More accurate depth measurements
An accurate insight into current water depths is important for shipping safety. The measurement data serve, for example, as input for the dredging frequency in and around the port of Rotterdam, so that it remains accessible to the largest ships. Echo measurements are an efficient method for this, but variation in the speed of sound under water influences the accuracy. Dr. Mirjam Snellen designed an algorithm to determine the sound velocity profile from the already measured echo data. The company Quality Positions B.V. Zeist has now implemented this algorithm in its commercial sonar data processing software.
Variable sound speed
In echo measurements (sonar) the time is measured between sending a 'ping' and receiving the reflected signal. Half of this time gives, with the sound velocity profile as a function of the depth, the distance from the echo sounder to the bottom.
The salinity and the temperature of water influence the speed of sound and thus the accuracy of depth measurements especially in estuaries and areas with tides. This can be overcome with additional equipment and measurements of the sound velocity profile.
Multi-beam sonar
Multi-beam sonar can be seen as an echo sounder that simultaneously emits several narrow sound beams. This allows one to map a wide line of soil in one go, perpendicular to the sailing direction of the research vessel. The entire bottom is charted with several parallel sailing movements. To avoid missing areas there is always some overlap in the measured data.
Smart use of data
Dr. Mirjam Snellen and Tannaz Haji Mohammadloo make clever use of this extra data, and of the physics of sound and the environment, to calculate the sound velocity profiles. The company Quality Positions B.V. (www.qps.nl) has added this fast method for automatic error correction to their QIMERA hydrographic software package. According to the company, this works better and more objectively than existing manual correction methods.
A broad spectrum of sound research
Dr. Mirjam Snellen is an associate professor at the Aircraft Noise and Climate Effects department and specializes in measuring and using sound, both above and below water. Look here for their work on the cutting edge of measuring and modeling