referring to fig1 there is shown a vessel , such as a submarine 10 , submerged in an underwater environment 12 to be used as a target for testing various performance characteristics of torpedos 14a - c . torpedo 14a is shown approaching vessel 10 on an aspect angle a . sub . φ , which is measured in a horizontal plane , and with respect to a x , the longitudinal axis of vessel 10 . in order to locate and home in on vessel 10 , torpedo 14a emits an acoustic locator signal 16 , comprising a series of brief , high frequency sonar pulses , of frequency h f , each having a very sharp leading edge . by selectively locating hydrophones h1 - h7 around the hull of vessel 10 , the leading edge of one of the pulses of locator signal 16 will arrive at different hydrophones at times which are detectably different . if d is the distance between any two of the hydrophones which receive a locator pulse , if t is the difference in the arrival times of the locator pulse at the two hydrophones , and if s v is the velocity of sound in water , then the angle a . sub . φ from which the pulse comes is a . sub . φ = tan - 1 √( d / s v t ) 2 - 1 . by comparing the values of a . sub . φ provided by different combinations of hydrophones receiving a locator pulse , the aspect angle of the pulse , relative to vessel 10 , may be determined with great accuracy . by determining a . sub . φ for successive pulses as torpedo 14a approaches vessel 10 , the course or trajectory of torpedo 14a may be closely tracked . hydrophones h1 - h7 are usefully spaced from one another on the order of 250 feet , and may be respectively positioned as shown in fig1 . however , it is to be understood that the practice of the invention is by no means limited either to such spacing or to such respective positionings , and the number of hydrophones may be either greater or less than seven . the outputs of hydrophones h1 - h7 are coupled to a signal conditioner - record system 18 aboard vessel 10 , hereafter described in greater detail . system 18 conditions each hydrophone output and records conditioned outputs , whereby data provided by hydrophones h1 - h7 may be subsequently analyzed , under controlled laboratory conditions . it has been found that the above process of data gathering and subsequent laboratory analysis provides extremely valuable information pertaining to the operation of a torpedo during the testing thereof . referring further to fig1 there is shown torpedo 14b striking or impacting vessel 10 at an impact point i on the hull thereof . upon impact , a very distinctive acoustic wave radiates from point i through vessel 10 , and particularly through the hull thereof . by monitoring the amplitudes of such wave at different hydrophones , in addition to monitoring comparative times of arrival , the location of point i on the hull of vessel 10 may be very accurately determined , by means of the aformentioned recording - subsequent analysis process . it will be noted that whereas the useful information for tracking an approaching torpedo is provided by locator signal 16 , which is of high frequency and narrow range , the useful information for determining impact location is provided by an acoustic impact wave having components in a frequency range which is on the order of 1 khz - 10 khz . system 18 must therefore be capable of conditioning and recording both high frequency and low frequency acoustic data . referring yet again to fig1 there is shown torpedo 14c missing vessel 10 , and passing by over the bow thereof . when analyzing the performance of a torpedo which misses its intended target , it may be very useful or essential to know the location on the target vessel which the torpedo came closest to . such location may be determined with great accuracy by comparing the amplitudes of torpedo motor noise which are detected by different hydrophones , since such noise rapidly decreases with distance . such data is preserved by system 18 for future analysis . it is to be noted that motor noise , the acoustic event employed to monitor torpedo 14c , is in the aforementioned low acoustic frequency range . however , discrete occurrences of such event are not clear enough as torpedo 14c passes by to enable differences in arrival times of such event at different hydrophones to be detected . referring to fig2 there is shown a visual display 20 , comprising a portion of system 18 , which is provided with two rows of light elements , such as light emitting diodes or the like . the upper row comprises a time row , and the lower row comprises an amplitude row , one element in each row corresponding to a different hydrophone h1 - h7 . panel 20 is provided to enable an observer aboard vessel 10 to readily approximate , from a particular pattern of light element illumination , the impact point of an impacting torpedo or the position on vessel 10 to which a passing torpedo comes closest . when a distinctive acoustic event occurs proximate to vessel 10 , the light element in the time row which corresponds to the first hydrophone to receive the event is steadily illuminated , the light element corresponding to the second hydrophone to receive the event slowly flashes on and off , and the third hydrophone to receive the event rapidly flashes on and off . in like manner , the light elements of the amplitude row corresponding to the hydrophones at which the amplitude of an acoustic event is first , second , and third greatest , respectively , are steadily illuminated , are slowly flashed on and off , and are rapidly flashed on and off . generally , to predict closest point of approach ( cpa ) of an approaching torpedo , illumination of the time row is most significant . to determine the impact point of an impacting torpedo , the illumination of both rows is significant and is generally identical or very close . to determine the closest point to the vessel of a torpedo missing the vessel , the illumination of the amplitude row is generally most significant . fig2 shows the illumination of panel 20 which occurs upon the impact of torpedo 14b , and enables a trained observer viewing the panel to readily approximate the impact point , to within a range which may be on the order of feet . panel 20 is provided with a selector switch 22 , which is set to &# 34 ; impact &# 34 ; when impact is being monitored , and which is set to &# 34 ; acoustics &# 34 ; when an approaching torpedo is being monitored . when panel 20 is in its &# 34 ; acoustic &# 34 ; mode , a selector switch 24 may be set to operate panel 20 in either a &# 34 ; sample / hold &# 34 ; mode or a &# 34 ; continuous &# 34 ; mode . referring to fig3 there is shown conditioner - record system 18 comprising two main components , signal conditioner 26 and a multi - channel data recording system 28 , such as an fr1300 ampex 14 - channel tape recorder . signal conditioner 26 is provided with seven data conditioning channels 30 , each receiving the output of one of the hydrophones h1 - h7 . each conditioning channel 30 includes a 20 db to 60 db compression amplifier 32 , for amplifying its received hydrophone output , and a filter 34 , for selectively filtering its received hydrophone outputs , to provide a conditioned output which is recorded as data on one of the channels of recorder 28 . since , as aforementioned , the frequency components of significant acoustic events in torpedo monitoring may be in either a narrow high acoustic frequency range or a wide low frequency range , each conditioning channel 30 must be capable of separately conditioning both high frequency and low frequency information , and of then summing the conditioned high frequency and low frequency information to provide a conditioned output for recording by recorder 28 . the output of each signal conditioner is also coupled to comparator electronics of panel 20 for illuminating light elements thereof to represent acoustic information detected by hydrophones h 1 - h 7 , as hereinbefore described . referring further to fig3 there is shown signal conditioner 26 including a channel 36 for amplifying information provided by a sonar system which is carried aboard vessel 10 , such sonar information being coupled to recorder 28 . conditioner 26 also includes a channel 36 for amplifying audio information coupled thereto from a microphone 38 . microphone 38 is provided to receive comments pertinent to an acoustic event which are made either by an observer of panel 20 , or by one listening to a hydrophone channel or to vessel sonar . since such comments are made upon the occurrence of an event , they may have great value for subsequent laboratory analysis of torpedo performance . a hydrophone h1 - h7 or vessel sonar is selectively listened to , either by means of headphones 40 or speaker 42 , by adjustment of a selector switch 44 . audio information passes thereto through audio amplifier - filter 46 . referring yet again to fig3 there is shown a time code generator 48 , located aboard vessel 10 , coupling a time code signal to recorder 28 . by recording such time code signal , data pertaining to the performance of a torpedo 14 which is provided by hydrophones h1 - h7 may be analyzed in relation to the movements of submarine 10 or other events which are concurrent with torpedo operation . referring to fig4 there is shown a data analysis system 50 comprising recorder 28 , a signal conditioner 52 , and a device 54 , such as a visacorder , for providing a graphic representation of data previously recorded on respective channels of recorder 28 . signal conditioner 52 is similar to conditioner 26 , and includes seven conditioning channels 30 . each channel 30 receives a conditioned output from recording system 28 when system 28 is operated in a reproduce mode , to eliminate tape recorder noise from the received output . the outputs of the conditioning channels 30 of signal conditioner 52 comprise conditioned hydrophone output signals cs1 - cs7 . each signal cs1 - cs7 is coupled through a mixer amplifier 56 to the triggering terminal tr of device 54 , device 54 being activated when a pulse is coupled to its triggering terminal which exceeds a selected threshold . referring further to fig4 there is shown each signal cs1 - cs7 coupled to a different data input terminal di1 - di7 of device 54 , the aforementioned time code signal being coupled from recorder 28 to data input terminal di8 of device 54 . when device 54 is activated , it graphically represents the data received at each of its data input terminals on a readout 58 , which may comprise a strip of photosensitive paper . the above triggering threshold is set so that it is reached when the amplitude of one of the signals cs1 - cs7 corresponds to the amplitude of an acoustic event previously sensed by one of the hydrophones , which was generated by torpedo operation in proximity to vessel 10 . device 54 is therefore activated by a signal corresponding to the output of the first hydrophone to detect such event . by comparing data graphically represented by device 54 after activation , the respective times at which the event arrived at other hydrophones may be readily determined . comparative amplitudes of a signal detected by different hydrophones are also provided by the graphic representation of device 54 , and a concurrent representation of the time code enables rapid determination of the actual time at which a hydrophone detected an event . referring to fig5 there is shown a selected segment of readout 58 . fig5 indicates that , for example , just after a time indicated by the time code signal to be xx01 , an event , such as a torpedo impact , was detected by hydrophone h1 . thereafter , the event arrived at other hydrophones , with diminishing amplitudes . from readout 58 , the differences in arrival times and amplitudes of the event at different hydrophones may be very precisely determined . by employing such information together with a simple triangulation formula , the location of impact of a torpedo on vessel 10 may be determined with great accuracy . as an alternative to visacorder 54 , signals cs1 - cs7 may be coupled to a counting device to determine , to within milliseconds , the differences in arrival times of an acoustic signal at different hydrophones . referring to fig6 there is shown a conditioning channel 30 of conditioner 26 receiving the output of one of the hydrophones , such output being coupled to a preamp 60 for initial amplification , the output of the preamp being coupled to both a high frequency conditioning channel 62 and a low frequency conditioning channel 64 . high frequency channel 62 includes three 12 db filter - compression amplifier stages 62a - c for providing an output centered at a frequency h f which rises and falls at 36 db . channel 62 further includes a high frequency automatic gain control ( agc ) 62d for regulating the gain of stages 62a - c , the output of filter 62c comprising a high frequency conditioned signal h cop , coupled to amplifier 62e . the output of amplifier 62e , h fb , is fed back to agc 62d , the sensitivity thereof being adjustable by means of a 10k resister coupled thereto . in like manner , low frequency channel 64 comprises interconnected compression amplifier - filter stages 64a and 64b and low frequency agc 64c , the output of filter 64b comprising a low frequency conditioned output signal l cop , coupled to amplifier 64d . channel 64 provides a pass band over the range 1 - 10 khz , which rises at 6 db and falls off at 24 db . low frequency automatic gain control 64c regulates the gain of stages 64a and 64b and amplifier 64d in response to a signal l fb , the sensitivity of agc 64c being adjustable by means of a 10k resistor coupled thereto . the high frequency output and low frequency output of amplifiers 62e and 64d , respectively , are coupled to summing amplifier 66 to provide the total conditioned output of a channel 30 . the threshold of agc 62d is usefully set to 1 volt rms , and the threshold of agc 64c is usefully set to 0 . 5 volts rms . by such respective settings , the respective contributions of the low and high frequency channels to the total conditioned output of a channel 30 can be very readily distinguished when the total conditioned output is graphically represented by device 54 . referring further to fig6 there is shown an automatic gain control adjustment 68 , which is provided for setting the attack and release times for both agc 62d and agc 64c . since the principle high frequency acoustic event monitored by hydrophones h1 - h7 is a brief high frequency locator pulse , it is important that attack time , or time required to reset the gain of stages 62a - 62c , be very , very fast , so that high amplification can be provided the instant a locator pulse is detected . at the same time , it is important that the release or recovery time of agc 62d be very short , so that the gains of stages 62a - 62c are diminished just as soon as the locator pulse ends and hydrophones h1 - h7 are only receiving ambient noise . the release or recovery time of agc 62d , set by adjustment 68 , should therefore be on the order of milliseconds . on the other hand , the significant low frequency events monitored by hydrophones h1 - h7 are impact waves and torpedo motor noise . since such events may continue over a period on the order of seconds , it is necessary for adjustment 68 to provide agc 64c with a recovery time on the order of seconds . a high frequency gain adjust signal h ga is coupled from agc 62d to amplifiers 62a - 62c and 62e to control the respective gains thereof . similarly , a low frequency gain adjust signal l ga is coupled to amplifiers 64a - 64b and 64d to control the gains thereof . in addition , signals h ga and l ga are coupled to an electronics package controlling the illumination of panel 20 . the electronics package , not shown , comprises any suitable circuit configuration having the capability of comparing the signals provided by different conditioning channels 30 , and of selecting the three of such signals which are the first to reach the panel electronics and / or which have the greatest amplitudes . the display electronics could , for example , include a configuration of flip - flops and sample / hold circuits , or , alternatively , a selectively programmed microprocessor . referring to fig7 there is shown a modification of the invention which is useful for monitoring the performance of a torpedo 70 during a test which requires that torpedo 60 sink an expendable unmanned target vessel 72 . in such modification , a number of hydrophones h1 - h7 are selectively positioned around the hull of vessel 72 to detect a locator signal or other acoustic information provided by torpedo 70 . the outputs of each of the hydrophones are coupled to a conditioner - recorder 18 which is contained in a buoyant protective container 74 . a coupling 76 detachably joins container 76 to vessel 72 so that upon the impact of torpedo 70 against vessel 72 , container 76 is enabled to break clear of vessel 72 . coupling 76 may comprise , for example , an explosive bolt system activated by impact . container 76 may be subsequently recovered for analysis of data contained within recorder 28 . referring to fig8 there is shown a second modification of the invention , wherein information provided by a torpedo 70 proximate to an unmanned expendable vessel 72 is detected by a selected array of hydrophones , the output of each hydrophone being coupled to a transmitter device 78 which transmits a signal representing the hydrophone output . for example , the hydrophone output could modulate a carrier wave generated by a device 78 . also , each hydrophone and transmitter 78 could comprise a standard sonobuoy . obviously , many other modifications and variations of the present invention are possible in the light of the above teachings , and , it is therefore understood that within the scope of the disclosed inventive concept , the invention may be practiced otherwise than as specifically described .