UNDERWATER TRACKING SYSTEM

• US 3,764,964 A
• Filed: 01/20/1967
• Issued: 10/09/1973
• Est. Priority Date: 01/20/1967
• Status: Expired due to Term

• Current Assignee: Francis P. Finlon, Ralph M. Seeley Jr
• Original Assignee: Francis P. Finlon, Ralph M. Seeley Jr
• Inventors: Seeley, Ralph M. Jr., Finlon, Francis P.
• Primary Examiner(s): Farley, Richard A.
• Application Number:
  US04/615,038
• Time in Patent Office: 2,454 Days
• Field of Search: 340/3T,6R,16R 343/1CL,113
• US Class Current: 367/117
• CPC Class Codes: G01S 3/808 using transducers spaced apart and measuring phase or time difference between signals therefrom, i.e. path-difference systems
• CPC Class Codes: G01S 5/20 Position of source determined by a plurality of spaced direction-finders
• CPC Class Codes: G07C 5/0875 using magnetic data carriers
• CPC Class Codes: Y10S 367/901 Noise or unwanted signal reduction in nonseismic receiving system

Abstract

The apparatus disclosed herein is a submarine based tracking system for tracking one or more independently movable underwater objects each equipped with system synchronized apparatus for transmitting underwater a PRN (pseudo random noise) signal characteristic of that particular object. The submarine is equipped with an array of precisely located hydrophones for sensing the PRN signals, a signal processor, a computer, and a display. The computer is programmed to direct the outputs of both a pair of selected vertically spaced hydrophones and a pair of selected horizontally spaced hydrophones to the signal processor which, in turn, provides to the computer signals indicative of the relative times of reception by the selected hydrophones of the PRN signal emanating from the tracked object. The computer utilizes the aboveindicated reception time indicia to ascertain and provide to the display signals indicative of the spherical coordinates of the location of the tracked object relative to the submarine. The signal processor is described in more detail as including reference signal generators providing a number of PRN signals each similar to that transmitted from the object and differing therefrom by a respective anticipated Doppler shift which would occur within an expected range of closing velocities. The processor further includes circuitry for down shifting the center frequencies of each of the received signals and each of the reference signals. Digital serial cross correlators are provided to obtain a band-pass correlation function for each of the received and reference signal combinations. The processor also includes circuitry for shifting the center frequencies of the carriers of the band-pass correlation functions upwardly to the level of the center frequencies of the hydrophone sensed PRN signals and circuitry for obtaining therefrom the reception time indicia indicated above as being provided to the computer.

Claims

1. Apparatus for tracking underwater objects remote to a vessel comprising:

transducer means adapted to be carried by the object for transmitting an underwater signal of known signature;

a plurality of hydrophones for sensing said underwater signal and each providing a hydrophone output signal, said plurality adapted to be carried by the vessel in an underwater array having a first pair of hydrophones spaced from each other in a first direction and having a second pair of hydrophones spaced from each other in a second direction transverse to said first direction;

signal processing means including a plurality of channels each connected to a respective said pair of hydrophones in said array for receiving said hydrophone output signal thereof, each said channel providing a time differential output signal indicative of the time difference between the respective times of reception of said underwater signal by said hydrophones in said respective pair;

computer means connected to said signal processing means for receiving said time differential output signals thereof for computing and providing therefrom a computer output signal indicative of the bearing of the object; and

display means connected to said computer means for receiving said computer output signal and indicating the bearing of the object.

2. Apparatus for tracking underwater objects remote to a vessel comprising:

transducer means adapted to be carried by the object for transmitting an underwater signal;

a plurality of hydrophones for sensing said underwater signal and each providing a hydrophone output signal, said plurality adapted to be carried by the vessel in an underwater array having a first pair of hydrophones spaced from each other in a first direction and having a second pair of hydrophones spaced from each other in a second direction transverse to said first direction;

reference signal generating means for providing a reFerence signal similar to said underwater signal transmitted by said transducer means;

a first plurality of modulator means each respective connected to receive one of said hydrophone output signals and said reference signal and providing for each said signal a modulated output signal;

digital correlation means connected to receive the said modulated output signals for correlating each modulated hydrophone output signal with said modulated reference signal and providing a band-pass correlation function corresponding to each said hydrophone output signal;

function processing means connected to receive said band-pass correlation functions for providing therefrom for each pair a time differential output signal indicative of the time difference between the respective times of reception of said underwater signal by said hydrophones in said pair;

computer means synchronized with said transducer means and connected to said signal processing means for receiving said time differential output signals thereof, said computer means being adapted for computing and providing therefrom location output signals indicative of the spherical coordinates of the location of the object; and

display means connected to said computer means for receiving said location output signals thereof and indicating the location of the object.

3. Apparatus according to claim 2 wherein said function processing means includes:

a plurality of peak indicating means each connected to said correlation means for receiving a respective said band-pass correlation function and providing a peak output signal when said respective function exceeds a predetermined threshold level;

clock means providing a clock frequency; and

counter means connected to said clock means for receiving said clock frequency and connected to two of said peak indicating means which respectively are connected with the hydrophones in one of said pairs for receiving said peak output signals thereof and providing said time differential output signal for said one pair of hydrophones.

4. Apparatus according to claim 2 wherein:

said reference signal generating means includes a plurality of reference signal generators each generating a Dopplerized reference signal having a respective difference in frequency from that of said underwater signal as transmitted which difference is equivalent to a respective predetermined Doppler shift, each of said predetermined Doppler shifts being within values for a predetermined range of closing velocities between said object and said vessel;

said digital correlation means includes means for correlating each of said Dopplerized reference signals with each of said hydrophone output signals and providing a said plurality of Dopplerized band-pass correlation functions corresponding to each said hydrophone output signal; and

said signal processing means further comprises means connected between said correlation means and said function processing means for receiving said Dopplerized band-pass correlation functions and selecting with respect to each hydrophone output signal the Dopplerized band-pass correlation function having the greatest peak above a predetermined threshold level and directing said selected functions to said function processing means.

5. Apparatus according to claim 2 further comprising:

a second plurality of modulator means each connected between said digital correlation means and said function processing means for receiving a respective said function and for providing to said function processing means a correlation function having a center frequency equivalent to that of the hydrophone output signal received by the corresponding one of said first plurality of modulator means.

6. Apparatus according to claim 5 wherein:

said reference signal generating means includes a plurality of reference signal generators each generating a Dopplerized reference signal having a respective difference in frequency from thaT of said underwater signal as transmitted which difference is equivalent to a respective predetermined Doppler shift, each of said predetermined Doppler shifts being within values for a predetermined range of closing velocities between said object and said vessel;

said digital correlation means includes means for correlating each of said Dopplerized reference signals with each of said hydrophone output signals and providing a said plurality of Dopplerized band-pass correlation functions corresponding to each said hydrophone output signal; and

said signal processing means further comprises means connected between said correlation means and said second plurality of modulator means for receiving said Dopplerized band-pass correlation functions and selecting with respect to each hydrophone output signal the Dopplerized band-pass correlation function having the greatest peak above a predetermined threshold level and directing said selected functions to said function processing means.

7. Apparatus comprising:

sensing means for sensing a remotely transmitted pseudo random noise signal and providing an output signal;

first modulator means connected to said sensing means for receiving said output signal and down shifting the center frequency thereof for providing a modulated output signal;

reference signal generating means for providing a reference signal similar to said pseudo random noise signal;

second modulator means connected to said generating means for receiving said reference signal and down shifting the center frequency of said reference signal for providing a modulated reference signal;

digital correlation means connected to said first and second modulator means for receiving and correlating said modulated output signal and said modulated reference signal and providing a band-pass correlation function;

third modulator means connected for receiving said band-pass correlation function for upshifting the center frequency of said function to one equivalent to that of said output signal received by said first modulator means and providing an upshifted band-pass correlation function; and

peak indicating means connected to said third modulator means for receiving said upshifted band-pass correlation function and providing a peak output signal when a peak in said upshifted band-pass correlation function above a predetermined threshold level occurs.

8. Apparatus comprising:

first and second sensing means spaced apart, each for sensing a remotely transmitted pseudo random noise signal and providing an output signal;

first and second modulator means connected to said first and second sensing means, each said modulator means being adapted for receiving a respective said output signal and downshifting the center frequency thereof for providing a respective modulated output signal;

reference signal generating means for providing a reference signal similar to said pseudo random noise signal;

third modulator means connected to said generating means for receiving said reference signal and down shifting the center frequency of said reference signal for providing a modulated reference signal;

first and second digital correlation means each connected to said third modulation means and to a respective one of said first and second modulation means for receiving and correlating the respective said modulated output signal and said modulated reference signal for providing a respective band-pass correlation function;

first and second peak indicating means each connected to a respective one of said first and second digital correlation means for receiving said band-pass correlation function thereof and providing a peak output signal when a peak in said band-pass correlation function above a predetermined threshold level occurs;

clock means providing a clock frequency; and

counter means connected to said first and second peak indicating means and to said clock means for receiving said peak output sigNals and said clock frequency and providing a time differential output signal indicative of the time difference between the respective times of reception of said peak output signals.

9. Apparatus according to claim 8 further comprising:

fourth and fifth modulator means each connected between a respective said correlation means and a respective peak indicating means for receiving a respective said band-pass function and upshifting the center frequency thereof for providing an upshifted band-pass correlation function having a center frequency equivalent to that of said respective output signal.