Services - Geophysical Investigations

The purpose of a geophysical investigation is to record geophysical data on all subsurface anomalies in a given area, and then select only those anomalies that resemble UXO/OE.

The bottom line of a geophysical investigation is to efficiently locate subsurface OE while minimizing the number of non-OE anomalies. Minimizing the number of subsurface contacts reduces the number of items requiring excavation, thus reducing the total overall duration and cost of a project.

Geophysical investigations are performed at UXO sites to accomplish the following actions:

• Geophysical Sampling
• Geophysical Mapping
• Geophysical Interrogation
  

Geophysical investigations are conducted with detection equipment using one of the following two analytical techniques:

• In real time data positioning and evaluation
• Post-processing involves the collection and recording of geophysical data. This data is then processed by commercial computer software to identify and spatially position electronic signals that are representative of anomalies.

Subsurface anomalies produce geophysical signatures. A geophysicist's task is to analyze these signatures and identify the signatures of subsurface UXO, like that shown above. Anomalies that are selected for excavation are mapped, documented, reacquired, and marked for follow-on investigation. The photo at right shows a project site with the subsurface anomalies marked for investigation.

OER can conduct geophysical investigations in real time as well as using post-processing methods.

OER has a complete geophysical data collection, mapping, analysis, and presentation package using state of the art instrumentation and navigation techniques.

While some navigation during geophysical surveys requires land survey techniques, OER typically uses differential global positioning system (DGPS) techniques to accurately geographically position geophysical data. Geographic positioning to within decimeter levels using DGPS can usually be achieved. DGPS systems are used to navigate towed array sensor systems.

Once geophysical data has been collected, computerized graphics and contouring programs are used to evaluate the data. The data analysis program (usually Geosoft) permits the data to be analyzed using several methods, which can aid in the discrimination of targets of interest from non-OE related scrap. Upon completion of the geophysical analyses, data may be exported in the format of choice to facilitate spatial analyses of anomalies and discovered items of interest using GIS packages.

OER's Geophysical Toolbox
OER has a wide array of geophysical instruments in various configurations at our disposal. Towed arrays of instruments are commonly applied to significantly reduce the effort and related costs to complete geophysical surveys in large areas (20 - 200+ acres). The key to a successful OE project is choosing the proper geophysical instrument for the required task. Our geophysical toolbox can be divided into the following four groups of instruments, based on the instrument's operational principles:
" Electromagnetic (EM) instruments are used to locate conductive metals. Some EM instruments are useful in highly mineralized soils. Some EM instruments that OER can choose from include the Geonics EM61 as well as all-metals instruments such as the White's SpectrumXLT and the Schiebel family of detectors.

• Instruments based on magnetometry are used to locate ferrous iron targets. Magnetometers available to OER include the Schonstedt GA-52Cx and GA-72Cd Locators, the Foerster FEREX 4.021 (known as the Mark 26 in the U.S. military), or the Vallon family of instruments
• Ground conductivity instruments are used to locate leach pits and areas of chemical contamination as well as as UXO. If required to use a ground conductivity instrument, OER could use a Geonics EM31.
• Ground penetrating radar (GPR) units are used to locate larger buried, non-conducive targets (such as USTs) as well as areas of disturbed soils indicating buiral pits. OER personnel would use a RAMAC digital GPR.