What is Drone-Based Infrared Thermography?
Drone thermography is a non-destructive test that carries an infrared camera over a surface to find differences in temperature.
How it works
The camera records the temperature of the surface. In a passive survey the sun heats the surface. A delamination is a layer that has separated from the one below it. Under good conditions the surface above it becomes up to several degrees warmer than sound concrete (FHWA).
The FAA lists infrared thermography as a nondestructive pavement test in AC 150/5320-6G, section 5.2.4.4.3. In drone thermography, a drone carries the camera over the area.
What it finds and what it does not
FHWA lists delamination, overlay debonding and voids in concrete decks and tunnels, and delamination in concrete pavements. The method gives no information about the depth of a flaw. A flaw deeper than about 4 to 5 inches (100 to 125 mm) is hard to detect.
Water, oil stains and debris on the surface can also change the temperature. A temperature difference is a sign, not a proof of a defect.
When to fly
FHWA gives a window of 5 to 9 hours after sunrise, or a similar period after sunset. Cloud and precipitation reduce the effect.
Airfield pavement
An FAA study flew small drones over airfield pavement. The thermal images showed potential to detect cracks, and the report recommends 30 mm per pixel or finer. This is research, not an inspection standard.
Standard
ASTM D4788 covers delaminations in portland-cement concrete bridge decks. It is not a standard for drones or airfield pavement.
Frequently Asked Questions
- What can drone thermography find?
- It finds defects that change the surface temperature. FHWA lists delamination, overlay debonding and voids in concrete decks and tunnels, and delamination in concrete pavements. It does not show the depth of a flaw.
- When must the survey flight take place?
- Fly when the sun has heated the surface for some hours. FHWA gives 5 to 9 hours after sunrise, or a similar period after sunset. Cloud and precipitation reduce the result.
- Is there a standard for drone thermography?
- No standard that is specific to drones was found. ASTM D4788 covers delaminations in portland-cement concrete bridge decks. FHWA refers to it for data collection procedures.
References
- fhwa-bridge-it
- Bridge - Infrared Thermography (IT) FHWA
- astm-d4788
- ASTM D4788-03 (2013), Standard Test Method for Detecting Delaminations in Bridge Decks Using Infrared Thermography ASTM International
- faa-ac-150-5320-6g
- AC 150/5320-6G, Airport Pavement Design and Evaluation FAA
- faa-tc-23-50
- DOT/FAA/TC-23/50, Small Unmanned Aircraft System for Pavement Inspection FAA Airport Technology R&D
This is a reference entry. TarmacView provides drone inspection services and doesn't sell the equipment or materials described in this glossary.
