Proton precession magnetometers, which measure total field intensities, have long been the instrument of choice for marine geophysical studies. Unfortunately, these instruments are subject to limitations, especially over N-S oriented ridges near the equator and anywhere that lineated short-wavelength anomalies or non-lineated fine-scale anomalies exist.
Vector magnetic field measurements provide a means to reduce or overcome these limitations of total field anomaly data. Horizontal and vertical components of the anomalous field are always greater than the total field anomaly, and these vector anomalies are significantly less affected by unfavorable geometries in equatorial regions. The PI's made initial tests of a vector magnetometer onboard a ship, but the ship's magnetic field introduced errors. They also tested a system on a deep towed vehicle. This method showed promise, but they did not have adequate motion compensation data. Therefore, the PI's, J. Gee and S. Cande, propose to develop a towed vector field magnetometer system. The system will use a SeaTex MRU-6 motion reference unit with triaxial magnetometers in a cylindrical anodized aluminum pressure case that is suitable for full ocean depth deployment. A towed system with a high precision motion sensor should eliminate the two significant sources of noise found in initial tests. The system will require a RS232 data transmission enhancer and a 300 m cable; it will be assembled at SIO. The PI proposes to test the system during a 4 day cruise off the coast of Hawaii where low amplitude anomalies (< 100 nT) exist.
This system should allow identification of spreading related anomalies in significant portions of the ocean basins where such identifications are not possible with existing instrumentation.
