MARINE MAGNETIC DATA-PROCESSING IN EQUATORIAL REGIONS OFF GHANA

Total field magnetic values recorded during a survey by RRS Charles Da rwin off Ghana yielded large track-crossover errors of up to 120 nT (R MS value of 58.7 nT), which masked the weak magnetic anomalies in this equatorial region, The heading effect of the ship's magnetic field an d strong diurnal variation in the Earth's held are likely causes of th e errors. A heading effect experiment shows differences of up to 30 nT for Charles Darwin on different headings, which have been corrected f or. The diurnal variation has been calculated by using the magnetic fi eld observations themselves, because observatories are either too dist ant or were inoperative at the time of the survey. A method that uses the anomalies corrected for heading effect and differences at track cr ossovers was found to produce an acceptable curve, with an amplitude o f 120 nT and a shape similar to that of equatorial observatories. Full y corrected anomalies have crossover errors of up to only 40 nT with a n RMS value of 17.5 nT, These anomalies reveal a linear magnetic anoma ly low along the continental slope off Ghana.