New multi-resolution and multi-scale electromagnetic detection methods for urban underground spaces

Abstract

The “transparent” detections of urban underground spaces pose difficult challenges in the field of geophysics. Due to the complexities of urban underground environments, the existing detection methods are hard to reach the high capabilities of radiation sources and distinguish small-scale abnormal bodies at the same time. The “transparent” detections of urban underground spaces must achieve multi-resolution and multi-scale detection abilities. The previously applied electromagnetic detection methods have displayed limitations in achieving high radiation capability and rich harmonic component detections. Therefore, this paper focused on three key scientific issues: the design of a high-performance excitation source; a multi-resolution detection theory; and a multi-scale information extraction technique. First, in order to increase the radiation intensity, improve the directional radiation capability, and realize powerful and directional radiation, a new type of high-performance transient electromagnetic source was designed. Then, complex waveforms would be transmitted in order to enrich the frequency component of the excitation signals. The complex excitations were carried out using pulse scanning technology for the purpose of obtaining increased abundant underground information. The multi-resolution detections of the underground targets were realized in combination with a superposition algorithm. Finally, based on a related superposition principle, multi-aperture synthetic aperture technology was examined. By setting the sizes of the apertures, the vertical and lateral resolutions were adjusted, and the multi-scale information extractions of the urban underground spaces were realized. In this study, a large number of numerical model tests and simulation calculations were carried out. The results confirmed that, from the point of view of a detection mechanism, a high performance radiant source combined with a multi-resolution method and multi-scale signal extraction technology could successfully obtain correct and effective clear detection results in both transverse and longitudinal directions. The research results of this study will significantly promote the development of urban underground space detection technology, which will potentially be of major importance in making the underground spaces up to 200 m ‘transparent’ in urban areas.