GOVERNMENT UPDATESonar & The USCGThe USCG Plans to Widen its use of the subsea surveillance technology. The question is: is the investment warranted?BY DENNIS L. BRYANTThe US Coast Guard is planning to A civilian contractor steadies a M18 Mod 2 King? sh Unmanned Underwater widely use sonar to support its maritime Vehicle (UUV) as it is lifted with a crane security and marine environmental pro-onto the deck of an 11-meter rigid-hull tection missions. The agency currently in? atable boat. The King? sh uses side has limited capability to detect objects scan sonar to search and discover ob-below the water’s surface and relies on jects of interest. This marks the ? rst others (such as the US Navy or the com-time these UUVs have been added to mercial sector) when such detection is mine countermeasure operations in the U.S. 5th Fleet area of responsibility.needed.Sonar is an acronym for Sound Navi-gation and Ranging. The principle is similar to radar, used in the atmosphere. While radar uses radio waves, sonar re-lies on sound waves, which propagate much better than radio waves do in wa-ter. There are two major types of so-nar – passive and active. Passive sonar only listens, detecting sounds made by vessels, persons, ? sh, and other things in the water, or the water itself (i.e., waves). Active sonar transmits a sound signal that then is re? ected off an object within range and returns to the trans-ducer. Measuring the time difference between transmission and reception provides an indication of the range of the target. Measuring the angle of the (U.S. Navy photo by Mass Communication Specialist 2nd Class Blake Midnight/Released)received signal provides an indication of the direction of the target. Sonar in the form of echo-sounders of characteristics such as bottom type delivery systems, such as those used in Sonar transmissions are made in a va-has been utilized for years by ships to (i.e., mud, sand, gravel) and depth to several of the James Bond movies. This riety of frequencies, depending upon determine the depth of water under the hard strata. This information can prove sonar provides detection, classi? cation, the intended purpose. Low frequency keel. A signal is transmitted straight valuable for determination of anchor- and tracking information on human un-transmissions have the advantage of down. The signal re? ects back when age grounds and for laying of subma- derwater incursions that could endanger very long range. On the other hand, it hits the seabed. The time difference rine cables and pipelines. lives or property. It is being employed these sonar transmissions can only de-provides the operator with an accurate Sonar is used commercially to exam- around some marine facilities world-tect very large objects and with mini-measure of the depth. More sensi- ine hulls, pilings, and underwater struc- wide, but not yet to a great extent. mal accuracy relative to range or bear-tive versions are in use as ? sh ? nders. tures such as offshore platforms. This Limpet mine imaging sonar is used for ing. Mid-frequency transmissions have These devices differentiate between the type of sonar is sometimes handheld by detection of small underwater objects. a range measured in miles and are able strong signal generated by re? ections a diver or mounted on the end of a pole. Originally used for detection of limpet to detect objects such as submarines off the seabed and weaker signals gen- Increasingly, it is mounted on remotely mines potentially attached to the hulls and large whales with good accuracy erated by re? ections off objects in the operated vehicles (ROVs) or on un- of ships, it can now be used to detect relative to range and bearing. This is water column. Sophisticated versions manned underwater vehicles (UUVs). caches of drugs and other contraband. the type of sonar utilized almost exclu-provide more detailed information, al- ROVs have greater capabilities regard- This type of sonar may also be used sively by the military, having virtually lowing determination of the size of the ing power and data transmission, since to detect hull damage and underwater no commercial application. High fre-? sh school, etc. Sonar transmitters can they are tethered to a shore location or structural damage.quency and ultra-high frequency sonar even be attached to trawl nets, allowing to a manned vessel. UUVs have less The Coast Guard proposes to utilize transmissions have a short range, but for better placement of the nets relative power and data transmission capabili- commercially-available sonar equip-are able to detect small objects. This to the target species. ties, but can get into tighter spaces and ment to broaden its capability to locate, type of sonar is utilized commercially Stronger and more sophisticated sonar have longer potential range. image, and classify submerged and un-and is the type under consideration by can be used to penetrate the upper layer Diver detection sonar is used for detec- derwater targets of interest (TOIs). This the Coast Guard.of the sea? oor, allowing determination tion of divers and submerged swimmer would include such things as terrorist 20 Maritime Reporter & Engineering News • JANUARY 2014MR #1 (18-25).indd 20 1/7/2014 10:24:20 AM