Geography Reference
In-Depth Information
2
Management Applications
of Optical Remote Sensing
in the Active River Channel
W. Andrew Marcus 1 , Mark A. Fonstad 1 and Carl J. Legleiter 2
1 Department of Geography, University of Oregon, Eugene, OR, USA
2 Department of Geography, University of Wyoming, Laramie, WY, USA
discusses imagery where the data are broken into narrow,
discrete wavelengths of light, as with hyperspectral sen-
sors. It also presents information on broad-spectrum
imagery where many wavelengths are bundled together,
as with panchromatic photography that encompasses all
visible wavelengths to form a single image representing
overall brightness.
The chapter also focuses on the 'active channel', which
is the low flow channel plus adjacent areas that are free
of vegetation and subject to scour or deposition under
typical hydrologic conditions. The active channel includes
the submerged channel, unvegetated mid-channel islands,
chutes, and exposed bars. The active channel has been
the focus of a great deal of remote sensing research
since the mid-1990s, a period that coincides with the
increased availability of centimeter- to meter-resolution
digital imagery. Prior to that time, research on remote
sensing of rivers was generally limited to film-based aerial
photos or digital multispectral satellite imagery. Studies
of the active channel with digital multispectral data were
limited because the pixel size of satellite imagery was too
large. A 30 or 80 m Landsat pixel from the 1970s or 1980s,
for example, would cover the entire active channel plus
large portions of the bank and floodplain in all but the
largest lowland rivers.
The vegetated floodplain is not included in our def-
inition of the active channel and is not discussed in
2.1 Introduction
As a potential user of remote sensing for river monitoring
and analysis, you may find yourself wondering 'what can
be measured, mapped, and/or modeled with remote sens-
ing?'; 'will clients accept results based on remote sensing?';
and 'why use remote sensing rather than classical field
methods?' These are all critical questions, and answer-
ing them correctly determines whether a remote sensing
approach will substantially benefit a project or detract
from the project's success.
This chapter addresses these questions in the context of
passive optical imagery of the active river channel . 'Passive'
refers to the measurement of light occurring naturally
in the environment - reflected solar energy. This is in
contrast to 'active sensors' such as radar and LiDAR,
which emit a pulse of energy and record the return of
that energy. Active sensors are explored in later chapters.
'Optical' refers to the dominant wavelengths of light orig-
inating from the sun: blue, green, red and near-infrared
wavelengths. The blue, green and red wavelengths are
'visible light' that we can see with our eyes. The near-
infrared is invisible to the human eye, but is still a
major component of sunlight. Passive optical imagery
is something we all have seen since childhood - most
photos are passive optical imagery, as are panchro-
matic, colour, and near-infrared air photos. This chapter
 
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