Hi Seden,
If you want serious portable power, you may want to look into renting something like this for your experiments:
http://www.starpowergenerators.com/1400_amp.htm
Of course, you will also want a 150 kva 3-phase transformer that brings the voltage up to 1kv or higher, and the associated high voltage rectifiers, and high voltage capacitors to smooth out the ripples.
For a more practical approach you may want to let a large high voltage capacitor bank do the work of sending the charge to the ground, and slowly charge it with a smaller generator before starting the test. A 2500 watt generator would probably be more than sufficient for this method, and much more portable. You could even build a circuit that charges a high voltage capacitor bank from your car battery as you drive to the test site. The only high power component needed would be the capacitor bank and a switch that connects it to the ground. The amount of charge needed in the capacitors would depend on the spacing of the ground probes and the conductivity of the ground. But be careful, high capacity capacitors at 1kv are deadly.
Another lower cost idea is if you have 100 friends who want to participate in the field test, they can all drive to the test site and park their cars side-by-side. If the battery from each car is linked together with cables, you will have a 1200 volt source of power with maybe over 100 amps available for short bursts. If you use this method, make sure you don't have any deficient electrical systems in the chain, and all the cables are connected tight.
If you just want to see some kind of results in a test bed, you could use lower voltages and currents in a small area with planted targets. You might start by putting a pair of probes connected to a car battery in the ground a few feet apart with a buried target planted in the path. If you are able to sense a phase angle in the ground signal, then try spreading the probes farther apart until the signal disappears. This will allow you to calibrate your sensing circuitry and give you some preliminary base data to help determine what size equipment you want to use for your field hunting.