Velocity measuring correlation sonar

• US 4,244,026 A
• Filed: 11/06/1978
• Issued: 01/06/1981
• Est. Priority Date: 11/06/1978
• Status: Expired due to Term

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: General Electric Company
• Inventors: Dickey, Frank R. Jr.
• Primary Examiner(s): Gruber, Felix D.
• Application Number:
  US05/957,908
• Time in Patent Office: 792 Days
• Field of Search: 364/565, 343/8, 324/175, 367/89, 367/90, 367/91
• US Class Current: 702/143
• CPC Class Codes: G01P 5/24 by measuring the direct influence of the streaming fluid on the properties of a detecting acoustical wave
• CPC Class Codes: G01S 15/60 wherein the transmitter and receiver are mounted on the moving object, e.g. for determining ground speed, drift angle, ground track

Abstract

The velocity measuring correlation sonar disclosed employs a planar array of receiving transducers spaced in the directions along which velocity components parallel to the plane of the array are to be measured, and includes means for transmitting a series of two or more identical pulses which are separated by a time interval selected in accordance with transducer separation and the estimated velocity components so as to place the expected point of maximum correlation of the echo return from one pulse with that from a following pulse within the boundaries of a set of spatial sample points representing relative spacings between pairs of receiving transducers. Correlation measurements are made corresponding to these relative spacings of the receiving transducers, with each such measurement being treated as a sample of a space-time correlation function of predetermined shape. The location of the peak of this function in each of the directions of interest is estimated by curve fitting techniques, and yields the velocity vector in that direction scaled by the inter-pulse time interval. The velocity component normal to the plane of the array may be derived by estimating the location of the correlation peak as a function of time and/or phase, using similar curve fitting techniques.

Claims

1. Apparatus for measuring the relative velocity of a wave energy source-sensor combination with respect to a field of scatterers separated therefrom by a medium through which the wave energy is propagated, comprising:

(a) a plurality of wave energy transducers included in said source-sensor combination, said transducers having directivity in the general direction of the scattering field and comprising an array of at least two receiving transducers separated from each other by known distances in a plane perpendicular to the major axis of directivity;

(b) means for energizing at least one of said transducers to emit a wave energy pulse train comprising first and second pulses having a predetermined pulse repetition period;

(c) means for sampling simultaneously the echo returns from said scatterer field to the receiving transducers of said array at predetermined sampling intervals;

(d) means for computing a set of measured values of complex correlation using time-delayed samples of echo returns from said first pulse and undelayed samples of echo returns from said second pulse, as sensed at a selected plurality of said receiving transducers, the period of delay of said time-delayed samples being equal to an integral number of sampling intervals and equal to said predetermined pulse repetition period;

(e) means for processing each of said measured values of complex correlation as a sample of a continuous function of position with each such sample being associated with a location equal to the vector spacing between the pair of receiving transducers from which the samples were obtained, and curve fitting such samples to said continuous function to provide an estimate of the location in vector space of the peak value of correlation magnitude; and

(f) means for deriving an output measure of velocity in each of two directions of relative motion by dividing the components of the location of the correlation magnitude peak along each of said directions by twice said predetermined interpulse interval.

2. The method of deriving a measure of the relative velocity of a wave energy source-sensor combination and a field of scatterers separated therefrom by a medium through which the wave energy is propagated, where the source-sensor combination includes as part thereof wave energy emission means and a plurality of wave energy receiving transducers located in a plane normal to the general direction of wave energy emission and with predetermined separation between transducers in the direction or directions along which relative velocity is to be measured, comprising the steps of:

(a) energizing said wave energy emission means to emit in the general direction of said field of scatterers a wave energy pulse train comprising a plurality of pulses having a predetermined pulse repetition period;

(b) sensing the echo returns from said scatterer field to each of said wave energy receiving transducers;

(c) complex sampling the echo return signal from each of said receiving transducers at sampling intervals equal to a submultiple of said pulse repetition period to provide a first set of complex samples;

(d) processing said first set of complex samples through delay means providing a time delay equal to an integer multiple of said pulse repetition period to provide a second set of complex samples delayed with respect to said first set;

(e) presenting to a complex correlator during each of said sampling intervals said first and second sets of samples from each of two or more transducers with the delayed set consisting primarily of echoes from the first pulse and the undelayed set consisting primarily of echoes from the second pulse, and forming as outputs the complex products of members of said first set with complex conjugates of members of said second set, to produce a set of correlation values the magnitude of each of which is associated with a particular pair of transducers and with a particular time delay;

(f) processing at least some of said correlation values as samples of a continuous function of position, the position associated with a given value being determined by the location of the first member of the particular transducer pair from which the complex product was derived relative to the location of the second member of the pair;

(g) curve fitting said samples to the magnitude or real part of said continuous function to provide an estimate of the location in vector space of the peak value; and

(h) dividing the components of the location of the correlation peak along each of said directions by twice said predetermined pulse repetition period, to yield an output measure of velocity in each of those directions.

3. A method for velocity measurement as defined in claim 2 further comprising the step of deriving a measure of relative velocity along the direction substantially parallel to that of wave energy propagation between the source-sensor combination and the scatterer field, by obtaining a measure of phase of the complex correlation at the correlation peak, and converting such phase measure to a time difference from which the desired measure of relative velocity can be derived.

4. A method for velocity measurement as defined in claim 3 wherein said measure of phase at the correlation peak is derived as a weighted sum of complex correlation values near said peak.

5. A method for velocity measurement as defined in claim 2 further comprising the step of deriving a measure of relative velocity along the direction substantially parallel to that of wave energy propagation between the source-sensor combination and the scatterer field, by curve fitting using the real part of said complex correlation values to yield a direct estimate of this velocity.

6. A method for velocity measurement as defined in claim 2 further comprising the step of deriving a measure of relative velocity along the direction substantially parallel to that of wave energy propagation between the source-sensor combination and the scatterer field, by generating sets of correlation values for two or more values of time delay differing from the pulse repetition period by increments equal to small integer multiples of said sampling interval, processing the correlation values as samples of a continuous function of position with position determined by the relative locations of said transducer pair and with the location of one of the pair effectively displaced in the direction of wave energy propagation by an amount equal to the product of the wave velocity times said time delay increment, curve fitting said samples to said continuous function to determine the correlation peak location in said direction, and deriving therefrom an output measure of velocity in that direction.

7. A method for velocity measurement as defined in claim 2 further comprising the step of deriving a measure of relative velocity along the direction substantially parallel to that of wave energy propagation between the source-sensor combination and the scatterer field, by deriving a coarse measure of correlation peak location as a function of time by use of amplitude values and applying a phase-derived measure of correlation peak location as a vernier on said coarse measure.

8. A velocity measuring correlation sonar system comprising:

(a) a plurality of receiving transducer elements disposed in a planar array with at least two thereof spaced in the directions along which velocity components parallel to the plane of the array are to be measured;

(b) pulse transmission means including means for emitting a pulse train comprising at least two identical pulses having a predetermined pulse repetition period;

(c) means for complex sampling simultaneously the echo returns to said receiving transducers at predetermined sampling intervals equal to a submultiple of said pulse repetition period, to produce a first set of complex samples;

(d) time delay means and means for applying said first sample set thereto to produce a second set of samples delayed with respect to the corresponding samples of said first set by a time interval equal to said pulse repetition period;

(e) means for computing a set of measured values of complex correlation using said set of time-delayed samples from an earlier one of said pulses and said set of undelayed samples from a later one of said pulses;

(f) means for processing each of said complex correlation values with each value corresponding to a location representing the vector spacing between the transducer pair from which the samples were obtained, and for curve fitting such samples to the correlation function to thus determine the location in vector space of the peak value of correlation magnitude;

(g) means for adjusting said pulse repetition period for the next following pulse train in approximate accordance with the correlation peak location; and

(h) means for deriving an output measure of velocity in said directions of relative motion by dividing the components of the location of the correlation magnitude peak along each of said directions by twice said pulse repetition period.

9. A velocity measring correlation sonar system as defined in claim 8 further including means for deriving from said set of complex correlation values a measure of the velocity component normal to the plane of the array by locating the correlation peak as a function of time or phase, or both.

10. A velocity measuring correlation sonar system as defined in claim 8 wherein said receiving transducer array comprises at least four transducer elements disposed in a square configuration with each providing both transmit and receive functions.