Inconsistent and unacceptable probability of detection (PD) and false alarm rates (FAR) due to varying environmental conditions hamper buried object detection. A 4-month study evaluated the environmental parameters impacting standoff thermal infra-red (IR) detection of buried objects. Field observations were integrated into a model depicting the temporal and spatial thermal changes through a 1-week period utilizing a 15 minute time-step interval. The model illustrates the surface thermal observations obtained with a thermal IR camera contemporaneously with a 3-d presentation of subsurface soil temperatures obtained with 156 buried thermocouples. Precipitation events and subsequent soil moisture responses synchronized to the temperature data are also included in the model simulation. The simulation shows the temperature response of buried objects due to changes in incoming solar radiation, air/surface soil temperature changes, latent heat exchange between the objects and surrounding soil, and impacts due to precipitation/changes in soil moisture. Differences are noted between the thermal response of plastic and metal objects as well as depth of burial below the ground surface. Nearly identical environmental conditions on different days did not always elicit the same spatial thermal response.
Two studies were conducted at 43° 43' 24" N, 72° 16' 24" W during which the thermal signature of an area containing buried objects was observed. The two periods were from September – November 2016 and May – December 2018. In the first phase, the soil was left in its natural state while in the second, it was removed to a depth of 65 cm, homogenized, then replaced. In both instances, the physical properties of the soil were fully characterized, the meteorological forcing recorded, and subsurface moisture and temperature states measured. In phase one four objects, two round and two rectangular, were buried so that their tops were at a depth of 5 cm. In the second experiment four rectangular objects were emplaced at depths of 5 and 25 cm. In both phases two of the objects were metal and two plastic. Differences in thermal signatures of the buried objects will be discussed as they relate to emplacement depth, soil properties, and object composition.