# Development of Multi-Channel Seismic-Electrical Combined Rolling Coverage Measurement System
## 2 Design of the Combined Measurement System
### Design of Coverage Cable  
This instrument supports the rolling coverage measurement method during electrical or seismic exploration, which is realized by a new type of coverage cable. Taking high-density electrical exploration as an example, as shown in Figure 10, the commonly used centralized high-density resistivity instrument cables (referred to as centralized cables) have enough taps set along a single cable to serve as connection points for the electrodes [30]. If the profile length to be measured is greater than the cable length, the cable and electrodes must be moved to cover the profile (as shown in Figure 11). All electrodes must be disconnected from the cable before moving them. After relocating the electrodes, the cable must be repositioned and aligned with the new electrode positions before reconnecting. This process is inconvenient, time-consuming, and labor-intensive. This paper uses an improved structure of cable, called the coverage cable, which is composed of several identical unit cables. Each unit cable has a male connector at one end, a female connector at the other, and several evenly spaced taps along its length to connect electrodes or geophones. Two cable units can be connected to each other through the male and female connectors. The core wires of the cable are offset and welded to the connectors in a regular pattern. If a group of cables consists of \(k\) unit cables, and each unit cable has \(m\) taps, the number of core wires in the cable is \(n=k\times m\). The \(i\)-th pin of the unit cable's female connector is connected to the \((i-m)\) mod \(m\)-th pin of the male connector at the  
Figure 8: Schematic diagram of the input stage of the analog channel and the preamplifier circuit. Figure 9: Schematic diagram of the filter circuit. other end via the core wire. Taking an eight-core cable as an example, as shown in Figure 12, this cable group is composed of four unit cables, each with two taps. As shown in Figure 12, core wires of the same color are internally connected, linking the eight electrodes to pins 1 through 8 of the instrument's female connector. Due to the use of a segmented unit cable structure that connects with each other, the movement of the cable electrodes and the cable itself becomes very convenient. The first unit cable can be detached and reconnected to the end of the last unit cable, as shown in Figure 13. Taking the two types of cables in Figures 13 and 14 as examples, the processes required for the centralized cable and coverage cable are shown in Table 2. Because adjacent coverage cables remain connected during relocation, their movement is counted as a single cable operation. Table 2 shows that, compared to the centralized cable system, the use of coverage cables reduces to eight electrode connections and disconnections, along with two cable movements and two instrument relocations. Therefore, using the coverage cable for resistivity profiling can effectively reduce both operational complexity and acquisition time. Figure 11: Resistivity profile coverage measurement. Each colored trapezoid represents a resistivity section from a separate acquisition with a different electrode configuration, together forming a full survey profile. Figure 10: Schematic diagram of the centralized cable. Numbers indicate the pin positions on the connector, and colored lines represent the cable cores connected to each pin. Figure 14: Schematic diagram of centralized cable measurement. Figure 12: Schematic diagram of the coverage cable. Numbers indicate the pin positions on the connector, and colored lines represent the cable cores connected to each pin. Figure 13: Schematic diagram of coverage cable measurement. When the coverage cable is used for seismic measurements, the two output terminals of each geophone are connected, respectively, to the core wire taps and the shield ground taps of the cable, as shown in Figure 15. The grounding shield layers of each unit cable are interconnected and connected to the instrument's ground.