Tools For Assessing Geophysical Survey Data Quality

Geophysical investigations for munitions and explosives of concern (MEC) are conducted principally using magnetic or electromagnetic geophysical methods. These data collection methods require that geophysical measurements are accurately tagged to a ground location. A number of simple and advanced survey methods have been used, ranging from “wheel mode” to global positioning system (GPS) methods. Advantages and limitations of each positional survey type have been evaluated and selected depending upon survey requirements and site conditions. This paper discusses geophysical surveys that were acquired at Vandenberg Air Force Base (AFB) to assess the potential presence of MEC within existing housing areas. The project scope required evaluation of geophysical systems that are proven effective in the detection of potential subsurface MEC. Additional requirements included sub-meter accuracy and “survey grade” location equipment. Following our testing of sensor technology and location equipment we selected off the shelf systems including the Geonics EM61 MK2 and Leica real-time kinematic (RTK) global positioning (GPS) technology. The nature of the terrain, vegetation, and the housing units provided numerous sources of interference. The survey was further complicated by multi-path interference, and unsuitable GPS satellite coverage, a result of low satellite number (nSat) and high position dilution of precision (PDOP) during significant portions of the work day. To address these difficulties, several unique data management tools were developed at the project outset. As a result, high-quality positional data were identified and used in the final data assessment. This paper provides a brief overview of the project, the instrumentation and procedures employed.