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Figure 4-21.-Simplified comparison of natural field density and submarine anomaly
MAGNETIC NOISE

Aviation Electronics Technician 1 (Organizational)
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Figure 4-22.-Submarine's magnetic moment. magnetic strength. In views C and D, the submarine’s magnetic field distorts the natural field as shown. The density of the natural field is decreased in view C and increased in view D. The natural angle of dip is also affected, but only very slightly. Submarine Anomaly The maximum range at which a submarine may be detected is a function of both the intensity of its magnetic anomaly and the sensitivity of the detector. A submarine’s magnetic moment (magnetic intensity) (fig. 4-22) determines the intensity of the anomaly. It is dependent mainly on the submarine’s alignment in the earth’s field, its size, the latitude at which it is detected, and the degree of its permanent magnetization. MAD equipment, in proper operating condition, is very sensitive; but the submarine’s anomaly, even at a short distance, is normally very weak. The strength of a complex magnetic field (such as that associated with a submarine) varies as the inverse cube of the distance from the field's source. If the detectable strength of a field source has a given value at a given distance and the distance is doubled, the detectable strength of the source at the increased distance will then be one-eighth of its former value. Therefore, at least two facts should be clear. First, MAD equipment must be operated at a very low altitude to gain the greatest proximity possible to the enemy submarines. Second, the searching aircraft should fly at a predetermined speed and follow an estimated search pattern. This ensures systematic and thorough searching of the prescribed area so that no existing anomalies are missed. Anomaly Strength Up to this point, the inferred strength of a submarine’s anomaly has been exaggerated for purposes of explanation. Its actual value is usually so small that MAD equipment must be capable of detecting a distortion of approximately one part in 60,000. This fact is made apparent by pointing out that the direction of alignment of the earth’s magnetic lines of force is rarely changed more than one-half of 1 degree in a submarine anomaly. Figure 4-23, view A, represents a contour map showing the degree of anomaly caused by a submarine. The straight line  is approximately 800 Figure 4-23.-A. Degree of anomaly. B. Anomaly stylus. C. Sample anomaly record. 4-17







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