On the reliability of the Autosub autonomous underwater vehicle

As autonomous underwater vehicles (AUVs) enter operational service an assessment of their reliability is timely. Using the Autosub AUV as an example, several design issues affecting reliability are discussed, followed by an analysis of recorded faults. Perhaps contrary to expectations, failures rarely involved the autonomous nature of the vehicle. Rather, faults were typical of those that occur with any complex item of marine electromechanical equipment. A statistical analysis showed that the failure rate decreased with distance travelled- an indicator that an AUV underway, submerged, is at less risk of a fault developing than during other phases of a mission. 1

On the radiated noise of the Autosub autonomous underwater vehicle

Autonomous Underwater Vehicles (AUVs) can be very quiet platforms from which to make observations of marine living resources. With few moving parts and very low propulsion power they should have a very low underwater radiated noise signature. The purpose of this paper is to describe measurements on Autosub to test this assumption. The measured noise level and spectrum are compared to the ICES proposal for the radiated noise of fisheries research vessels. Integrated over the band 100 Hz to 5000 Hz the AUV source level, at 124 dB relative to 1mPa at 1 m, was about 39 dB below of the ICES specification and about 30 dB quieter than the noise-reduced vessel "Scotia". Autosub is in fact exceedingly quiet. The difficulties of making measurements of the underwater radiated noise of a quiet submerged vehicle are discussed and suggestions are made for improvements in techniques

An investigation of avoidance by Antarctic krill of RRS "James Clark Ross" using the Autosub-2 autonomous underwater vehicle

The autonomous underwater vehicle (AUV) Autosub-2 was deployed on eight missions ahead of RRS James Clark Ross in the northern Weddell Sea and in the Bransfield Strait, Southern Ocean, to assess avoidance of the research vessel by Antarctic krill Euphausia superba. The AUV was equipped with the same type of scientific echosounder as the research vessel (Simrad EK500 operating at 38 and 120 kHz) and measured the density of krill along transect acoustically (g m-2 wet mass) prior to the ship's arrival. We hypothesised that if krill avoided the ship, perhaps in response to radiated noise, then the ship should detect less krill than the AUV which is known to have much lower noise levels than the ship. We were unable to detect any significant difference between the density of krill detected by the ship or the AUV, either at the transect level or at finer scales within transects. We conclude, therefore, that avoidance by krill of RRS James Clark Ross will not significantly bias acoustic estimates of krill abundance by this vessel

Antarctic krill under sea ice: elevated abundance in a narrow band just south of ice edge

We surveyed Antarctic krill (Euphausia superba) under sea ice using the autonomous underwater vehicle Autosub-2. Krill were concentrated within a band under ice between 1 and 13 kilometers south of the ice edge. Within this band, krill densities were fivefold greater than that of open water. The under-ice environment has long been considered an important habitat for krill, but sampling difficulties have previously prevented direct observations under ice over the scale necessary for robust krill density estimation. Autosub-2 enabled us to make continuous high-resolution measurements of krill density under ice reaching 27 kilometers beyond the ice edge