## 2 Borehole Multi-Source Data Acquisition Technology
### Borehole Directional Acoustic Scanning Technology  
The borehole directional acoustic scanning technology mainly uses the reflection characteristics of the acoustic pulse to reflect the structural characteristics of the rock mass inside the borehole-surrounding rock, and realizes the acoustic scanning of the borehole-surrounding rock structure by using the technical method of combining the directional acoustic probe, rotating the device and positioning the device [20; 21]. On the horizontal section at a certain depth of the borehole, the directional acoustic transducer vertically transmits a series of acoustic signals to the borehole wall, receives the reflection signals of the rock mass inside the rock wall, uploads the signals to the ground computer and stores them. Then, driven by the rotary device, the directional acoustic transducer rotates according to a fixed angle, and the directional acoustic transducer vertically transmits a series of acoustic signals to the borehole wall. It also receives the reflection signal of the  
Figure 3: Schematic diagram of panoramic image solution. rock mass inside the rock wall, uploads the signal to the ground computer and stores it. This process is repeated to achieve complete scanning of the section. At the same time, it records the azimuth information of each wave in real time through the positioning device, including the depth and azimuth information of the directional acoustic transducer. The scanning diagram is shown in Figure 4.  
In order to more intuitively display the abnormal regional characteristics of the borehole-surrounding rock, it is necessary to reconstruct the image of the borehole-surrounding rock. In the composite section diagram of fixed depth, a circular scanning matrix diagram is established, as shown in Figure 5a. The innermost circle of the circular diagram represents the acoustic reflection signal of the borehole surface, and the outermost circle represents the maximum scanning value of the directional acoustic wave, that is, the maximum detection range around the surrounding rock. Its size is determined by the performance of the equipment and the acoustic propagation characteristics of the rock. Different detection environments usually differ in size. The single scanning length is twice the maximum detection range, and its single scanning length is the product of sampling points, sampling interval time and rock acoustic propagation speed. Other circles in the interior are arranged from inside to outside according to time, and their size is the amplitude of the acoustic echo signal. This process is determined by the number of sampling points. Thus, if there are n sampling points in a complete scanning wave, the sector area \(S|_{h,i,1}\) formed by the innermost circle and the second inner circle display the information represented by the first sampling point of the scanning signal, and the sector area \(S|_{h,i,n}\) formed by the second outermost circle and the outermost circle display the information represented by the nth sampling point of the scanning signal. If the number of scanning lines of each section is m, then the sector area \(S|_{h,i,j}\) is used to represent the surrounding rock structure information of the j-th sampling point on the i-th scanning line at the depth h, where \(1\leq i\leq\) m, \(1\leq j\leq\) n,  
Figure 4: Scanning diagram of directional acoustic probe. Figure 5: Schematic diagram of surrounding rock structure scanning. (**a**) Circular scanning matrix. (**b**) Borehole-surrounding rock section. the included angle of the span of sector area \(S\big{|}_{h,i,j}\) is \(2\pi/\text{m}\), and the span width of sector area \(S\big{|}_{h,i,j}\) is \(\Delta t\), where \(\Delta\)T is the sampling interval of the signal.