Marine object detector

Claim 1

Apparatus for sensing an anomaly in a body of electrically conductive liquid, said apparatus comprising: a first transmitter of first radio wave signals having a predetermined frequency, said first transmitter being operative to broadcast said first radio wave signals through the air adjacent said body of liquid; a first receiving antenna at a predetermined first location for receiving said first radio wave signals through the air from said first transmitter; a second transmitter, connected to said first receiving antenna, for transmitting into said liquid second radio wave signals having the same frequency and modulation as said first radio wave signals, said second radio wave signals being transmitted by said second transmitter with greater power than said first radio wave signals as received by said first receiving antenna, so as to be receivable through said liquid at a predetermined second location; a second receiving antenna, at said second location, for receiving said first radio wave signals through the air from said first transmitter; a third receiving antenna, at said second location, for receiving said second radio wave signals through said liquid from said second transmitter; phase comparator means, coupled between said second and third receiving antennas, for comparing phases of said first and said second radio wave signals as received through said air and said liquid, respectively, and for generating therefrom phase difference representative signals; and phase monitor means, connected to said phase comparator means and responsive to said phase difference representative signals, for indicating changes in phase difference when an anomaly intrudes in a zone of said liquid between said first and second locations.