Thermal Image Of A Roof Leak

This image shows what a previoiusly-undetected bay window roof leak in Ashburn, Virginia looks like to a thermal infrared camera.  An infrared camera detects temperature differences, and captures images like the one you see here.  The cooler temperature here appears as purple to dark purple.  Such a temperature difference indicates moisture.  It was reported by the owner that puddles were seen on the floor inside the bay window area for some time, but the source of any leaking was never determined until the thermal image revealed its location.