measurement device. It has been demonstrated
baseball could be adapted for measuring ice ve-
that the MMW FMCW radar is capable of mea-
locity. Since these units cost only a few hundred
suring ice velocity, while the short-pulse radar can
dollars or less, it may be worth investigating its
profile the channel bed if operated at low enough
applicability for measuring ice velocity. This
of a frequency. If ice velocity could be correlated
would provide a very portable unit for field esti-
to the average stream velocity below it, discharge
mation of ice velocity during an ice run, for in-
could be determined by taking the point measure-
stance. These would only provide an instanta-
ments of depth multiplied by ice velocity corrected
neous value of velocity at a single point, but still
to an average velocity. This instrument could be
may be useful for random, rather than continu-
mounted on a vehicle and driven over bridges, or
ous, monitoring.
it could be mounted on an aircraft flying sections
across the river. Some type of GPS unit could be
Stage, ice thickness
used to determine cumulative distance across the
A commercially available depth finder or fish
stream as the units collect data. Two constraints
finder could potentially be used for measuring
of this conceptual system are operating within the
stage, ice thickness, or even ice movement. The
range of the radar units and whether the FMCW
sensor unit could be positioned on the bottom of
system can accurately determine ice velocity while
the bed and pointed upwards, as suggested in
in motion itself. Data processing would be the
Rossiter and Crissman (1994). The sensor would
other constraint of such a system. Several years of
be able to detect the bottom of the ice cover; if the
work would probably be required to make such a
elevation of the sensor was known and stage mea-
system workable.
sured with another instrument, then the ice thick-
ness of a floating ice cover could be approximated.
Ice volume
The sensor may possibly be able to detect the wa-
Another possible use of radar would involve
ter surface if free of ice; if so, then stage could be
estimation of ice volume. If the ice cover could be
determined for open water conditions. The sen-
profiled for thickness from an aircraft, it would be
sor may be able to be used to estimate the under
possible to estimate volume using average chan-
surface roughness of an ice run or ice jam, if these
nel widths and open areas. A more precise way to
events take place above the sensor. Most units have
get channel width and open area measurements
visual display capability; this would make the unit
would be with the use of videography. A video
easy to use and best suited for making random
camera could be used to capture the river below,
measurements. The sensor would need to be per-
and computer processing could be used to pro-
manently mounted or placed before the ice sea-
cess which areas are covered by ice and which are
son to be effective, but the remainder of the depth
not. The ice thickness measurement could be in-
finder unit could be carried between sensor sites
corporated into this to obtain a cumulative total
as a portable unit or could possibly be connected
of ice volume over the reach desired. A drawback
to a DCP for a permanent installation. Use with a
to such a system is the range of radar; all airborne
DCP would require some modification of the unit
radar systems have flown at relatively low alti-
to convert the signal normally fed to the display
tude, while the use of video would require a com-
screen to a value the DCP could transmit. The rela-
paratively high flight altitude. A radar system
tively low cost of a depth finder unit may make it
could possibly be substituted for the video, but
possible to investigate its potential for making
the ice would probably need to be relatively
these measurements. It may even be possible for
smooth, and it is unknown how accurately radar
biologists to use the depth finder in this configu-
could measure ice coverage on a wide river if at a
ration for detecting fish movement under an ice
low altitude. Such a system is not highly likely to
cover, if desired.
be implemented in the field soon.
Ice coverage, ice velocity, stage
Ice velocity
Lasers may be useful for obtaining measurements
It has been suggested* that a radar gun such as
such as ice coverage, ice velocity, and stage, but the
is used for measuring the velocity of a thrown
ability of laser to make any of these types of mea-
surements is unknown. The use of laser, as well as
all other optical means, will be limited by particu-
*Personal communication with Richard T. Pomerleau,
late conditions that affect visibility, such as fog, snow,
Senior Hydraulic Engineer, St. Paul District, U.S. Army
rain, etc.; lasers would not be affected by darkness,
Corps of Engineers, 1996.
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