Underwater remote sensing

Abstract

An underwater communications system is provided that transmits electromagnetic and/or magnetic signals to a remote receiver. The transmitter includes a data input. A digital data compressor compresses data to be transmitted. A modulator modulates compressed data onto a carrier signal. An electrically insulated, magnetic coupled antenna transmits the compressed, modulated signals. The receiver that has an electrically insulated, magnetic coupled antenna for receiving a compressed, modulated signal. A demodulator is provided for demodulating the signal to reveal compressed data. A de-compressor de-compresses the data. An appropriate human interface is provided to present transmitted data into text/audio/visible form. Similarly, the transmit system comprises appropriate audio/visual/text entry mechanisms.

1 . An underwater remote sensing system comprising a transmitter for transmitting an electromagnetic signal, a receiver for receiving an electromagnetic signal reflected from an object and determining means for determining the location of the object using the received signal, wherein at least one of the transmitter and receiver is underwater. 
   
   
       2 . An underwater remote sensing system as claimed in  claim 1  wherein the determining means are operable to determine the location of the object using the field strength at three or more receiver positions. 
   
   
       3 . An underwater remote sensing system as claimed in  claim 2  wherein three or more receiver antennas are provided and the determining means are operable to determine the location of the object by comparison of the field strength of the signal received at each antenna. 
   
   
       4 . An underwater remote sensing system as claimed in  claim 2  wherein a single receiver antenna is provided and the determining means are operable to determine the location of the object by comparison of the field strength of the signal received at three or more different receiver locations. 
   
   
       5 . An underwater remote sensing system as claimed in  claim 1  wherein at least one of the receiver and transmitter has a magnetic coupled antenna. 
   
   
       6 . An underwater remote sensing system as claimed in  claim 1  wherein at least one of the receiver and transmitter has an electrically insulated antenna. 
   
   
       7 . An underwater remote sensing system as claimed in  claim 6  wherein each insulated antenna is surrounded by an impedance-matched low conductivity medium, for example distilled water. 
   
   
       8 . An underwater remote sensing system as claimed in  claim 1  wherein the receiver antenna is a directional antenna and the means for determining are operable to use the directionality of the receiver to determine the relative directional position of the reflecting target. 
   
   
       9 . An underwater remote sensing system as claimed in  claim 1  wherein means are provided for varying the frequency of the transmitter signal. 
   
   
       10 . An underwater remote sensing system as claimed in  claim 1  wherein the transmitter and receiver are operable to implement a communications link. 
   
   
       11 . An underwater remote sensing system as claimed in  claim 1  wherein the receiver shares an antenna with the transmitter. 
   
   
       12 . An underwater remote sensing system as claimed in  claim 1  wherein the receiver is remotely located from the transmitter. 
   
   
       13 . An underwater remote sensing system as claimed in  claim 1  wherein the transmitter and receiver are substantially co located. 
   
   
       14 . An underwater remote sensing system as claimed in  claim 1  wherein the location of the object is determined relative to at least one of the receiver, the transmitter or a pre-determined reference. 
   
   
       15 . An underwater remote sensing system as claimed in  claim 1  wherein the transmitted signal has a frequency of below 3 MHz. 
   
   
       16 . An underwater remote sensing system as claimed in  claim 15  wherein the transmitted signal has a frequency in the range of 1 MHz to 3 MHz. 
   
   
       17 . A system for determining underwater electromagnetic signal propagation direction comprising at least one receiver for receiving the electromagnetic signal and determining means for determining the direction of propagation using field strength at three or more receiver locations. 
   
   
       18 . A system as claimed in  claim 17  wherein three or more receiver antennas are provided and the determining means are operable to determine the location of the object by comparison of the field strength received at each antenna. 
   
   
       19 . A system as claimed in  claim 17  wherein a single receiver antenna is provided and the determining means are operable to determine the location of the object by comparison of the field strength received at three or more different receiver locations.