An aero-towed vector magnetic system

The three components of the crustal magnetic field provide essential constraints on the structure of the source layer as well as its age. In marine equatorial regions where the mid-ocean ridges are oriented north-south, the traditional total field anomalies are tiny, making them essentially undetectable. Still, the vector components of the equatorial magnetic field are detectable and can thus provide the only means of dating the oceanic crust there. However, collecting vector magnetic anomalies is difficult as it requires excellent knowledge of the three orientation angles. The existing vectorial systems are either installed on the carrying platform (airplanes or ships), thus suffer from significant magnetic contamination, or they are towed behind ships but suffer from poor constraints on the heading direction. Here we present the first aero-towed vector magnetic system (AeroVmag) that we have recently developed in order to reduce the magnetic contamination level to essentially null while maintaining excellent knowledge of the orientation angles. The system contains three independent sensors: a vector magnetometer, a scalar magnetometer, and a dual-GNSS/INS orientation sensor (accuracy of 0.02º). We tested the system by collecting data at a low altitude (100 m) above the northeast part of the Sea of Galilee, Israel. Data were collected at a high (200 Hz) sampling rate along a dense grid of profiles that allowed us to evaluate the error levels of our measurements. The scalar results compare favorably with an earlier sea surface total field survey. Together with the vector data, our observations also unravel the location of the main segment of the Dead Sea Transform fault that straddles the survey area. To conclude, this new system will allow the collection of cost-effective and accurate vector magnetic anomaly data. We expect this system to be most valuable over ice-covered, equatorial, and strongly magnetized regions.