Magnetic field

Magnetic anomalies in an area help to detect accumulations of minerals, volcanic activity or metallic structures deposited on the sea bed. This study consisted of acquiring magnetic data using a magnetometer towed by a ship and then the data was processed to obtain magnetic anomalies in comparison with the mean magnetic field.

Data acquisition was done with a SeaSpy magnetometer by the personnel of the CSIC Marine Technology Unit (UTM) aboard the oceanographic vessel Ramón Margalef, sailing transects in the test bed area shown in the graph below.

Process and results

The magnetic data acquired was processed by the staff of the Naval Royal Observatory. The measurement of the earth’s magnetic field reflects the contribution from several different sources, including the contribution made by the internal field that accounts for 95% of the measurement, and then the effect of external magnetic fields. The value of the magnetic anomaly has to be derived from these contributions.

The IGRF-11 (International Geomagnetic Reference Field) model provided by NOAA was used to determine the internal field.

The data from the Güimar Observatory (Tenerife) over a period of almost a month (1-23 April) were used to determine the external field, choosing nocturnal periods as solar activity is lowest at these times.

Other levelling processes have been carried out to minimise differences in readings at the cut-off points between transect lines and finally, the data have been interpolated at points without data between transects.

The result of this process is the field of anomalies shown in the graph below, where one of the anomalies identified was the wreck of the Arona, the presence of which had already been validated by underwater videos. The other anomalies detected could be associated with the morphology of the sea bed.