Data Processing

Navigation

The kinematic DGPS data collected during Field Activity 2015-611-FA were postprocessed using three CORS stations. The identification codes of the CORS stations are NJGT, NJOC, and NJCM, and they were located approximately 23, 50 and 55 km away from the study location respectively. It was necessary to use multiple CORS stations for postprocessing because some stations were not operated during portions of the data collection process. The CORS station data used for postprocessing the GPS data were obtained from the National Oceanic and Atmospheric Administration (http://www.ngs.noaa.gov/CORS/). The CORS station coordinates were imported into NovAtel Waypoint Product Group software program GrafNav, version 8.4, and the data from the rover GPS unit used to collect data at each sample site were postprocessed to the concurrent CORS session. The position data were then exported as a GGA string in American Standard Code for Information Interchange (ASCII) format and applied to the GPR data in Sandmeier Scientific Software’s Reflexw Version 7.2.2.

Ground-Penetrating Radar

Sandmeier Scientific Software’s Reflexw Version 7.2.2 geophysical near surface processing and interpretation software was used to process the GPR data; GPR data were acquired in DZT format, imported into Reflexw, and converted into a Data file (DAT). For archival purposes, non-proprietary versions of the raw data were created by exporting the DAT files from Reflexw and saving the files in ASCII format. The data were processed in the following order: (1) static correction was applied, (2) subtracting-mean (dewow) was conducted, (3) header gain was removed, (4) user-defined gains were applied, and (5) postprocessed DGPS data were imported into the trace headers to produce the elevation corrected profile. A velocity of 0.06 meters per nanosecond (m/ns) was assumed and applied to all elevation-corrected profiles to display depth. Data were inspected visually after each step, and all profiles were analyzed for errors in navigation or trace data. The GPR profiles were then converted to the Joint Photographic Experts Group (JPEG) images included in this report. Raw GPR data and elevation-corrected profiles can be downloaded from the Data Downloads page.