Testing a Prototype Digital Hydrophone for Use at Mod Maritime Acoustic Ranges

QinetiQ have utilised analogue hydrophones on MoD maritime acoustics ranges for decades.As part of a wider modernisation programme, the requirement for a digital hydrophone emerged.A supplier was chosen from a short list who could meet QinetiQ's requirements, primarily that the hydrophone self-noise should reach an acceptable compromise between self-noise and measurement bandwidth.This is to attain the widest possible bandwidth for which self-noise remains below Sea State 0, whilst permitting accurate measurement at high frequencies, for example One-Third Octave centered on 100kHz.The former requires a large sensor element but the latter requires a small one, which presents a design challenge to overcome that dichotomy.QinetiQ first chose Seiche Ltd as their partner to design and develop a prototype Ethernet hydrophone in 2017, to include auxiliary sensors for temperature, depth, vibration and orientation.Since then the hydrophone transitioned through multiple iterations, with fully operational prototypes of the QQ1000 1 delivered to QinetiQ in 2021.These prototype hydrophones were thoroughly tested for two years, and in 2023 QinetiQ approved the design ready for deployment on several MoD maritime acoustic ranges for the purpose of quantifying ship noise.This paper reviews the final stage of testing which QinetiQ undertook to inform their decision to approve the design of the hydrophone, which involved testing the prototype alongside an NPL-calibrated analogue hydrophone in June 2023.