Abstract: In one method of non-destructive inspection of bodies of ferromagnetic material such as buried or submerged pipelines, probes containing magnetic sensors scan the surface of the body to detect flaws as local variations in the magnetic field. Such sensors are sensitive to changes in velocity of the probe carrier which manifests itself in variations of output signal amplitude. Such variations are eliminated by matching the sensor with a correction circuit having complementary frequency response characteristics.This technique may be used in conjunction with a threshold circuit to eliminate unwanted data.