Final answer:
The remote sensing technique leveraging the Earth's magnetic field to probe beneath the ground is known as magnetic survey or magnetics, utilized in various fields like mineral exploration and archaeology.
Step-by-step explanation:
The remote sensing technique that uses the Earth's magnetic field to detect variations beneath the ground is known as magnetic survey or magnetics. The Earth is like a giant bar magnet with a strong magnetic field produced by moving material in its liquid metallic core. As this metallic fluid circulates and convects, it generates electric currents, which in turn produce the Earth's magnetic field. When a magnetic survey is conducted, variations in the Earth's magnetism caused by geological structures or different types of rocks can be detected because they disturb the magnetic field in measurable ways. This technique is widely used in mineral exploration, archaeology, and even in detecting unexploded ordnance.