The instrument estimates distance by measuring acoustic travel time and converting it using a vertically averaged speed of sound. Salinity has a relatively small effect on the speed of sound (approximately 1.34 m/s per psu at 0°C). Therefore, uncertainty in salinity is not expected to significantly affect the acoustic range data. For example, uncorrected salinity variations over the range of 30-35 psu would contribute errors in calculated water depth of only about 0.05 m. Temperature has a stronger effect on the speed of sound. An uncorrected temperature change from -2.5°C to +2.5°C would result in a depth error of approximately 0.15 m. By correcting the speed of sound using the measured temperature, and by estimating salinity under the assumption that the water column is near the seawater freezing point, the residual error due to density uncertainty can be reduced to less than ±0.05 m. During ice-covered conditions, the water column is typically weakly stratified, which supports this assumption.
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