Magnetic loops as submarine detectors

An analysis is given of shallow water submarine detection by a buried magnetic loop. The submarine signal and interfering geomagnetic, ocean wave, and thermal noise are included in a simple, flexible detection range model. Sample detection ranges are presented and appear encouraging. Conditions which can limit detection are discussed. A simple experiment is planned as the logical next step. The detection model calculates detection ranges as a function of loop signal-to-noise ratio. The model allows for variation of loop, target, and ambient parameters as well as the detection criteria. Results illustrate that magnetic loops can be effective detectors. The loops are ambient noise limited. Random fluctuations about the earth´s steady magnetic field; i.e., geomagnetic micropulsations, are the most serious noise source. Ocean wave induced noise creates a zone of intermediate depths where detection is impossible if the surface waves are large enough (such large, long-period waves are rarely encountered). Thermal noise arising from resistance in the loop´s wire is very small. The thermal noise limit can be approached if the geomagnetic noise is highly correlated. A differential loop configuration (employing two loops) could then subtract out the geomagnetic noise yielding increased detection ranges.