Surveillance Towed Array Sensor System
Encyclopedia
_surtass_gear.jpg)
Towed array sonar
A towed array sonar is a sonar array that is towed behind a submarine or surface ship. It is basically a long cable, up to 5 km, with hydrophones that is trailed behind the ship when deployed. The hydrophones are placed at specific distances along the cable...
sonar
Sonar
Sonar is a technique that uses sound propagation to navigate, communicate with or detect other vessels...
system of the United States Navy
United States Navy
The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...
.
SURTASS began as development program in 1973 using the new research vessel Moana Wave. In 1980 SURTASS passed OPEVAL
OPEVAL
An Operational Evaluation , the final phase of operational test and evaluation prior to fielding of a system or new equipment, is a process used by NATO military forces and designed to be no more than a 'customer acceptance' test...
. The new Stalwart class ocean surveillance ships had the first contract awarded on 26 September 1980 and were similar to the prototype ship, the Moana Wave. Initially the SURTASS system were passive, receive only sonar systems. The array was towed miles behind the ships and were designed for long range detection of submarines.
As the passive systems were being deployed, an active adjunct known as the SURTASS Low Frequency Active (LFA) systems was designed for long range detection. The active system must be used in conjunction with the passive received system. The active component transmits an audio signal between 100 Hz and 500 Hz from an array suspended below the ship while the passive SURTASS array is towed miles behind to receive the signal after it had reflected off the submarine. The active LFA system is an updated version of the fixed low frequency surveillance system known as Project ARTEMIS
Project ARTEMIS
Project ARTEMIS was a project undertaken by the United States Navy in the 1960s, which produced a Low Frequency Active Sonar system that could detect submarines at long range. Robert A. Frosch, in his capacity as Technical Director of Hudson Laboratories , was Technical Director of the project. Dr....
. Although the Navy took steps to mitigate the environmental damage, environmental NGO's urged the Navy to prepare a public environmental impact statement. In 1996 the Navy published a notice of intent to prepare an environmental impact statement. The Navy has spent over $16 million on scientific research on the effects on marine mammals and mitigation systems as well as the development of an Environmental Impact Statement.http://www.surtass-lfa-eis.com/KeyFacts/index.htm
SURTASS Twin-Line consists of either the long passive SURTASS array or the Twin-line array consisting of two shorter passive arrays towed side by side. The Twin-line Engineering Development Model was installed on USNS Assertive
USNS Assertive (T-AGOS-9)
USNS Assertive was a Stalwart class Modified Tactical Auxiliary General Ocean Surveillance Ship of the United States Navy.NOAA acquired Ex-USNS Assertive from the United States Navy on 31 March 2004, intending to replace NOAA David Starr Jordan R444 after the Assertive underwent a conversion for...
, and the first production model was installed on USNS Bold
USNS Bold (T-AGOS-12)
The Ocean Survey Vessel Bold is operated by the United States Environmental Protection Agency. Originally commissioned as the USNS Victorious, it was renamed USNS Bold and was a Stalwart-class Modified Tactical Auxiliary General Ocean Surveillance Ship of the United States Navy.Stalwart class...
.http://www.navy.mil/navydata/policy/vision/vis02/vpp02-ch3t.html Both ships are no longer serving as SURTASS units.
_aft_surtass_equipment.jpg)
USNS Victorious (T-AGOS-19)
USNS Victorious is a Victorious-class ocean surveillance ship which was acquired by the U.S. Navy in 1991 and assigned to the Military Sealift Command Special Missions Program.-Built in Morgan City, Louisiana:...
-class and single T-AGOS 23 Impeccable-class Small Waterplane Area Twin Hull
Small Waterplane Area Twin Hull
A Small Waterplane Area Twin Hull, better known by the acronym SWATH, is a twin-hull ship design that minimizes hull cross section area at the sea's surface. Minimizing the ship's volume near the surface area of the sea, where wave energy is located, maximizes a vessel's stability, even in high...
(SWATH) vessels.http://www.msc.navy.mil/inventory/inventory.asp?var=OceanSurveillanceship.
Low Frequency Active Sonar
- The SHIPPYTHING Low Frequency Active Sonar system, on board Impeccable, commenced sea trials in late February 2004. During the spring and summer of 2004, Impeccable conducted five training missions in the Philippine Sea and the northwest Pacific Ocean. All LFA sonar operations included the operation of the High Frequency / Marine Mammal Mitigation sonar and compliance with all mitigation requirements.
- Total operational days on board the Impeccable using the LFA array: 26.2 days with 63.0 hours of transmissions 9.4 days with 22.7 hours of transmissions 22.5 days with 39.4 hours of transmissions.
- The ship had five years of active and passive operations in the Western Pacific before the incident in the South China Sea.
SURTASS LFA sonar description
SURTASS LFA is a long-range, all-weather, sonar system that operates in the low frequency (LF) band (100–500 hertz [Hz]). There is presently two SURTASS LFA sonar systems, one each on board the USNS Impeccable and Able, both operating in the northwestern Pacific Ocean. These systems have both passive and active components.The active system component, LFA, is an adjunct to the passive detection system, SURTASS, and is planned for use when passive system performance proves inadequate. LFA is a set of acoustic transmitting source elements suspended by cable from underneath a ship. These elements, called projectors, are devices that produce the active sound pulse, or ping. The projectors transform electrical energy to mechanical energy that set up vibrations or pressure disturbances within the water to produce a ping.
The characteristics and operating features of LFA are:
- The source is a vertical line array (VLA) of up to 18 source projectors suspended below the vessel. LFA’s transmitted sonar beam is omnidirectional (i.e., a full 360 degrees) in the horizontal (nominal depth of the LFA array center is 120 m [400 ft]), with a narrow vertical beamwidth that can be steered above or below the horizontal.
- The source frequency is between 100 and 500 Hz (the LFA system’s physical design does not allow for transmissions below 100 Hz). A variety of signal types can be used, including continuous wave (CW) and frequency-modulated (FM) signals. Signal bandwidth is approximately 30 Hz.
- The source level (SL) of an individual source projector is approximately 215 decibels (dB). The sound field of the LFA array can never be higher than the SL of an individual projector.
- The typical LFA transmitted sonar signal is not a constant tone, but a transmission of various waveforms that vary in frequency and duration. A complete sequence of transmissions is referred to as a ping and lasts from 6 to 100 seconds, although the duration of each continuous frequency transmission is never longer than 10 seconds.
- Duty cycles (ratio of sound “on” time to total time) are less than 20 percent—20 percent is the maximum physical limit of the LFA system. Typical duty cycles are approximately 7.5 to 10 percent.
- The time between pings is typically from 6 to 15 minutes.
The passive, or listening, part of the system is SURTASS, which detects returning echoes from submerged objects, such as submarines, through the use of hydrophones. These devices
transform mechanical energy (received acoustic sound wave) to an electrical signal that can be analyzed by the signal processing system of the sonar. The SURTASS hydrophones are mounted on a horizontal receive array that is towed behind the vessel. The array length is 1,500 m (4,900 ft) with an operational depth of 150 to 460 m (500 to 1,500 ft). The SURTASS LFA ship must maintain a minimum speed of approximately 6 kilometers per hour (km/h) (3 knots) through the water in order to tow the hydrophone array in the horizontal plane. The return signals or echoes, which are usually below background or ambient noise level, are then processed and evaluated to identify and classify potential underwater targets.