Metal detection techniques are used to locate and identify buried metal objects, such as artifacts, pipes, cables, and even buried treasure. Here are some of the most common metal detection techniques:

1. Electromagnetic Induction (EMI): EMI is a geophysical technique that uses a metal detector to measure changes in the Earth's magnetic field caused by metallic objects. By measuring the amplitude and phase of these changes, geophysicists can determine the location and depth of the metal object.

2. Ground-Penetrating Radar (GPR): GPR uses radar waves to image the subsurface and can be used to detect buried metal objects. Since metal objects reflect radar waves, they can be identified as reflections in the GPR data.

3. Magnetometry: Magnetometry is a geophysical technique that measures the strength and direction of the Earth's magnetic field. Buried metal objects can cause distortions in the magnetic field, which can be detected using a magnetometer.

4. Pulse Induction (PI): Pulse Induction metal detectors use short bursts of high-frequency magnetic fields to induce eddy currents in metallic objects. By measuring the decay rate of these eddy currents, the metal detector can determine the presence and location of a metallic object.

Each of these metal detection techniques has its strengths and weaknesses, and the most appropriate method will depend on the specific characteristics of the buried metal object and the geological conditions of the area being surveyed. Geophysicists often use a combination of these techniques to obtain a more comprehensive picture of the subsurface geology.