Joint Inversion and Application of DC and Full-Domain TEM with Particle Swarm Optimization

Transient electromagnetic method (TEM) data suffering from the “turn-off effect” can influence its inversion results and thus may further affect the joint inversion results of direct current (DC) and the TEM. In this study, the law of inversion results of TEM data suffering from the “turn-off effect” are summarized, and the necessity of full-domain TEM inversion is proven. The synthetic data of DC and TEM suffering from the “turn-off effect” are used to test the effect of the joint inversion of DC and full-domain TEM, and the result is compared with that of the single method. Then, the joint inversion is applied to field data detecting the water abundance of weathered rocks, and the delineated anomalies are found to be accurate and reliable by borehole verification. Results of the joint inversion of DC and the TEM are remarkably affected by TEM data suffering from the “turn-off effect,” which is harmful to fine interpretation. Nevertheless, the influence of the “turn-off effect” is effectively reduced by the joint inversion of DC and full-domain TEM, and the accuracy of joint inversion results is better than that of each method. In summary, the joint inversion of DC and full-domain TEM is proved to be necessary to realize fine processing and interpretation for the water abundance of weathered rocks.