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USS Greeneville (SSN 772) incident

The Search and Survey Process
Pacific Fleet Information Paper

An Outline of Key Points to Help Explain the Search and Survey Process
(Feb. 19, 2001)

One of the first steps taken before any salvage operation is to collect data to determine the feasibility of salvage and to determine the dynamics of each situation.

Data is collected to answer questions such as:

- What is the condition of the vessel that may be salvaged (structural integrity, stability, positioning, etc.)?

- What is the environment around the vessel (bottom composition, bottom terrain, debris, obstacles, currents, etc.)?

Personnel on surface vessels use a variety of equipment to help gather the data needed to answer these questions. With the case of Ehime Maru, both side-scan sonar and remotely operated vehicles are being used to collect data.

This data collection survey commenced on Feb. 16 and is expected to take several days.

Side-scan sonar:

Side-scan sonar creates the equivalent of a relief map of the features on the ocean bottom. In this operation, the type of side-scan sonar being used is the Shallow Water Intermediate Search System or SWISS. SWISS consists of a fish-shaped piece of equipment called a "towfish" and display equipment housed on a surface support vessel.

In this operation the support vessel is USS Salvor (ARS 52). The towfish is towed behind USS Salvor at a speed of 1-to-5 knots. Sonar return is transmitted from the towfish via a fiber optic tether to USS Salvor. Sonar return is processed on board USS Salvor, producing analog and digital displays of features on the ocean bottom. Higher frequency sonar will be used to map bottom features and contacts.

In the case of Ehime Maru, higher frequency sonar will be used to survey or map a 2-by-3 nautical mile area or box around the ship. The survey begins at one corner of the box and continues in a back-and-forth pattern (much like mowing a lawn) until the entire area is mapped.

Remotely Operated Vehicles:

Once a vessel or object is located, remotely operated vehicles are used to conduct a detailed visual inspection in areas of interest to salvage planners.

Scorpio II
In this case, the remotely operated vehicle Scorpio II was flown in from the Navy's Deep Submergence Unit in Coronado, Calif., as a first response. Scorpio II was loaded on board the Motor Vessel C-Commando in Pearl Harbor and was sent to Ehime Maru's last reported location. Using sonar, Scorpio II began a search pattern to locate Ehime Maru. When sonar returns indicated a large object, video cameras aided by lights were used to conduct a visual search. Ehime Maru was located, and a detailed visual inspection of the ship was conducted. Video footage taken by Scorpio II will augment video gathered by another remotely operated vehicle, Deep Drone.

Deep Drone
The remotely operated vehicle Deep Drone, a salvage asset of the Navy's Supervisor of Salvage and Diving, along with SWISS was flown in from Upper Marlboro, Md. This equipment was loaded on board USS Salvor. Deep Drone will expand the detailed visual survey begun by Scorpio II and conduct detailed engineering assessment surveys of the Ehime Maru.

Analysis of data:

Data gathered by SWISS, Scorpio II and Deep Drone, as well as other data such as prevailing wind and sea conditions, will be used in analyzing the technical feasibility of salvage.

The analysis of the survey data and the development of salvage options available, if any, are expected to take several weeks.

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Revised: 2/19/01