Geography Reference
In-Depth Information
As with SAV, the literature on algae focuses on large
water bodies. Mapping of marine algae is so well estab-
lished that satellites have been launched largely to monitor
chlorophyll concentrations and map phytoplankton (e.g.,
the Coastal Zone Color Scanner in 1978). High spatial res-
olution imagery can provide good measurements of algal
blooms over time in lake settings (Hunter et al., 2008).
Hoogenboom et al. (1997) and Quibell (1991) describe
some of the basic optics to consider in mapping algae
with remote imagery.
Research on algae mapping in rivers suggests signif-
icant potential for this application. Hick et al. (1998)
found high correlations between the 750 nm band and a
number of algal parameters (Table 2.3) and concluded
that only three to four bands were needed to map algal
blooms over large areal extents, provided that in-water
calibration data are available. Marcus et al. (2001) used
hyperspectral imagery and pixels from an algae filled pool
to train a matched filter to find similar sites throughout
a backcountry region. In a subsequent survey of the
stream, 75% of the sites they classified as algae had algae
(Table 2.3) and led to the discovery of four previously
unknown amphibian sites. This application demonstrated
the value of remote sensing for exploratory purposes in
inaccessible regions.
sensing to show that classical downstream hydraulic
geometry relations do not provide accurate predictions of
depth. This finding has significant implications for stream
restoration, which frequently uses hydraulic geometry to
estimate target depths (and other parameters) for natu-
ralising streams. Ongoing work by the authors and others
is examining the potential to use parameters derived
from remote sensing to document habitat impacts of
low-head dams, model water quality, and target river
reaches for restoration. The list of potential applications
is expanding rapidly, especially if one includes work that
is examining fusion of optical data with LiDAR or radar,
which can enable extraction of other hydraulic vari-
ables such as water surface slopes, velocity, and Froude
numbers. Carbonneau et al. (2011), for example, used
topographic information derived from radar imagery to
obtain water surface slopes and used optical imagery
to measure wetted widths and water depths, then com-
bined these data to derive stream power and velocities
every meter along 16 km length of a stream. Because they
mapped water depth and substrate size for every square
meter along the stream, they were also able to derive
continuous metrics of spawning habitat suitability for the
entire stream.
2.12 Management considerations
common to river applications
2.11 Evolving applications
The applications discussed above are ones for which there
has already been a substantial body of work. Several
evolving lines of research are also worth tracking depend-
ing on management needs. Forecasting and detection of
ice breakup on large rivers is receiving increased atten-
tion (Pavelsky et al., 2004; Morse and Hicks, 2005, Kaab
and Prowse, 2011). This application has the potential to
become a major tool in inaccessible sub-polar and polar
rivers, just as detection of floods has become one of the
established applications of remote sensing. There is also
an emerging effort to use remote sensing measurements
from streams to map derived variables such as stream
power (Jordan and Fonstad, 2005; Carbonneau et al.,
2011), although most of these require merging active and
passive sensors.
Moving beyond technique development, researchers
are now beginning to apply the remote sensing methods
discussed above to better understand rivers, although this
work is just now beginning to appear in the published
literature. Marcus and Fonstad (2008, 2010), for example,
used continuous data on depths derived from remote
Our discussion so far has focused on reasons for using
remote sensing, potential applications in river settings,
and some of the potential complications specific to indi-
vidual applications (e.g., problems associated with depth
measurement). But there are also issues common to
almost any effort to use remotely sensed data to obtain
river information on turbidity, SAV, or whatever. These
issues are discussed in detail in Marcus and Fonstad
(2008). Rather than repeat their work, we summarise
their discussion in Table 2.4 and focus here on issues
of particular relevance to stream managers. In doing so,
we assume that the manager is working with a remote
sensing professional who has addressed issues of data
acquisition, quality and analysis. In this circumstance, the
manager will be given remote sensing results, probably in
the form of maps and, preferably, accuracy assessments.
The manager is then faced with interpreting those results,
presenting them to other users, and determining whether
and to what extent this information can be incorporated
into management plans.
Search WWH ::
Custom Search