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Geophysical System Verification
Geophysical System Verification (GSV) is a physics-based alternative to the traditional geophysical prove-out (GPO) used on munitions response projects. The GSV concept was developed by ESTCP, in collaboration with the military Services, State and Federal regulators, and the National Association of Ordnance and Explosive Waste Contractors (NAOC). It moves resources from an upfront evaluation of geophysical systems that are already well-understood to ongoing verification of system performance, building confidence that data generated throughout a munitions response project is meeting project objectives.
The evaluation and cleanup of current and former military sites contaminated with buried munitions relies on two well-understood geophysical technologies to detect the munitions: magnetometry and electromagnetic (EM) induction. As these technologies were introduced in munitions response projects, the GPO was developed to provide proof that the geophysical data collected would meet project objectives.
Over the last 15 years, numerous GPOs have been performed on a variety of site conditions, and a significant body of knowledge has accumulated documenting the performance of these technologies. This accumulated understanding, along with the recognition that magnetic and EM responses of munitions may be predicted reliably using physical models, presents the opportunity for both streamlining and enhancing the GPO with a more rigorous physics-based approach.
The Geophysical System Verification process will allow the resources that in the past were devoted to a GPO to be reallocated to support simplified, but more rigorous, verification that the geophysical system is operating as intended. This process also will provide ongoing monitoring of production work. The two main elements of the process are:
- Instrument Verification Strip – The GPO, which consists of several tens to a hundred or more targets, is replaced by an instrument verification strip (IVS) containing a handful of targets. The objective of the IVS is to verify that the geophysical detection system is operating properly. The IVS targets should be observed in the data with signals that are consistent with both historical measurements and physics-based model predictions. Adjacent measurements of the site noise determine whether targets of interest can be detected reliably to their depth of interest under the site conditions.
- Blind Seeding Program – The production site is seeded with targets at surveyed locations that are blind to the data collection and processing teams. The objective of the seed program is to provide ongoing monitoring of the quality of the geophysical data collection and target selection process as it is performed throughout the project. The blind seeds should be numerous enough to be encountered on a daily basis, should be selected as potential targets, and their signals should be consistent with both historical measurements and physics-based model predictions.
Both the IVS and the seeds rely on the availability of well-characterized targets. Sensor response to a variety of targets has been characterized using models developed to interpret data from the Geonics EM61-MK2 electromagnetic induction sensor and the various magnetometers. Blind tests have validated the models and their predictions can now be used to verify that sensors are detecting expected signals and are working as intended. As next generation sensors become available, similar predictions can be generated.
For the purpose of verifying sensor operation, an “industry standard object” (ISO) is used in place of the actual munition. Munitions can vary by make and model number. There are many different types of 60-mm mortar, for example. ISOs, in contrast, have the advantage in that they will be made to the same specification regardless of where they are obtained. Three sizes of commonly available pipe sections have been characterized. Together, the three sizes should meet the objectives of most munitions response projects.
GSV retains the essential functions of the GPO while shifting project resources from upfront confirmation of what is already known to ongoing monitoring of project quality. This approach reduces the logistical burden of multiple mobilizations and acquisition of surrogates in the current process. The approach also results in greater confidence in the performance of the production geophysics and the success of the overall project. GSV is one component of a quality project. All normal data and process QC measures would continue to be implemented in addition to the IVS and production blind seed program.