described as being more expensive than alterna-
Sensing (ERS) satellite will be capable of provid-
tive methods. They also state that systems capable
ing data on river ice conditions that are necessary
of observing an ice cover can also be used to esti-
for navigating through ice and evaluating the po-
mate ice speed, if properly calibrated and if
tential for river ice jams and ice erosion along
trackable ice features are present. The method de-
shorelines. He notes two limitations on the use of
scribed by Bjerke (1991) previously also shows
SAR: resolution prevents showing distinct images
promise for daylight measurements of ice concen-
on rivers narrower than 3035 m and on shallow
tration, particularly if more sophisticated cameras
streams with boulders above the water level, and
and computer techniques can be utilized.
the single band and polarization may limit the
Areal ice coverage also was given low ranking in
differences in ice it can detect. Shokr et al. (1996)
the survey. Typically, as presented earlier, areal ice
report the use of ERS-1 SAR images to monitor
coverage is currently most commonly observed
sea ice conditions along the east coast of Canada
from an elevated vantage point or from an aircraft.
and in the Gulf of St. Lawrence. They found that
Toikka (1987) describes the use of an impulse radar
the images were useful in detecting the differ-
to measure distribution of frazil under the ice cover
ence between ice and open water, but that rough-
using a radar unit towed by a snowmobile. The sig-
ness and other structural information about the ice
nal processor and video display used were devel-
was not consistent. Further investigation is needed
oped in the Radio Laboratory of the Helsinki Uni-
to more fully develop the potential of SAR imagery.
versity of Technology. It seems plausible that if the
ASCE (1995) reports that EarthWatch, Inc. plans
system could be used to assess distribution of frazil
to launch a system capable of 3- m resolution (pan-
below an ice cover that it could also be adapted for
chromatic), while systems capable of 1-m resolu-
assessing floating frazil distribution, although it is
tion will fly by 1997. If this type of resolution will
unknown how reliable or accurate this system
truly be available, remote monitoring of ice cov-
would be for determining moving ice coverage.
erage would be greatly enhanced, even if imag-
Another method of ice concentration monitor-
ery would be available on a 2- or 3-week cycle.
ing, satellite imagery, currently has limited poten-
Computer analysis of this satellite imagery could
tial, but as satellite systems capabilities improve,
be highly beneficial, but it is unknown what the
so will the potential for monitoring ice conditions.
processing requirements or acquisition costs may
Gatto (1988a, 1988b, 1989) describes efforts to post-
be for such fine resolution. The processed infor-
monitor ice conditions on the Ohio, Allegheny, and
mation would need to be stored in a format that
Monongahela Rivers and Illinois Waterway over
could be read by CADD or GIS users.
a 13-year period using available Landsat images.
Gatto notes several disadvantages to the use of
Other parameters/instrumentation
Landsat imagery: the number of usable images is
Researchers have pursued a number of other
limited due to long satellite repeat cycle and fre-
instruments that measure parameters other than
quent cloud cover, river ice is not always appar-
those mentioned above, or feature configurations
ent because the instantaneous field of view of the
not found in present instrumentation. Some of
satellite sensors are sometimes insufficient to de-
these systems may merit future consideration, but
tect the amount and type of ice present, and pho-
may or may not be very feasible. A few are pre-
tographic images do not show all the detail col-
sented below.
lected by Landsat sensors, but computer analysis
Hanagud and Craig (1974) describe monitor-
would be necessary to evaluate the additional in-
ing the underwater acoustics of an ice cover as it
formation.
is subjected to temperature changes, and trying to
McGinnis and Schneider (1978) discuss the use
develop a correlation between the two as a means
of Landsat, NOAA, and GOES satellites. NOAA
of predicting ice breakup. They concluded that for
and GOES provide much coarser resolution but
such a system to be effective, measurements would
offer daily coverage, compared to 18-day cover-
have to be made at several locations, rather than
age by Landsat. However, geostationary satellite
at one location. They also concluded that it would
imagery is not of much use above 50 latitude,
not be good for a general survey, but rather serve
owing to distortion. The authors conclude that op-
as an indicator at critical portions. One applica-
erational environmental satellites could be used
tion might be in monitoring or forewarning of
to create an early warning monitoring system.
unusual or severe ice forces on various hydraulic
Gatto (1993) suggests that the synthetic aper-
structures. Bogorodskii et al. (1978) also discusses
ture radar (SAR) aboard the European Remote
this concept.
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