Magnetic gradient measurementsp ossesss everal advantages compared with other magnetic field measurementsin<br>shallow-site investigations, hazardous-waste site characterization, and other investigations to locate buried ferromagnetic<br>objects. These advantages include (1) immunity from time-varying geomagnetic noise, (2) improved spatial resolution<br>because of the more rapid spatial attenuation of the gradient components compared with magnetic field components, and<br>(3) generally low-background gradient values from geological effects. For this reason, conventional magnetic surveys for<br>site investigations and for object detection routinely acquire the vertical gradient of the total magnetic field with a pair of<br>identical proton or alkali vapor (e.g., Cesium) magnetometers with spatial separations of a few feet.<br>Quantitative interpretation of magnetic gradient data requires the knowledge of several components of the gradient (Hood<br>1965; Reid et. al 1990). Theoretically, these gradients can be calculated from a properly sampled map of one of the<br>components of magnetic field (Nabighian 1984), but the advantage to their direct measurement is that interpretation can<br>be performed with data acquired at a few data points along a profile. Consequently, interpretation in near real time either<br>during acquisition or immediately after it is therefore quite feasible.


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