# Multi-Means Comprehensive Forecasting Technology for Water Inrush in Long Tunnels
## 3 Comprehensive Geophysical Exploration Techniques
### Ground Penetrating Radar Method  
Ground penetrating radar operates by transmitting high-frequency electromagnetic waves (typically ranging from 10 MHz to 2.5 GHz) into the subsurface and analyzing the reflected signals to identify contrasts in dielectric constants, thereby generating detailed images of subsurface structures. The system emits high-frequency, broadband electromagnetic pulses into the rock mass ahead of the workforce. As these electromagnetic waves propagate through the rock medium, they encounter subsurface features with distinct electrical properties, such as voids or interfaces, causing reflections. These reflected waves return to the workforce and are captured by receiving antennas. The collected electromagnetic signals are then processed and analyzed based on waveform characteristics, signal amplitude, and two-way travel time. This analysis enables the determination of the spatial location, structural features, electrical properties, and geometric configuration of subsurface targets, facilitating the detection of hidden underground features.  
Ground penetrating radar relies on high-frequency electromagnetic waves for subsurface exploration. According to electromagnetic wave propagation theory, the behavior of these high-frequency waves in a medium is governed by [PERSON]'s equations, which describe the fundamental principles of electromagnetic field interactions. Specifically, the propagation and reflection of electromagnetic waves in heterogeneous media can be modeled using these equations, providing a theoretical foundation for interpreting ground penetrating radar data and reconstructing subsurface profiles.  
\[\
abla\times\mathbf{E}=-\frac{\partial\mathbf{B}}{\partial t} \tag{3}\]  
\[\
abla\times\mathbf{H}=\mathbf{J}+\frac{\partial\mathbf{D}}{\partial t} \tag{4}\]  
\[\
abla\cdot\mathbf{B}=0 \tag{5}\]  
\[\
abla\cdot\mathbf{D}=\rho \tag{6}\]  
Here, \(\rho\) represents the charge density (C/m\({}^{3}\)), \(\mathbf{J}\) denotes the current density (A/m\({}^{2}\)), \(\mathbf{E}\) signifies the electric field intensity (V/m), \(\mathbf{D}\) corresponds to the electric displacement (C/m\({}^{2}\)), \(\mathbf{B}\) indicates the magnetic induction intensity (T), and \(\mathbf{H}\) represents the magnetic field intensity (A/m).  
The propagation characteristics of electromagnetic waves through rock mass media are fundamentally governed by the medium's dielectric permittivity, which dictates critical parameters including wavelength, phase velocity, and reflection coefficients. Interface reflection phenomena are primarily determined by contrasts in dielectric permittivity between adjacent media layers, with electrical conductivity exerting negligible influence on  
Figure 2: Schematic diagram of the principle and observation of seismoelectric effect: (**a**) schematic diagram of the principle; (**b**) schematic diagram of the observation of seismoelectric effect.  
reflection magnitude. This reflection mechanism occurs specifically at boundaries where dielectric permittivity discontinuities exist.  
While higher-frequency antennas achieve superior spatial resolution through reduced wavelength dimensions, their operational utility is constrained by pronounced signal attenuation resulting from conductive and dielectric loss mechanisms. Consequently, such high-frequency systems exhibit limited penetration depths, typically restricted to shallow subsurface investigations.