The need frequently arises among individuals whose work must be
carried out on the ice in rivers, lakes, and reservoirs for an instrument
which conveniently measures ice layer thickness. Safety is possibly the most
important consideration. In addition scientific studies of the processes
involved in ice jam formation or of the effect of the ice layer on the ecology
of the river lake or reservoir could be enhanced by an instrument that could
conveniently and quickly measure ice thickness. At present ice thickness can
be reliably determined by drilling a hole and measuring the thickness by
some form of hook gage. This procedure requires, however, that individuals
venture out on what is possibly "too thin" ice to make the measurement.
For a number of thickness measurements over an area, surface drilling
becomes a time consuming process.
The various forms of nondestructive measuring devices currently in use
employ an echo ranging technique with electromagnetic or acoustic waves.
These devices are known by a number of acronyms such as; LASER ranging,
RADAR, and SON AR. Their usefulness for ice- layer thickness
measurements would depend, in addition to other considerations, on the
strength of the reflection from an ice water interface. The expected distance
to be measured is estimated from 1 cm to 100 cm (in the Minnesota
Region) from the ice surface to the ice-water interface below. The velocity
of propagation of electromagnetic waves of nearly 300,000,000 mls indicates
echo ranging with electromagnetic waves would require the measurement of
very small time intervals to infer distances as small as one centimeter. The
time required for distance measurement using ultrasound, with a sound wave
velocity of 3200 mls in ice, would be considerably longer, typically a few
hundred microseconds. While the technology exists for the measurement of
the extremely short transit time of electromagnetic pulses, the cost and
complexity compared to the measurement of a considerably longer time for a
acoustic pulse to travel the same distance is considerably greater.
Killen, John M.; Gulliver, John S..
The Usse of SONAR to Measure Ice Thickness.
St. Anthony Falls Hydraulic Laboratory.
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