Geography Reference
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post-processing, applies also to other remote imaging
sensors; thus, standard methods can be used. Airborne
data also need to be calibrated. For example, as described
previously in Handcock (2006), the flight team for the
MASTER multispectral data collection processed the TIR
data to 'radiance-at-sensor.' using onboard calibration
targets and an onboard GPS to record the aircraft's
location. Ground-based data can also be used to calibrate
raw TIR data, as will be explored in Section 5.6.
If the objective is to create continuous imagemosaics of
riverine systems or large water bodies, the acquisition of
overlapping images becomes especially important, as does
the timeliness of image acquisition (see Section 5.6.1).
The ability to capture images efficiently at fine spatial
resolutions, particularly on smaller streams, is paramount
to minimising the diurnal change in water temperature
during the image capture. For example, a recent 48 km
stretch of the Anchor River (AK, USA) was flown by
helicopter in 0.6 hr at a spatial resolution of 60 cm GSD.
A flight plan for the same corridor, using a fixed-wing
aircraft at the same GSD, would have required a flight
time of approximately 2.4 hr.
sensor with five bands (8.12-11
m) with 90m pixel
size and an NE
Δ
Tof
≤
0
.
3
◦
Cat27
◦
C (Gillespie et al.,
1998; Yamaguchi et al., 1998). While the pixel size of the
ASTER TIR sensor is fine in terms of a satellite-based
imaging sensor, it is 'medium' based on the multi-sensor
criteria defined previously. The revisit time for ASTER
is 16 days, and the FOV of the system is 60 km. As
well as raw TOA ASTER data which are not radiometri-
cally corrected, a number of higher-level products have
been are available, including temperature, emissivity, and
ground-leaving spectral radiance.
The NASA EOS MODIS sensor is also on the Terra
platform (imaging in the morning), as well as a second
MODIS sensor onboard Aqua (imaging in the afternoon).
MODIS has ten TIR bands (6.54-14
.
65
μ
.
39
μ
m) with a pixel
05
◦
Cat27
◦
C
(Barnes et al., 1998). Although MODIS has more bands
than ASTER and a wider FOV (2330 km), the larger pixels
limits it to observations of wide rivers. One advantage of
MODIS is that images of the entire globe are acquired
daily (and more frequently for higher latitudes). As well
as raw TOA MODIS that have not been radiometrically
corrected, a number of higher-level products are available,
including temperature and emissivity.
The Landsat ETM
+
sensor on Landsat-7 is in the same
orbit as Terra, which allows images to be acquired
size of 1000m and an estimated NE
Δ
Tof0
.
5.5.3 Satellite imaging
Space-borne TIR imaging sensors can cover a greater
aerial extent than airborne TIR imaging sensors and
cover a range of pixel sizes, number of bands, FOV, revisit
times, and sensor sensitivities. If TIR satellite images are
available for the study time, and are of a suitable pixel size
compared to the thermal application (see Section 5.4.2),
they can be an attractive source of broad-scale data
due to their low cost, capability for regional coverage,
and the potential for repeat monitoring with systematic
image characteristics. While TIR satellite-based images
generally cover large areas, their coverage may still not
be extensive enough to fully track some water bodies.
Therefore, measurements of long channel reaches may
have to be compiled over several days or weeks depending
on the satellite orbit.
TIR imaging sensors typically have larger pixel sizes
than do visible and near infrared (VNIR) imaging sen-
sors, with the pixel size being determined by the sensor
specifications (e.g., aperture, sensitivity of the detector,
and the desired NE
20
min apart with a 16-day revisit time. The single TIR band
of Landsat ETM
+
(10.40-12
∼
m) has inherent pixel
size of 60m (National Aeronautics and Space Adminis-
tration, 1998), which is more recently available resampled
to 30m for easier comparison with other Landsat bands.
The NE
.
50
μ
22
◦
C
at 7
◦
C (Barsi et al., 2003), and the FOV of the system
is 185 km. The TIR sensor on Landsat was historically
not always switched on to acquire data; however, the
large number of images in the Landsat archive, the ongo-
ing acquisitions, and the recent availability of free data,
makes Landsat TIR an attractive option if it meets an
application's specifications.
ToftheLandsatETM
+
TIR band is 0
Δ
.
5.5.4 Keypoints
•
The choice of TIR imaging sensor and whether the
platform is ground-, air-, or satellite-based will depend
on many factors, including the size of the area that
has to be covered, how frequently data are required,
cost and sensor availability, and whether the accuracy
requirements of the application require a TIR imaging
sensor with on-board calibration sources.
T). For example, the Advanced
Spaceborne Thermal Emission and Reflection (ASTER)
radiometer (Kahle et al., 1991; Yamaguchi et al., 1998),
mounted on NASA's Terra spacecraft, has a VNIR sensor
with three bands (15m pixel size), a shortwave infrared
(SWIR) sensor with six bands (30m pixel size), and a TIR
Δ
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