• NWT

Magnetics

Airborne magnetics is probably the cheapest, fastest and most effective way to get a 'first look' at an exploration area without the need for camps, line cutting or other infrastructure. For this reason it has long been a standard exploration tool, particularly in the early stages of an exploration program.


The earth's magnetic field interacts with the magnetic materials in the near surface rocks creating easily measurable features representing changes in magnetic susceptibility. These changes most often reflect changes in rock type, which means that when we map the magnetic field we are also mapping geologic structure.


Modern high resolution airborne magnetic systems are sufficiently precise to allow measurements not only of the total magnetic field, but also of the magnetic gradients in the horizontal and vertical plane. Magnetic gradients are very useful when applying a quantitative interpretation of the magnetic field as they help to constrain the number of possible solutions, which is otherwise infinite.


The simplest example of automated interpretation is the process of gridding, which produces a 2 dimensional picture (or grid) of the measured quantity from a series of 1 dimensional survey lines. The measured horizontal gradients can be used within the gridding algorithm to guide and constrain the between line interpolations, improving the look and interpretability. Click here to read more about gradient enhanced gridding.


Since gradients are directional, much care must be taken when collecting gradient data to remove the effects of aircraft attitude as the pilot reacts to cross winds and terrain. Goldak has developed a multi-GPS based Attitude Determination System (ADS) to capture the actual attitude of the aircraft for every sample and 'derotate' the gradients to the ideal measurement plane parallel to the line direction.