Relationships Between Soil Properties and High-Resolution Radiometrics, Central Eastern Wheatbelt, Western Australia

Abstract

A quantitative investigation was undertaken to ascertain the relationships between radiometrics and surface soil properties within a 77 km2 survey area, on the Elashgin Creek catchment, Wyalkatchem, Western Australia. A high-resolution airborne gamma-ray survey, with a measurement ‘footprint’ width of approximately 40 m and length of 80 m, provided measurements of radionuclide distributions across the study area. Ground-based gamma-spectrometry measurements, with a much smaller ‘footprint’ of one metre diameter, were also made at the majority of sampling sites. Field texture and gravel content from 132 sampling sites were recorded, with particle-size and mineralogical analysis conducted on a selection of sites. Mineralogical analysis provided an understanding of the sources of radionuclides. Using discriminant function analysis (DFA), areas of shallow soil over rock and rock outcrop were successfully discriminated using airborne radiometric and DEM data. The presence or absence of gravel grades was also successfully discriminated with radiometric data using DFA. In addition, a statistically significant correlation was identified between airborne thorium/potassium ratio and ironstone gravel content in the top 0 to 10 cm of soil (r2 = 0.56, P-value < 0.001). Stronger linear relationships were identified between airborne data and surface texture (e.g., 0–10 cm % clay and total count, r2 = 0.71, P-value < 0.001). Signal attenuation prevented the accurate determination of deeper subsurface soil texture (e.g., 20–30 cm % clay and total count, r2 = 0.24, P-value < 0.05). Of the airborne radiometric data, total count exhibited the strongest correlation to soil texture and potassium the least. It is concluded that high-resolution radiometric data can aid the mapping of important soil properties such as shallow granitic bedrock, presence or absence of gravel and the percentage clay in the top 0–10 cm of soil.