Applications for Aerial Infrared Thermography

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Applications for Aerial Infrared Thermography

Gregory R. Stockton, PresidentStockton Infrared Thermographic Services, Inc.8472 Walker Mill Road

Randleman, NC 27317-7331(800) 248-7226www.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 areathermal mapping, landfill fire examination, underground steam system leaks, electrical powerline surveys and search and rescue operations.

Author Biography:

Gregory R. Stockton is President of Stockton Infrared Thermographic Services, Inc. Based inRandleman, NC; the corporation operates six complete infrared systems in five divisions. Greg isan Infraspection Institute Certified Infrared Thermographer (#3583). He has twenty-two yearsexperience in the construction industry, specializing in facilities construction, maintenance andenergy-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 astraight-down view and/or large area view is needed, and those where long distances must becovered in a limited amount of time. Most aerial infrared imaging is performed at night becausedaylight solar radiation usually adversely affects the imagery.

EQUIPMENT AND CREW

Aircraft and infrared imagerAerial 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 andcan get closer to the ground. Light airplanes fly higher, have less vibration problems, have fasterferry speeds and are less expensive to operate. In either case, a reliable, well maintained aircraftand an imager capable of the resolution required for the intended task is recommended. Ahelicopter can operate closer to the ground so the number of pixels the infrared imager has is not


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as critical. If intended for use from a light airplane (see Figure 1), where imaging altitudes areusually 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 alwaysbetter to have more pixels, although larger lenses can help if some signal strength degradation isacceptable.

The infrared camera may be hand held but it will be harder to get professional results. It is betterto 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 theaircraft 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 trackingcapabilities. They are expensive, typically $200K-$500K new and are usually certified andapproved for a specific aircraft or series of aircraft. A manually articulated camera mount is costeffective and works well through a conventional airplane camera hole. Federal aviationauthorities however, have very strict rules with regards to mounting something on, or modifyingan aircraft.

Recording equipment

The type of infrared imager used will dictate how images are recorded and saved. Moderninfrared cameras have a variety of storage media, but must be within reach and/or have remotecontrols so that the camera can be moved, lenses adjusted and the images can be stored. Nomatter what type of imager or storage medium, a videotaped record of all the raw infraredimaging should always be made. Often the image will pass by before it can be saved on aflashcard. Important images can be lost if the thermographers attention is turned away from thescreen for a second. Once over the target area the best policy is turn on the recorder and leave iton. The audio from the communication system can also be recorded, giving a narration to thevideo. Tapes are inexpensive. Digital videotape is best. It is important to have a good monitorwith 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 infraredoperations. The longer the crew spends finding and imaging a particular target, the higher thecost and less work that can be done that night. Also, some targets are in controlled air space andair traffic control authorities may limit the time over the target due to other air traffic in thevicinity, such as commercial air carriers in and out of a hub airport. Add the fact that the pilotmay be unfamiliar with the area and it is dark outsideand global positioning system (GPS)becomes a necessity. GPS receivers are very accurate. Combining the GPS with a mobilemapping program on a computer and a video encoder-decoder (VED) that encodes and displaysthe video signal, makes the operation more efficient and safer. GPS is used to find targets, planroutes and during post-flight processing the encoded and displayed information(latitude/longitude, altitude, date, time and speed, etc.) is extremely valuable (shown in Figure4).

Equipment secured


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

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

Back on the groundThe 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 digitalphotographic and thermographic imaging peripherals for handling infrared images, daylightphotographs and capable of producing high quality reports. Also needed are specialized videocapture, image processing, CAD software and mapping software necessary for producingdrawings and specialized parts of the final report product. Finally, a high quality printer isrequired 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 bedifferentiated between through the use of high-resolution thermal imaging because thetemperatures are almost always different. Often these liquids can be followed back to theirsource. 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 becovered to find or define thermal targets. Below are some of these applications.

Animal Counts


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Many warm-blooded animals can be found and counted from the air. It is far more accurate thanany other method and is used primarily by government agencies. Deer population densityinformation is used to monitor and control the population of deer on city, county, state andfederal lands (see Figure 5, 5a). Counting animals on the ground over large areas would seem tobe 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 iseffectively and efficiently covered using a flight pattern (grid) and altitude that will allow theaerial infrared thermographer to find the animals and accurately identify and count them.

Underground Geothermal ImagingWhen a road or building complex is planned, the site can be flown to see if any geothermalactivity is present at the surface.

Surface and Subsurface FiresThe 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 bemonitored using aerial infrared thermography. Landfill fires (see Figure 6, 6a, 6b) can behazardous to the surrounding environment. Knowing where, how many and the extent ofunderground fires is useful to those in charge of containing and/or extinguishing them. More andmore 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. Withsubsurface and structural fires, where theres smoke, theres fire does not necessarily hold truesince smoke may come out in one place, but the hottest part of the fire is in another. Peat, coaland wood chip piles (see Figure 7) can combust spontaneously.

Indian TrailsWhere ancient Indian trails cross the desert, the land under the trails has been compacted. Byusing nighttime aerial infrared imaging the aerial infrared thermographer can see this higherdensity differentiated from the lower density adjacent to the trails.

Underground Steam System SurveysEven from high altitudes, steam line inspections are one of the easiest applications for aerialinfrared thermographers. Thermal contrast between active steam lines and the surroundingground 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 withother applications. The hardest part of the job is making sure that complete coverage of the lineshas been made and recorded.

Electrical Power Line Surveys

High voltage electrical transmission lines (see Figure 9) can be imaged from an airplane buthelicopters are better suited for this application. No matter which platform is used, the operationis dangerous. In mountainous areas the pilot will have to watch for changing distance to theground, watch the changing direction of the lines and changing distance to the target lines. Thebest 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


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substation (see Figure 9a). It is not possible to measure exact temperatures from one-quarter of amile away so all anomalies should be compared to adjacent like-loaded components and ifwarranted, re-inspected by a ground crew. Because they are smaller, lower to the ground and runthrough populated areas, electrical distribution lines are difficult to see against all the thermalclutter 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 infraredthermographers.

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

Search andRescue (SAR)

SAR operations are often rush jobs where conditions are less than ideal. Aerial infrared SAR isbetter than ground-based SAR in most instances, however it is overrated. People targets either donot want to be seen, are disabled and unable to move to an area where they can be seen, or aretrying 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 infraredsurveys help the owner to assess the roofs condition at all stages of its service life. Thisinformation is an important part of the overall roof asset management program. At night, areas ofsubsurface roof moisture are warmer (because the stored heat from daylight sunshine in thetrapped water mass) as compared to the dry, functioning insulation or roof substrate. Aftersunset, when the roofs structure cools down, wet areas of roof insulation and other materialsstay warm longer, allowing infrared cameras to detect the sources of heat and record them forlater analysis.

Rotor-Wing versus Fixed-WingBoth helicopters and light airplanes can be used to perform qualitative aerial infrared roofmoisture surveys. The helicopter is best used if the number of targets or distance between targetsis low because the inherent problems of vibrations, slow ferry speeds and higher operating costsare 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 areused 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 thedistance.


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On-Roof versus Aerial

Straight down aerial imagery is far more useful to the owner than walk-on or on-roof imagery fortwo reasons: A) The images are plan view and B) large areas can be seen all in one image (seeFigure 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 noway, without taking multiple shots and pasting them together, that one can get these areasresolved on the screen in one infrared image. Multiple shots make the report confusing and thematching visual images are hard to reconcile with the infrared. In the United States, roofers androof consultants (not infrared thermographers) perform most of the infrared roof moisturesurveys. They survey on-roof and attempt to make up for the lack of quality imagery by markingthe roof with paint, instead of producing thermographic reports. Someone must go on the roof toverify all infrared data and analyses. The aerial infrared report should be reviewed and theprinted data taken on the roof to aid in visual, destructive and non-destructive testing. Infraredimages of the roof, no matter how spectacular, are only signatures of heat. There are manycauses 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 SuperiorAerial is the best platform for performing infrared roof moisture surveys for the followingreasons:

High-resolution aerial images capture large areas at once, making the report easier andless 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 easyto understand.

Plan view imaging allows for the accurate marking of areas of suspect roof moisturecontamination. AutoCAD drawings (see Figure 10c, 10d) can be made by drawingover the captured visual and infrared images on the screen. Hatch marked areas indicateprobable and possible wet areas. The infrared, visual and AutoCAD components canbe separated. Even if dimensional information is not available, the drawings becomescalable and easily updated at any time in the future once quantitative data is provided. Ifdimensional information is available, this allows for the creation of a quantitative, scaledAutoCAD drawing of the suspect roof moisture contamination on the roof.

The printed AutoCAD drawings can be used on the roof to paint areas of moisturecontamination directly on the roof, if desired.

The aerial infrared thermographer can wait for a good night for imaging, surveying manyroofs under good conditions. If the image quality is not acceptable on a particularbuilding roof early in the night, he can return at different times during the night, in orderto 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 owners representative, and a roof consultant) for a night to perform asurvey, an airplane crew of two can do many times as much data collection, and thenprocess the data (not in a hurry on a freezing cold night) under comfortable conditions ata consistent pace in the office.


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Instead of imaging an average 100,000-300,000 square feet in a night (highly dependenton 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 orangle. I am referring to the roofs that, for instance, have a lot of ballast, are covered withreflective coatings or ones that for whatever reason are impossible to image from the roof. Withhigh-resolution aerial imagery, slight nuances of temperature can be seen from far enough awayto 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 thermographers

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 canbe provided at various levels of completeness, detail and complexity. These different levels ofreporting, 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 reportcomponents, with the cost being determined by the options purchased. Also, since the digitalvideotape (a record of the roof on that night) is archived, he/she can use this information later, tocompare 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, imagerand crew must be capable of performing the task of providing professional results the first timesince the operation is expensive. Flying around and accurately maneuvering, mostly at night, atlow altitudes is not a task for the weak of stomach [inner ear] or the untrained, inexperiencedinfrared thermographer or pilot. It is a serious business with serious intellectual and financialrewards, most often used whenever the application is beyond the capability of less expensiveground-based thermography.

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Applications for Aerial Infrared Thermography