The evolution of network-centric warfare, which enables enhanced situational awareness, rapid target assessment, and distributed weapon assignment, is dependent upon the geospatial information collated from warship sensors
Warships at sea are humming with inputs from a multitude of sensors. Sensors ensure the survivability of a warship at sea during peace time as well as war. A warship has basic sensors, implying thereby that their outputs are required for practically all operations at sea. These include meteorological sensors, conductivity, temperature and density sensors, ship’s speed sensors or logs, depth sensors or echo sounders and satellite signal receivers. Apart from these, a ship utilises radar, sonar, and communication sensors for its operations.
Meteorological sensors: A warship requires accurate measurement of wind speed and direction, temperature, pressure, humidity and other local environmental parameters. This is required for various tasks including flight operations, gunnery, rocket and missile firings, etc. AGIMET is one of the manufacturers for such systems.
▶ Speed Log: For measurement of a ship’s transversal and longitudinal speed, single and dual axis speed logs as well as dual axis doppler logs, are available. The speed logs provide ship’s speed, drift speed and angle at all times and in any depth. Raytheon Anshutz manufactures some of the popular ship logs. Conductivity, temperature and density (CTD) are used extensively for the measurement of temperature and salinity, and also for deriving parameters of density and speed of sound. Teledyne RDI Citadel CTDs fall under this category.
▶ Expendable Bathythermograph: It is used by a warship to obtain an ocean temperature versus depth profile. It is useful for anti-submarine warfare (ASW) by warships and for anti ship warfare by submarines. Lockheed Martin Sippican has manufactured over 5 million XBTs since the 1960s.
▶ Echo Sounder: Data consisting of the immediate depth and a record of soundings are required for navigation. Kongsberg’s EN 250 is one such navigation echo sounder.
▶ Satellite Signal Receivers for Communication and Navigation: As far as communication systems are concerned, use of satellites is fairly well understood and is common knowledge with deep inroads made by mobile telephony and the Internet. Methods of navigation have changed throughout history. New methods often enhance the mariner’s ability to complete his voyage safely and expeditiously, and make his job easier. Commonly recognised types of navigation methods which involve ‘sensors’ are:
- Piloting: Involves navigating in restricted waters with frequent or constant determination of position relative to nearby geographic and hydrographic features.
- Radio Navigation: Using radio waves to determine position through a variety of electronic devices.
- Radar Navigation: Using radar to determine the distance from or bearing of objects whose position is known.
- Satellite Navigation: Using radio signals from satellites for determining position.
Modern integrated systems take inputs from various ship sensors, electronically and automatically chart the position, and provide control signals required to maintain a vessel on a preset course. With the advent of automated position fixing and electronic charts, modern navigation is almost completely an electronic process. The mariner is constantly tempted to rely solely on electronic systems. But electronic navigation systems are always subject to failures, like user mistakes, multipath interference, satellite and receiver clock errors, orbit errors, satellite geometry, atmospheric interference and “selective availability by intentional degradation” (limits accuracy of satellite signals) of the GPS system by the nation operating the satellites.
Thus, with convergence of sensors on board through integration we see that geospatial information has now become the cornerstone of not only navigation but also a host of other operations such as precision weapon firings and weather predictions, etc. For better appreciation of major sensors, a brief description of radar, sonar and communication systems is provided in succeeding paragraphs.
Radar is used in a range of diverse applications in the civil and military field. The applications include, weather sensing, air traffic control, navigation, target detection, acquisition and tracking, missile and gun direction, airborne systems, research and so on. Military radars can be classified in many ways. They can for instance be based upon the type of platform, i.e. land-based, ship-borne or air/space-borne; or be mission-based for example, early warning, tracking, fire control, weather, etc; or they may be classified based upon radar characteristics like wave form, frequency used, type of antenna, etc. Most prevalent classification is according to frequency or waveform utilised.
Radar technology has largely kept pace with the miniaturisation as well as digitisation of electronic components. It has also been possible for the radar designers to meet the changing multi-mission requirements of modern naval warfare post the cold war. Today, by using single multi-function radar, a ship can track and attack emerging fast cruise missile and aircraft threats, ballistic missile attacks, swamp attacks by fast small craft in littorals and carry out various missile and gunfire surface warfare functions. The versatility and adaptability of the radar technology has thus ensured its continued relevance to the naval designers and war fighters.
Specific types of radars
Stealth Radars or low probability of intercept (LPI) radars: LPI radars transmit weak signals, which are difficult to detect by an enemy intercept receiver. The LPI radars are continuous wave, wide bandwidth radars emitting low power signals. This makes LPI radars difficult to detect by passive radar detection systems. Such radar is used in Super Hornet aircraft of the US Navy.
2D, 3D, and 4D Radars: A 2D radar provides range and azimuth information about the target. 3D radar, in addition provides the elevation information. An example is AN/SPY-1 phased array radar on Ticonderoga class of guided missile cruisers.
4D radar is Pulse-Doppler radar: Capable of 3D functions and determines a target’s radial velocity as well. This type of radar has great applicability in defence, since it can detect targets by removing hostile environmental influences such as electronic interference, birds, reflections due to weather phenomenon etc. TRS-4D surveillance radar with Active Electronically Scanned Array (AESA) technology is in use by the German Navy.
An example of good radar is Raytheon’s AN/SPY-5, which is an X-band multi-tracking, target-illuminating system for surface combatants that can simultaneously search, detect, and precisely track multiple surface and air threats. A single radar system consists of three 120-degree beam faces providing full 360-degree azimuth coverage. The mission capabilities include low-altitude horizon search; focused volume search; surface search; missile and surface gunfire control; simultaneous threat illumination; and missile midcourse guidance and terminal homing. SPY-5’s size, weight, and overall self-defense capabilities make it equally well suited for largedeck aircraft carriers and amphibious assault ships as well as corvettes.
Radars in Indian Navy
The Indian Navy has various types of indigenous and imported radars. Among the indigenous radars, it has L Band surveillance radar RAWL MK II &III; F Band combined warning and target indication radar RAWS 03 Upgrade, 3D surveillance radar Revathi and navigation radar APARNA. Among the imported radars, it has a mix of radars from both the east and the west. Some of the imported radars are MF-Star 3D phased array, MR-760 Fregat M2EM 3-D, MR-90 Orekh fire control, Signaal D Band, MR-310U Angara air surveillance, MR-775 Fregat MAE air surveillance, Garpun-Bal fire control, MR-352 search etc. The P8i Maritime patrol aircraft, which was recently delivered to India, will be operating AN/APY-10 multi function, long-range surveillance radar capable of operating day and night under all weather conditions. It provides mission support for intelligence, surveillance and reconnaissance (ISR), anti-surface and anti-submarine warfare. It has both synthetic aperture radar (SAR) and inverse SAR capability. The Inverse SAR can detect, image and classify surface targets at long ranges.
Sonar can be passive or active type depending upon whether it only listens to sound signals or it sends and receives the reflected echo and processes it for information. Active sonar is similar to radar in that while it allows detection of targets at a certain range, it also enables the emitter to be detected at a far greater range, which is undesirable. Use of active sonar is generally limited to surface ships, aircrafts, helicopters, since it compromises the location of the host platform. Passive sonar has the advantage of longer target detection range and anonymity.
Sonar systems have benefited enormously with the advances in digital electronics, and signal processing. Many a algorithms applicable to radar systems have been adapted in sonar. Use of synthetic aperture methods in sonar has increased the quality of image and robustness of the system. Use of multiple transducer sensors and sophisticated beam forming techniques adapted from improvements in target detection in radar has yielded similar benefits in sonar.
Thales Underwater Systems has developed and produced Sonar 2087. It has been designed to be a variable depth, towed active and passive sonar system that performs in conjunction with Sonar 2050 bow-mounted active sonar on UK’s Type 23 frigates. Digital technology in signal processing and COTS hardware has been used extensively. It is claimed that S2087 will be suitable for both, littoral environments and deep ocean.
Raytheon has developed the AN/SQQ-90 tactical sonar suite for the US Navy’s DDG 1000-class multi-mission destroyer. It comprises the AN/SQS-61 hull-mounted high-frequency sonar, AN/SQS-60 hull-mounted mid-frequency sonar, and the AN/SQR-20 multi-function towed array sonar and handling system.
Atlas Elektronik will supply Active Towed Array Sonar (ATAS) to the Indian Navy, which will equip the Delhi and Talwar class ships. ATAS would be subsequently manufactured in India under cooperation with BEL.
EdgeTech, has delivered 12 advanced side scan sonar systems (mine warfare) for the Indian Navy.
Indigenous Sonars with Indian Navy
Indigenous sonars held by the Indian Navy are manufactured by Bharat Electronics (BEL). Two important sonars manufactured by BEL are the Advanced Active cum Passive Integrated Sonar System (HUMSA-NG) and the Integrated Submarine Sonar (USHUS).
HUMSA-NG is an advanced active cum passive integrated sonar system to be fitted on a wide variety of Indian Navy platforms such as the Project 17, Project 15A and Project 28 class ships. HUMSA-NG is an advanced version of the HUMSA sonar presently fitted on P16, P15, Ranjit, and Talwar Class of ships. It is designed for enhancing the system performance, reliability, and maintainability. It is capable of detecting, localising, classifying, and tracking sub-surface targets in both active and passive modes. The system provides simultaneous long-range detection in active and passive modes. The sonar is capable of localisation and automatic tracking of up to eight targets in both active and passive modes. The sonar integrates the operation of the UWT and XBT systems. The system is integrated with FCS systems such as IAC MOD ‘C and CAIO for exchange of relevant information.
Integrated Submarine Sonar (USHUS) is used to detect, localise, and classify underwater submerged and surface targets through passive listening, interception of signals and active transmissions of acoustics signals. It has both analogue and digital external system interface. It is modular and rugged in design with upgradeable performance features. The underwater communication system has multiple mode acoustic communication in dual frequency to meet NATO and other requirements, voice, telegraph, data, and message modes of operation. Its obstacle avoidance sonar is a high frequency short range sonar with rectangular transducer array and its transmission covers three sectors of 30° each.
Navies use visual, sound, and electrical means for communications. Telecommunication includes in its ambit transmission, reception, signals, images, sounds, and intelligence information by visual, oral, wire, radio, or other electronic systems. Ships use radiotelephony because of its ease of operation, directness, and convenience. In navy, it is used for communication between shipto- ship, ship-to-shore, shore-to-ship, air-to-ship, ship-to-air, air-to-ground, and ground-to-air. The most important use of radiotelephone is in short-range tactical communication.
Radio communication has become a specialised field of electronics. Naval communication systems vary in complexity depending upon their role, compatibility, and flexibility. Due to scarcity of space on board a ship, the communication equipment is spread across the ship’s compartments; however, it is ensured that the sets are capable of operating separately as well as concurrently. Complex interconnections provide the ability of selectively switching different configurations.
Communication technology developments to provide ever-increasing requirements of multiple bands and bandwidths, foresee a need for large rotating antennas. These pose several problems on board warships like space availability, electromagnetic interference and increase in ships radar signature. The trend is tilting towards development of single unit consolidating antennas and sensors.
US Navy has begun the deployment of wireless link interface technology on board 97 of its ships for maritime interception operations. The wireless system will allow communication directly with boarding teams several miles away. Interdiction units will be able to transmit biometrics data, scanned documents, digital photos, and emails, back to the ship using the data link. The US Navy has successfully tested microwave- based wireless wide-area network (WWAN) between ships to enable incorporation of Long-Term Evolution (LTE) standard, generally referred to as 4G LTE. The LTE network would let sailors on ships receive real-time video streaming from air nodes mounted on helicopters, which in turn would permit officers to make accurate decisions. Oceus Networks is the likely provider of the systems.
Vitavox has been providing the world’s largest navies with military communications equipment since 1933. The audio equipment provided by Vitavox can be used in a variety of applications, both above and below deck as well as above and below surface.
Rohde & Schwarz in Europe was commissioned to design and build a navy-wide communications network encompassing shore stations, corvettes, patrol boats, landing craft of many sizes and with diverse applications, coastal mine hunters, and maritime patrol aircraft (MPA). Tailored voice and data communications solutions have been defined for shipboard internal communications and external line-of-sight (LOS) and beyond-line-ofsight (BLOS) radio communications. A navy-wide military message handling system (MMHS) covers both strategic and tactical communications.
DCNS has developed SySmart, a commercial wireless communications and tracking system. It enables exchange of video, voice, and data wirelessly from anywhere on board a ship using handheld devices. Internet linked video and infrared cameras and other shipboard sensors can be accessed by the sailors. The system is built around existing Ethernet systems and other proprietary wireless networks. It has been successfully tested on French naval ships and is to be incorporated in the next generation of French submarines in 2017.
Communication Systems in Indian Navy
The Indian Navy is using indigenous systems extensively on its warships. Some noteworthy systems already on board warships and scheduled for fitment on ships under production are manufactured by BEL.
- Synchronous Transfer Mode (ATM) Based Integrated Shipboard Data Network (AISDN): It is a multi-services shipboard network designed to converge all voice traffic, real time video and traditional data communications onto a single broadband infrastructure. It integrates various equipment and systems on board namely EW Systems, Radars, Sonars, CAIO (Computer Aided Information Organization), Fire Control Systems, and a number of other equipment for Ship’s Household Data (SHHD). It integrates all sensors, weapons, and communication services onto one single broadband network.
- Composite Communication System (CCS) Mk III: It is a new generation ATM based communication system that provides ship-to-ship, ship-toshore and ship-to-air communication. It is designed as a voice and data integrated network providing connectivity between radio equipment and remote user onboard for accessing and monitoring and control of radio equipment.
- Versatile Communication System (VCS) Mk III: It is a versatile system designed to provide internal communication facilities and display of status of various equipment and systems onboard naval ships. The system is highly flexible and re-configurable and can be configured for all classes of ships.
Future Trend — Consolidated Antennas and Sensors
A warship requires concurrent functioning of various navigation and combat systems. Thus, information flow is necessitated between various systems and equipments, for example, a warship’s navigation and combat systems require information of ship’s course, speed, water depth, and geographical position. The sensors have to feed different systems simultaneously in an integrated manner. This implies an in-tandem functioning of different systems in a coordinated and unified manner. This is a formidable task since systems are highly complex, diverse electronic units sourced from multiple sources with different standards. The integration unit should be able to comprehend the language of different units, extract relevant information, and feed it to systems in the acceptable format. It should have flexibility to integrate upgrades and new equipment.
Thales Netherlands is developing its integrated sensor and communications suite, which will house radio and data– link communication systems, radar and electro-optical subsystems and IFF in a single unit. The US Navy has awarded 18 contracts to develop integration and management technology for radio frequency radar and communications functions. The objective of the advanced multifunction radio frequency concept is the integration of radar, electronic warfare and communications into a common set of apparatus with signal and data processing, signal generation and display hardware.
The profound impact of geospatial technology can be witnessed in maritime domain awareness, command and control elements, operations, telecommunication systems, navigation, and precision targeting. Geospatial technology today is at the core of network centric warfare and warships sensors constitute its elements. In future, with India’s own Indian Regional Navigation Satellite System (IRNSS), fusion with integrated functioning of the national spatial data infrastructure, space-based surveillance, information from unmanned vehicles, sensors from services, would provide unprecedented battle space transparency enabling bearing of tremendous force on the adversary.