Marine magnetic data processing in equatorial regions off Ghana

Abstract

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