Research on dynamic three-dimensional terrain correction methods of quantitative inversion for airborne gamma-ray spectrometer

摘要: Aerial survey is a dynamic and continuous process, and there are also different height distributions of the ground in the measurement area, which leads to problems such as overlapping of measurement areas and inaccurate altitude correction during the survey process. Commonly used terrain correction methods are based on the concept of finite elementization of ground surface radioactive sources, using GPS coordinates, radar altitude, and ground elevation distribution information from aerial surveys, combined with the sourceless efficiency calibration method to construct a response matrix, and then inverted for surface nuclide content. But most of the sourceless efficiency calibration methods used are numerical calculations that consider the body detector as a point detector and do not take into account the changes in intrinsic detection efficiency under different incident directions of gamma rays. Therefore, when the altitude of the measurement area varies greatly or the flight altitude of the aerial survey is relatively low, such sourceless efficiency calibration method calculations tend to have a large bias, which affects the accuracy of the terrain correction. To address the above problems, this paper employs a novel sourceless efficiency calibration method based on the Boolean operation of the ray deposition process, and simplifies the traditional body source measurement model to the surface source measurement model to achieve fast and accurate efficiency calibration; and then, through the discretization of the measurement process, superposes the static measurement process as equivalent to the dynamic measurement process, and builds and optimizes the dynamic measurement response matrix based on the calibration method; Finally, the PSO-MLEM algorithm is used to solve the dynamic measurement response matrix to achieve the dynamic terrain correction of aerial survey data. Analysis of the Baiyun'ebo test area reveals that, after applying dynamic terrain correction, the inverted anomalies in uranium (eU), thorium (eTh), and potassium (K) concentrations are closer to ground measurements (within 5.72%–30.79%) and exhibit clearer anomaly boundaries compared to traditional height-based corrections. However, due to the inherent statistical fluctuations and the characteristics of matrix inversion, higher measurement values tend to absorb lower ones, potentially enlarging anomalous regions. Nevertheless, the high-anomaly regions after inversion largely coincide with ground truth validation, demonstrating that the proposed method can effectively correct airborne gamma spectrometry data.