Doppler sonar utilizing period measurement with thresholded receivers

Claim 2

Improved-accuracy doppler sonar equipment of the type in which reflected acoustic energy is evaluated during desired measurement intervals, said improvement comprising signal processing channel means having input means for providing a voltage representative of the instantaneous value of the received acoustic energy, means for detecting the envelope of the signalplus-noise fluctuations of voltages produced by said input means, thresholding means responsive to the output of said detecting means for producing an enabling signal when and only when said envelope exceeds a predetermined threshold, zero-crossing comparator means for producing output pulses when the instantaneous voltage from said input means traverses the zero axis, N-period counter means coupled to receive pulses from said zero-crossing comparator means, means to produce a doppler gate signal in response tO the occurrence of an enabling signal during a measurement interval, means to permit the N-period counter to count pulses only during the occurrence of a doppler gate signal, and means to terminate said doppler gate signal when the N-period counter has responsed to N counts; said equipment further including means responsive to the time integral of the doppler gate signals for determining the net time required for the Nperiod counter to count N pulses during a given measurement interval, and means for displaying the net time so determined in desired units.

Claim 3

The device of claim 1 wherein the equipment is of the Janus type utilizing a pair of azimuthly opposed acoustic beams, and wherein said signal processing channel means includes first and second individual channels responsive to received acoustic energy from first and second beams in said pair respectively, said doppler gate responsive means being coupled to respond differentially to the doppler gate signals from said first and second individual channels, said doppler gate responsive means further being characterized in that such means provides an indication of the difference in net times required for the N-period counters in the individual channels to respond to N counts.

Claim 4

means for displaying a measured time interval in response to the simultaneous occurrence of first and second COUNT COMPLETE signals.

Claim 5

means for displaying a measured time interval in response to the simultaneous occurrence of first and second COUNT COMPLETE signals.

Claim 6

N-period counter means responsive to instances when the received signal traverses a zero reference level, said counter means including means for producing a first COUNT COMPLETE signal when the stored count reaches a preselected value,

Claim 7

N-period counter means responsive to instances when the received signal traverses a zero reference level, said counter means including means for producing a first COUNT COMPLETE signal when the stored count reaches a preselected value,

Claim 8

condition responsive means for producing a first doppler gate for turning on said N-period counter when and only when said threshold comparator produces an enabling signal during a desired measurement interval, said condition responsive means being further arranged to terminate the doppler gate in response to a first COUNT COMPLETE signal from said N-period counter,

Claim 9

condition responsive means for producing a first doppler gate for turning on said N-period counter when and only when said threshold comparator produces an enabling signal during a desired measurement interval, said condition responsive means being further arranged to terminate the doppler gate in response to a first COUNT COMPLETE signal from said N-period counter,

Claim 10

The device of claim 2 wherein the doppler gate responsive means includes a calibrated source of clock pulses and an up-down counter coupled to receive clock pulses through gating means enabled by doppler gate signals from both signal processing channels, and wherein said doppler gate terminating means in each signal processing channel further includes means for providing signals to said doppler gate responsive means when the respective N-period counters have responded to N counts, said gating means including a first gate arranged to apply clock pulses to said up-down counter in a first direction in response to the presence and absence of doppler gate signals in said first and second signal processing channels respectively, and to apply clock pulses to said up-down counter in the opposite direction in response to the presence and absence of doppler gate signals in said second and first signal processing channels respectively, said doppler gate responsive means further including shift register means for reading out and temporarily storing information from the up-down counter in response to the occurrence of signals from the doppler gate terminating means in both signal processing channels, and means for re-setting the up-down counter after the information has been stored in the shift register, said device being still further characterized in that the display means includes means for converting the information stored in said shift register into equivalent units of speed measurement.

Claim 11

The device of claim 3 in which the means for reading information out of said up-down counter further includes means for re-setting the N-period counters in both signal processing channels and means to produce a COUNT READY signal for preparing said doppler gate signal producing means for initiation of a new measuring interval.

Claim 12

means for applying said first doppler gate and said first COUNT COMPLETE signal to said signal combining and display means, E. means for generating a second doppler gate and a second COUNT COMPLETE signal during a desired measurement interval, F. means for applying said second doppler gate and said second COUNT COMPLETE signal to said signal combining and display means, G. said signal combining and display means including:

Claim 13

means for applying said first doppler gate and said first COUNT COMPLETE signal to said signal combining and display means, E. means for generating a second doppler gate and a second COUNT COMPLETE signal during a desired measurement interval, F. means for applying said second doppler gate and said second COUNT COMPLETE signal to said signal combining and display means, G. said signal combining and display means including:

Claim 14

The device of claim 4 in which the equipment is a pulsed doppler system having pulsed transmitter means for launching bursts of acoustic energy and means for producing a range gate signal at a predetermined time after the inception of each burst of transmitted energy, said improvement being further characterized in that each doppler gate signal producing means includes a doppler gate generator and turn-on logic means for preparing said doppler gate generator for the initiation of a doppler gate signal, said doppler gate generator being connected to receive pulses from the corresponding zero-crossing comparator means and output signals from the turn-on logic means, said turn-on logic means being constructed to provide an output signal in response to the simultaneous occurrence of a range gate signal, a COUNT READY signal, and an enabling signal from said thresholding means, said doppler gate generator being Constructed to initiate a doppler gate signal upon the reception of the first pulse from the zero-crossing comparator occurring after the appearance of an output signal from said logic means.

Claim 15

The device of claim 5 further characterized in that each doppler gate signal producinng means includes turn-off logic means for producing an output signal that prepares the doppler gate generator for terminating a doppler gate signal upon the reception by said generator of a pulse from said zero-crossing comparator, said turn-off logic means being constructed to produce an output signal in response to either the absence of an enabling signal from said thresholding means or the appearance of a signal from said terminating means indicating that the corresponding N-period counter has counted N pulses.

Claim 16

The device of claim 6 wherein said envelope detecting means is an R-C circuit proportioned so that the voltage output from said detecting means follows the relatively slow fluctuations of the desired signal in the received energy but averages the relatively rapid noise fluctuation therein.

Claim 17

The device of claim 7 wherein said input means includes transducer means and a tuned limiting amplifier responsive thereto, said amplifier being tuned to pass frequencies within the range of doppler shifts expected for all ship speed conditions, said amplifier further having substantially constant gain for all signal levels up to a limiting value which is greater than said predetermined threshold value.

Claim 18

Sonar doppler equipment for a marine vessel including: A. means for transmitting a beam of acoustic energy outwardly from the hull of said vessel, B. receiving means responsive to reflected acoustic energy returning to the vessel along the path of said beam, C. signal combining and display means, D. a signal processing channel for coupling signals from said receiving means to said signal combining and display means, said processing channel including:

Claim 19

Sonar doppler equipment for a marine vessel including: A. means for transmitting a beam of acoustic energy outwardly from the hull of said vessel, B. receiving means responsive to reflected acoustic energy returning to the vessel along the path of said beam, C. signal combining and display means, D. a signal processing channel for coupling signals from said receiving means to said signal combining and display means, said processing channel including:

Claim 20

The equipment of claim 9 wherein the transmitting means includes means for simultaneously launching beams of acoustic energy in azimuthly opposed directions downwardly and outwardly from the hull of the vessel, and wherein the receiving means includes individual means responsive to reflected energy returning from each of the azimuthly opposed directions, said equipment being further characterized in that the means for applying the secoNd doppler gate and the second COUNT COMPLETE signal includes a second channel identical to said signal processing channel, said signal processing channel and said second channel being responsive to signals received from the first and second of said azimuthly opposed directions respectively.

Claim 21

The equipment of claim 10 wherein the means for measuring a time interval includes first and second AND gates connected to receive doppler gates from said signal processing channel and said second channel respectively and inverted doppler gate signals from said second channel and said signal processing channel, respectively, both of said AND gates being further coupled to receive signals from a clock source, said measuring means further including an up-down counter coupled to receive up-counting and down-counting pulses from said first and second AND gates, respectively, said measuring means still further including register means arranged for temporarily storing information read out of said up-down counter in response to COUNT COMPLETE signals appearing simultaneously in both of said signal processing and second channels, said display means being constructed and arranged for providing a visual indication of the information temporarily stored in said register.