| Due to its broad applicability, cost effective mobilization and high coverage in surveying area, airborne transient electromagnetic(ATEM) have been widely applied as an efficient method, especially in developed countries like Australia and Canada. As the scanning measurement covering a large area,the large quantities of the observation data have brought great difficulties for the 3D interpretation. Therefore, a rapid and effective method for data processing and interpretation is urgently in demand. This paper presents a fast and efficient imaging method for ATEM data based on qualitative and quantitative interpretations, which provides a new solution for ATEM explanation.Presently, the apparent resistivity parameters are still widely used in the interpretation of time domain electromagnetic method(TEM). It can directly reveal the existence of underground electric interfaces, and especially suitable for qualitative interpretation of ATEM data. Traditional TEM apparent resistivity definition using iterative algorithms is restricted by offset and time approximation conditions, which will cause interpretation errors and reduce the efficiency of the data interpretation. Therefore, based on the analysis of the characteristics of the non-center responses, a full-domain apparent resistivity definition method is presented in this paper, which is suitable for both ground and airborne systems. Moreover, this method has higher precision and faster computing speed, and it can realize full-time and full-space apparent resistivity calculations.Helicopter ATEM systems with flexible moving platforms can be effectively applied to complex geological and topographical conditions. Airborne data measured at areas with a rolling topography always contain terrain information, which is actually a noise to the measured data. To better understand the influence of the terrain to our survey, a modeling of 3D ATEM considering terrain influences is implemented based on the finite-different time-domain(FDTD) method. We will be able to have more intuitive understanding about terrain effects by modeling complex 3D models. At last, the impact of various factors of ATEM data, such as depth and width of the terrain, electrical parameters, flight path and flight height on ATEM data are examined. The study provides an important theoretical basis for the recognition of topographic effect, topographic correction and furtherly, the inversion interpretation.Conventionally, ATEM data are interpreted directly on profiles of multiple time channels, or carrying out 1D imaging or inversion. The difficulty with carrying out rigorous inversions in higher dimensions lies in the fact that Maxwell‘s equations must be solved individually for each transmitter. Realization of high resolution 3D ATEM imaging research will be a breakthrough in the interpretation of ATEM system inversion. In order to improve the resolution of ATEM interpretation, the pseudo-seismic interpretation technique is introduced into the ATEM data processing procedure, and the algorithm used in transforming diffusion field into wave field is also studied. However, the wave field transformation is an ill-posed process, its transformation matrix has a very large condition number. Therefore, the preconditioned regularization method, wavelet transform method and SVD method are used respectively in the wave field transformation. A method with high resolution and stability is presented in this paper, which is used in multi-sweep-time wave field transformation. After transforming ATEM data to the wave field, the migration imaging method based on Kirchhoff integral is introduced to image the geometry of underground medium.Combining the characteristics of the ATEM system with the principle of synthetic aperture radar, we fulfill multi-aperture data synthesis and realize fast real-time imaging of the ATEM data. In order to further improve the resolution and interpretation accuracy, this thesis makes an in-depth study on the key techniques of synthetic aperture algorithm. The optimum aperture can be derived by numerous numerical modeling on its function expressions. Multiple model examples show that the synthetic aperture imaging method can effectively improve the resolution, both laterally and vertically, with characteristics of fast computing speed. Meantime, it is not affected by the impact of the massive air data. Thus it is proved to be useful for real-time imaging.In this paper, a set of fast imaging systems for ATEM data with high-resolution are given based on qualitative explanation and quantitative interpretation. The research furtherly improves the accuracy of the interpretation, enriches the ATEM interpretation and provides favorable conditions for ATEM effective promotion. |
PDF Full Text Request