Understanding Infrared Thermography Reading 3

Underground Void Detection
The detection of underground voids is based, for the most pan, on the
difference in thermal capacitance between solid earth and the air cavities
formed by buried tanks, eroded sewers and storm drains and improperly filled
excavations. Typical programs to detect underground voids are performed
using the sun as a basic source of thermal energy. During the day, the heat
from the sun penetrates the earth and heats both the earth and the voids. The
voids have a lower thermal capacitance and store less heat than the
surrounding earth. On the subsequent thermographer they appear as cool
areas. As in roof surveys, apparent findings are usually confirmed by means
of other disciplines. Ground penetrating radar has come into use as a
confirming discipline for thermographic underground void detection.
Charlie Chong/ Fion Zhang