advice for buying potassium mag/gradiometer

[bushido]

greetings,
please i need advice before spending a lot of money buying a potassium magnetometer from Gemsys.
It's a professional instrument and i'm buying it in order to look for magnetic anomalies caused by buried metallic objects and voids in a depth going from 0 to 15 meters deep.
would this magnetometer be the best choice?

[99thpercentile]

Magnetometers are a very poor choice for void detection. The magnetic susceptibility of the air in the void is zero. The magnetic susceptibility of most soils is pretty low outside of tropical regions. So you would be looking for a very low contrast anomaly to start with. Generally, for most geophysical methods it is easier to detect anomalies at depth the are more magnetic or more electrically conductive, than those that are lower.

Magnetometers are passive instruments that detect ferrous metal targets at depth. They are also powerful tools for mapping geology, but that doesn’t sound like your application.

My general suggestion to most of these types of requests is to start with a frequency domain electromagnetic induction (FDEM) instrument like the Geonics EM31 or a competitor. These types of tools will let you detect a lot of different targets in the top 6 m (~20 ft), can collect a lot of data fairly quickly, and are pretty easy to interpret.

[gmradar]

I agree with Ryan above. Do not buy a Mag for voids. GPR are also a good choice for voids detection, depending on depth.