Geology Reference
In-Depth Information
(Optional)
Direct
film
recorder
Magnetic
tape recorder
Modulated
light source
Recorder
mirror
Liquid
nitrogen
container
Amplifier
Scan
mirror
Signal
Detector
Controlled radiant
temperature sources
(for calibrated imagery)
Instantaneous field
of view (2-3 milliradian)
Focusing
mirrors
Angular
field
of view
(90-120°)
Scan pattern
on ground
Aircraft
flight
direction
Ground
resolution cell
Figure 13.1.1. Diagram of the TIR scanner and its operation Sabins, 1997.
The TIR instrumentation (Figure 13.1.1) is mounted in an airplane, which flies over the study area at a
predetermined altitude (e.g., 1525m (~5000 ft)) above average ground level. The TIR sensor makes a series of
rapid, side-to-side sweeps to cover the land surface in a swath on either side of the airplane (Sabins, 1997).
Although the instrumentation shown in Figure 13.1.1 has a magnetic tape recorder, essentially all the data are now
recorded in digital format and then transferred to strips of film for use.
The differences in radiant flux occurring on the land surface are shown as variations in the brightness of the TIR
imagery (on a gray scale) and are a good approximation of the temperature of the ground surface at the time of the
TIR survey (Loughlin, 1991). Warm areas appear as shades of white or light gray in the TIR imagery while cool
areas appear as shades of dark gray.
The instantaneous field of view (IFOV) is the amount of area on the ground that is viewed by the scanner at any one
instant. The IFOVof the TIR scanner affects the resolution of the imagery because a smaller IFOV can detect smaller
and subtler anomalies than can an instrument with a larger IFOV. For example, an instrument with an IFOV of
1milliradian will have a better resolution than an instrument with an IFOV of 3milliradian. The temperature
sensitivity of an instrument is also important in whether it can detect subtle anomalies in ground temperature.
Airborne TIR has been used more for studying coal fires because the smaller IFOV provides much better resolution.
The author Vice (2007) found that both the time of day and the time of year are important in conducting TIR
surveys for geothermal energy in the Pacific Northwest. Predawn surveys were needed to reduce the number of
