## 4 Laboratory Experiment Verification of space state Transformation
### Experiment Procedure
Saline water with a concentration of 5% at 25 degrees Celsius was pre-configured by mixing solid sodium chloride with water. The resistivity of the salt water was approximately equal to 5.0 \(\Omega\)-m, so salt water was selected as being similar material for the surrounding rock. The length and the number of turns of the transmitting and receiving coils were taken as 5 cm and 30 turns, respectively. The transmitting current was taken as 0.5 A. The high-resistance filler was placed on one side of the model container, according to the design requirements. The high-resistance filler and the model container are shown in Figure 11. According to the designed solution concentration, 50 kg of solid particle salt was added, and 750 L water was added. In order to prevent the salt water from entering the high-resistance filler, a polyethylene waterproof plastic film was laid outside the high-resistance filler to isolate the high-resistance filler and salt solution, as shown in Figure 12. According to the coil layout in Figure 8, the transmitting coil and receiving coil were placed at the center of the salt solution. The transient electromagnetic equipment was used to measure the electromagnetic intensity in a 3/4 space state. The indoor field layout is shown in Figure 13.  
Figure 11: High resistance filler and model container. Figure 12: Salt aqueous solution for experiment. Figure 13: Schematic diagram of the indoor transient electromagnetic spatial transformation problem. Meanwhile, the apparent resistivity inversion results could be obtained, based on the experiment results of the three ideal space states, as shown in Figure 10.0  
It can be seen from Figure 16 that the apparent resistivity inversion results basically showed a linear decline in the early and middle periods under a single logarithmic coordinate condition, based on experimental data. On the whole, the apparent resistivity result of the half space inversion was the largest, the apparent resistivity result of the full space inversion was the smallest, and the apparent resistivity result of the 3/4 space inversion was in the middle. It should be noted that the apparent resistivity result was greater than the resistivity of the actual model in the early period, which meant that there were still some differences between the apparent resistivity inversion results and the actual model resistivity. According to the proportional coefficient, the inversion results of the three ideal space states could also be illustrated, as in Figure 10.1 Taking the first eight-time gates as the analysis object, the full space inversion results based on the proportional coefficient were smaller than those of the experimental data, while the 3/4 space inversion results, based on the proportional coefficient, were larger than those of the experimental data. Through the calculation of different types of inversion data, the average relative errors of the first eight time gates of the inversion results of different methods were 5.32% and 12.21%, respectively, which meant that the inversion error was within the allowable range. Based on the saline model in the 3/4 space state, the electromagnetic response curves of saline conductors were measured when the transmitting coil and the receiving coil moved at different distances simultaneously. The results are shown in Figure 10.2  
It can be demonstrated from Figure 16 that there were certain differences in the amplitude of the response curve of the saline model under different offset distances in the early and middle stages. In the middle and late stages, the response curves of the saline model under different offset distances were the same, and the amplitude was close to the level of air noise response. To compare the response differences of saline models under different offset distances, the results of the first eight time gates were taken as the analysis object, and the local amplification diagram of the results is shown in Figure 10.3 According to  
Figure 10.4 Apparent resistivity inversion results of three ideal space states.