Abstract: An acoustic sensor system for the detection, location and classification of sound-generating targets, such as helicopters, from a ship includes a base station aboard the ship, having a radio transmitter/receiver (B-Tx/Rx) and a digital signal processor unit (DSP). A plurality of floating remote stations, which in use are positioned remotely from the ship, are each arranged to carry apparatus including an electrical power source, a radio transmitter/receiver (STx/Rx) suitable for two way communication with the B-Tx/Rx, a control unit, sound detectors, and a data processor (DP). The control unit is responsive to signals transmitted from the B-Tx/Rx and received by the S-Tx/Rx for controlling provision of electrical power for the apparatus. The DP is operative to classify electrical signals generated by the sound detectors in response to the reception thereby of sound signals, and to initiate, dependent upon classification, transmission of data from the S-Tx/Rx to the B-Tx/Rx appertaining to the sound signals.

Abstract: A communication line joint arrangement comprising two parts between which relative rotation and the transmission of at least two channels using electromagnetic energy such as light is facilitated, each part comprising polarising beam splitter means operatively associated with quarter wave plate means, wherein the polarising beam splitter means of the two parts are arranged to pass two orthogonally related polarised input channel signals to the quarter wave plate means associated therewith, so as to produce two corresponding circularly polarised channel signals of opposite directional sense which are transmitted between the quarter wave plate means, across an interface between the parts, so as to produce two corresponding orthogonally polarised output channel signals from the polarising beam splitter means.