Did you know the earth is a big magnet? You probably did, but you may not have realized it. A compass works because the needle aligns with the earth's magnetic field. But have you ever tried to use a compass when you are near a large metal object like a car? What happens? The needle doesn't give a true indication of North. And if the metal in the car is impacting the performance of the compass needle, then it is also affecting the earth's magnetic field - even if only by a fraction.

A Magnetometer is an instrument that will show us to what degree a ferrous (metal) object is affecting the earth's magnetic field. There are several kinds of magnetometers, but the types we are most interested in are the kinds that can be towed underwater.

As you probably know, we are searching for World War II training aircraft call Harvards. The Harvard has a very useful characteristic when searching with a magnetometer - it has a 400lb engine in it.

As we search the waters around Ontario for crashed Harvards, we use a magnetometer, towed behind a boat to search for ferrous deposits (like an aircraft engine) by looking for disturbances in the earth's magnetic field.

The magnetometer we use looks much like an orange torpedo and has three sensors in it, which makes it rather experimental as normal magnetometers are not similarly equipped.

As we drag the magnetometer behind the boat, we might end up with data that converts into images that look like the image here. Changes in the colouring are interpretations by the software of the varying amounts of ferrous materials in different locations.

The magnetometer is an excellent tool that allows us to cross reference its data against the information we glean from Side Scan Sonar. While side scan gives us a profile of the bottom, the magnetometer confirms for us that the target we are looking at is, indeed, metal. This speeds our search as we don't need to dive on a target that is non-ferrous.

Image Courtesy of JW Fishers