Airborne geophysical survey: South-Central Piedmont, Virginia

Conversion of measured values to geographic position and magnetic values was performed by the contractor using industry standard practices. Details are found under Horizontal_Position_Accuracy_Report, and Vertical_Position_Accuracy_Report Unless noted, conversion processes were not reported to the USGS. Unpublished products generated by the contractor included magnetic tapes, a map of residual or total field magnetics, and perhaps some written documentation.

USGS reformatting of contractor data to standard format. USGS personnel used the software package Oasis Montaj by Geosoft, Inc., to read in the original contractor's data. Latitude, longitude, altitude, and magnetic values were checked for obvious errors or spikes and values of -9999.9 were given where the value could not be reasonably corrected. Other errors in the data were not corrected. Horizontal positions were converted to latitude and longitude if the original values were UTM meters. Elevations were converted from meters to feet (1 m = 3.2808 ft). Often the digital data did not contain date information and only the month and year flown or just a starting date were stated in the written documentation. In these cases, the first day of the month or the date the survey began was used as the Julian date and added to the digital data. Other information was added that was missing from the data file but was recorded elsewhere. The reformatted data were written in the format described in the section on Digital_Transfer_Information.

Added keywords section with USGS persistent identifier as theme keyword.