(click to enlarge)
General
Aerial thermal mapping of your facility, complex, campus, military
base or city every few years will reveal leaks in all types of
systems, like steam and condensate return lines,
hot water lines,
chilled water lines, supply water mains, distribution pipes, storm
water drains, building heat loss and moisture leaks into your roofs.
Aerial photographs should be taken every few years as well. They are
inexpensive and can be a great asset when discussing future building
additions with management, planning utility repairs and improvements,
drawing CADs of the facilities and for uses as simple and handy as
'showing' outside contractors where not to park.
The methodology for taking infrared (IR) thermographs is similar in
many ways to taking aerial photographs. To collect the data, the
aircraft flies over a given area with a camera mounted to the airframe
and oriented looking straight-down (NADIR) to the ground. Oblique or
lower angle shots are taken out the side of the aircraft by pointing
the camera at the desired angle. The imagery is stored on film or a
computer hard drive and later copied it to a convenient deliverable,
such as a DVD. Obviously, aerial photos are taken during the day
because the sun provides brilliant visible light so one can see
features on the ground, like buildings, bridges, roads, etc.
Where aerial infrared thermography differs from aerial visible
photography is the time of day when the survey occurs and the
wavelength of the imagery that the detector collects. IR thermography
of ground objects is performed at night because the sun and its
effects on objects is a tremendous distraction in the imagery.
Thermography reveals sources of heat and the relative differences in
heat from one object to another. Infrared imagery is a grayscale
picture whose scales (or shades of gray) represent the differences in
temperature and emissivity of objects in the image. Objects in the
image that are lighter in color are warmer and darker objects are
cooler. No object in an IR image is detected via visible light
wavelengths (400-700 nanometers) rather, only from thermal infrared
wavelengths in the 3000-5000 nanometers or 8000-14000 nanometers
range. Lights and other relatively hot objects are very evident, but
as a result of their heat emissions, not their light emissions.
Collected IR imagery may then be modified in a number of ways to
enhance its value to the end user, such as digitally adjusting the
imagery to find particular anomalies and zooming in on different areas
of interest (see figure 1). These post-processed images can then be
used to prepare predictive maintenance reports on the various systems.
Thermal Mapping and Ortho-Rectification
Using an aerial high-resolution imager, surveying a couple of
buildings or a mile or so of underground lines can be done by flying
over and locating the target(s) in the imagery, saving the data and
putting it together into a report. Scale information can be gathered
by taking off the existing CAD drawings or having someone walk over
the area with a tape measure. This works fine for small areas, but it
is not possible to make precise thermal maps of a whole complex,
campus, military base or city without ortho-rectification of the
imagery.
Figure 1) Ortho-rectified, geo-TIFF mosaic thermal image of a small
city. (click to enlarge)
In order to produce ortho-rectified thermal maps, the ultimate [most
useful] product, much more information must be gathered and tagged to
the IR imagery. During the flight, the aircraft flies straight, smooth
lines on a pre-planned grid, allowing 25% side lap of the imagery. The
IR operator manages the sensor data-acquisition (see figures 2, 3)
following a structured checklist for orderly data file management. The
imagery must be collected with a precise direct-digital timing system,
a 3-axis ring-laser-gyro and an inertial navigation system (INS),
which is tightly-coupled to a real-time differential GPS satellite
positioning system that provides x, y, z positioning of the aircraft
at all times. After imagery is collected and QC is verified, the
digital infrared imagery is then processed into a series of ortho-rectified
image tiles, which are stitched together to create a giant mosaic
image. An on-board computer system puts all this information together
using a digital elevation model (DEM) of the scene that consists of a
uniform grid of point elevation values and the position and
orientation of the camera with respect to a three-dimensional
coordinate system. The result is presented as a high-resolution IR
image in the form of a geo-TIFF, which is compatible with any GIS
software such as ESRI ArcView, AutoCAD 3-D Map, Global Mapper,
MapInfo, etc.
Once high quality digital thermal and photographic ortho-rectified
maps are created, these can be added as layers to existing CAD and GIS
systems and to other data sets. By post-processing the imagery, many
wasteful conditions can be found and reported. The maps and reports
help facility managers keep up with their assets in a very efficient
manner. Below, some of the low-hanging fruit of back-end
post-processing of the information is discussed.
 
Figures 2, 3) Aircraft and installed data acquisition systems.
(click to enlarge)
The farther one can get from the subject of any imaging survey, while
maintaining the resolution to achieve the needed image quality, the
more useful the data becomes. This is the aerial advantage. But, one
needs to obtain very high resolution imagery in order to survey large
areas.
It is true that a picture is worth a thousand words; so get the big
picture of your facilities and start speaking volumes about its
condition.
Three uses for Thermal
Infrared Map Data
(Click Links for Examples and Explanations.)
A) Steam Leak Surveying
B) Roof Moisture Surveying
C) Liquid Leak Surveying of Water Utilities
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