Geography Reference
In-Depth Information
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Figure 5.9
Change in temperature over time over a day for four locations: (a) a large river with an open riparian zone, (b) a small
stream with an open riparian zone, (c) a large river with forested riparian zone, and (d) a small stream with forested riparian zone.
1
◦
C from the TIR image,
a window of more than 4 hr is possible, but to constrain
measurements to within
validation sites, and hand-held TIR sensors can be used
to survey a region to determine optimum locations for
deploying thermometers for longer-term monitoring.
Where digital spatial datasets of roads and river chan-
nels are available, an initial set of sampling locations can
be devised by identifying locations where rivers and roads
cross or come very close to each other. Otherwise local
maps can be used for a similar search. In some cases
it may be possible to determine if sites are inaccessi-
ble from available maps, air photos, and other spatial
data layers within a GIS or Google Earth (Google Inc.,
2010). For example, such data sources can be used to
identify the presence of restricted lands, steep slopes, or
channels that are not visible from above through dense
riparian canopies. However, in many cases determining
accessibility will require a survey of the locations to avoid
inappropriate sample sites.
When identifying sampling locations, care should
be taken to avoid locally cool or warm locations. These
can be caused by the influence of tributaries, back-water
should not vary by more than
±
5
◦
C a window of less than
±
0
.
2 hr may be better.
5.6.2 Samplingsiteselection
The number of sampling sites is dictated by the (1) length
of river to be measured, (2) its accessibility, and (3) the
location of temperature extremes within the river. River
length to be measured will be controlled by the method
used for TIR image collection. For example, a single
TIR image frame collected from a bridge, helicopter,
or balloon may simply require field technicians to walk
the length of the river reach, collecting representative
temperature measurements. However, multiple aircraft
images or even a single satellite image may cover 10s to
100s of kilometers of river channel, requiring in-stream
sampling at many locations with multiple field teams. If
recent TIR images are available, they can be used to select
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