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ABYSS AUV In Seafloor Volcano Study
Bathymetry Collected at Higher Resolution Vs. Surface-Ship Readings


Graham Lester

GEOMAR's the ABYSS and its
launch and recovery system.
As is often said, the scientific community knows more about outer space than it does about the depths of the oceans. The sheer magnitude of the Earth's oceans—covering more than 130 million square miles of the planet's surface—coupled with the extreme technological challenge of collecting quality data beneath miles of water, makes it difficult for scientists and surveyors to perform truly comprehensive and valuable deepwater exploration. For the most part, ocean exploration has been dominated by surface-ship technology since World War II. Recent advances in the reliability and capability of AUVs, however, have sparked a renaissance in deepwater exploration and survey, giving users access to more valuable data than ever before.

For nearly half a decade, scientists and engineers at the German research facility GEOMAR - Helmholtz Centre for Ocean Research Kiel have been using a specially designed REMUS 6000 AUV built by Hydroid Inc. (Pocasset, Massachusetts) to gather detailed geological data from the ocean floor. It is named the ABYSS, which refers to the huge depths between 3,000 and 6,000 meters in which the AUV works. The basic mission of the ABYSS is deep-ocean exploration, specifically in volcanically and tectonically active parts, such as midocean ridges. With a maximum mission depth of 6,000 meters, the AUV uses several technologies to map the seafloor accurately and determine its geological structure.

Locating Undersea Volcanoes
The ABYSS is a modular AUV and can be equipped with several different sensors, depending on the needs of the mission. When it is used to explore volcanically active areas of the ocean, the AUV uses side scan sonar, often in combination with a multibeam echosounder, to collect high-resolution bathymetric data. Additionally, an onboard turbidity sensor helps identify areas of recent volcanic activity by detecting the plumes of mineral-laden hot water it generates.

'As always in ocean science, one of our primary challenges is that the ocean is so huge,' said Dr. Colin Devey, scientific head of the AUV team at GEOMAR. 'However, the long dive times made possible by the ABYSS allow us to cover a lot of ground in one dive. For instance, in our recent South Atlantic trip which ended March 5, we were able to cover over 1,100 kilometers in only 12 dives, with only four hours of technical downtime. These long dive times allow us to really make inroads into the vast area of the ocean floor.'

Additionally, the two lithium-ion battery packs that power the ABYSS allow a maximum mission time of 22 hours, depending on the modules being used. During the recent GEOMAR expedition to the South Atlantic, these capabilities enabled the team to explore several regions of the seafloor that were previously uncharted, even by surface-ship bathymetry.

The turbidity sensor on the AUV also helps it locate areas of undersea geothermal activity, including hydrothermal vents and black smokers that typically occur in volcanically active regions of the seafloor. Once these regions are located, they can be further examined by the ABYSS using other onboard instruments.

One of the primary techniques used by the ABYSS is high-resolution bathymetry. For seafloor volcano research, GEOMAR uses a combination of sensor technology that is unique to the ABYSS to obtain high-resolution bathymetric data on the landforms created by undersea eruptions. The data that the ABYSS provides allows a very detailed view of undersea landforms. The data that the ABYSS collects is at a much higher resolution than anything that can be generated using surface-ship bathymetric readings.

Bathymetry has been measured from surface ships for centuries, but the so-called 'wavelength handicap' limits the resolution of acoustic imaging from a surface ship in deep water. Acoustic penetration to 6,000-meter depths requires relatively low frequency (about 15 kilohertz), which corresponds to relatively long wavelength (about 10 centimeters) and poor resolution. An AUV flying about 10 meters above the seafloor enables high-frequency, high-resolution, shallow-water imaging technologies to be applied in deep water. Therefore, instruments onboard AUVs provide a level of detail that had previously been unattainable. Scientists at GEOMAR have thus observed seafloor volcanic landforms with unprecedented clarity, allowing them to gain deeper insight into the workings of undersea landforms and volcanoes and make direct comparisons with features they know from land.

Having access to this extremely detailed information on the geological and chemical structure of the seafloor allows further understanding of the interrelations of volcanic activity, tectonic activity and hydrothermalism. The data has implications that extend across multiple disciplines, including how chemosynthetic life is distributed and the location of marine mineral resources.

Onboard Equipment
The ABYSS, like all REMUS 6000 AUVs manufactured by Hydroid, has several configuration options to meet a variety of mission requirements. Standard data collection instruments used on the ABYSS include an acoustic Doppler current profiler, side scan sonar, pressure, altitude, conductivity and temperature sensors. Additional sensor options for Hydroid REMUS 6000-type AUVs include dual-frequency side scan sonar, acoustic imaging, environmental characterization optics (ECO) sensors, a sub-bottom profiler and a still-camera system.

While the ABYSS is on board the support vessel or surfaced, engineers can interface with it using the same Vehicle Interface Program (VIP) used by all Hydroid REMUS AUVs. This highly refined software runs on a ruggedized, waterproof laptop, allowing it to be operated safely in poor weather conditions. In addition to mission planning, the VIP software helps users export data, maintain the vehicle and perform quality-control checks. To continue this article please click here.

Graham Lester is the director of Hydroid Europe in the U.K., a division of Hydroid, a Kongsberg company. Lester has 20 years of experience with military, oceanographic, geophysical and hydrographic equipment, including a detailed understanding of integrated solutions for underwater vehicles. He joined Hydroid in 2006 as business development director before moving to the U.K. to establish Hydroid Europe. He has worked internationally to introduce AUV technology into global markets for defense, offshore and academia. He holds a higher national certificate in electronics and communications engineering.

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