Acoustic, underwater, telemetry system

Abstract

An acoustic, underwater, telemetry system between two vehicles, a free-rung, deep-operating, sonar platform, or Sonaray vehicle, to overcome refraction, and a surface ship to provide processing of the sonar data gathered by the Sonaray vehicle. The telemetry system is required to communicate analog sonar information, digital command to control the platform, and digital information concerning the status of the platform, between the Sonaray vehicle and the surface ship. The Sonaray concept requires more than 32 channels of analog information for sonar data transmission, each corresponding to a particular received azimuthal beam and each having an information bandwidth of 1 kHz. The output of the analog channels consists of raw data from the search sonar. Because of the long range and very high reliability of the transmission required for the status and control channels, sonar processing by cross-correlation is used to search in both range and doppler. Because the arrival time of the telemetered signal at the surface ship differs from the time of transmission from the Sonaray vehicle, a time-determining code is telemetered simultaneously with the analog information from the Sonaray vehicle. A frequency-diversity encoding scheme overcomes the problem of absorption of acoustic energy in seawater by allowing separate signal normalization in each frequency band. A phase-lock loop overcomes the effects of the large doppler shift which normally occurs. Two maximal length shift-register sequences, often called p-n sequences, are used with phase modulation for the digital information.