EM Bird
This is a large gadget used to detect terrestrial magnetism (anomalies may indicate the presence of minerals). It costs around $1.2 m and needs to be flown very accurately at specific heights and speeds, for which you need at least a radalt and GPS, although some setups use a laser altimeter, which is accurate to the foot. It is generally well behaved, but can be tricky at slow speeds, and the data gets fuzzy above 80 kts. It is at the end of a 100-foot line, and needs to be 100 above the ground anyway, so you will be at 200 feet, unless you’re over water or ice, down to 30. There will be a 10-14 foot height window to operate in.
There is a  PDU (Pilot Display Unit) on the top of the instrument panel that gives you information on the line you're flying or intercepting, with horizontal track bars indicating your distance from the centreline in metres. Although done in VFR, it’s the sort of job where a little IFR training comes in handy, as it allows you to keep your head in the cockpit a little more and cope with doing several things at once, such as thinking several hundred metres ahead, planning approaches to hills, power lines and other obstacles. This will include power and speed requirements, and fuel.
The operation is dependent on may things which are critical, such as maintenance, weather, solar activity, magnetic storms, etc., so bring a book. Or three.

Aerial Application

Aerial application (of pesticides or fertilizers) means either crop-spraying or top dressing, the latter being used in forestry (although you can spray cut blocks with booms on). Top Dressing is more akin to load slinging, except you use engine driven devices like buckets to spread solutions over forests. Unlike crop spraying, it can be done in strongish wind conditions, but, otherwise, it's characterised by always being in, or very near, the avoid curve and many other situations that you're taught to avoid normally. You can tell with forests that have been sprayed in the early stages of their growth as to whether the pilots were successful or not—you very often see trees shorter than others, which is where they missed. Helicopters are particularly useful when the leaves need to be sprayed from underneath, because of the downwash.
In fact, your downwash (or rotor wake) can be used to good effect. At low speed, you can spray a small area underneath the flight path. At higher speeds, the wake helps spread the load behind and to either side (the term rotor wake means all the air displaced by the helicopter, as opposed to just the downwash). Knowledge of wake management will therefore help you become a better spray pilot.