## 3 Integrated Geophysical Exploration Techniques for Earth and Rock Dams
### Principles of Integrated Geophysical Exploration Information Fusion Technology  
The principle of integrated geophysical exploration information fusion technology is to fuse and reconstruct the information obtained by different detection techniques through the unified inversion model of multi-physical parameters. In this paper, we take the electrical resistivity tomography method, surface wave method, and ground-penetrating radar method as examples to introduce the process of using the integrated geophysical exploration information fusion technology. Firstly, the hidden hazard information obtained by different detection techniques is pre-processed. The hidden hazard information obtained by geophysical exploration techniques mainly includes the shear wave velocity distribution obtained by the surface wave method, the apparent resistivity distribution obtained by the electrical resistivity tomography method, and the electromagnetic wave velocity distribution obtained by the ground-penetrating radar method. The processed information is reconstructed into a unified parameter by using the multi-physics field joint inversion model. The information obtained from the inversion is fused and reconstructed by the data fusion method to obtain the complete geologic body data. The location and channel of the leakage hazard of the geologic body are determined by the leakage hazard identification criteria. The research process for the theoretical model of integrated geophysical exploration information fusion is shown in Figure 14.  
The theoretical model of the joint multi-physics field inversion is shown in Equations (1) and (2). Equation (1) is the mathematical conversion method of apparent resistivity by surface wave method. Equation (2) is the mathematical conversion method of apparent resistivity of the ground-penetrating radar method (see Appendix A for full trans). \[R_{l}=\frac{ln\left[\frac{0.65\left(\sqrt{\frac{2(1-v)}{1-2v}}V_{\rm S} \right)^{1.05}}{RH}\right]}{ln\left[\frac{0.65\left(\sqrt{\frac{2(1-v)}{1-2v}} V_{\rm S}\right)^{1.05}}{1-2v}V_{\rm S}\right]} \tag{1}\]  
Figure 14: Research process for theoretical model of integrated geophysical exploration information fusion. \[R_{t}=6.8006562\times 10^{5}.\left(\frac{v}{c}\right)^{5.7143} \tag{2}\]  
where \(K\), \(C\), and \(d\) indicate the stratigraphic parameters, \(v\) indicates the Poisson's ratio, taking the value of 0.35, \(R_{t}\) indicates the resistivity of the underground medium, \(\Omega\cdot\)m, \(v\) indicates the propagation speed of the electromagnetic wave in the underground medium, m/ns, \(c\) indicates the propagation speed of the electromagnetic wave in vacuum (c = 3 \(\times\) 10\({}^{8}\) m/s). The apparent resistivity data obtained by different geophysical exploration techniques need to be aligned in their spatial dimension before information fusion. It mainly contains the calibration of the plane position within the geodetic coordinate system and the data conversion between the time and depth domains. It is necessary to ensure that the data acquired by different geophysical survey techniques come from the same profile, in accordance with the calibration requirements for planar positions within the geodetic coordinate system. Spatial alignment in the longitudinal domain needs to be accomplished in the process of joint inversion. The data information after spatial alignment has met the requirements in the spatial dimension, but before data fusion, it is still necessary to standardize the data information. There are two main steps in data standardization. Firstly, the scale of the detection data should be unified. Due to the different detection principles of the three geophysical exploration techniques, the resolution of their respective detection information is inconsistent. In order to ensure that when data fusion is carried out, the detection information of different physical exploration techniques can correspond to each other in the profile, it is necessary to unify their scales.