Acoustic amplitude-doppler target ranging system

Claim 2

An acoustic amplitude-doppler system for determining the distance to the closest point of approach to a munition and the time of arrival thereat of a moving target, said acoustic amplitude-doppler system comprising an acoustic sensor circuit for sensing moving target sound waves and generating an input amplitude function signal P in response thereto, a differentiating circuit receiving said input signal and developing signals P, P and P, said developed signals representing respectively the first, second and third derivatives of said input signal, a time determining circuit receiving said second and third derivative signals P and P and generating from the times t 2 , t 3 of the zero crossings thereof and from a time interval ratio K, a response indicating the predicted time t c of target arrival at said closest point of approach, and a distance determining circuit receiving (a) a signal having a frequency f o responsive to spectral lines in said moving target sound waves, (b) input amplitude function P and (c) first derivative signal P, and developing therefrom a response indicating the predicted distance d of the closest point of approach of said target to said munition.

Claim 3

An acoustic amplitude-doppler system as defined in claim 1 including comparator means comparing the response d developed by said distance determining circuit with a preselected distance signal d (max) and providing an output in response to the conditions of d being equal to and less than d (max), and an AND gate, said AND gate receiving the response generated by said time determining circuit and the output of said comparator means and outputting a munition fire signal in response thereto.

Claim 4

An acoustic amplitude-doppler system as defined in claim 2 wherein said predicted distance d is developed from (a) the normalized amplitude of said first derivative signal P at times t 2 and t 3 , (b) the frequency f 2 at time t 2 , (c) the frequency f 3 at time t 3 and (d) the change in frequency Δf 32 between times t 2 and t 3 .

Claim 5

An acoustic amplitude-doppler system as defined in claim 3 wherein said time interval ratio K is derived from the equation ##EQU15## and said predetermined distance d is derived from the equation ##EQU16## wherein v a is the sound velocity and f o ≃f 2 .

Claim 6

An acoustic amplitude-doppler system as defined in claim 4 wherein the interval ratio value K is equal to 1.3660.

Claim 7

An acoustic amplitude-doppler system as defined in claim 4 wherein the interval ratio value K is equal to 1.3285.

Claim 8

An acoustic amplitude-doppler system as defined in claim 3 wherein said differentiating circuit comprises a first differentiating operational amplifier receiving said input signal P, a second differentiating operational amplifier receiving the output P of said first differentiating operational amplifier, and a third differentiating operational amplifier receiving the output P of said second differentiating operational amplifier, said time determining circuit comprises a first zero crossing detector receiving the output P of said third differentiating operational amplifier, a second zero crossing detector receiving the output P of said second differentiating operational amplifier, and an up-down counter means receiving the outputs of said first and second zero crossing detectors and outputting the predicted time of arrival response t c , and said distance determining circuit comprises a first divider circuit receiving said input signal P and said first derivative signal P, first and second sample and hold circuits receiving the output P/P of said first divider circuit, a first subtractor circuit receiving the outputs of said first and second sample and hold circuits, filter means receiving said signal having a frequency f o , third and fourth sample and hold circuits receiving the output of said filter means, a second subtractor circuit receiving the outputs of said third and fourth sample and hold circuits, a second divider circuit receiving the output of said fourth sample and hold circuit and the output of said second subtractor circuit, and a third divider circuit receiving the output of said second divider circuit and the output of said first subtractor circuit and outputting a response indicating the predicted distance d.