" The detection array consisted of 2 separate induction coils (one for the left side and one for the right side) that detected magnetic fields below the vehicle. The detection array was suspended between the 2 axles of the vehicle. When the detector encountered a metallic object, the operator would be notified by an audible signal in the earphone and a visual signal on the dashboard that denoted which side array detected the object. The operator would then stop the vehicle, back it up, and reencounter the metallic object. The MDV had 2 detection modes. The locate mode was used to identify the metal object and the pinpoint mode was used to find the center of the object. When the operator encountered the strongest signal, they would activates the marking system, deploying a water-based ink onto the roadway. The marking system consisted of a nozzle mounted on the rear frame and centered on each detection array."
https://www.globalsecurity.org/military/systems/ground/ivmmd.htm The frames beneath the cab are the magnetic induction detectors (metal detectors) and the spray marker is included in the frame as well.
The flat "plates" out front are the GPR, Ground Penetrating Radar, which detects objects and cavities in the ground.
https://en.wikipedia.org/wiki/Ground-penetrating_radar / Robin