After the Second World War, the U.S. Navy recognized a need to significantly improve their anti-submarine warfare (ASW) capability. During the war, the German U boats roamed free on the high seas and lurked off the U.S. harbors, virtually undetected except when they were on the surface and close enough to a ship or aircraft to be spotted visually. There-fore, a special study was commissioned that resulted in the Hartwell Report. This discussed, among other things, the phenomenon of acoustic transmission in the ocean and the ability to recognize various types of ships by their acoustic emissions. A national strategy was developed to acquire wide-area undersea surveillance. This became known as the Sound Surveillance System (SOSUS) and the first site was commissioned in 1954. At that time, the extent of the emerging Cold War was not yet fully recognized. Over the years, additional sites were commissioned and the U.S. Navy and some of its closest allies achieved an effective counter to the growing submarine threat.
Through the 1960s and 1970s, while the Cold War was escalating, SOSUS proved to be the force multiplier that gave the U.S. Navy an ASW superiority. Surveillance had been established in both the Atlantic and Pacific oceans, and work was ongoing to field a mobile extension called Surveillance Towed Array Subsystem (SURTASS). SURTASS joined SOSUS in 1984, and the combined name for these two systems became the Integrated Undersea Surveillance System (IUSS). The IUSS continued to be an effective force multiplier right up to the end of the Cold War when the Berlin Wall fell. With the Cold War over and the balance of power shifting, the U.S. Navy refocused ASW efforts to a regional conflict capability. Work by the U.S. Navy in ASW during the 1990s has emphasized warfare in shallow littoral water.
These regions are typically acoustically harsh areas. Over the past few years, they have been studied and considerable progress has been made in understanding the acoustical characteristics of these difficult regions.
The point of this short historical review of undersea surveil-lance is to emphasize how important long range strategic planning is to effective ASW. In most cases, the U.S. Navy made the investment in undersea surveillance to keep ahead of an emerging Cold War threat. A similar situation remains today for many nations. Any country that wants to develop an ASW capability should look closely at the U.S. Navy’s success in undersea surveillance and include it as part of their strategic planning. Surveillance relieves some of the burden on tactical assets (ships, aircraft, etc.) for open ocean search. The tactical assets can then be used more intelligently, and to much better effect, by follow-up prosecution on known threat targets that have already been classified and localized by area surveillance.
With the collapse of the Soviet Union and the relaxation of the continual confrontation with the USSR, the need for strategic and very responsive surveillance in the deep oceans-traversed by nuclear submarines, has diminished. Russia does, however, seem intent on maintaining a very credible nuclear submarine force; therefore, the capability to counter an open-Ocean, highly sophisticated threat must be maintained. [Editor’s Note: Recent U.S. news media reports have indicated Russian submarine activity in the vicinity of Trident bases in both Washington and Georgia.]
Today’s emphasis on ocean surveillance relates to the rest of the world’s (ROW) submarines, a collection of hundreds of conventional boats and several non state–0f-the-art nuclear subs. Within this diverse order of battle are some very troublesome threats which have to be detected and tracked by ocean surveil-lance systems.
The primary ROW subs include export versions of the Russian Kilo class diesel/electric submarine and the German built 209 class. These submarines can conduct very quiet operations while on battery power. Their duration has been significantly improved but is still limited and eventually requires snorkeling which supports detection by surveillance systems.
The conventional submarine is currently undergoing a drastic, perhaps revolutionary, change in design. German manufacturers of the impressive 209 class are now under contract to deliver the initial four units of the new 212 class to the Federal German Navy. The 212 will incorporate Air Independent Propulsion (AIP), and will represent a very formidable challenge for surveil-lance systems. With the number of ROW submarines continually increasing, and the quality improving, surveillance systems tailored to the requirements of the many ROW countries is becoming increasingly difficult.
In addition, the requirements for surveillance systems have shifted considerably, from military-only to surveillance of many activities with a potential adverse impact on a nation’s stability or economy. These activities include illegal immigration, drug trafficking, terrorism, environmental pollution, fishing violations and even piracy. All of these activities involve ships/craft conducting operations in violation of a country’s laws, within the coastal boundaries of the country. Surveillance of a country’s coastal waters and harbors must support timely prosecution of violators. The requirements for detection and recognition of contacts involved in these illegal activities is quite different from that of the traditional surveillance against deep ocean going submarines.
These targets of interest vary considerably from one type of activity to another. Illegal immigration might very well be conducted with a relatively small freighter, large enough to transport dozens of people in rather inhumane conditions. A drastically different craft, however, used frequently in illegal drug activities, is the high speed Cigarette boat. These two examples represent quite different requirements for an undersea acoustic surveillance system because the general acoustic frequency spectrums of interest are quite different. Sound associated with propeller noise-the predominant source for underwater acoustic detection-is at low frequency for the small freighter and at a significantly higher frequency for the Cigarette boat.
In addition, the various illegal activities noted above also require a surveillance system to provide localization/tracking information to support evaluation of suspicious maneuvering. With these detection/recognition and localization/tracking capabilities, a properly implemented undersea coastal surveillance system can prove to be extremely beneficial in countering illegal activities which are economic drains on a nation’s economy.
Today most nations attempt to find threats (both military and non-military) with tactical platforms. Surface ships, maritime patrol aircraft and helicopters are serving as the current method of surveillance. It is very difficult for a country to deploy these assets over large areas for a long duration as the operational costs quickly became prohibitive. Rather, it would be wiser and more cost effective for a country to utilize these precious tactical assets for follow-up prosecution after a threat has been identified and localized by an Underseas Coastal Surveillance System (UCSS).
Coastal surveillance can be used to detect/recognize and localize/track all surface and subsurface contacts within its assigned coverage space. The preferred surveillance might take the form of a sizable area or a specific barrier. In either case, UCSS will perform continuously-every hour of every day. for years. The cost for surveillance per square kilometer per hour by an area system is a fraction of the cost of surveillance using ship or aircraft platforms.
There are a variety of surveillance systems employed. SOSUS has already been mentioned as the first fixed passive system employed to detect, classify and localize submarines. A more recent addition to fixed systems surveillance is the Fixed Distribution Systems or FDS.
The FDS underwater system was built on commercial fiber optic technology to transmit the high data outflow from the sensors. The signal processing or Shore Segment Information Procession System (SSIPS) developed is based on commercial-off-the-shelf (COTS) and Non-Development Item (NDI) computer hardware and reusable software in workstation configurations.
Where permanent installations mounted on the ocean bottom do not provide the flexibility needed to monitor all threat activity. a mobile system that can bring surveillance assets to any area of the world in a matter of days could solve part of this problem. This is the significant advantage of SURTASS, whose detection capability is provided by a deployable towed array mounted on an ocean-going auxiliary ship class ship.
Other U.S. undersea surveillance systems include the Mobile In-shore Undersea Warfare (MIUS) system to be used primarily for port area security in regional conflicts. And, of course, there is now the development of the Undersea Coastal Surveillance System (UCSS) that we are addressing in this paper.
Certainly the U.S. developed surveillance systems have met the free world’s surveillance requirements, but there are also significant offerings from Europe, including systems from Russia, France, England, Germany and Finland.
The first step in building an effective undersea surveillance system, as with any other military equipment, is to understand fully the operational requirements. It is absolutely imperative that all performance requirements of the system be taken into consideration before it is designed. What is the threat to be met? What is the mission? Is the system single purpose or multipurpose? Who is going to use the information from the system and how are they going to use it? What type of follow-up assets, such as aircraft or surface ships, will they be using?
Once the mission requirements are understood, the designer needs to know what the performance expectations are. What probability of detection is wanted, how accurate does localization of the threat need to be, and how responsive from a time-late standpoint must the system be? Is the need for large area surveillance, or surveillance of a specific high value area, or is a barrier or trip wire warning system wanted?
Lastly, the designer needs to understand the acoustic environment where the surveillance is needed. Factors such as depth of water, bottom composition, and surface traffic patterns and density must be known. Ambient noise sources, be they manmade, biological, or weather induced, must be considered and the temperature structure known to account for the Sound Velocity Profile (SVP). Seasonal variations, and transmission loss characteristics, in addition, will all greatly affect system design and ultimately performance. All these factors are then influenced by the various threats and vulnerabilities to the system, such as fishing trawlers, cable landing sites, shore site security, and covertness in installing and operating the surveillance system.
Understanding all these factors is accomplished in a variety of ways. Database reviews of available literature can help focus the efforts. Onsite acoustic and bathymetric surveys of the region will characterize the environment, and modeling will give the ability to analyze various system designs against this data. This is where cost factors come into play (different designs cost different amounts of money), because the reality of all these systems is that they must be affordable and provide optimum performance for the cost. Lastly, before that buy/no buy decision, a demonstration of a small surveillance system in actual waters of interest can ensure that all factors have been considered and give the opportunity to see a system’s actual performance in the water of interest.
Over the past five years, the ability to tailor undersea surveil-lance systems to the specific requirements has been greatly facilitated by the introduction of COTS hardware and software systems into the defense industry. With COTS and an open system architecture, the surveillance system design can effectively support the latest upward technology growth as new capabilities become available and can reduce both spare parts requirements and system maintenance costs.
Traditional Navy surveillance systems have generally relied on specialized signal processing and display hardware. The use of COTS hardware takes advantage of the intense competitive environment of the commercial computer marketplace to ensure that hardware costs are continually dropping while the available performance is increasing. Because commercial standards are effective at ensuring compatibility between vendors, solutions are available from the very smallest to the very largest systems, without changing system architecture or incurring excessive integration costs. A standard UNIX workstation is the UCSS basic hardware unit. Every unit has the same type operating systems, disk drives, CPUs, memory and all other essential components. Individual units are tailored to perform their specific function {signal processing, database, operator workstation, etc.) by adding more disks, video screens, or an array processor card according to the functional requirements of the unit. This standardization simplifies sparing and maintenance. Because these are standard commercial units, upgrades are much easier. Commercial vendors realize that upgrades must be simple and foolproof or they will not be able to sell the larger disk or faster CPU. As an example, in a recent upgrade some systems went from a 2.1 Gb disk to a 10 Gb disk as part of normal maintenance. This operation consisted of simply unplugging the smaller and plugging in the larger. CPU upgrades from 50 Mhz to 90 Mhz were equally easy. Building military surveillance systems from COTS hardware offers the opportunity to profit from the dramatic and continuous improvements in commercial systems.
Software systems also are based on modern object oriented programming techniques. Virtually all of the operator interface programming is done in C + + and built on commercial user interface packages. This object oriented approach facilitates the tight integration of multiple operations on a single object. This object approach enhances the tailorability of the system. Every system is at least slightly different: different mission, different sensors, different acoustic processing, different geography, etc. Tailoring a system is easily accomplished by modifying the internal components of these underlying objects. Each object, whether a geographic display, beam former processing, or acoustic display is individually configurable. These configurations are represented external to the software in a set of system specific configuration files.
The undersea subsystem comprises both acoustic and non-acoustic sensing and data transmission subsystems.
The basic acoustic sensor is comprised of a series of air backed (for shallow water) or oil backed (for deep water) ceramic cylinder hydrophones. The exact number is dependent on the voltage sensitivity required to meet the overall sensor noise goal. If the environment so dictates, non-acoustic sensors such as magnetic and electric field sensors can be employed. The array design is considered once the basic sensor is chosen.
With the need for system protection, usually by burial, the role of the cable route surveyor fundamentally changed. The main objective of the modem survey is to eliminate cable faults and maintain the protection of the surveillance system. Given that trawler fishing damage accounts for a majority of system unavailability. a carefully planned survey and plowability study is the first step to reduce substantially this risk.
By taking all these factors into account, installation of a UCSS can be cost effective and can be carried out in virtually any part of the world.
To date, cable installers have used fairly conventional installation techniques. With the advent of optical systems, cables are becoming smaller. In order to drive down costs, some installation companies have used a vessel of opportunity for cablelaying.
In other situations such as relatively shorter systems, a cableship may transport an entire system on a single load, while a smaller vessel of opportunity may require multiple loads. When selecting the vessel, the number of cable loads and handling, the shore-end requirements, and potential weather delays need to be considered.
It can be seen that to develop and install a UCSS that meets all the military requirements is no trivial matter. It requires a relationship between the provider of the system and its users. All the salient factors must be considered and the appropriate trade offs made. Risks must be reduced as much as possible, and a long term, strategic mentality must be adopted to clearly focus on the value of such an investment.
