Applications for Aerial Infrared Thermography

Gregory R. Stockton, President

Stockton Infrared Thermographic Services, Inc.

8472 Walker Mill Road

Randleman, NC 27317-7331

(800) 248-7226

www.stocktoninfrared.com

ABSTRACT

In certain applications, aerial infrared thermography is superior to ground-based infrared. Examples include roof moisture surveys, some environmental surveys, animal counts, wide area thermal mapping, landfill fire examination, underground steam system leaks, electrical power line surveys and search and rescue operations.

Author Biography:

Gregory R. Stockton is President of Stockton Infrared Thermographic Services, Inc. Based in Randleman, NC; the corporation operates six complete infrared systems in five divisions. Greg is an Infraspection Institute Certified Infrared Thermographer (#3583). He has twenty-two years experience in the construction industry, specializing in facilities construction, maintenance and energy-related technologies. Greg has performed infrared thermography since 1989.

Keywords: Aerial, Infrared, Thermography, Roof Moisture Surveys, Environmental Surveys, Animal Counts, Wide Area Thermal Mapping, Landfill Fire Examination, Underground Steam System Leaks, Electrical Power Line Surveys, SAR, Search and Rescue.

INTRODUCTION

Aerial infrared thermography applications can be divided into two categories. Those where a straight-down view and/or large area view is needed, and those where long distances must be covered in a limited amount of time. Most aerial infrared imaging is performed at night because daylight solar radiation usually adversely affects the imagery.

EQUIPMENT AND CREW

Aircraft and infrared imager

Aerial infrared imaging operations can be performed by using either helicopters or airplanes. There are advantages with both platforms. A helicopter is more maneuverable over the target and can get closer to the ground. Light airplanes fly higher, have less vibration problems, have faster ferry speeds and are less expensive to operate. In either case, a reliable, well maintained aircraft and an imager capable of the resolution required for the intended task is recommended. A helicopter can operate closer to the ground so the number of pixels the infrared imager has is not as critical. If intended for use from a light airplane (see Figure 1), where imaging altitudes are usually higher, a larger detector may be required. The needed ground resolution element (GRE) or the size of one pixel on the ground should be known before an imager is selected. It is always better to have more pixels, although larger lenses can help if some signal strength degradation is acceptable.

The infrared camera may be hand held but it will be harder to get professional results. It is better to have a fixed mount. The camera can be mounted solid, turret-mounted or manually articulated. A solid mount is very simple and cost effective, but can be more difficult to use because the aircraft will have to be in just the right position to obtain imagery of a small target. Turret-mounted camera systems allow for multiple lenses or sensors and may have automatic tracking capabilities. They are expensive, typically $200K-$500K new and are usually certified and approved for a specific aircraft or series of aircraft. A manually articulated camera mount is cost effective and works well through a conventional airplane camera hole. Federal aviation authorities however, have very strict rules with regards to mounting something on, or modifying an aircraft.

Recording equipment

The type of infrared imager used will dictate how images are recorded and saved. Modern infrared cameras have a variety of storage media, but must be within reach and/or have remote controls so that the camera can be moved, lenses adjusted and the images can be stored. No matter what type of imager or storage medium, a videotaped record of all the ‘raw’ infrared imaging should always be made. Often the image will pass by before it can be saved on a flashcard. Important images can be lost if the thermographer’s attention is turned away from the screen for a second. Once over the target area the best policy is turn on the recorder and leave it on. The audio from the communication system can also be recorded, giving a narration to the video. Tapes are inexpensive. Digital videotape is best. It is important to have a good monitor with a screen large enough to see the infrared details of the particular job that is being performed.

Navigational aids

Precise navigation is important in any aircraft and particularly so in nighttime aerial infrared operations. The longer the crew spends finding and imaging a particular target, the higher the cost and less work that can be done that night. Also, some targets are in controlled air space and air traffic control authorities may limit the time over the target due to other air traffic in the vicinity, such as commercial air carriers in and out of a hub airport. Add the fact that the pilot may be unfamiliar with the area and it is dark outside…and global positioning system (GPS) becomes a necessity. GPS receivers are very accurate. Combining the GPS with a mobile mapping program on a computer and a video encoder-decoder (VED) that encodes and displays the video signal, makes the operation more efficient and safer. GPS is used to find targets, plan routes and during post-flight processing the encoded and displayed information (latitude/longitude, altitude, date, time and speed, etc.) is extremely valuable (shown in Figure 4).

Equipment secured

All equipment in the aircraft must be secure. There can be nothing loose, obstructing the view of the instruments or interfering with the controls of the aircraft. All wires should be labeled, shielded from electromagnetic interference and out of the way.

Crew

Depending on the particular job, the pilot may be the only crewmember. But it almost always helps to have a trained infrared thermographer, navigator and/or helper, depending on the requirements of the project, flight duration, seating and weight limitations. Nighttime infrared imaging is NOT a job for amateur pilots or airsick prone equipment operators. I am referring to those pilots without lots of experience and those who do not fly for a living. Know the qualifications of the person who has your life in his hands. Flying low, slow and maneuvering without much room for recovery in the middle of the night – this is aerial infrared thermography.

Back on the ground

The office equipment needed to analyze imagery and produce reports is the same as that used by any ground-based thermographer. This includes a computer workstation complete with digital photographic and thermographic imaging peripherals for handling infrared images, daylight photographs and capable of producing high quality reports. Also needed are specialized video capture, image processing, CAD software and mapping software necessary for producing drawings and specialized parts of the final report product. Finally, a high quality printer is required for printing the report, unless it will be presented on CD-ROM.

Environmental Impact Surveys

When a liquid is introduced into a body of water (ocean, river, stream, lake) the former can be differentiated between through the use of high-resolution thermal imaging because the temperatures are almost always different. Often these liquids can be followed back to their source. Some of the uses for this application are:

§ Detecting illegal dumping/discharge.

§ Tracking pollution such as waste spills or oil spills.

§ Monitoring effluents from storm drains (see Figure 2, 2a) and sewage treatment plant discharge.

§ Monitoring ground water seepage into rivers, streams and lakes (see Figures 3, 3a).

§ Managing heated water from power plant cooling towers (see Figure 4, 4a, 4b).

§ Measuring the amount of fresh water from ground sources that is introduced into an estuary.

Wide Area Thermal Mapping

Wide-area thermal mapping is any application where large areas or great distances must be covered to find or define thermal targets. Below are some of these applications.

Animal Counts

Many warm-blooded animals can be found and counted from the air. It is far more accurate than any other method and is used primarily by government agencies. Deer population density information is used to monitor and control the population of deer on city, county, state and federal lands (see Figure 5, 5a). Counting animals on the ground over large areas would seem to be an easy job but animal counts are difficult to perform. Environmental and weather conditions need to be right. Flight planning and precise navigation are a must. Factors such as topography, forest growth, target size and animal behavior should be considered so that the study area is effectively and efficiently covered using a flight pattern (grid) and altitude that will allow the aerial infrared thermographer to find the animals and accurately identify and count them.

Underground Geothermal Imaging

When a road or building complex is planned, the site can be flown to see if any geothermal activity is present at the surface.

Surface and Subsurface Fires

The U.S. Forest Service uses aerial infrared imaging to monitor forest fires. This information can be sent immediately to those in charge of controlling fire lines. Subsurface fires can also be monitored using aerial infrared thermography. Landfill fires (see Figure 6, 6a, 6b) can be hazardous to the surrounding environment. Knowing where, how many and the extent of underground fires is useful to those in charge of containing and/or extinguishing them. More and more fire departments are purchasing IR imagers for ground-based fighting of structural fires. Aerial infrared can be especially helpful on large, single story buildings that are on fire. With subsurface and structural fires, “where there’s smoke, there’s fire” does not necessarily hold true since smoke may come out in one place, but the hottest part of the fire is in another. Peat, coal and wood chip piles (see Figure 7) can combust spontaneously.

Indian Trails

Where ancient Indian trails cross the desert, the land under the trails has been compacted. By using nighttime aerial infrared imaging the aerial infrared thermographer can see this higher density differentiated from the lower density adjacent to the trails.

Underground Steam System Surveys

Even from high altitudes, steam line inspections are one of the easiest applications for aerial infrared thermographers. Thermal contrast between active steam lines and the surrounding ground are usually good. The reason for conducting these surveys is to detect and locate leaks (see Figure 8, 8a). Environmental and weather conditions are not as important as they are with other applications. The hardest part of the job is making sure that complete coverage of the lines has been made and recorded.

Electrical Power Line Surveys

High voltage electrical transmission lines (see Figure 9) can be imaged from an airplane but helicopters are better suited for this application. No matter which platform is used, the operation is dangerous. In mountainous areas the pilot will have to watch for changing distance to the ground, watch the changing direction of the lines and changing distance to the target lines. The best time to perform this type of survey is during high load conditions and in dim light (dawn, dusk, or on a cloudy day). There are few problems on transmission lines as compared to inside a substation (see Figure 9a). It is not possible to measure exact temperatures from one-quarter of a mile away so all anomalies should be compared to adjacent like-loaded components and if warranted, re-inspected by a ground crew. Because they are smaller, lower to the ground and run through populated areas, electrical distribution lines are difficult to see against all the thermal clutter on the ground such as trees, street lights, people, animals, etc. These facts make the infrared inspection of electrical distribution lines a job for ground-based infrared thermographers.

Pipelines

For the same reasons that electrical distribution lines are difficult to follow, pipelines are also difficult to survey. Also trees, shrubs, brush and water often cover the pipeline. Some types of pipelines can benefit from an aerial infrared inspection include petroleum, natural gas and steam.

Search and Rescue (SAR)

SAR operations are often ‘rush’ jobs where conditions are less than ideal. Aerial infrared SAR is better than ground-based SAR in most instances, however it is overrated. People targets either do not want to be seen, are disabled and unable to move to an area where they can be seen, or are trying to keep the warmth of their body close by insulating themselves, so they cannot be seen. The key is to narrow the search area and image out the side of the aircraft instead of down.

Roof Moisture Surveys

Basics

Aerial infrared roof moisture surveys are used to find and quantify the area of moisture (water) contamination in an insulated flat or low-slope roof (see Figure 10). Regularly scheduled infrared surveys help the owner to assess the roof’s condition at all stages of its service life. This information is an important part of the overall roof asset management program. At night, areas of subsurface roof moisture are warmer (because the stored heat from daylight sunshine in the trapped water mass) as compared to the dry, functioning insulation or roof substrate. After sunset, when the roof’s structure cools down, wet areas of roof insulation and other materials stay warm longer, allowing infrared cameras to detect the sources of heat and record them for later analysis.

Rotor-Wing versus Fixed-Wing

Both helicopters and light airplanes can be used to perform qualitative aerial infrared roof moisture surveys. The helicopter is best used if the number of targets or distance between targets is low because the inherent problems of vibrations, slow ferry speeds and higher operating costs are offset by being able to use a standard focal plane array camera with only 256 x 256 (65, 536) pixels or less. As stated earlier, the imager in an airplane must have a higher spatial resolution (more pixels) because the airplane must operate at higher altitudes. Infrared cameras that are used in a light airplane to survey for roof moisture must have at least 512 x 512 (262,144) pixels, which is four times the resolution of the 256², allowing the same resolution from four times the distance.

On-Roof versus Aerial

Straight down aerial imagery is far more useful to the owner than walk-on or on-roof imagery for two reasons: A) The images are plan view and B) large areas can be seen all in one image (see Figure 10a). When one is standing on a roof, at best eye level is five feet above the surface. Looking out over a roof with large or long areas of moisture contamination there is virtually no way, without taking multiple shots and pasting them together, that one can get these areas resolved on the screen in one infrared image. Multiple shots make the report confusing and the matching visual images are hard to reconcile with the infrared. In the United States, roofers and roof consultants (not infrared thermographers) perform most of the infrared roof moisture surveys. They survey on-roof and attempt to make up for the lack of quality imagery by marking the roof with paint, instead of producing thermographic reports. Someone must go on the roof to verify all infrared data and analyses. The aerial infrared report should be reviewed and the printed data taken on the roof to aid in visual, destructive and non-destructive testing. Infrared images of the roof, no matter how spectacular, are only signatures of heat. There are many causes of heat (or apparent heat) on a roof. This is why professional verification (the duty of roof consultants) is so important.

Why Aerial Surveys are Superior

Aerial is the best platform for performing infrared roof moisture surveys for the following reasons:

§ High-resolution aerial images capture large areas at once, making the report easier and less expensive to produce.

§ High angle, straight down infrared images lessen reflection problems.

§ Plan view imaging allows for infrared images, visual images and AutoCAD™ drawings to be reconciled closely (see Figure 10b). As a result, the report is clear, concise and easy to understand.

§ Plan view imaging allows for the accurate marking of areas of suspect roof moisture contamination. AutoCAD™ drawings (see Figure 10c, 10d) can be made by ‘drawing over’ the captured visual and infrared images on the screen. Hatch marked areas indicate probable and possible wet areas. The infrared, visual and AutoCAD™ components can be separated. Even if dimensional information is not available, the drawings become scalable and easily updated at any time in the future once quantitative data is provided. If dimensional information is available, this allows for the creation of a quantitative, scaled AutoCAD™ drawing of the suspect roof moisture contamination on the roof.

§ The printed AutoCAD™ drawings can be used on the roof to paint areas of moisture contamination directly on the roof, if desired.

§ The aerial infrared thermographer can wait for a good night for imaging, surveying many roofs under good conditions. If the image quality is not acceptable on a particular building roof early in the night, he can return at different times during the night, in order to image the building under the best possible conditions.

§ Instead of inefficiently using as many as four people (a certified infrared thermographer, a helper, a building owner’s representative, and a roof consultant) for a night to perform a survey, an airplane crew of two can do many times as much data collection, and then process the data (not in a hurry on a freezing cold night) under comfortable conditions at a consistent pace in the office.

§ Instead of imaging an average 100,000-300,000 square feet in a night (highly dependent on the number of problems), up to ten million square feet can be imaged in a night.

§ Access to multiple levels of the roof is never a problem.

Perhaps the biggest advantage of aerial infrared is not its use on roofs that have well-defined areas of moisture at all, but those roofs that are the most difficult to image from any distance or angle. I am referring to the roofs that, for instance, have a lot of ballast, are covered with reflective coatings or ones that for whatever reason are impossible to image from the roof. With high-resolution aerial imagery, slight nuances of temperature can be seen from far enough away to actually see the pattern of heat.

There are two advantages to on-roof infrared.

§ It is cost-prohibitive to fly small roofs far away from the aerial infrared thermographer’s operational area.

§ Since on-roof verification does have to take place at some point by a qualified professional, if a roof consultant is on the roof on the night of the survey, all areas that exhibit heat can be tested right then, so that only verified wet areas get marked.

A big advantage to the end user of an aerial infrared roof moisture survey is that the report can be provided at various levels of completeness, detail and complexity. These different levels of reporting, in order of costs are: unedited videotape, edited videotape, printed thermographs, aerial photographs and AutoCAD™ drawings (optionally scaled), in digital and/or printed form. The buyer of this service has the advantage of obtaining any one or all of these report components, with the cost being determined by the options purchased. Also, since the digital videotape (a record of the roof on that night) is archived, he/she can use this information later, to compare proportional images of that same roof to images from a later date.

CONCLUSIONS

Aerial infrared thermography has a military past and a commercial future. The aircraft, imager and crew must be capable of performing the task of providing professional results the first time since the operation is expensive. Flying around and accurately maneuvering, mostly at night, at low altitudes is not a task for the weak of stomach [inner ear] or the untrained, inexperienced infrared thermographer or pilot. It is a serious business with serious intellectual and financial rewards, most often used whenever the application is beyond the capability of less expensive ground-based thermography.

IMAGERY FROM PRESENTATION BELOW…