SLIM LINE TOWED ARRAY (SLTA)
Category : Sim Line Towed Array (SLTA)
Manufacturer :
Detail
Introduction
Detection of surface and sub-surface targets in ‘High Seas’ has always been a challenge due to varying sea / environmental conditions in the area. GIDS/MSL has designed and developed a Slim Line Towed Array Sonar to address the inherent limitation of the ‘Hull Mounted’ SONAR due to own noise and environmental conditions of the sea.
The designed is aimed towards long detection ranges (relevant to the prevailing sea conditions). The SLTA comprises the Wet End sub-system i.e. an Analogue Linear Array towed behind the submarine and the Dry End sub-system which is the onboard processing hardware.
Wet-End Configuration
* DCM - Deck Cable Module
* TCM - Tow Cable module
* AAM - Acoustic Array Module
* VIM - Vibration Isolation Module
* SDM - Snubber Drogue Module
Features
1.
Outer Diameter
Less than 55 mm
2.
No of Acoustic Channels
More than 75
3.
Overall Weight
1,000 kg approx.
4.
Handling Onboard
5-6 men
5.
Installation Procedure
- Simpler
- Allows free movements
6.
Deployment & Recovery
Easy
Dry End
SLTA dry-end is a reliable product from MSL that enables the user to acquire, monitor, process and display acoustic data in real time. The system consists of following major modules.
a. Front End Conditioner Module ( FECM) . The FECM performs amplification of multi-channel analogue acoustic signals from wet end. It performs a multiplexing, analogue-to-digital conversion and then grouping the channels according to wet-end geometry. It provides an adequate dynamic range, anti-aliasing filtering function with variable sampling rate and accuracy. The resulting data from FECM is then transferred for further processing on the DSP cards.
b. Digital Signal Processing Module (DSPM). The DSPM is responsible for signal processing of the digitised data. It performs beam forming, high-resolution spectral analysis, and audio processing for target detection purposes. The DSPM forms beams of signal coming from the wet-end and also performs vernier analysis on selected channel groups. Audio beams are also formed in DSPM and passed to DPM for performing and classification. After signal processing the resultant data is forwarded to DPM for further processing.
c. Data Processing Module (DPM). The DPM receives digitised data from DSP module and then performs post detection processing, involving parameter estimation, and data transformation in accordance with operator requirements for Sonar Display. It performs normalisation, multi-target-tracking and DEMON analysis for target localisation and classification purposes. The output data of DPM is then displayed on the screens running on the MMI machine.
d. Control Processing Module (CPM). The CPM is responsible for overall system synchronisation and message passing among the processing chain modules. It performs event initialisation, performance monitoring and fault localisation.
e. Man Machine Interface Module (MMIM) . This module is responsible for operator interaction and exhibits all the functionality of the SLTA system in the form of displays that operator can manipulate according to the scenario. The major passive displays are broadband surveillance, broadband history, narrowband surveillance, narrowband review, signals analysis, performance monitoring and fault localisation.
MMI Software Characteristics
The MMI is a part of dry end sub system. It provides the operator with the control to interact with the system through displays and input devices. The five octaves are processed simultaneously and their results are displayed on the MMI. Tracking capability is given in the MMI. Provision is given to the operator to listen to the audio.
Broad Band Surveillance
The TA Broadband Surveillance provides a basis for the following functionalities:
* Initial detection i.e. identification of a signal as a possible contact
* Initiation and maintenance of target tracks achieved by tagging it with an OIT (Operator Initiated Track).
* To show the real time behaviour of the contact over short period of time by providing a history of contact motion to allow the operator to predict future movement and possible destination of target.
Fig. 2 SLTA Broadband Surveillance
Broad Band History
The TA Broadband History provides the following functionalities:
* Initiation and maintenance of target tracks achieved by tagging it with an OIT (Operator Initiated Track).
* To show the behaviour of the contact over a long period of time by providing a history of contact motion to allow the operator to predict future movement and possible destination of target.
* Representation of broadband events as indication of signal to noise ratio in selected bands.
Fig 3 Broadband History
Narrow Band Surveillance Task
The SLTA Narrowband provides:
* Narrowband surveillance by providing detection capability of particular tonals generated by some targets (the lines in the frequency spectrum generally generated from rotating machines such as pumps, cavitating propellers, etc.).
* LOFARgrams, FRAZ and Vernier displays for narrowband surveillance and classification.
* A fine frequency resolution (FEW) which offers the capability to carry out the detection at an early stage.
* Retrieval and display of normalized frequency for improved detection and enhanced the display presentation.
* Selectable integration time optimizing the detection range as a function of contact dynamics and signal to noise ratios.
Narrow Band Review Task
The Narrowband Review task provides:
* The octave selected in the surveillance mode as ranges of frequency received from a particular bearing.
* An indication of the frequency region of best signal-to-noise ratio (SNR) for detection and tracking (strong contact, narrow beam).
* The overall distribution of acoustic energy in the ocean.
* A display of the beam at each bearing as a LOFARgram thus giving a series of LOFARgrams atop each other.
* Narrowband Review is used to show the overall acoustic energy in the ocean.
The operator can change/set the display and process parameters for the displayed LOFARs.
Signal Analysis Task
The TA Signal Analysis task provides:
a. Further refinement of the information gained during initial detection using the broadband and narrowband surveillance analysis screens.
b. LOFAR Analysis which includes fine spectrum analysis in each frequency band and very fine spectrum analysis (Vernier) as a classification aid.
c. Vernier display; used to further refine the narrowband classification, for measurements of Doppler shifts, frequency modulation and harmonic families association.
d. Identification of tonal using Vernier display plays an important role in the classification of contact by specifying the type of machinery being used in individual contacts. This categorisation is possible due to the correlation between the signal tonal and machinery noises.
e. DEMON Analysis allows the operator to gauge the number of propellers on the contact identified as well as the shaft rate at which those propellers are running.
f. Demon analysis provides an important matrix to the operator to judge the size of the contact and to determine its overall profile for classification.
lrsa
Fig 4 Signal Analysis
Audio Task
The SLTA Audio task provides the following capabilities:
a. A High fidelity audio channel is provided.
b. The parameter (Bearing, Track, Channel) with which the audio beam is associated can selectable by the operator.
c. TA Audio is the common task which can be invoked from other primary MMI tasks.
The operator is provided with options of allocation of audio channels to headphones, the DRRM and SLTA console. Audio filters can be applied on the audio by specifying a maximum and minimum frequency limit.
Tracking
SLTA tracking is a common task which operator can invoke from other primary MMI tasks. System has provision to carry out tracking in the following three modes:
* Auto. Tracking is carried out automatically in auto mode.
* Manual. Tracking is done by the operator in manual mode.
* Prediction. A third option is to use prediction mode in which the track is generated by predicting the future course of the target with the help of bearing rate.
Documentation
Following documentation will be provided with the product:
* Technical manual
* Schematics and layouts of system
* Operator/User manual
* Maintenance manual
Warranty
The system will have one year warranty after sale.
Training
A comprehensive training course will be designed to train the operators/users for operation and maintenance of the system
Onboard and Depot Spares
Standard spares for onboard and depot inventory would be provided.
