We report on the development of a magnetic gradient tensor sensor based on high-T c SQUIDs for marine surveying applications. The proposed system uses six planar gradiometers incorporated into a hexagonal pyramid structure where the combined output will provide a measure of the gradient tensor. This report focuses on the development and characterization of long baseline high-T c SQUID gradiometers for this purpose. We compare the performance of two separate fabricated gradiometer designs. These devices both consist of a large 40 mm × 20 mm gradiometric pickup loop antenna flip-chip coupled to a small readout SQUID gradiometer. We have thus far demonstrated an unshielded gradient sensitivity of ∼29 fT cm −1 Hz −1/2 at 1 kHz and ∼170 fT cm −1 Hz −1/2 at 10 Hz through optimizing the coupling inductances of our device.

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