SQUID GRADIOMETERS FOR A FUNDAMENTAL-STUDY OF UNDERWATER MAGNETIC DETECTION

An LTS SQUID gradiometer measuring six elements of Ist order magnetic gradient was produced for a fundamental study of magnetic detection an d localization under the water. It was to be installed at the sea bott om shallower than 30m and to measure magnetic noises which might degra de its detecting performance. Noises caused by the imbalance of gradio meters' pickup coils were suppressed by using auxilialy three-axis SQU ID magnetometer output. The imbalance parameters were determined by me asuring geomagnetic variations surrounding the sea bottom. A test for trial detection of an iron boat was conducted with a use of this gradi ometer. It resulted in obtaining a higher signal-to-noise ratio for th e gradiometer than that for the magnetometer.