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timing and scan information suitable for integration with
airborne Global Position System (GPS)/inertial measure-
ment units (IMU) for direct geo-referencing. Similarly,
the FLIR Systems SC6000 QWIP frame based sensor
(8-9
data acquisition, the desired TIR imaging sensor spatial
resolution, and the characteristics of the river.
The advantage of a fixed-wing aircraft is that the post-
processing of TIR images is simplified by the relative
stability of the platform, whereas a helicopter will typ-
ically have more variable flight characteristics such as
altitude, yaw, roll, and pitch, which require additional
processing and can introduce artifacts into the image
which makes image interpretation more complex. Fixed-
wing aircraft have long been used for aerial photography
and other airborne remote sensing tasks. Consequently,
finding a commercial charter for a fixed-wing aircraft with
an existing camera port and appropriate flight character-
istics, which is also located close to almost any project site,
is relatively straightforward. Additionally, the instrumen-
tation on fixed-wing aircraft is normally located inside the
aircraft so that the installation, operation, and transport
of the sensor is simplified when compared to operating
from a helicopter. On rotary-winged aircraft, the instru-
mentation is most often external to the aircraft in a
weatherised pod. In general, helicopters have a smaller
range and higher operating costs than fixed-wing aircraft,
but are more suitable for certain data-collectionmissions.
Fixed-wing aircraft are generally preferred inTIR image
collections where flight parameters (altitude, speed) can
remain relatively constant over the project area, such
as for large water bodies or targeted sections of river
with limited terrain relief. Helicopters are more suitable
for collecting images along a sinuous corridor at very
fine resolutions where the helicopter's slow speed and
maneuverability are an advantage, and the acquisition of
ultra-high resolution images is needed (e.g. for studying
complex braided floodplains). Inmany cases, a fixed-wing
aircraft may have to collect multiple lines of image data
to capture the same areas, and may be unable to safely
maneuver at the low altitudes required to capture images
of the same spatial resolution.
As TIR imaging sensor systems decrease in size and
cost, their application from airborne platforms is likely
to increase. Smaller TIR imaging sensors can also be
mounted within unmanned aerial vehicles (UAVs),
including remotely controlled aircraft (e.g., Berni
et al., 2009) and under balloons (N. Bergeron, Institut
National de la Recherche Scientifique, Quebec, Canada,
pers. comm.).
m) has accurate timing and triggering capability
that allow direct integration with an aircraft's modern
GPS which records its geographical location, and its IMU
which record the aircraft's velocity, orientation, and grav-
itational forces. An IMU greatly simplifies the process of
extracting ground control points (GCPs) used for ortho-
rectification of the image data. When an IMU is not
available, as is more common in older systems, these
GCPs need to be extracted from other image sources,
base-maps, or manual or surveyed GPS locations. The
process of identifying GCPs in the image is simplified
when a concurrent visible image is obtained with the
TIR image, otherwise distinguishing water from the bank
material can be difficult when, for example, a shaded
gravel bar is colder than water and confused for a cold-
water spring, or dead wood in the stream is confused for
a warm water input.
TIR imaging systems have progressively increased the
size of the detector arrays, allowing a broader range of
options for smaller GSDs or larger ground footprints at
fine and medium pixel sizes. In general, this also allows
a broader range of platform options since fine-resolution
pixel sizes that were once achieved from a helicopter can
be designed for higher flying aircraft capable of covering
greater areas in shorter amounts of time. For example, the
FLIR Systems SC6000 offers multiple lens options, has a
pixel array of 640
.
2
μ
035
◦
C. With
×
512, and an NE
Δ
Tof0
.
5
◦
FOV (25mm lens), a 1m pixel can be achieved
with a 644mwide ground footprint. The previously men-
tioned ITRES TASI 600 is a pushbroom hyperspectral
thermal imaging sensor that acquires an image with 600
pixels across its track with a
a
±
17
.
±
20
.
0
◦
horizontal FOV
and 32 bands within the 8-11
m spectral range (the
advantage ofmulti-band thermal imaging sensors was dis-
cussed in Section 5.4.1). Finally, technological advances
have made small, relatively inexpensive handheld thermal
imagers appealing for mounting on airborne platforms.
However, these image systems typically do not have the
radiometric features or durability suitable for the airborne
environment.
.
5
μ
5.5.2.1 Helicopter versus fixed-wing aircraft
TIR imaging sensors have been mounted on both heli-
copter and fixed-wing airborne platforms. The selection
of platformdepends in a large part on the objectives of the
5.5.2.2 Airborne image analysis
Some of the factors and considerations of using TIR
imaging sensors on airborne platforms, and their
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