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

CADalyst, Sept, 2004 by Gregory R. Stockton

Underground steam system surveys. Even from high altitudes, steam line inspections are one of the easiest applications for aerial IR 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. This works also for high-temperature hot water systems.

An Example of Aerial IR Combined with CAD and GIS

Annually, Stockton Infrared's AITscan Division performs hundreds of aerial IR surveys for various commercial, industrial, institutional, and governmental customers. Many of these clients have large facilities and campuses. We are developing a system to add to our deliverables the option of a single IR image and a single visual image, where each of the images is combined into one seamless file. Ideally, these single image files will help us work more efficiently on creating a single CAD file as well. One image file will be more manageable for our clients than a series of files. It will also be easier for them to make visual assessments by looking at the imagery across the entire area of interest (full scene). The reports could be three large-format drawings: visual, infrared, and CAD.

Currently we use digitally video-captured IR images, but we can also capture 14-bit full dynamic range images directly to a computer hard drive. This gives us greater flexibility during postprocessing and optimization of the images. Also, temperatures can be measured pixel-by-pixel. These images can then be made into a composite image. Instead of printing multiple images of, say, a large building roof or a steam distribution system, why not print one big image? The same concept applies to a three-story building, tall smokestack, or giant boiler.

The problem in any imaging endeavor is resolution. We can fly high above a building or steam system and get imagery of a large roof or campus in one image, and we often do for reference purposes. But the GRE is unacceptable from far distances. To make a high-resolution image, we must mosaic many high-resolution images. This may seem a simple, albeit time-consuming, task because software is available off-the-shelf for pasting photographs together. The problem is that these software products are designed to work with large color photographs that contain much more image information than IR images do. Also, slight variations in altitude and the optical characteristics of the IR cameras make the task beyond the capability of the software.

So we must first capture and correct the images, then paste them together by hand. To add even more difficulty, some customers want orthorectified and georeferenced images. We currently use GPS to navigate to targets and collect the imagery. However, the exact geo-location may be inaccurate because the GPS records a signal once per second, but the plane moves up to one hundred feet per second.

The AITscan Division wants to not only create a single seamless image, but also provide correctly georeferenced images to our clients--especially those who use GIS to maintain their facilities. A georeferenced image could easily be brought into the client's GIS database. The client could then interpret additional information from the images and combine them with other information to get an overall visual impression of the areas of interest. We are developing a prototype GIS database for our clients and potential clients to show how their data can be integrated with other data sets. This database will be georeferenced and will include related facilities management information, such as thermal steam and roof survey imagery, aerial photographic imagery (color and panchromatic), CAD drawings that outline the features of interest, links to Stockton Infrared's reports, and information such as roads, buildings, electrical distribution, original and edited supply and return carrier pipe layouts, and other utilities within the area of interest. It could include digital elevation data, digital orthophotography, or any other imagery or layouts.