Sea Technology

NOV 2018

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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Page 17 of 52 November 2018 | ST 17 age them to consider deploy- ment of their sensors on mi- cro-AUV platforms with all that this entails in terms of size, power and weight. An early adopter of this philoso- phy was Valeport Ltd. Based in southwest England, Vale- port has an enviable reputa- tion for producing high-qual- ity sensors designed and manufactured in-house with the inherent ability to adapt quickly to meet the needs of potential end-users such as ecoSUB. Alternative to XBT One of the many potential applications of micro-AUV technology identified by the market study was an alter- native to the XBT (expendable bathythermograph). The XBT has been used by oceanographers for many years to obtain information on the temperature structure of the water column. It was later adopted by naval forces and others to locate the thermocline. Added conductivity sensors facilitate calculation of speed of sound for sonar calibrations. The XBT is dropped from a ship and measures the tem- perature and conductivity as it falls through the water. Two very small wires trans- mit the temperature data to the ship, where they are post-processed to provide temperature-salinity pro- files. The probe is designed to fall at a known rate, so that the depth of the probe can be inferred from the time since it was launched. By plotting temperature as a function of depth, the user can get a picture of the tem- perature and salinity profile of the water column. Using standard formulas, speed of sound can be calculated from this information. Although extremely useful, XBT technology has a number of limitations. First, data are provided only di- rectly below the deploying platform (ship). Second, im- portant data such as depth and salinity are calculated or inferred rather than measured. Third, XBTs are one-shot devices providing a single profile per XBT. These limita- tions are addressed using ecoSUB technology combined with a time-of-flight sound velocity sensor provided by Valeport. Using ecoSUB-ยต5 combined with a specially adapted Valeport SV (sound velocity) sensor provides a real-time physical measurement of speed of sound, accurate depth The pressure-tolerant electronics.

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