The term ‘underwater threat’ immediately evokes images of a submarine armed with torpedoes. These days, however, underwater threats are much more diversified. In order to spot these threats in time, state-of-the-art sensors are required. The main underwater sensor is sonar, which transmits sound waves, and the reflected echoes of these waves enable the user to determine whether a threat is present and where. It is a sort of underwater radar, except it transmits sound waves instead of electromagnetic radiation.
Underwater Threats
Elta, a subsidiary of Israel Aerospace Industries (IAI), realized years ago that underwater threats are becoming more severe. Seaport and offshore oil and gas drilling rigs have become targets for enemies, and primarily for terrorists. A world leading manufacturer of radar systems, Elta entered this field as it offers a substantial business potential and as there is a considerable demand, in Israel and elsewhere, for the protection of maritime installations.
Ram Agadi is the executive in charge of marketing Elta’s underwater sensors, and according to him, the threats have become more serious, and the needs have evolved accordingly. “If we go back to the submarine image,” Agadi says, “while a standard radar sensor cannot detect a submarine traveling even a few meters under the sea surface, a SAR (Synthetic Aperture Radar) sensor can do it easily. In other words, what could not be achieved using the old sensors can now be achieved using SAR sensors of the type installed on airborne vehicles as well as on Israel’s spy satellites.”
In order to protect seaports and maritime installations all over the world, Elta develops smart sensors based on optics, sonar and radar technologies. In order to demonstrate the importance of these technologies, imagine and old WWII movie showing an underwater metal net that divers must cut in order to allow a submarine to enter a port unobserved. Apparently, this underwater net has not gone out of fashion, but has become much more sophisticated. While such a net provided a physical metal barrier in WWII, today it constitutes one elaborate sensor. If anyone touched or attempted to cut it, it would trigger an immediate alert.
“We manufacture this high-tech net ourselves and have already delivered a few, which now guard the entrances of several harbors around the world,” says Agadi. He was not forthcoming with any more technical details, as the protective net undoubtedly has a few surprises in store for anyone attempting to break through it. At the same time, Agadi explains that in addition to the metal wires, the underwater net also includes optical fibers, each one of which is, in fact, a long sensor. Any contact or attempt to cut such a sensor will alert the security personnel on the shore. The smart protective net can provide an accurate alert with a resolution of 50 cm of the break-in attempt, so that a defensive force may be dispatched to the location and neutralize the threat.
Elta also offers effective solutions in the shore-based naval radar system category. Elta’s ELI-3320 Port Guard Integrated Protection System combines a radar surveillance sensor with a sonar sensor and electro-optical sensor to provide multilayered surface and sub-surface surveillance performance. According to Agadi, this solution can detect a swimmer even in choppy sea conditions, and for this reason it is installed at numerous sites where the attempted break-in by a single terrorist carrying an explosive charge is a viable threat.
In some cases, the actual detection takes place when the swimmer comes ashore. For this purpose, Elta offers its ELM-2112 Persistent Ground & Coastal Surveillance Radar System. This radar ‘stares’ at a specific direction where a threat is expected to appear, and detects anysuspicious motion on the shore. This system may also be integrated with a sonar sensor to provide excellent surveillance performance.
Underwater Loudspeakers
Sound waves propagate very effectively under water, and Elta has also developed a system of underwater loudspeakers. When a swimmer or diver is detected in the water, he may be addressed in the style of ‘you have been spotted, surrender!’ Such loudspeakers were installed at some of the sites for which Elta supplied the naval protection systems.
Water temperature and salinity affect the detection ranges of sonar systems. Background noises such as the noise generated by sewage pipes emptying into the sea, close to the shore, also have an effect. “When we install a naval protection system, we take into account all of the environmental conditions, so as to enable detection under all circumstances,” Agadi says.
Elta also offers interesting combinations associated with IAI’s unmanned capabilities for the maritime medium. One such system involves an unmanned surface vessel fitted with a radar sensor, which can perform routine security operations over many hours around such strategic targets as offshore oil or gas drilling rigs. “The market for maritime installation protection is growing constantly and today, countries and corporations defend maritime installations that were hardly ever defended in the past,” says Agadi.
I like reassuring news like this. However, I would like an explanation about the finer differences between sonar, optic, and radar detectors.