On the probability of underwater glider loss due to collision with a ship

Abstract

The demonstrated fitness as a measurement platform for the open ocean has sparked a growing interest to operate underwater gliders also in shallow coastal areas. In this environment gliders face additional challenges such as strong (tidal) currents and high shipping intensity. This work focuses on the probability of losing a glider resulting from a collision with a ship. A ship density map is constructed for the German Bight from observed ship movements from Automatic Identification System (AIS) data. A simple probability model is developed to interpret ship densities in terms of collision probabilities. More realistic, but also more computationally expensive Monte-Carlo simulations were carried out for verification. The model can be used to generate geographic maps showing the probability of glider loss due to collisions. Such maps can serve as an aid in planning glider missions. Keywords gliders • collision • AIS • German Bight 1 Introduction Underwater gliders, or gliders for short, are buoyancy-engine propelled autonomous underwater vehicles (AUVs): they can attain positive or negative buoyancy to climb or sink, respectively. Being a torpedo-like shape of about 1.5 m in length and equipped with wings, vertical motion leads to a horizontal velocity, enabling a glider to traverse the oceans in a saw-tooth way down to depths of 1000-1500 m. When at the surface, gliders use global positioning system (GPS) for navigation and two-way satellite communication systems, allowing them to be controlled from shore. Davis et al. [1] give an in-depth account of the principles of operation.

Summer upwelling at the Boknis Eck time-series station (1982 to 2012) – a combined glider and wind data analysis

“…For future missions it has to be considered that this study was carried out in a restricted area and as such the glider's navigation was unaffected by ship traffic. This is only in selected areas of the Baltic Sea the case -for instance 57 000 ships pass Fehmarn Belt and another 54 000 Öresund Strait every year (HELCOM, 2010) and special attention must be given to ship avoidance strategies when surveying such areas (Merckelbach, 2013). …”

“…We thank the crew from RB Polarfuchs and M. Schlundt for assistance in the glider operations at sea, J. Herford for assistance in the data preparation, and H. Bange for providing the BE data and organizing the BE site. The research leading to these results have received funding from the European Union 7th Framework Programme (FP7 2007-2013, under grant agreement no. 284321 GROOM (www.groom-fp7.eu) and by EGO-COST Action ES0904.…”

The Coastal Observing System for Northern and Arctic Seas (COSYNA)

“…Due to bathymetric constraints, currents can reach magnitudes in excess of the nominal glider speed, making it difficult to follow a prescribed transect. Intense commercial and recreational shipping traffic significantly increases the likelihood of a glider-ship collision (Merckelbach, 2013). This will almost certainly result in the loss of the glider and possibly in a hull rupture, if a fast lightweight craft is involved (Drücker et al, 2015).…”

Towards building a safety case for marine unmanned surface vehicles: A Bayesian perspective

“…Whilst a large number of risk and reliability studies for autonomous underwater systems have been conducted that quantify risks (Brito et al, 2008), (Brito et al, 2010), (Brito et al, 2012), (Podder et al, 2004), (Merckelbach, 2013) (Brito, 2015), to this date there has been no concerted study that focus on the quantification of safety integrity. Studies of safety integrity for buoys, moorings and remotely operated underwater robots is presented (Vedachalam et al, 2016), (Venkatesan et al, 2014), (Venkatesan et al, 2015) but these do not apply to MUSVs.…”