Calibration and characterization of the ELVIS hydrophones

Abstract: Calibration is an important _eld and is used everywhere from education, research and industry. Every electrical equipment has to be calibrated during manufacturing and even over time as it is worn down. The purpose of calibration is to come as close as possible to the true value. The question is how close is close enough and how close is possible? Because even the equipment used for calibration needs calibrating, which in turn also needs calibrating and so on. This thesis will be about the hydrophones used by the system ELVIS. The method of choice is calibration by comparison. Its idea is to compare the signal received by the uncalibrated transducer with the same signal received by an already calibrated one. This might seem trivial but there are many things to be considered. ELVIS uses 47 hydrophones. The frequency range subjected to calibration is 30-250 kHz which leads to a huge amount of data to be recorded, analysed and presented. The result shows that each individual hydrophone performs similar to each other. Because of the insecurities regarding the reference hydrophone, no absolute measurements will be presented.