Abstract:
A dual class amphibious target discriminator distinguishes between waterborne carriers and bottom traversing fording vehicles. The distinction is accomplished by examining the seismic signal produced by a candidate target for significant characteristics unique to the specific targets.

Description:
BACKGROUND OF THE INVENTION 
     There exists a requirement for a device to accurately and quickly distinguish at a remote distance a waterborne object from an object moving along the bottom of the water. This information could be used for tactical advantage to determine the threat level of fording vehicles. Also, a device of this nature could be incorporated into a mine, to provide target selectivity, or to enhance kill probabilities against the different targets by modifying event criteria. The present invention provides the aforementioned device. 
     SUMMARY OF THE INVENTION 
     A dual class amphibious target discriminator is provided which distinguishes, at a remote location, quickly and accurately between an object traversing the bottom of water from a moving waterborne object. A geophone placed on the bottom of the water being crossed converts the seismic signals from aforesaid objects into their representative signals. The representative signals are detected to provide a series of varying width logic pulses. This pulse train is applied simultaneously to a first counter and to a width discriminator followed by a second counter. The first and second counters count the number of pulses occurring during a predetermined period. Whenever either counter reaches a preset count, an output flip-flop is set. This flip-flop retains the output for a set number of periods, should the respective counter not attain the required count level again. The output channel including the width discriminator is indicative of a waterborne object. The other channel responds to bottom traversing targets. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The single FIGURE shows in block diagram form the preferred embodiment of the dual class amphibious target discriminator. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Now referring to the single FIGURE, there is shown geophone 1 placed on the body of water being traversed by a waterborne object or an object moving at the bottom. The geophone (velocity sensor) is conventional and responds to seismic signals from the objects and converts the seismic signals into their representative electrical pulses. The geophone acts as a transducer. The waterborne object could be carriers such as M113&#39;s, LVTP-7&#39;s and LVTP-5 &#39;s. The object moving at the bottom of the water could be snorkeling tanks. 
     The signal from geophone 1 is passed through amplifier 2 and bandpass filter 3 to emphasize the target characteristics. The signal is then applied to a very low conventional threshold (nearly zero) level detector 4. The output of level detector 4 is a series of varying width logic pulses. This pulse train is applied simultaneously to conventional pulse width discriminator 5, which rejects those pulses exceeding a predetermined set width, and to sampling counter 6. Sampling counter 6 counts the number of pulses occurring during a sample interval determined by conventional asynchronous clock 7. The edited pulse train from pulse width discriminator 5 is similarly applied to sampling counter 8, the sampling period of which is controlled by the same clock signal. Flip-flops 9 and 10 are associated with sampling counters 8 and 6, respectively, and both flip-flops receive the same signal from clock 7. 
     Whenever either sampling counter reaches a preset count, an output flip-flop is set. This flip-flop retains the output for a set number of clock periods, should the respective sampling counter not attain the required count level again. The output of the channel including the pulse width discriminator is indicative of a waterborne object (target). The other channel responds to bottom traversing objects (targets). Hence, a prioritizing logic circuit is used to provide final class separation. This is accomplished by output priority logic 11 which is of conventional logic design. The output of the two flip-flops is input to the priority logic which provides a bottom traversing indication when only the bottom traversing flip-flop is set, and a waterborne indication whenever the waterborne flip-flop is set, regardless of the state of the bottom traversing flip-flop. Of course no indication is given when neither flip-flop is set. 
     It is noted that the target discriminator of the present invention will provide at the output of flip-flop 9 a signal indicative of a waterborne object and from flip-flop 6 a signal indicative of a bottom traversing object. The priority logic permits a more sophisticated output signal, however it is not a necessity. Other conventional means in place or priority logic 11 may be substituted. 
     It is emphasized that the discriminator of this invention provides a means of remotely determining the threat level of fording vehicles. This information could be used to tactical advantage. Also, the discriminator could be incorporated into a mine to provide target selectivity, or to enhance kill probabilities against different targets by modifying event criteria.