Ice concentration (i.e., how much of the chan-
strumentation in the field is assessed, and some
nel is covered by floating ice pieces) is estimated
ideas for future instrumentation research are pre-
from visual observations from a structure, shore,
sented.
or aircraft. Estimating an ice concentration suffers
from the same disadvantages as estimation of ar-
Stage and discharge
eal ice coverage. An additional disadvantage is
Stage and discharge were rated the two most
that the estimation is highly subjective. Two indi-
important parameters to measure by survey re-
viduals viewing the same flow may interpret the
spondents. Stage and discharge are also very com-
concentration of ice pieces as being quite differ-
monly monitored remotely, mostly through the use
ent, even if given guides demonstrating the dif-
of a stage recorder connected to a DCP. However,
ferences between different levels of concentration.
there is potential for development of some por-
Bjerke (1991) reported using a "frame-grabber" to
table or temporary instruments that could be used
capture and digitize videotaped images of mov-
at various sites with little user interface other than
ing ice. The digitized image was rotated through
to set up the unit and collect the data.
the use of a computer algorithm to provide a ver-
Ultrasonic instruments have been used for a
tical view, from which ice piece size and concen-
number of years with varying levels of success.
tration can be determined. He found fairly reason-
They have the advantage over traditional water
able results using this method, although the
level recorders that direct contact with the water
smaller flow could be discerned.
is avoided, thus decreasing the incidence of freez-
ing and damage by water-borne debris. Ultrasonic
instruments are susceptible to rapid changes in air
Developing or future instrumentation
Many of the methods of data collection cur-
temperature, and wind can disturb the water sur-
rently used by USACE Districts rely upon visual
face enough to cause loss of return signal
observations. Visual observations are inexpensive
(Abraham and Hall 1994). The absolute accuracy
and easy to make but are highly dependent upon
of the ultrasonic sensor is relative to its range, al-
weather and lighting conditions, as well as access.
though resolution may be to 0.01 ft (3 mm). In other
Some of the collection methods require personnel
words, two sensors with the same range may not
to be exposed to dangerous elements, including
have the same accuracy if their relative accuracy
cold air temperatures, low wind chill, and ice.
varies, or two sensors with the same relative ac-
Other methods require higher maintenance re-
curacy will not have the same absolute accuracy
quirements or suffer from more breakdowns or
if their ranges differ. Capabilities of individual
periods of in operation. The observation of some
sensors will vary with manufacturer and cost. It
parameters is not deemed to be very important,
is not known how an ultrasonic sensor would per-
but this may be due in part to lack of inexpensive,
form over an ice surface.
proven observational techniques or instruments.
In order to be a truly portable unit, the sensor
The survey results support the need for con-
and its recorder and power source must be self-
tinuing development or refinement of observation
contained in a small, lightweight package. Such a
techniques or instruments, especially for those
conceptual package is demonstrated in Figure 10.
parameters that have been identified as most im-
The unit would need to be contained in a weather-
portant by District personnel. The use of instru-
tight box that could either be permanently
mentation to remotely monitor ice-related param-
mounted on a surface such as the side of a bridge
eters is not very high in importance in the Corps
or could be temporarily hung over the side of a
of Engineers District offices. This can be attributed
bridge. If the housing were permanently installed,
to several reasons, including high cost, low reli-
the components within could be removed and
ability, lack of need or perceived need, and resis-
used between various locations. Selection of a data
tance to change. Development of future instrumen-
logger and ultrasonic sensor must consider ex-
tation for field use will require that these issues
pected operating climate, data requirements and
be addressed. Some codevelopment of instrumen-
operating parameters. A power source would need
tation with other agencies, such as the USGS, may
to be provided; either a dry-cell battery or a solar
be necessary. Continued support by District offices
cell would probably be adequate.
will also be necessary. This section, instrumenta-
Radar systems have been used to attempt ice
tion that has been developed to measure various
thickness measurements for a number of years. Re-
parameters but is not yet ready for widespread
cently, several other potential uses of radar have
field use. The feasibility of implementing such in-
been explored in research work, including the
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