Autonomous underwater vehicles (AUVs) and investigations of the ice–ocean interface in Antarctic and Arctic waters

Abstract

Limitations of access have long restricted exploration and investigation of the cavities beneath ice shelves to a small number of drillholes. Studies of sea-ice underwater morphology are limited largely to scientific utilization of submarines. Remotely operated vehicles, tethered to a mother ship by umbilical cable, have been deployed to investigate tidewater-glacier and ice-shelf margins, but their range is often restricted. The development of free-flying autonomous underwater vehicles (AUVs) with ranges of tens to hundreds of kilometres enables extensive missions to take place beneath sea ice and floating ice shelves. Autosub2 is a 3600 kg, 6.7 m long AUV, with a 1600 m operating depth and range of 400 km, based on the earlier Autosub1 which had a 500 m depth limit. A single direct-drive d.c. motor and five-bladed propeller produce speeds of 1–2 m s−1. Rear-mounted rudder and stern-plane control yaw, pitch and depth. The vehicle has three sections. The front and rear sections are free-flooding, built around aluminium extrusion space-frames covered with glass-fibre reinforced plastic panels. The central section has a set of carbon-fibre reinforced plastic pressure vessels. Four tubes contain batteries powering the vehicle. The other three house vehicle-control systems and sensors. The rear section houses subsystems for navigation, control actuation and propulsion and scientific sensors (e.g. digital camera, upward-looking 300 kHz acoustic Doppler current profiler, 200 kHz multibeam receiver). The front section contains forward-looking collision sensor, emergency abort, the homing systems, Argos satellite data and location transmitters and flashing lights for relocation as well as science sensors (e.g. twin conductivity–temperature–depth instruments, multibeam transmitter, sub-bottom profiler, AquaLab water sampler). Payload restrictions mean that a subset of scientific instruments is actually in place on any given dive. The scientific instruments carried on Autosub are described and examples of observational data collected from each sensor in Arctic or Antarctic waters are given (e.g. of roughness at the underside of floating ice shelves and sea ice).

Detection of Oil in Ice and Snow

“…Underwater acoustic measurements of the ice/water surface have taken place for many years and this is a prime method for determining under-ice roughness [13]. This method may also be useful for oil under ice as it has been suggested that the oil/water and oil/ice interfaces may be detectable and also that the oil would change the underwater ice profile [13][14][15][16].…”

“…This method may also be useful for oil under ice as it has been suggested that the oil/water and oil/ice interfaces may be detectable and also that the oil would change the underwater ice profile [13][14][15][16].…”

“…When placed in a magnetic field, NMR active nuclei (such as 1 H-protons or 13 C-carbon 13) absorb electromagnetic radiation at a frequency characteristic of the isotope. The resonant frequency, energy of the absorption and the intensity of the signal are proportional to the strength of the magnetic field.…”

“…These earth magnetic field NMR devices are relative cheap but suffer from a number of limitations; especially in mobile applications as there is an absolute need for a homogeneous magnetic field to operate. As there is water everywhere, with two hydrogen atoms, one must either separate the water-hydrogen signal from the oil-hydrogen signal or use 13 C to measure the oil. However, the latter signal is relatively weak.…”

Ice sheets viewed from the ocean: the contribution of marine science to understanding modern and past ice sheets

“…Investigations using an ROV showed that sediments were being deposited predominantly by the squeezing out of diamicton from beneath the grounding line and subsequent remobilization by mass flow ( figure 9). In the last decade, technological advances in the development of AUVs has allowed access to a range of ice-ocean settings, including the cavities of large Antarctic ice shelves, the fronts of marine-terminating outlet glaciers in Greenland and sub-sea-ice investigations [103][104][105]. The UK has played a central role in this research, perhaps most notably through the design and implementation of the Autosub AUV.…”