Aerial infrared thermography: linking thermal mapping results to CAD and GIS systems

CADalyst, Sept, 2004 by Gregory R. Stockton

When you need a thermal image of an area, aerial IR (infrared) thermography is superior to ground-based infrared in applications where a straight-down and large-area view is needed and where large areas and long distances must be covered in a limited amount of time. Most aerial IR imaging is performed at night because daylight solar radiation tends to adversely affect the imagery. Applications of aerial IR thermography include roof moisture surveys, environmental impact surveys, animal counts, wide-area thermal mapping, landfill fire examination, underground steam system surveys, electrical power line surveys, and search and rescue operations.

Equipment and Crew

Aircraft and infrared imager. Thermographers perform aerial IR imaging from helicopters and airplanes, each of which has advantages and disadvantages. Light airplanes are less expensive to operate and ferry speeds are higher, allowing more work to be accomplished in a night. On one hand, helicopters are more maneuverable over a target and can get closer to the ground. On the other, they suffer from more vibration problems, take more time to move between targets, and are very expensive to operate. In either case, your thermographer needs a reliable, well-maintained aircraft and an imager (figure 1) capable of the resolution required for the intended task. Working from a light airplane, where imaging altitudes are higher, requires a larger detector. You should know the needed GRE (ground resolution element), the size of one pixel on the ground, before you select an imager. It's always better to have more pixels, although larger lenses can help if some signal strength degradation is acceptable. No matter which system your thermographer uses, the imager must be fixed-mounted. Dangling a handheld IR camera out the open window of an aircraft does not produce professional results.

[FIGURE 1 OMITTED]

Recording equipment. The type of IR imager used dictates how images are recorded and saved. Modern IR cameras offer a variety of storage media, but all must be within reach or have remote controls so that the thermographer can move the camera, adjust lenses, and save images.

No matter what type of imager or storage medium, there should always be a videotaped record of all the raw IR imaging. Often the image passes by before it can be saved on a flashcard. If the thermographer's attention is turned away from the screen for a second, important images can be lost. It's also a good idea to record the audio from the communication system to narrate the video. Tapes are inexpensive, and digital videotape is best. It's important to have a good monitor with a screen large enough to see the infrared details of the job.

Navigational aids. Precise navigation is important in any aircraft and particularly so in nighttime aerial IR operations. The longer a crew spends finding and imaging a particular target, the higher the cost and less work that can be done that night. Also, air traffic control authorities may limit time over a target due to other air traffic in the vicinity. Add the fact that the pilot may be unfamiliar with the area and it's dark outside, and GPS (global positioning system) becomes a necessity. Combining the GPS data with a mobile mapping program on a computer and a VED (video encoder-decoder) that encodes and displays the video signal makes the operation safer and more efficient (figure 2).

[FIGURE 2 OMITTED]

Your thermographer can use GPS to find targets and plan routes, and it's extremely valuable post-flight to process the encoded and displayed information such as latitude and longitude, altitude, date, time, and speed.

Secure equipment. Make sure that all equipment in the aircraft is secure. Nothing should obstruct the view of the instruments or interfere with the controls of the aircraft. All wires should be labeled, shielded from electromagnetic interference, and out of the way.

Aircrew. Nighttime infrared imaging is not a job for amateur pilots or airsick-prone equipment operators. Aerial IR thermography is about flying low, slow, and maneuvering without much room for recovery in the middle of the night--it's a job for professional aviators only.

Back on the ground. The office equipment you need to analyze imagery and produce reports includes a computer workstation with digital photographic and thermographic imaging peripherals for handling infrared images and daylight photographs. These should be capable of producing high-quality reports. You also need specialized video capture, image processing, CAD, and mapping software to produce drawings and specialized parts of the final report. Finally, a high-quality printer is necessary.

Applications for Aerial IR Thermography

Animal counts. Used primarily by government agencies, aerial IR thermography is far more accurate than any other method for finding and counting warm-blooded animals. Deer population density information is used to monitor and control the deer population on city, county, state, and federal lands. Counting animals on the ground over large areas may seem easy, but it can be difficult.