Regional aeromagnetic/radiometric surveys: a perspective

During the planning and monitoring of the airborne magnetic/radiometric survey of the Phanerozoic Cover Rock area of Saudi Arabia, we examined established concepts and methods and tried to formulate a cost-effective programme that would maximise the information obtained from the data. This paper outlines the decision-making process and uses the concept of 'data structure' to guide evaluation. Survey parameters were evaluated in terms of spatial resolution and the spectrum for 3-D, 2.5-D and 2-D magnetic sources and the circle of influence of the spectrometer. The resulting choice of 2 km line spacing at 122 m was a compromise between magnetic and radiometric requirements and cost. The important decision was to acquire relatively high sensitivity, high resolution data, utilising a large crystal volume multichannel gamma ray spectrometer and a quality proton precession magnetometer. The magnetic and radiometric data were processed conventionally and compiled on to contour maps and multi-parameter flight-line profiles. A pilot interpretation was carried out to evaluate alternatives for the full-scale interpretation project. This enabled us to define the 'data structure' and assess data presentation methods. Examination of the pilot study contour maps revealed problems of aliasing and loss of resolution in the gridded data and emphasised the value of colour image presentation. The second main decision was to enhance critical high-frequency data using nested profile data analysis and presentation. These employed, among other things, variabie area derivative profiles and conventional analytic signal profiles for magnetic data, and colour bar plots of the radiometric profile data.