Advances in Selected Applications and Methodology for Aerial Infrared Thermography

Download this paper as a .pdf

ABSTRACT
In applications where a straight-down view or large area view is needed; or where long distances must be covered in a limited amount of time, aerial infrared thermography is superior to ground-based infrared. The selection of the aircraft, camera mount, infrared imager, navigational aids, recording medium, workstation computer equipment, pilot and crew are critical to success. There are inherent dangers to flying low, slow and in the middle of the night. The job must be done right and safely…the first time. This paper focuses on recent and ongoing advances in methodology, platform and software that will bring the end-user a superior product.

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 four divisions. He has twenty-three 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, environmental impact infrared surveys, animal counts, geothermal, forest fires, subsurface fires, structural fires, landfill fires, peat, coal and wood chip piles, Indian trails, steam line inspections, high voltage electrical transmission lines, high voltage electrical distribution lines, pipelines, search and rescue (SAR), roof moisture surveys, high temperature hot water system (HTHW), computer aided design & drafting (CADD), global positioning system (GPS), geographical information system (GIS), digital elevation model (DEM), orthophotography, NASA, Affiliated Research Center (ARC), Brown University. 


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. We are constantly striving to provide the client with the highest quality end product at a competitive price. To do this we need to collect the data efficiently and effectively and produce an easy to understand, high quality and useable report. Both helicopters and light airplanes can be used to perform aerial infrared surveys. The helicopter is best used if the number of targets or distance between targets is low because the inherent problems of vibrations, slower 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. If a light airplane 

(see Figure 1) 

is used, the imager must have a higher spatial resolution (more pixels) because it must operate at higher altitudes (farther away from the target). This requires the use of an infrared camera with at least 512 x 512 (262,144) pixels, allowing the same resolution from four times the distance. In either case, a reliable, well maintained aircraft and an imager capable of the resolution required for the intended task should be selected. The needed ground resolution element (GRE) or the size of one pixel on the ground should be known before the aircraft and imager is selected. It is always better to have more pixels, although larger lenses can help if some signal strength degradation is acceptable. 


EQUIPMENT AND CREW
The infrared camera used for aerial applications 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 fixed mounted solid, turret-mounted or manually articulated. 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. Precise navigation is important in any aircraft and particularly so in nighttime aerial infrared operations. A global positioning system (GPS) is necessity. Combining the GPS with a mobile mapping program on a computer and a video encoder-decoder (VED) that encodes and displays GPS and other (latitude/longitude, altitude, date, time and speed, etc.) information 

(see Figure 2) 

through the video signal is extremely valuable. All equipment in the aircraft must be secured with wires labeled, shielded from electromagnetic interference and out of the way. Nighttime infrared imaging is NOT a job for amateur pilots or airsick prone equipment operators. The pilot should be trained, experienced and professional. He will be flying low, slow and maneuvering without much room for recovery in the dark. Once back on the ground, the report must be prepared. 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.


COMMON APPLICATIONS
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. These environmental impact infrared surveys can be used to: detecting illegal dumping and/or discharge, track pollution such as waste spills or oil spills, monitor effluents from storm drains and sewage treatment plant discharge 

(see Figure 3), 

monitor ground water seepage into rivers 

(see Figure 4), 

treams and lakes, manage heated water from power plant cooling towers, measure the amount of fresh water from ground sources that is introduced into an estuary. 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. Animal counts, such as deer population density information is used to monitor and control the population of deer on city, county, state and federal lands. When a road or building complex is planned, the site can be flown to see if any geothermal activity is present at the surface. 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 5) 

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. Peat, coal and wood chip piles which combust spontaneously, can also be monitored.

Aerial infrared can be helpful to the firefighters of structural fires especially on large, single story buildings. 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. Even from high altitudes, steam line inspections 

(see Figure 6) 

are one of the easiest applications for aerial infrared thermographers. Thermal contrast between active steam lines and the surrounding ground are usually good. High voltage electrical transmission lines can be imaged from the air. Even from shorter distances, accurate temperatures of electrical faults are almost impossible to measure, because the spot size to target distance ratio problem. Detecting electrical faults is much easier and can be accomplished. Specification writers have not yet realized the simple physics of this problem and continue to ask that quotations include providing quantitative data on fault areas. Because they are smaller, lower to the ground and run through populated areas, High voltage electrical distribution lines are much more difficult to see against all the thermal clutter on the ground such as trees, street lights, people, animals, etc. They are best left to ground-based thermographers. Pipelines are also difficult to survey. Trees, shrubs, brush and water often cover the pipeline. Search and rescue (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 still 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. 

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 7). 

Regularly scheduled infrared surveys help the owner to assess the roof’s condition at all stages of its service life. 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. In the United States, roofers and roof consultants (not infrared thermographers) perform most of the infrared roof moisture surveys. 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 (see Figure 8) to be reconciled closely. 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 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 (see Figure 9, 9a) 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. 

• 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. 

• 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. 

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

2. 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.

THE END PRODUCT NOW
The product that the end user receives is a report of some type. In the past, our end product has consisted of the following:

• A videotape copy of the archived original digital videotape of raw and edited aerial imagery,

• A CD-ROM containing all digital files from the project,

• A CD-ROM containing JPEG format images within a key-word database file and the software necessary to view and search for images of a given location. 

• A bound report notebook containing:

• High resolution printed thermographs,

• 8.5” x 11” photographic enlargements,

• A written report describing the findings,

• CADD drawings.

THE END PRODUCT IN THE NEAR FUTURE
The NASA/ARC Project: Infrared Imaging of District Heating Underground Infrastructure for Energy Losses & Diagnostics, and the Incorporation and Development of a Demonstration Spatial Database Model. 
This project is funded by NASA and being developed in a joint effort by Stockton Infrared Thermographic Services, Inc. and the Affiliated Research Center (ARC) of Brown University in Providence RI. The program came about as a result of a contract between Brown University’s Facility Management Group and Stockton Infrared to fly the High Temperature Hot Water System (HTHW) loop for the purpose of identifying and highlighting the areas within the system that are believed to be problem sites. It was agreed that we would fly and produce our usual report product first and then upon review of the data, perform further processing if needed. Visual and infrared flights were carried out on April 19, 2001. We recorded both visual and infrared digital imagery using a global positioning system (GPS) receiver, mobile mapping program on a computer and a video encoder-decoder (VED). 

HTHW Loop 
A videotape copy of the archived original digital videotape of raw and edited aerial imagery was made. Infrared image captures were made of all underground lines and saved with coded JPEG format image file names. These images were then put into a database so that they could be searched and recalled from the file by key words and viewed. Individual images of suspect problem sites were pointed out (arrows) and saved. A PowerPoint™ file was created with all suspect site images, explanations and summary of findings. The file was then printed in high resolution using glossy photo paper. A CD-ROM was made containing all files from the project. 

Roofs 
While negotiating the contract for the HTHW loop survey, as is often the case, we proposed to also fly the roofs for the purpose of finding subsurface moisture contamination. Since we would be flying over the roofs anyway (albeit at a different altitude), we would fly the flat/low-slope insulated roofs at the university. The Facility Management Group agreed. Brown University’s campus is made up of many small to medium-sized roofs (between 10,000 and 100,000 square feet). So one or two images were sufficient to cover most roofs. We produced a report similar to the HTHW report. 

The Concept
Annually, Stockton Infrared’s Aerial Division performs hundreds of IR roof moisture surveys on various commercial, industrial and institutional buildings. Many of our clients have medium to large (100,000-1,000,000 square feet) roofs. In mid-1999, one of our clients (a large Midwest roofing company) showed me a blueprint-sized print of building that he had had produced from an aerial infrared contractor from Ohio who has since gone out of business. The print was a photograph of a ~50,000 square foot building which was flown with an infrared camera in the mid-eighties. No infrared images accompanied the photo. Instead, areas of suspect moisture contamination had been “drawn in” over the photograph. I did not…and still do not like the idea of drawing infrared (or overlaying infrared) imagery on top of a photo. This shows me that the imagery must not be worth printing. However, I did like the concept. Instead of printing multiple images of a building roof-which on large roofs can be confusing, why not print one big image. For that matter, the same concept can be used for a three-story building, tall smokestack or giant boiler, etc. The problem, of course in any imaging endeavors, is resolution. We can fly high above a building and get imagery of a large roof in one image. In fact, we often do for reference purposes. We start off high then descend to a lower safe altitude to obtain the higher resolution we need for the report. To composite together imagery (infrared or visual) is a time-consuming task. Slight variations in angle, altitude and optical characteristics can make the task difficult. When Brown approached us, we were interested to say the least. 

What we are striving for
Stockton Infrared would like to add to our deliverable, the option of a single infrared image and a single visual image, where each of the single images are mosaiced 

(see Figure 10)

 into one (seamless) file. Ideally, this single image would allow us to work more efficiently on creating a single CADD file as well. One image file will be more manageable by customers then a series of image files. For a smaller facility/area there will be few files, however, for larger facilities/areas there can often be hundreds of images. One image may prove more manageable; also, it may be easier for them to make a visual assessment by being able to look at relative piping, roof, boiler, etc., imagery, across the entire area of interest (full scene). The reports could be three blueprint-sized drawings-visual, infrared, and CADD. 

Currently we are using digital videotape-captured images, but it is possible to capture 14-bit full dynamic range images directly to a computer hard drive. Capturing the full dynamic range image, allows for greater flexibility for post-processing and optimizing of the images. Also, temperature data is available allowing one to measure pixel-by-pixel, the temperatures, etc.

 (see Figure 11). 

These images can then be made into a composite image 

(see Figure 12). 


We presently use GPS to navigate to targets, collect and sort images, etc., however the exact geo-location may be inaccurate because the GPS records a signal every one-second, but the plane moves one hundred feet each second. We would like to not only to create a single seamless image, but also be able to provide a correctly geo-referenced image to provide to our clients, especially those using GIS to maintain their facilities. A geo-referenced image could easily be brought in to the user’s GIS database. This would allow the user to interpret additional information from the image, allowing them to combine that image with other information and to get an overall visual impression of the area of interest.

We are developing a prototype GIS database, which we will take to our clients and potential clients, to show them how their data could be integrated with other data sets. This database will act to highlight their data, but also to show how it can be used to edit or build upon other data sources the user may have. This database will be geo-referenced, and is estimated that it will include relative facilities management information, such as thermal steam survey imagery, thermal roof survey imagery, aerial imagery (color or panchromatic digital photography), CADD drawings outlining the features of interest, links to Stockton Infrared's written report, other related information (roads, buildings, electrical distribution, other utilities, etc., within the area of interest), original and edited supply and return carrier pipe layout, available digital elevation model (DEM) data, available digital orthophotography, or any other imagery/layouts.


CONCLUSIONS
Aerial infrared thermography has a great 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. With improvements in camera quality (IR and visual), methodology, platform and software, aerial infrared thermography and aerial infrared reports are getting better and more useable all the time.
 

Copyright 1999-2005. All rights reserved.