Transient electromagnetic 1D inversion based on the PSO–DLS combination algorithm

To improve the inversion results of roadway or tunnel transient electromagnetic detection data, particle swarm optimisation (PSO) and damped least squares (DLS) algorithms are combined. This overcomes the shortcomings of the PSO algorithm, namely that it has lower optimisation efficiency in the later stage, and the DLS algorithm, which requires manual assignment of initial values. With reference to actual stratum data, the mathematical model is established, and the inversion trial calculation is carried out using PSO, DLS and the proposed combined PSO-DLS algorithm. The results show that the combined PSO-DLS algorithm has higher optimisation efficiency without manual assignment of the starting model. The combined PSO-DLS algorithm is used to invert the measured transient electromagnetic data of the mine roadway, which realises separation of the mine roof and floor resistivity anomalies. Compared with PSO and DLS, the interpretation results for PSO-DLS are most consistent with the logging data, geological data and roadway exposure conditions.