NAVAL APPLICATIONS 1 BACKGROUND - UNDERWATER GLIDERS – FORCE MULTIPLIERS FOR NAVAL ROLES

UNDERWATER GLIDERS – FORCE MULTIPLIERS FOR NAVAL ROLES

4. NAVAL APPLICATIONS 1 BACKGROUND

For naval forces, the threat environment has moved from the “blue water” to “brown water,” or littoral regions, with attention being drawn to “asymmetric threat” and terrorist actions. With this change in emphasis, new capabilities will be required of naval forces in the areas of maritime intelligence, surveillance, and reconnaissance (ISR); oceanographic bathymetric surveys; battlespace preparation; battlespace awareness;

mine warfare; antisubmarine warfare (ASW); special operations and strike support; surface warfare (including interdiction); littoral ASW with emphasis on diesel submarines; and base and port security. These missions, in turn, require focus on integrated, persistent ISR;

command, control, and communications (C3); and distributed, real-time knowledge. The increasing needs arising from the new threats may be alleviated, to a growing extent, by networking sensors and

communications to the greatest possible advantage, and by using unmanned surface vehicles (USVs) and unmanned undersea vehicles (UUVs) as nodes in sensor and communications networks [37].

In the present scenario of shrinking defence allocations and increasing asymmetric threats, there is therefore a need for a paradigm shift in focus from manned to unmanned assets. While manned assets will remain essential for majority of naval roles, unmanned vehicles can reduce their workload and improve their coverage, thus acting as force multipliers.

Initial developments of Underwater Gliders (in 1990s) at WHOI, SIO and University of Washington were all sponsored by the Office of Naval Research of the US Navy. The US Navy’s UUV Master Plan identifies the utility of UUVs for maritime reconnaissance (passive electromagnetic/electro-optical (EM/EO) localization, and indications and warning), undersea search and survey, communication and navigational aids, and submarine track and trail [37].

4.2 POTENTIAL ROLES OF GLIDERS

4.2 (a) Intelligence, Surveillance and Reconnaissance The task of Intelligence-gathering, Surveillance and Reconnaissance (ISR) is one of the primary responsibilities of any naval force. In peace time, this occupies a significant proportion of naval assets. Even with the present-day coverage of satellites, this aspect of naval operations remains a challenge. Submarines are a very useful asset for this important function. The number of platforms available and duration of such surveillance becomes a limitation, resulting in gaps in monitoring.

Underwater Gliders could potentially perform this role by periodically taking a peek on surface, raising an unobtrusive antenna that is a fraction of the size of a periscope. Gliders could be programmed to remain stationary with antenna hoisted, periodically transmitting data captured (optical or electronic), and correcting for drift in position by taking a plunge to head towards a new location. A pack of Gliders could thus monitor a harbour or choke point on continuous basis.

4.2 (b) Anti-Submarine Warfare

Anti-Submarine Warfare (ASW) remains one of the major challenges in naval technology, with submarines usually staying a step ahead of detection techniques in the race. Locating a submarine in an area is generally more difficult than detecting the passage of a submarine past a choke point (such as exit from harbour). The US has a sophisticated worldwide network of underwater hydrophones forming the SOSUS array, providing continuous acoustic data from a series of strategically located arrays. Underwater Gliders could be valuable for such an application for two basic reasons: low self-noise and low cost. Gliders could be used to patrol not only

Warship 2011: Naval Submarines and UUVs, 29 – 30 June, 2011, Bath, UK

but also undertake methodical search patterns in wider areas of interest. Being virtually undetectable itself, it could enable a continuous, unobtrusive watch to be maintained to detect and localize the presence of any submarine. The information could be passed to shore monitoring stations for deployment of conventional ASW assets (such as Maritime Reconnaisance aircraft) to pursue the contact further, in a hostile scenario. The X- Ray glider’s primary function is to track quiet diesel–

electric submarines operating in shallow-water. It can be programmed to monitor large areas of the ocean. The glider is very quiet, making it hard to detect using passive acoustic sensing [19]. Gliders could multiply manifold the capability of sonobuoys and magnebuoys and transform the very nature of ASW.

4.2 (c) Mine Countermeasure

AUVs inducted into navies so far have been primarily for mine-hunting / minesweeping. The very nature of this activity suggests obvious advantages in using an unmanned platform. Therefore, AUVs such as HUGIN and REMUS have been widely inducted to locate mines in a designated area. However, the endurance of such AUVs that are propelled using batteries is of the order of 24 hours, which is a fraction of the endurance of Underwater Gliders. A glider could potentially be deployed for minesweeping designated channels on a

continuous basis for, say, 6 months at a time. Several glider-borne optical package suites have been demonstrated to aid in MCM by determining the visibility in littoral areas in advance of deployed assets [4].

4.2 (d) Harbour Patrolling

Analogous to their application for intelligence-gathering in enemy harbours, Gliders could be valuable for policing applications in a defensive role. When periodically surfacing and raising its transmitter, a Glider could also capture visual images of the surface scenario.

The advantage of a Glider compared to an Unmanned Surface Vehicle (USV) would again be its endurance, since it is dependent upon buoyancy change for its forward motion in the designated direction. Moreover, by being visible on surface only sporadically, it offers lower probability of detection than a USV.

4.2 (e) Military Oceanography

Military oceanography can be conducted from shore establishments, piloting the gliders remotely instead of sending a big submarine (in the case of covert operations) to undertake temperature and salinity profiles in the ocean. This is the most direct extension of the proven scientific functions for which gliders are presently being used worldwide today.

Table 3 Mapping of potential naval role descriptions to future types of underwater gliders Role Description for Specific Glider Type

Role Categories

Depth-Unlimited Depth-limited Virtual Station- keeping

Level flight hybrids 1. ISR

(a) Surveillance Long-range Coastal - -

(b) Perimeter Patrol In deep water Coastal round-trip patrol

- -

mental assess-ment

Target recci; Virtual periscope

- -

2. ASW

(a) Detection/

Neutralisation

Re-configurable vertical arrays

Patrolling sonobuoys;

neutralization

Re-configurable arrays; Magnebuoys

ASW Patrol

(b) Training Submarine simulator

- - Target simulator

3. MCM - Dumb minehunting

& neutralization

- Mobile MCM,

Pattern search 4. Harbour Patrolling

(a) Perimeter defence In deep-water Coastal defence &

barriers

- -

(b) Sentry - Coastal Trip-wire sentry for

choke points

- 5. Military Oceanography Oceanic

environment characterization

Littoral acoustic profiling

Fixed-point profiling

Seafloor mapping

6. Payload Delivery Long-range clandestine delivery

Delivery of ordnance (mines, charges, etc.) in hostile littorals

Mother vehicle for delivery of AUVs to search/ Patrol areas; Assistance for terminal homing of long-range torpedoes.

Warship 2011: Naval Submarines and UUVs, 29 – 30 June, 2011, Bath, UK

Gliders are scalable, and as mentioned earlier, larger gliders offer certain advantages in transport efficiency.

Such large gliders could potentially undertake delivery of ordnance as well as static sensors, in situations where delivery time is not required in a matter of hours or days.

4.2 (g) Correlation of Roles to Glider Types

Depending upon the chosen role, glider design may be oriented towards that particular function. A study [27] for the US Navy categorises potential classes of gliders as follows:-

x Depth-unlimited: Similar to ‘legacy’ gliders, with deep zigzags.

x Depth-limited: Flat glide slopes and higher cruise speeds compared to ‘legacy’ gliders; similar to

‘Flying Wing’ design.

x Virtual station-keeping: Hovering/ anchoring/

bottoming capability, with adequate thrust to counter ocean currents.

x Payload Delivery: Combination of deep-water and depth-limited operational capabilities.

x Level Flight Hybrids: Glider provided with alternative thruster, offering level flight capability when necessary.

Based on the above categorization of types of gliders, their specific potential naval roles have been are summarized in Table 3.

4.3 TRIALS UNDERTAKEN

Legacy gliders have participated in various US Naval exercises (e.g. RIMPAC-04, TASWEX-04). The first launch of an underwater glider from a submarine was in November 2006. A Slocum Glider was launched with the aid of Navy divers from the Dry Deck Shelter onboard USS Buffalo (Los Angeles class SSN). The Glider gathered and transmitted information for five days in an area off the Southwest coast of Oahu, Hawaii. For retrieval, it was envisaged that the Glider would be located via GPS and divers would retrieve it and bring it aboard [38].

In January 2011, an exercise was conducted by the Office of Naval Research (ONR) of the US Navy at the Southern California Anti-Submarine Warfare Range (SOAR) to analyze the performance of near-real-time passive acoustic detection, classification, and localization systems integrated onto a set of autonomous platforms, including buoyancy-driven underwater gliders (Z-Ray, Seaglider, Slocum glider), autonomous surface platforms, and profiling floats, to monitor marine mammal calling activity [23]. This programme dates back to 2007, when ONR started the Passive Acoustic Autonomous Monitoring (PAAM) of Marine Mammals program to develop near-real-time monitoring systems on autonomous underwater vehicles.

NATO tested three Gliders in the Mediterranean Sea in February 2011 as part of the alliance’s largest annual anti-submarine warfare exercise “Proud Manta 11”. In 2009, a glider of the same type had completed a trans- Atlantic crossing that lasted 221 days. The gliders were at sea for three weeks during the exercise, traveling up to 300 miles, collecting data on water salinity and temperature and relaying it to the shore [39].

4.4 FUTURE PROGRAMMES

In Oct 2010, iRobot Corporation received two contracts from the US Naval Oceanographic Office for delivery of Seagliders and to refurbish, upgrade and support the Navy’s existing fleet of Seaglider systems [40]

Figure 10. PLUSNet concept of operations [41]

The US Navy’s Persistent Littoral Undersea Surveillance Network (PLUSNet) demonstrates multi-sensor and multi-vehicle anti-submarine warfare (ASW) by means of an underwater acoustic communications network [41].

This ONR-funded multi-institution effort is part of a larger research and development framework which aims to provide autonomous detection and tracking of quiet submarines in support of the Navy Sea Power 21 concept. The PLUSNet concept is an Unmanned Systems Approach to Distributed Sensor ASW Surveillance. The network is aimed to be environmentally and tactically adaptive, employing a cable-free sensor network,

Warship 2011: Naval Submarines and UUVs, 29 – 30 June, 2011, Bath, UK

Autonomous processing and Nested communication structure. Gliders are intended to function as mobile sensor nodes in this concept, with tasks to assess environment, detect and redeploy (adapt), acting in coordination as sensor "wolf packs” against intruding submarines. The PLUSNet concept would serve as clandestine undersea surveillance for submarines in far- forward and/or contested waters of order 10³-10⁴ square nautical miles, shallow and deep water, operating for months. In the environmental assessment role, gliders could be used for acoustic assessment, such as for bathymetry, Sound Velocity Profiling, detection ranges.

This data could be used to finalize network cluster topology and fixed/mobile mix of sensors [42]. Sensor deployment of fixed and mobile sensor nodes could be by launching from submarine, ship or USV, in order to deploy for optimum surveillance coverage. Target initial detection would be communicated to network. The mobile asset "wolfpack" would then respond to detection to achieve weapon firing criteria. Persistent surveillance could be ensured through power saving sensing technology and intelligent AUV behaviors. The concept is illustrated in Figure 10.

5. TECHNOLOGICAL CHALLENGES

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