Abstract

The remote sensing of terrestrial gamma rays has application in geologic mapping, mineral exploration, reactor site monitoring, location of lost radioactive sources, measurement of the water equivalence of snow, and soil mapping. Although the state of the art is quite good, there is a need to reexamine the use of detectors other than thallium activated sodium iodide detectors (e.g., plastic scintillators) to improve the corrections used for altitude variations and to present the data as apparent concentrations of potassium, uranium, and thorium rather than as counts per unit of time.In an attempt to improve data analysis, the technique known as factor analysis has been applied to airborne gamma-ray spectrometric data from a survey in South Texas. This analysis technique allows the geologist/geophysicist to perform a coordinate transformation from the four count rates [potassium (K), equivalent uranium (eU), equivalent thorium (eTh), and total count] and the three ratios, (eU/K, eU/eTh, eTh/K) to a system of three independent coordinates. These three coordinates are constrained to reproduce the total variance of the original data, and the data can be separated into groups using the criterion that similar data points have similar coordinates. The distribution of the separated groups can be mapped for comparison with other information such as the mapped geology. This map of the groups represents a synthesis of all of the radiometric data.

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