Saturday, 25 May 2013

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Underwater Pipeline Protection Systems

The DDS Diver Detection Sonar is designed to counter the threat of sabotage and terrorism for naval bases, commercial ports, oil platforms, etc.

Therefore, the system has to perform the following tasks:

Detection of divers, swimmers and swimmer delivery vehicles (SDV) in automatic and manual modes;
Automatic target tracking;
Depth classification of detected targets;
Determination of target data like bearing, range, course, depth, speed, aspect angle, length and level;
Display of processed detection and classification echoes together or alter¬native to acoustic" raw" data;
Display of tactical information on the surveillance display with graphical picture of the protected area, sector coverage of the sonar head, target markers, track symbols, track history;
Interfaces to external communication and radar equipment (option);
Guiding of a patrol boat with the underwater attack force to the location of the intruder;
Initiating an electronic countermeasure (low frequency high power sources).

Mounted on a mooring pile

Divers will be detected in a radius of 700 m around the DDS Node
Note: DDS is also available with a radius range of 2000m

All the DDS hardware is above the waterline in the container.

Only the transmitting- and receiving antennas are mounted on a rotating tube in 5m water depth.

The DDS node data is coupled to the surveillance centre by WLAN.

The Diver Detection Sonar performs a horizontal coverage of 360 Deg (It is a motor driven phased array sonar); the horizontal coverage of the phased array sonar is 98 Deg.

The orthogonal transmitting antenna covers the whole vertical domain due to a transmitting beam former.

The Underwater Node of the DDS covers up to 360° horizontal by maximum 50°/100 ° vertical sector which acquires the water volume to be protected in three dimensions.

By having the flexibility to adjust the size of the vertical sector according to the actual water depth the DDS can be always operated in an optimised form.

The volumetric coverage is given by the Receive and Transmit array. The volume will be scanned elec¬tronically with a total number of 96 horizontal receive beams.

A vertical beam-former generate up to 64 vertical transmit beams, the number of vertical beams needed is a function of water depth, in total the system generates 6144 beams.

Actual ping period display;
Multi-ping integration display;
"Weighted" difference display;
Area of all sonar Underwater Nodes, sector of a single sonar Node, selected magnified area;
Suppression of fix targets (known objects such as sunken ship, piles, water break etc.);
Fix target are "learned" by the system or can be defined by the user as suppression zones.

Further displays are available for the pre-setting of the sonar, the evaluation of the actual sonar propagation and for test purposes.

Additionally the operator can select an area of interest and analyse it by magnifying, the sonar display is also used for menu information in order to pre-set the sonar or for test purposes.

A top-level operating menu headline is shown in the upper part of the display, after selection of an item from the top-level menu a pull-down menu will give access to further operations.

The following Figure shows the typical layout of a sonar display. Typical layout of Sonar Display

Special Characteristics of DDS

Real 3-D sonar;
High horizontal- and vertical resolution;
Low sensitivity against surface and bottom reverberation;
Wide observation sector;
Long detection ranges;
Fully automatic operation.

Operation

The system is working fully automatically, after detection of a target based on the continuous measurement of the ambient noise/reverberation and automatic threshold setting, the detection, tracking, classification, and depth functions are initialised without operator inputs.

These are:

Static signal suppression;
Separation of moving/non moving targets;
Tracking in range and bearing in automatic and prediction mode together with a presentation of the expectation area;
Calculation of course & speed;
Comparison with programmable detection and classification parameters;
Marking of targets, audio/video alarms;
Presentation of new targets.

Besides these fully automatic functions the system can be operated interactively/ manually by the operator, in the manual mode all detected echoes are shown as a colour-coded presentation of the echo levels.

The operator can select or input by menu technique parameters of the displays, such as:

Actual ping period;
Data of the ping-to-ping integration function;
Data of the difference detector/new target detector based on the difference between actual ping period and the ping integration memory;
Data of the Underwater Node status;
Magnifiers (zoom) for analysis.

Depth information and parameters, such as:

Transmission mode CW, FM, pulse length;
Criteria for automatic detection and classification;
Sector scan/full picture scan;

Operator inputs are via:

Pull down menus;
Trackball.

The system is mainly controlled by graphical control with the trackball.

Alarm Levels

For all echoes which exceed the detection threshold a sonar internal tracking (max. 500 channels) and analysis will sort out the echoes with the highest probability to be from a real target such as diver, swimmer or delivery vehicle based on the criteria.

Diver and Swimmer (Parameter set 1)

Moving/Non Moving;
Speed;
Course;
Length;
Depth;
Approaching/Departing;
Initial detection range.

Swimmer Delivery Vehicle (Parameter set 2)

Moving/Non Moving;
Speed;
Course;
Length;
Depth;
Approaching/Departing;
Initial detection range.

Two different parameter sets can be input with upper and lower limits, due to criteria which are met; different alarm levels with audio and video alarms are given.

The detection and classification process runs in the following steps:-

Step 1: Selection and suppression of static signals.

Step 2: Selection of moving echoes within a target strength range, which is of interest for diver, swimmer and swimmer delivery vehicles.

Step 3: Tracking the detected echoes within the defined range and calculation of expectation areas, speed and course, decision between fast and slow moving echoes.

Step 4: Analysis of the track history and speed comparison.

In order to get the best performance with the lowest possible false alarms this alarm logic is user programmable so that optimisation due to experience and test in the original environment is easily possible.

Technical Detail

Performance Characteristics

Detection 3D;
Tracking;
Classification Depth;
Performance Prediction;
Built in Test Equipment (BITE).

Detection Modes
Narrow-band Detection 3D

Horizontal detection sector 96°;
Horizontal beam width 2 ζ-3dB hori. <= 1.0°;
Vertical detection sector max. 50°;
Vertical beam width 2 ζ-3dB vert. <= 1.6°;
Range scales (first 30 m is blanked) 200, 500, 1000, 2000m;
Transmission Pulse type CW or FM;
Transmission frequency 60 kHz;
Frequency band 5 kHz;
Transmission power max. 220 dB;
Pulse length (four steps) 250 µs - 10.0 ms;
Pulse repetition time (depending on range scale) 0.5 - 4 sec;
Receiving beams 96;
Transmitting beams 64;
Bearing accuracy on display (R=400 m, T=-10 dB, Scale= 00 m)<= 0.5°;
Range accuracy on display (R=400 m, T=-10 dB, Scale= 00 m)<= ± 1%.

Target Tracking

This subparagraph describes the target tracking characteristics of the DDS.

Target Tracking Echo

This tracking function is used to stabilise the magnifier window on fixed or moving targets.

Bearing accuracy (R=400 m, T=-10 dB, Scale=500 m) (Root mean square deviation)<=0.5°;
Range accuracy (R=400 m, T=-10 dB, Scale=500 m) (Root mean square deviation) <=±1%.

Target Tracking Position

This tracking function is used to stabilise the magnifier window on fixed targets (Bottom bound).

Number of track channels 16;
Bearing accuracy (R=400 m, Scale=500 m)<=0.5°;
Range accuracy (R=400 m, Scale=500 m) <=± 1%.

Classification

Based on the target image characteristics and image processing techniques; It provides automatic target classification with the possibility of operator intervention and final decision, It discriminates against noise and fish and separates the target class (surface swimmer, diver with close circuit breathing system, diver with open circuit breathing system, SDV, surface boat, etc).

Built-In Test Equipment (BITE)

For automatic fault detection the DDS BITE information is displayed on the operator's monitor. A localisation of faults down to the level of a single PCB and a proposal for repair is given.

Power Supply

Mains Power for Electronics: Nominal Voltage 115 or 230 VAC, 50/60 Hz;
Voltage and frequency tolerances according to the requirements of lEC945;
Operating power consumption (Node) approx. 0.8 kVA.

A silenced water-cooled two cylinder generator in the container (If needed) delivers the power for the system and the air-conditioning.

Type: Honda: Model: EV 3610 Generator;
Power 3.3 KVA;
Voltage control: AVR;
Current max: 15A;
Protection: IP21;
Motor Type: 4cycle-OHV GX 360/2cyl, water cooled;
Power: 8.8KW /12HP;
Noise level: 94dBA;
Weight: 92 Kg.

Sonar Performance

Performance calculations where carried out with the aid of arsTECH Sonar Performance Prediction Model (SPPS)

The Environment Summarised parameters of assumed environment
The warm water high salinity scenario is used to identify the"worst case" limits of the detection ranges; lower temperature and lower salinity would result in longer detection ranges.

Display Presentation

The main operations of the system are performed by means of the Tactical surveillance display (tactical display) or the Sonar detection and analysis display (sonar display)

Tactical Display

In the standard automatic mode the operator is supported by an easy-to-read tactical display. The main items of this display are:

Graphical presentation of the area to be protected (ECDIS);
Sector coverage of the sonar heads, incl. range scales and colour-coded guard zones;
Individual target symbols for sonar contacts (classification symbols) with track history and track number;
Special target symbol for the transponder tracking of a patrol boat;
Picture In Picture (PIP) display for target data;
Picture In Picture (PIP) display for threshold pre-settings.

The tactical display is conceived in such a way that the tactical situation can be interpreted in a glance, especially in alarm situations.

All sonar contacts coming from the automatic detector are displayed in the tactical display. Sonar contacts of moving targets are displayed with track history and track number. For swimmer delivery vehicles (SDV), divers and swimmers approaching special symbols together with a track number are generated and superimposed.

The parameters of each sonar contact can be read from a PIP (Picture in Picture) display on operator's request. The following parameters are shown:-

Course;
Bearing;
Depth;
Speed;
Distance;
Track number.

When a target is detected and its level exceeds a preset threshold and its size and shape on the screen is typical to real target (diver, SDV etc.) the symbol becomes flickering and an audio alarm is set.

Additionally a threshold display shows in which frame the upper and lower limits are set.

Besides the general operating menu headlines time and date are displayed. There are also fault indication and warning hints.

In order to guide a patrol boat easily to the detected target, the boat will use a hand held Direction Unit (option) that presents the tactical situation, boat location relative to target, distance and direction to the target and instructions on best course to approach the target.

Sonar display

In the interactive mode the operator has access to raw sonar data presented in the sonar display. This sonar display is used for the detailed analysis of automatically detected targets or for the detection and classification of targets beyond the limits of the automatic detection and classification function.