Magnetics is an effective and efficient method to survey large areas for buried metal objects such as tanks and barrels. Buried metal objects create anomalies in the earth's magnetic field. To detect these anomalies, we measure the earth's total magnetic field and local magnetic gradients. Portable proton precession or cesium vapor magnetometers are used to take these measurements. The magnetometers internally store the magnetic readings, the readings' locations and other useful data. The data are downloaded to a computer, processed and contoured. Magnetic contour maps are then superimposed onto site plans. The results are very accurate plots of the buried metal at a site. Often we can tell what an object is from its anomaly or we use a ground penetrating radar to help identify the object. Magnetic surveys are done quickly and are useful in:
Magnetic surveys are frequently done to find faults. Faults can juxtapose materials with different magnetic susceptibilities. Where juxtaposition occurs a distinctive magnetic anomaly appears. We collect lines of magnetic data at several locations across a suspected fault to detect these anomalies. Data are also collected at a base station to correct for drifts in the earth's total magnetic field. Unlike environmental studies where anomalies are quite large, anomalies caused by faults are subtle and careful data processing is required. Once the data are processed and plotted, the location of a fault can be determined.
At J R Associates we stand ready to apply our geophysical expertise to your particular requirements. Please contact us to discuss how our combination of techniques, knowledge and experience can provide you with a window on what's underground.