Detection of mobile targets from a moving platform using an actively shielded, adaptively balanced SQUID gradiometer

Tests have been performed with a moving HTS dc SQUID gradiometer mounted on a nonmetal motion table. The system operated with sensitivity of 80 pT/m/√Hz (1 Hz) and 1 pT/m/√Hz (white) whilst undergoing pitch, roll and yaw motions of ±5° in an outside environment. Gradient anomalies of ≥ 1 nT/m were detected with 12 dB signal-to-noise ratio and a measurement bandwidth of 1 kHz. In this paper, we describe the performance of the gradiometer at measuring remote moving ferromagnetic targets whilst it is in motion. These measurements have an important bearing on understanding the viability of SQUID-based systems as magnetic anomaly detectors, when mounted on airborne or seaborne platforms. In one early test, a target of approximately 300 Am² travelling at 2-5 m/s was detected at 25 m range with a signal to noise ratio of 4:1, whilst the gradiometer was undergoing motions of ±5° in pitch roll and heading.