GB2280750A

GB2280750A - Underwater target tracking system

Info

Publication number: GB2280750A
Application number: GB8426238A
Authority: GB
Inventors: Sidney George Smith
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1983-10-24
Filing date: 1984-10-17
Publication date: 1995-02-08
Anticipated expiration: 2004-10-17
Also published as: GB8426238D0; GB8328391D0; GB2280750B

Abstract

At least three sonobuoys 1 - 3 operate actively in a ranging mode and are deployed around the target 4. The sonobuoys transmit on demand from an aircraft transceiver 6 ranging sonar pulses and detect their respective target echo pulses. The pulse transmission times from the sonobuoys are adjusted such that they arrive simultaneously at the target or in a pre-determined time sequence. The ranging pulses are received by the torpedo 7 and its heading is adjusted so that the difference between the times of reception of the ranging pulses approaches zero or the pre-determined time sequence. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO UNDERWATER TARGET TRACKING SYSTEMS The present invention relates to underwater target tracking systems and particularly, though not exclusively, relates to systems for tracking a target submarine and providing sonar signals to enable a torpedo to steer to within homing range of the submarine.

A known method for attacking submarines from the air includes the use of passive sonobuoys to locate a target submarine and transmit information relating to the submarine's location to an aircraft by a radio link. Active sonobuoys are then dropped in the target zone for target location refinement. Finally, a torpedo is dropped close enough to the target to enable a homing system in the torpedo to guide the torpedo to the target.

Our copending UK patent application No 8316851 discloses an underwater target tracking system which is capable of tracking target submarines and tracking and guiding a torpedo from a point where it enters the water to within homing range of the target.

The present invention provides a further underwater target tracking system which provides underwater sonar signals which form a navigation grid for one or more torpedoes to enable them to steer to within homing range of the target.

According to the present invention an underwater target tracking system includes at least three sonobuoys, transceiver means adapted to receive from the sonobuoys signals which are indicative of the range of the target from each of the sonobuoys and to transmit to the sonobuoys command signals to initiate acoustic ranging pulses such that the pulses arrive simultaneously at the target or in a predetermined time sequence, and guidance means carried by a torpedo and adapted to receive the ranging pulses and control the heading of the torpedo such that the difference between the times of reception of the ranging pulses approaches zero or the pre-determined time sequence.

The transceiver means may be carried in an aircraft, or one of the sonobuoys, or other waterborne or airborne vehicle.

Preferably the signals transmitted by and to the sonobuoys are transmitted on different frequencies or are coded so that the source or destination of the signals can be identified.

The present invention operates to establish a relative navigation grid for the torpedo and to guide the torpedo to the target. The navigation grid is moved continuously relatively to the sonobuoys as the target moves relatively to the sonobuoys.

The invention will now be described, by way of example only, with reference to the schematic drawing which shows three active sonobuoys 1, 2, 3 which have been dropped in a triangular pattern around a target submarine 4. An aircraft 5 carries a transceiver 6 which is adapted to receive radio signals from the sonobuoys and transmit command signals to the sonobuoys. A torpedo 7, which is air-launched, has a guidance system which includes an acoustic receiver 8 for receiving ranging signals from the sonobuoys, a signal processor 11 for deriving guidance signals from the receiver 8, and an inertial gyro 9 having an output torpedo reference heading. The torpedo also includes an acoustic homing head 10, a propulsion system and warhead.

During a first cycle of operation, each of the sonobuoys 1, 2, 3 emitSon a different frequency a sonar ranging pulse on receiption of a command signal from the aircraft transceiver 6, and receive an echo at the sonobuoy frequency from the target submarine 4. The arrival of each echo at the respective sonobuoy is relayed to the aircraft transceiver and the transit time from emission to echo reception for each buoy is found.

In the next cycle the command signals to the sonobuoys are sequenced such that the ranging pulses are triggered by the command signal to arrive simultaneously at the target submarine. As the position of the submarine relative to the sonobuoys changes, the timing of the command signals is continuously varied to maintain simultaneous arrival of the ranging pulses at the target. The ranging pulses arrive at the torpedo receiver 8 at intervals during each cycle of operation whilst the torpedo is at a distance from the submarine. The torpedo is initially held on a constant heading whilst the signal processor 11 receives input from the receiver 8 and compares the time difference between the ranging signals in one cycle with those in a later cycle. The processor derives a heading change signal from the time difference changes.The heading change signal and a heading signal from the gyro 9 are input to a steering control circuit 12 of the torpedo to steer the torpedo onto the changed heading. The heading signal from the gyro is a reference signal only as an absolute heading signal is not necessary.

The torpedo will move along a path towards the submarine as further time difference measurements indicate heading changes.

The actual values of the time differences give a measure of the target range and can be used to initiate further stages in the control of the passage of the torpedo. For example the signal processor may be arranged to guide the torpedo horizontally to within a predetermined range and then provide vertical guidance to the correct depth.

When the distance between the torpedo and the target reaches a predetermined value, the homing head 10 determines the remainder of the torpedo's travel to the target.

In the above embodiment the command signals from the aircraft are sequenced to produce simulteneous arrival of ranging pulses at the target. It will be appreciated that any fixed time sequence may be used by the aircraft transceiver and the torpedo guidance system to achieve the same result.

In the above embodiment three sonobuoys are used in a triangular pattern. It will be appreciated that further sonobuoys may be used to give a degree of redundancy to the system to obviate failure of one or more of the sonobuoys.

Other ranging systems known in the art may be substituted for the ple ranging system described above to provide an antijamming and anti-spoofing capability.

Although the above tracking system is described with reference to a single torpedo, one or more additional torpedoes having guidance means in accordance with the invention could be used simultaneously to improve the chances of hitting the target.

Claims

1. An underwater target tracking system including at least three sonobuoys; transceiver means adapted to receive from the sonobuoys signals which are indicative of the range of the target from each of the sonobuoys and to transmit to the sonobuoys command signals to initiate acoustic ranging pulses such that the pulses arrive simultaneously at the target or in a predetermined time sequence; and guidance means carried by a torpedo and adapted to receive the ranging pulses and control the heading of the torpedo such that the difference between the times of reception of the ranging pulses approaches zero or the pre-determined time sequence.

2. An underwater target tracking system as claimed in claim 1 wherein the transceiver means is adapted to be carried in an aircraft.

3. An underwater target tracking system as claimed in claim 1 or 2 wherein the signals transmitted by and to the sonobuoys are transmitted on different frequencies so that the source or destination of the signals can be identified.

4. An underwater target tracking system as claimed in any one preceding claim wherein the signals transmitted by and to the sonobuoys are coded so that the source or destination of the signals can be identified.

5. An underwater tracking system substantially as described with reference to the accompanying Drawing.