Marine DC resistivity and self-potential survey in the hydrothermal deposit areas using multiple AUVs and ASV

Abstract

Detecting resistivity and self-potential (SP) anomalies is useful for the exploration of hydrothermal deposits. Using autonomous underwater vehicles (AUVs) can increase survey effectiveness because it allows stable posture control without a towing wire cable from a ship. We propose a new style for geophysical surveys using multiple AUVs without a towing electrode cable for marine direct current resistivity (MDCR) and SP survey. We used two AUVs for electrical signal transmission and their receiver. We successfully conducted MDCR and SP surveys in hydrothermal deposit areas using two AUVs with 20 m tow-rods. One AUV was assisted by an autonomous surface vehicle (ASV) for monitoring and controlling via satellite and the public broadband mobile communications radiowave. The survey covered an area of about 1 square kilometer, spending only 4 hours near the seafloor with the vehicle's speed maintained at 2-2.5 knots at distance between the AUVs of 200-300 m during most of the survey. The SP and apparent resistivity were calculated along the main survey line crossing known hydrothermal mounds of sulfide ore. The distribution of the negative SP anomalies obtained in the dive is similar to that obtained from our earlier survey using a deep-tow. The apparent resistivity is generally low (0.2 ohm-m or less) above the mounds. The averaged distance between the vehicles and the averaged altitude are respectively about 250 and 70 m. Therefore, the estimated apparent resistivities are the averaged value to several tens of meters below the seafloor. These positions show good agreement with the locations of known hydrothermal deposits.

Deep-Sea DC Resistivity and Self-Potential Monitoring System for Environmental Evaluation With Hydrothermal Deposit Mining

“…First, we discuss the apparent resistivity variations. The absolute values of apparent resistivities are comparable to those of other data obtained by AUVs at and near this site (Kasaya et al, 2020). However, we Figure 3A.…”

“…(E) Enlarged (10 min) time series obtained the electrode pair (ch. 6-1) recording the responses of rectangular waveforms from the transmitter unit used for the present study and a transmitter loaded on an AUV during another survey (Kasaya et al, 2018;Kasaya et al, 2020).…”

“…Many spike-like waveforms are signals from the transmitter. The sweep-wave-like waveforms from 0:00 to 4:00 in Figures 5A-D are also signals from a transmitter loaded on an AUV during a different experimental geophysical survey using two AUVs (Kasaya et al, 2020). The variation of electric field calculated from the electrode pair closest to the mound (ch.…”

“…The apparent resistivity was calculated using the geometry of the current transmitter electrodes and the receiver electrodes. These apparent resistivity estimations followed the procedure explained by Kasaya et al (2020). The absolute values of apparent resistivity, however, have uncertainly because we were unable to carry out the resistivity calibration using data acquired in the middle sea layer.…”

Joint Interpretation of Marine Self‐Potential and Transient Electromagnetic Survey for Seafloor Massive Sulfide (SMS) Deposits: Application at TAG Hydrothermal Mound, Mid‐Atlantic Ridge

“…Recently, SP and other geophysical methods have been used to jointly investigate SMS deposits. For instance, Kasaya et al (2020) successfully conducted marine DC resistivity and SP surveys in hydrothermal deposit areas using two AUVs. Deep-sea passive electric measurements combined with high-resolution magnetic measurements based on AUV were also used in SMS exploration (Szitkar et al, 2021).…”