cessing and display of ice thickness, as well as the
there is still a need for a signal processing unit
capability to store the collected information for
that costs several thousand dollars.
later use. The collection of data requires a great
Another method by which ice thickness mea-
deal of storage; as an example, O'Neill and Arcone
surements have been made are electromagnetic in-
(1991) point out that with a helicopter speed of 2
duction methods. CANPOLAR Consultants (1985)
m/s and a digitization rate of 25,000 samples/sec-
reports on several manufacturers with electromag-
ond, approximately 12.5 MB of data are produced
netic induction instruments used for measuring
per kilometer of survey.
ice thickness from the ice surface. They also state
The MMW FMCW radar system suffers from
that electromagnetic induction methods appear to
most of the disadvantages of the short-pulse ra-
be the most promising technology for remote mea-
dar, but it is capable of doing things that the short-
surement of ice thickness, although a great deal of
pulse radar unit is not. The FMCW system is not
work is needed for a usable device. Arcone et al.
capable of penetrating water; thus, once the ice
(1987) report on the use of magnetic induction (MI)
surface begins to melt and water begins to pool
to detect frazil deposits. They report that the MI
on the surface, the system would lose ability to
method would work best on frazil with low water
determine ice thickness. However, this could be
content and work less well on shallow streams with
used to advantage if it was used to determine
bottom sediments, such as gravel or gravelly sand,
when a previously stable ice cover is nearing
that could be confused for frazil. So far, the use of
breakup conditions. Due to its shorter wavelength,
magnetic induction instruments from an airborne
the MMW FMCW system has been capable of
platform does not appear to have been done.
profiling much thinner ice than the impulse radar
system has. It can be mounted from a helicopter
Ice movement and velocity
for ice thickness profiling (Yankielun et al. 1993),
Although ice movement scored comparatively
and research continues on mounting the radar
low in the survey, a recent ice motion detector de-
system from a fixed wing aircraft. This system is
veloped at CRREL (Zufelt 1993) shows great prom-
likely to be less expensive than the impulse radar
ise for simple and inexpensive monitoring. This
system, as the radar front end can be found at
unit has been successfully field tested and is prob-
most well-supplied electronics stores for under a
ably capable of being installed in the field by ca-
few hundred dollars. Toikka (1987) also discusses
pable technicians in each District, although CRREL
the use of an FMCW radar for measuring ice
personnel may be requested to assist on a first in-
thickness.
stallation. Rachuk and Rickert (1986) describe the
Rossiter and Crissman (1994) mention the pos-
use of a similar concept in Canada on the
sibility of using upward-looking sonar to deter-
Athabasca River, using an array of sensors embed-
mine ice thickness. The sonar sensor would need
ded in the ice. The MMW FMCW radar system
to be anchored to the river bed below a level which
described earlier is also capable of detecting ice
ice could not cause damage. This system would
motion as well as ice velocity with slight modifi-
only be capable of point measurements and thus
cation (Ferrick et al. 1995). This system has the
could also be used to estimate ice speed (but not
capability of detecting ice movement in the period
direction).
before a stable ice cover forms, unlike the unit
Cost is likely to be a major factor in implemen-
developed by Zufelt (1993), which requires a stable
tation of any radar system in the near future. Re-
ice cover or ice jam for installation.
cently, a commercially produced radar unit has
been made available from Dedicated Electronics
Ice coverage and concentration
of Chester, New Hampshire, that is capable of
Rossiter and Crissman (1994) describe the use
point measurements of ice thickness and costs
of low-light-level television (LLLT) video cameras
about ,000. The unit is unproved in the field as
and marine radar for measuring ice concentration
of yet and Yufit (1990) report the manufacture of a
on the Upper Niagara River for the New York
vehicle-mounted radar unit by the State Hydro-
Power Authority and Ontario Hydro. Each
logical Institute in the former USSR, but do not
method had a limited range of observation (less
provide details on cost. Yankielun (1992) estimates
than 3 km). The LLLT cannot be used in dark or
the cost of his FMCW radar system at approxi-
snowy conditions and the imagery is subjective
mately ,000 if all new components were pur-
to interpretation. Software must be developed to
chased off-the-shelf. Even if the radar front end
allow the marine radar to differentiate between
can be purchased for a few hundred dollars,
moving and stationary ice, and the system was
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