A Systematic Approach to the Evaluation of the Quality of Time Domain AEM Data

Abstract

A recent airborne electromagnetic (EM) survey in Papua New Guinea (PNG) has provided an opportunity to trial systematic measures of data quality in a similar manner to those routinely employed in airborne magnetic and radiometric surveys. These calibration checks are designed to demonstrate the integrity of the acquisition system from a client perspective. AeroTEM IV data were acquired over two project areas in PNG during 2008/9, and a set of check flights were acquired over pre-determined test lines in each area. These were (a) pre-survey check flights and (b) repeat check flights. Pre-survey check flights consisted of a range of helicopter and bird manoeuvres carried out along line to assess system performance under varying survey conditions. These manoeuvres included: typical survey-type flight, bird swing, speed increase/decrease, ascent/descent, and flight at altitude with the transmitter on and off. Repeat check flights consisted of acquiring data along the same line at survey height and speed, at the commencement of each sortie. The 45 check flights acquired during the survey are used to demonstrate the amplitude of noise due to aircraft manoeuvre, and the detection of system error using repeat data. Recommendations are made for the evaluation of data quality consisting of the pre-survey and repeat check flights listed above, plus a heading check. Spectral fast Fourier transform (FFT) plots can be usefully employed to identify unwanted noise sources. Inversion of one or more lines of data from each flight is recommended to check the geologic value of the data.