordinates and elevations interpolated from USGS topographic 7.5’ quadrangles, field notes on station location, analog photographs of each station, GPS coordinates from the reoccupation of these sites, coordinates determined from The National Map, and LiDAR data giving high accuracy elevation data. A comparison of these different data sources shows that over 85% of the stations could be positioned on the national database within a horizontal distance of 15 m of the GPS reoccupation location and, as significantly, within 2 m of the LiDAR elevation data. While the on-line database coordinate accuracy is likely to improve with time (especially elevation), our results imply that web databases have already matured to where it is possible to integrate survey coordinate data with a reasonable assurance of positional accuracy.