Summary We report on the research and development of a TDEM data acquisition system (SQUITEM) by JOGMEC using a highly sensitive high-temperature superconductor (HTS) SQUID vector magnetometer cooled by liquid nitrogen, which is suitable for mineral exploration. JOGMEC has achieved stable long-term operation of all three channels during field tests. SQUITEM meets high requirements for slew rate (6.8mT/s), dynamic range (100dB) and bandwidth (DC -100kHz). It offers deeper penetration of depth than the induction coil system because it can record the step response that decreases with time slower than the impulse response of the induction coil system. SQUITEM also performs horizontal gradient observations that can provide much better resolution of shallow conductive targets than conventional EM field component observations. We have obtained good reproducibility of SQUID data and correlation between the output signals of the reference induction coils and the derivatives of the SQUID signals in TDEM field tests
