Qinetiq Limited

Sonardyne International Limited

Jonathan James Davies

Stephen Arthur Pointer

Shaun Michael Dunn

Samuel William Downer

Philip Hugh Bennet

Peter James Rapson

Robert James Crook

Darryl Newborough

An underwater acoustic receiver apparatus () comprises an acoustic reflector () and an acoustic device () aimed at the acoustic reflector (). The acoustic reflector () is disposed at a predetermined distance and orientation relative to the acoustic device ().

Underwater acoustic receiver apparatus and method of monitoring a target portion of a water column

Measuring apparatus for providing information on the relative location of a target site which is radiating a target signal that includes a predetermined pulse signal, comprises receiver means for providing a pair of temporally spaced output pulses in response to a single received said predetermined pulse signal and cross-correlation means coupled to said receiver means for cross-correlating said pair of output pulses or signals derived therefrom.

Underwater location apparatus

For digital underwater transmission an information sequence () of digital bits is partitioned into a succession of symbols each comprising n bits where n is equal to or greater than one (2potential symbols), each symbol () is replaced () a corresponding base code sequence of length m bits and the result () is passed to an acoustic transducer after bi-phase modulation () on a carrier. The code has good correlation properties, e.g. a pseudo-random maixmal length sequence, a Gold code or a Kasami code, and the value of m/n is at least (32). Preferably the base sequence is cyclically extended at one or both ends prior to modulation, and Solomon Reed redundancy coding () is initially applied to the information sequence. The output () of modulator () may be prefaced () by a pair of chirp waveforms (). Provision is made for Doppler and multi-path correction.

Communication system for underwater use

In a digital acoustic transmission device in which a digital sequence () is electrically modulated () on a carrier cos &#x3c9;t, the modulated carrier () is prefaced with at least two pulse signals () of known timing relative to each other and to the modulated digital sequence to provide an output signal () for acoustic transmission. The pulse signals indicate to receiver the start of a transmission, and contain Doppler information for resampling the modulated signal prior to demodulation. Where the information sequence is in encoded blocks of equal length, the relationship between successive blocks can be used to update the Doppler information for use with the following block. Channel information can also be derived from the pulse signals and/or blocks for raking the next part of the incoming signal. Preferably the pulse signals have good correlation characteristics. In the embodiments the pulse signals are an immediately successive identical pair of linearly rising chirps.

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Dorchester, United Kingdom

Jonathan James Davies