A recent series of major deepwater discoveries promises exciting opportunities for the offshore oil industry. But with them comes the problem of how to carry out the precision surveys needed for subsea installations. Manufacturers and underwater contractors alike are getting their feet wet in the new AUV waters. Maridan A/S and C & C Technologies are featured in this article.
Until recently, AUVs were restricted to prototypes in oceanographic research institutes and military establishments, but the potential they offer for cost savings in deep waters has opened up a number of potential applications for these new high-tech free-swimming robots. John Westwood of oil and marine industry analysts Douglas-Westwood Associates sees great potential for the new technology. In a key-note speech at Ping'99, he stated that AUVs also had the potential to greatly increase the efficiency of hydrographic survey operations. "I envisage several AUVs running in parallel with a survey or research vessel, doubling or trebling its efficiency," he said, "or in some instances, AUVs could replace the vessel completely." Quoting from his company's study Ocean Survey III, he stated that the world survey market - currently valued at $1.1 billion - is expected to grow by 32 percent over the next five years "and AUVs will have an increasing role to play."
In an effort to circumvent the problems associated with deep-towed survey systems, Kongsberg Simrad, in conjunction with C&C Technologies, is developing the Hugin 3000 AUV, which has evolved from a program amassing more than one hundred missions since 1995. The HUGIN 3000 will be integrated with an "acoustic tether" to monitor data acquisition and optimize system performance.
Maridan's Martin AUV has been developed to be a modular and inherently stable platform capable of carrying a variety of sensor payloads for different purposes. It is a true AUV, capable of operating autonomously without needing continual reference to external positioning systems or vessels. For early 2000, Maridan has contracted to the National Museum of Denmark to carry out an extensive survey for archaeological relics in Danish waters. The vehicle will carry sidescan sonar and sub-bottom profiler as its principal survey instruments plus a still digital camera for visual records of individual sites.
For survey work, AUVs offer a number of advantages over conventional towed or ship-borne instrumentation. Reduced dependence upon or elimination of the surface vessel offers great cost savings. And even where a vessel is used during a survey, it can continue with other tasks or deploy multiple AUVs in the same area for parallel operations. Particularly in deepwater, data can be acquired at a higher rate than with a towed vehicle, especially where the survey calls for a large number of line changes and turns. Data quality is much improved by placing sensors in stable conditions closer to the seafloor, thus minimizing errors through ray-path distortion from water layers of differing densities. Isolation from the surface minimizes vehicle disturbance via the cable from the parent ship. Inaccessible or difficult areas, such as under ice or close to fixed structures, can also now be successfully surveyed.