Page 10 - Marine Magnetometer Processing

Figure 3: Geomagnetic reference field model for total field strength (BGS) Over small areas covered by marine surveys the magnetic field does not change very much, so with no magnetic objects nearby a magnetometer would read the same value over the whole survey area. However, many rocks are magnetic so the underlying geology can affect the magnetic field measured in a survey area. Often this is seen as a gradual change in the field measurements over the site with one area showing a higher magnetic field measurement than another. The effect is often very noticeable so magnetometers have been used for prospecting for minerals buried beneath the ground. The magnetic field at a point on the Earth also changes with time, an effect known as diurnal variation. This is caused by the rotation of the Earth within the magnetosphere as different parts of the Earth face the sun and forms a regular daily cycle. Diurnal variation can cause the magnetic field measured at a place on Earth to be different in the morning and in the afternoon. Solar storms can also affect the Earth’s magnetic field causing large changes in the background magnetic field strength. Marine Magnetometer Processing \[9\] © 3H Consulting Ltd Figure 4: Aquascan AX2000 proton magnetometer deployed from a small inflatable boat