Airborne Geophysical Survey Maps

Reduced-to-Pole Magnetics

To compensate for the shift of the true anomaly position over the causative source, due to the magnetic inclination and declination, the magnetic data was recomputed so that magnetic anomalies will appear as they would if located at the north magnetic pole. The result of this operation is that in theory, the magnetic anomaly is located directly overtop of the causative source. The computation is referred to as "reduced-to-the-pole" (RTP). The RTP not only shifts the anomalies to their correct position with respect to the causative magnetic bodies, but assists in the direct correlation and comparison of magnetic anomalies, trends, structural axis, and discontinuities with mapped geologic surface expression.

First Vertical Derivative (1VD)

Vertical derivatives compute the rate of change of the magnetic field as it drops off when measured vertically over the same point (upward continuation). The First Vertical Derivative (1VD) has the effect of sharpening anomalies, which allows for better spatial location of source axes and boundaries

Second Vertical Derivative (2VD)

To enhance local anomalies and to outline the edges of anomalous bodies within the data, a Second Vertical Derivative (2VD) is computed. The 2VD is a powerful interpretive tool and that is used to assist in the delineation of causative bodies and to accurately locate changes in the magnetic field gradients. Better definition of discontinuities and their relationship to geology can be gained from the use of this tool. A 2VD will show steep gradients over faults and positive closures over the "up thrown" blocks.

Apparent Resistivity

Apparent resistivity maps are extremely valuable for geological mapping and interpretation. Apparent resistivities can be calculated from each electromagnetic frequency used in the survey. However, the horizontal coplanar coil configurations are most often used because they have maximum coupling to horizontal layering. The apparent resistivity map shows the results for the 6600 Hz data.