Author(s): Martin Jasek; John Marko
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Abstract: An upward looking sonar instrument was deployed on the riverbed in November 2007. The instrument package contained a 545 KHz sonar transducer, as well as temperature-, 2-axis tilt- and pressure- sensors as well an onboard heater and a warm water supply hose to prevent anchor ice formation. The sonar instrument measures the distance to the water surface or the undersides of drifting or stationary ice. By computing the difference between the acoustically-derived distance to the ice and an independently measured water level, the draft of the floating ice can be determined at one second sampling intervals. The instruments can also record the profile of acoustic backscatter returns through the body of the river water column allowing detection of the presence and depth of suspended frazil ice. Data quantity and quality from prior deployments since November 2004 of this and a lower frequency unit (235 kHz) have been compromised by anchor ice formation on the instrument. This paper describes a new and a much successful design of a mooring system that prevented anchor ice interference. The location of the underside of the ice cover and the presence of suspended frazil ice as detected both prior to, during and after the formation of the winter ice cover was recorded by this higher frequency instrument for the first time. Relative concentrations of suspended ice and the concentrations and thicknesses of surface ice pans were measured. The ice cover formation (stabilization and shoving events) were also captured for the first time at continuous 1 second full depth-profiling sampling rate.
Year: 2008