Geography Reference
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such as vertical profiles of atmospheric water vapour.
Some of these parameters can be estimated from stan-
dard atmospheres or models. For example in a study of
TIR remote sensing of streams and rivers in the USA
(Handcock et al., 2006), a radiosonde was launched on
a weather balloon concurrent with sensor overpasses,
and
L
g
and
assumption is made that if a single uniform atmospheric
correction had been applied across the whole image
then its quality only affects the absolute accuracy and
not the uncertainty of remotely sensed river-temperature
measurements. The resulting relative temperatures can
be used along with image interpretation of the river
with its terrestrial and aquatic context for applications
where knowing absolute temperatures is not critical. For
example, to identify hydrological features such as seeps
(e.g., Figure 5.1), confluences of streams or rivers with
contrasting temperatures (e.g., Figure 5.7), as well as
thermal refugia or possible pollution sources. In some
situations having absolute temperature is still essential,
such as mapping thermal characteristics of fish habitat.
were determined for each image using
the Penn State/NCAR mesoscale model (MM5) (Dudhia,
1993). The MM5 column atmospheric water vapour or
radiosonde profile water vapour was used as an input to
radiative transfer modeling (MODTRAN 4.0, Berk et al.,
1989; Ontar Corporation, 1998) to determine the spec-
trally varying atmospheric
τ
and
L
p
to correct each image
(Kay et al., 2005).
While critical to accurately retrieving temperature
from TIR data, atmospheric correction can be time
consuming and expensive. An alternative is to use non-
atmospherically corrected water temperature data to
assess relative spatial patterns within a single image. The
τ
5.3.6 Keypoints
•
Interpretation of TIR image data to determine water
temperature can be complex. However, understanding
Temperature
°
Temperature
°
C
C
35
18
17
0
10
km
N
(a)
(b)
Figure 5.7
Confluence of the Mississippi and Ohio rivers in (a) September 2001 and (b) November 2001 as viewed in Landsat 7
ETM
images. Monitoring bulk river temperature in this region is complicated by the mixing of cooler water from the Mississippi
River and warmer water from the Ohio River, which continues to affect downstream temperature for more than 10 km.
+
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