Doppler navigation system for nautical vessels

Claim 1

IN A DOPPLER NAVIGATION SYSTEM FOR NAUTICAL VESSELS OF THE TYPE WHEREIN HIGH FREQUENCY SOUND SIGNALS ARE RADIATED IN TWO MUTALLY PERPENDICULAR DIRECTIONS AND THE ECHOES SUBSEQUENTLY RECEIVED ARE MIXED WITH THE RADIATED SIGNALS TO PRODUCE HIGH FREQUENCY DOPPLER SHIFT SIGNALS WHICH ARE REGISTERED IN A COUNTER DURING A GIVEN TIME INTERVAL, THE COMBINATION OF MEANS FOR RADIATING LOW FREQUENCY SOUND SIGNALS ALONG THE SAME TWO DIRECTIONS WHEN SAID HIGH FREQUENCY SIGNALS LOSE CONTACT WITH THE OCEAN BOTTOM BECAUSE OF ATTENUATION LOSSES AND REVERBERATION ECHOES ARE RECEIVED; MEANS FOR PRODUCING LOW FREQUENCY DOPPLER SHIFT SIGNALS INDICATIVE OF THE VELOCITY COMPONENTS OF SAID VESSEL ALONG TWO DIRECTIONS WITH ANY GROSS DRIFT OF THE OCEAN TAKEN INTO ACCOUNT; MEANS FOR DERIVING FROM SAID LOW FREQUENCY DOPPLER SHIFT SIGNALS AND SAID HIGH FREQUENCY DOPPLER SHIFT SIGNALS DRIFT CORRECTION SIGNALS INDICATIVE OF THE GROSS OCEANS DRIFT VELOCITY COMPONENTS IN SAID TWO DIRECTIONS; MEANS FOR CHANGING THE COUNT REGISTERED IN SAID COUNTER BY EITHER ADDING OR SUBTRACTING SAID DRIFT CORRECTION SIGNALS, DEPENDING UPON WHETHER OR NOT THE GROSS OCEANS DRIFT IS IN THE SAME OR OPPOSITE DIRECTION AS THE VESSEL''S MOVEMENT; AND MEANS FOR POSITIONING A PLOTTING BOARD IN TWO MUTUALLY PERPENDICULAR DIRECTIONS IN ACCORDANCE WITH THE CHANGED COUNTS.