Q

Quadrature  – the imaginary component of Analytic Signal which has the same Amplitude Spectrum as the real component but differs in phase by 90º. For 2-D profile data or 3-D gridded data, Q. can be calculated using Hilbert Transform. For 3-D data, Q. is sometimes estimated by subtracting the grid data (as the real component) from the calculated 3-D analytic signal. ^{[94, 236]} See also Quadrature Image and Three-Dimensional (3-D) Analytic Signal.

Quadrature Image  – an image of the gridded potential field data which is obtained from the calculation of Quadrature. Since Q.I. incorporates a 90º phase shift of the original data, the single peak anomalies on the standard image will appear as combinations of peaks and troughs on Q.I. This doubling of the number of anomalous features often contributes to the higher resolution of the subsurface discontinuities. Position of the magnetic sources is assumed to be approximately aligned with the crossovers from the positive to the negative parts of Q.I. anomalies for near-vertical magnetic sources with strikes orthogonal to the traverse survey lines. ^[94]. See also Quadrature.

Quality Control (QC)  – the in-field and in-office processing of the recorded measurements in order to identify and, if possible, correct data acquisition problems. ^[58]. See also Post-Flight Quality Control.

“Quick-And-Dirty” Peters Method  – a simplified version of Peters Half-Slope Method of the magnetic source depth estimate using map data without the need to plot the magnetic anomaly profile. It includes the following steps: 1) determine the distance between map contour lines at the area of the maximum gradient of the selected anomaly; 2) locate the points on either side of the gradient area where the distance between contour lines is twice that of the maximum gradient – these points correspond to the Peters half-slope points; 3) measure the obtained half-slope distance (i.e., Peters Length) and divide it by 1.6 to determine the depth (if the survey is airborne, subtract the flight elevation from the determined depth value to get the actual depth below the Earth’s surface). ^[215]. See also Depth Rules.