Abstract:
Devices and methods for aiding a large area search for submerged objects such as aircraft. A searcher transmits interrogation signals to be received by a device at the target object. The interrogation signals have a long range relative to that of returned signals. The target device responds with a ping signal modified to be more easily found by means of information contained in the interrogation signal. The information may be inherent in the nature of the received signal or data encoded and embedded by the searching device. The target device may use a microprocessor to do complex operations using the information from the interrogation signal and other information. Detection of a weak ping is facilitated by such means as being beamed in the direction of the interrogation, arriving at a predictable time, or having parameters adapted to values requested by the searcher.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of provisional patent application Ser. No. 61/977227 filed Apr. 9, 2014 by the present inventor. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Present Invention 
         [0004]    The field of the present invention is aircraft safety investigation in conjunction with vehicle navigation and relative location. 
         [0005]    2. Background Concerning the Need and Use of the Current Invention 
         [0006]    Aircraft lost over water are often extremely difficult to locate. Location is important because data and voice information recorded on the vehicle and physical evidence from the wrecked vehicle are essential to investigation of the cause of the loss. Larger aircraft are currently required to carry acoustic pingers attached to their recording devices that are intended to allow searchers to locate not only the recording device but the lost aircraft itself. Because of the vast spaces in large bodies of water such as oceans, the initial discovery of even the approximate location is the crucial step. The search can take a long time and the power source of the pinger is subject to exhaustion before this step is accomplished. Because of limitations concerning space, weight and power conservation the range of pinger devices is limited. This limitation is a major factor in the difficulty of location. 
         [0007]    The current invention is directed to a solution of this difficulty. Because a searcher can use substantial and renewable power resources, it is possible to broadcast a signal from the searcher to the pinger device with much greater ease and at a much greater range than from the pinger to the searcher. Even before the searcher has made any discovery that the pinger is in its neighborhood, the pinger can be enabled to modify the ping signal on the basis of information gained from the receipt of the broadcast interrogation signal. Doing this in a way that increases the ability of the searcher to discover the hard to find ping signal is a solution to this difficult location problem and the principle subject of the current invention. 
         [0008]    This is distinct from just making a more effective pinger, because it works in the phase of the search where one way communication only is established and uses that communication to facilitate discovery. There are many ways the ping signal can be modified for this purpose. Some of them are described in the embodiments disclosed. The most salient ones include timing the ping to arrive at a time predictable by the searcher, beaming the ping in the direction from which the interrogation signal arrived and implementing the ping with parameters requested by the searcher. This last method is important because the searcher with its greater resources may know its own best modes of search and have current information about the search environment. If information based on that is broadcast and received by the pinger device, then the ping can be adapted with the benefit of information available to either the searcher or the pinger. 
         [0009]    There are many kinds of information that can be taken from the interrogation signal for the purpose of determining the best mode of transmitting pings. First, there is the fact of receipt of the interrogation signal itself, distinct from any information about the nature of the signal. This can initiate pinging or wake up portions of the pinger device. This is primarily a way of conserving power to enable a more robust energy budget for powerful pinging and for extending the life of the power source. Second, the ping device can measure parameters of the incoming interrogation signal such as the intensity and the direction of arrival. This has many uses in determining the best mode of pinging. Third, the search device can encode and embed information in the interrogation signal. This can carry useful information about the location of the searcher, time of transmission of the interrogation signal, ping characteristics requested by the searcher, the current search environment and other things known to the searcher. 
         [0010]    Existing systems using transceiver technology often have interactive methods of facilitating communication, but they do not use the ability to broadcast into a large space in an effort to locate a difficult to detect responder having the ability to tailor its response on the basis of the interrogation. They, especially, do not use this technology as the basis of an extended long term search for an object requiring a large number of interrogations from different locations to have a significant chance of being located. 
       Prior Patents to be Distinguished from the Current Inventive Concept 
       [0011]    US Patent Application 2013-0070556 to Huskamp discloses a system for reflecting acoustic signals directed to a sunken aircraft. It contemplates passive reflectors with specific frequency characteristics to allow identification of the reflected signals without use of power allowing unlimited life. If differs from the current invention in not having a signal receiver and a signal transmitter and in not modifying the return signal. 
         [0012]    U.S. Pat. No. 5,582,566 (A) to Imasaka concerns a transponder which returns a signal with a fixed delay. The delay is used to provide an offset to the distance measurement for a device using the transponder. This invention is not concerned with lost or submerged objects and does not vary the return signal. 
         [0013]    U.S. Pat. No. 6,469,654 (B1) to Winner concerns a transponder landing system and discusses a protocol for increasing the accuracy of tracking the transponder. It discusses a “Dual Diversity Antenna System” in the background section wherein a transponder with two antennas returns a signal using only the antenna which receives the stronger interrogation signal. This differs from the current invention in that it is not concerned with lost or submerged objects as herein defined. The purpose is to maintain continuous and reliable communication during maneuvers of the aircraft. The selection of the antenna for response is not a variation of a parameter of the ping signal as herein defined; because the antenna selection is not done to vary the signal in any way, but is done specifically to maintain an unvarying signal despite changes in the attitude of the aircraft. 
         [0014]    U.S. Pat. No. 7,646,330 (B2) to Karr concerns a two way communication system where the remote transponder makes its return signal coherent with the interrogation signal. It describes a wake-up process to periodically listen for interrogations, which is distinct for a low power listening mode. The purpose of this system is to provide reliable two way communication of identification codes and other information with very low power use by the remote device and not to provide initial discovery of the remote device by the interrogating device. It is not concerned with lost or submerged objects as herein defined. 
         [0015]    U.S. Pat. No. 8,624,774 (B2) to De Rosa concerns a device to locate an associated device. It uses a low power listening receiver to wake up the device on receipt of an interrogation. It is not concerned with lost or submerged objects as herein defined. The patent is directed to a method of measuring the relative locations of the device and making this information available to the search device. 
         [0016]    The differences described above between the current inventive concept and the patents cited are only illustrative and there are many other distinctions in each case. 
       Prior Patent for Reference 
       [0017]    The patent in this section is referenced to provide clarity to the use of various technologies used in the embodiments described herein and to provide further enablement in the implementation of those embodiments. 
         [0018]    The patent listed in this section is incorporated herein by reference in its entirety. Furthermore, where a definition or use of a term in a reference, which is incorporated by reference herein, is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply. 
         [0019]    U.S. Pat. No. 4,613,864 (A) to Hofgen describes the use of one way ranging from multiple locations to calculate the relative location of a user device from the signals of multiple satellites. This is the basic technology of GPS systems. The technology is here used in an embodiment to calculate the relative location of a target device to a moving search device on the basis of the receipt of multiple interrogation signals. 
       BRIEF SUMMARY OF THE INVENTION 
       [0020]    The present invention is directed to methods and devices for locating a object lost in a space which is large in comparison to the range of an associated signaling device. The object is submerged in a medium denser than air. A searching device which is looking for the lost object sends interrogating signals from many successive positions which are typically able to be received at long ranges because of the availability of a large or renewable power source such as the power generated by a ship or other vehicle carrying the search device. 
         [0021]    The broadcast search signal when received provides a target device with information about the search device that is attempting to detect a ping signal transmitted from the target device. The information may be inherent in the nature of the interrogation signal, embedded as data in the signal or simply the presence of an interrogation signal. The information may be combined with local sensor information and changed by a local microprocessor, but remains a function of information from the interrogation signal. The ping signal is modified on the basis of this information to allow detection with greater probability or at a greater range. 
         [0022]    The information received by the target device includes signal characteristics such as signal strength and direction. The processing may include decoding embedded location data, combining multiple interrogation signals, calculating direction of signals from phase data and calculation of signal transit times. The modification of the ping signals may include producing signals with parameters requested by the search device, beaming the signal in the direction of the search device, or sending signals timed to arrive in a window predictable by the search device. Certain embodiments may use interrogation information including the mere arrival of an interrogation signal to conserve power by not transmitting ping signals unlikely to be detected. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0023]    The features and advantages of the various embodiments disclosed herein will be better understood with respect to the following drawings in which: 
           [0024]      FIG. 1  is an overall elevation of an embodiment and the situation in which it is employed. It shows a search vessel  40 , a search device  41 , the surface of a large body of water  42 , interrogation signals  43 , a lost object which in this case is a crashed aircraft  44 , the bottom of the body of water  45 , a target device  46 , and a ping signal  47 . 
           [0025]      FIG. 2  is a block diagram of the target device of an embodiment which is suitable for the situation of  FIG. 1 . It shows an interrogation signal  43 , a target device  46 , a ping signal  47 , an interrogation signal receiver  50 , a ping signal transmitter  51 , a power source  52 , transfer of seeker information  53 , and a power control  54 . 
           [0026]      FIG. 3  is a block diagram of the target device of an embodiment which adds a microprocessor. It shows an interrogation signal  43 , a target device  46 , a ping signal  47 , an interrogation signal receiver  50 , a ping signal transmitter  51 , transfer of seeker information  53 , a microprocessor  62 , and control signals  63 . 
           [0027]      FIG. 4  is a block diagram of the target device of an embodiment which adds an absolute clock to the embodiment of  FIG. 3 . It also shows the use of embedded seeker information. It shows an interrogation signal  43 , a target device  46 , a ping signal  47 , an interrogation signal receiver  50 , a ping signal transmitter  51 , a microprocessor  62 , and control signals  63 , an absolute clock  71 , and transfer of embedded seeker information  72 . 
           [0028]      FIG. 5  is an overall elevation of an embodiment and the situation in which it is employed. In this situation a search vessel sends interrogation signals from multiple locations and the target device combines embedded search information from the signals to calculate the relative positions of the target device and the projected position of the search vessel and search device when a ping would be received. It shows search vessels  40 , search devices  41 , the surface of a large body of water  42 , interrogation signals  43 , a lost object which in this case is a crashed aircraft  44 , the bottom of the body of water  45 , a target device  46 , a ping signal  47  and the projected position of the search vessel  80 . 
           [0029]      FIG. 6  shows a block diagram of an embodiment which uses multiple sensors and multiple transducers to determine the direction of an interrogation signal and to direct ping signals toward the source of the interrogation signal. It shows an interrogation signal  43 , a target device  46 , a ping signal  47 , transfer of seeker information  53 , a microprocessor  62 , interrogation signal sensor  81 , a ping signal transducer  82 , an interrogation signal multi-sensor  83 , a ping signal multi-transducer  84 , a multiphase interrogation signal receiver  85 , a ping timing and phase signal  86 , and a multiphase ping signal transmitter  87 . 
           [0030]      FIG. 7  shows a block diagram of an embodiment which uses multiple sensors to determine the direction of an interrogation signal. It has a microprocessor which combines information, which is here seeker information but not embedded seeker information, with information from local sensors to calculate the relative positions of the search device and the target device. It then calculates the transit time of a ping enabling the transmission of the ping to be scheduled to arrive at a predetermined delay from the transmission of the interrogation signal. It shows an interrogation signal  43 , a target device  46 , ping signal  47 , a ping signal transmitter  51 , transfer of seeker information  53 , a microprocessor  62 , control signals  63 , an interrogation signal multi-sensor  83 , a multiphase interrogation signal receiver  85 , an accelerometer  91 , and a pressure sensor  92 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Definitions 
       [0031]    Embedded seeker information, throughout this specification and in the claims, refers to information that is encoded in the interrogation signal by the search device. It may be used by the target device to determine one or more parameters of the ping signal. It may include the time of transmission, location of the search device, ping parameter values known to the search device to be effective in a particular situation, a description of environmental variables, a description of the search device, or other information. 
         [0032]    Interrogation signal, throughout this specification and in the claims, refers to a signal broadcast by a search device or by a device associated with one or more search devices. The signal is intended to inform a target device of the presence of the search device or to pass information to the target device to be used to initiate or modify the transmission of ping signals. An interrogation signal may be implemented by acoustic or electromagnetic waves including visible or invisible light waves. 
         [0033]    Interrogation signal information, throughout this specification and in the claims, refers to information that is embedded seeker information, seeker information, the fact of receipt of an interrogation signal, or a combination thereof. 
         [0034]    Lost object, throughout this specification and in the claims, refers to an object being searched for with an expectation that hundreds or more of interrogation signals from different locations will be required to successfully detect a ping signal in response and whose location is unknown in a region that is substantially larger in at least one dimension than the range at which a ping signal can be detected. 
         [0035]    Microprocessor, throughout this specification and in the claims, includes any computer and non-computer circuitry with a complexity requiring at least 100 logical gates for implementation. 
         [0036]    Parameters of the interrogation signal, throughout this specification and in the claims, are measurements made at the target device of one or more of (a) arrival time relative to a known or estimated transmission time or relative arrival time of different components of the interrogation signal, (b) signal strength, (c) signal direction or (d) other characteristics of the interrogation signal to be used to determine one or more parameters of the ping signal. The fact of receipt of an interrogation signal in itself is specifically excluded in this definition from being a parameter of the interrogation signal. 
         [0037]    Parameters of a ping signal, throughout this specification and in the claims, refers to time of transmission; frequency; pulse timing, length, and shape; embedded data; embedded identification; direction of emission; amplitude; and other characteristics of the signal that may affect the probability of detection, range of detection, or the ease of detection of the ping signal. 
         [0038]    Ping signal, throughout this specification and in the claims, refers to a signal emitted by a target device to be detected by a search device. Successful detection and identification of a ping signal at least approximately locates the target device. After detection of a ping signal the search device may continue to attempt to detect additional ping signals or other search methods may be enabled after the approximate location is determined. A ping signal may be implemented by sound or electromagnetic waves including visible or invisible light waves. 
         [0039]    Seeker information, throughout this specification and in the claims, refers to one or more of embedded seeker information or of interrogation signal parameters, 
         [0040]    Search device, throughout this specification and in the claims, means a device to detect a ping signal. 
         [0041]    Submerged object, throughout this specification and in the claims, refers to an object which is covered by material denser than air which impedes its discovery or location by means more convenient than detecting a ping signal. The material may be water but may also be other continuous or discontinuous, liquid or solid substances such as snow, ice, mud, earth, rock or rubble. It may limit the approach of a search device to areas outside the material and, thereby, require a minimum detection range for successful detection. 
         [0042]    Target device, throughout this specification and in the claims, means a device associated with the searched for object. The target device receives interrogation signals and emits ping signals. 
       DETAILED DESCRIPTION OF THE DRAWING AND CERTAIN EMBODIMENTS 
       [0043]    Referring to  FIG. 1 , an embodiment is depicted in which the lost and submerged object is an aircraft  44  which is located at the bottom  45  of a large and deep body of water with a surface  42 . A search vessel  40  carries search device  41  which emits acoustic interrogation signals  43  to be received by a target device  46 . The target device responds with acoustic ping signals  47  to be received by the search device. The interrogations have a long range because the search vessel can supply a large amount of power for their generation, but the ping signals have a limited range because of the limited power available to the target device. The aircraft is a lost object because its location is unknown and the range of the ping signals is much smaller than the dimensions of the body of water. The aircraft is a submerged object because it is covered by a body of water that prevents its location by longer range and more convenient methods such as visual search or exchange of radio signals. The search vessel moves about the surface to locate the aircraft and if a ping signal is identified the aircraft is discovered to be in a region limited at least by the range of the ping signal and smaller than the entire body of water. 
         [0044]      FIG. 2  is a block diagram of the target device which depicts other details of this embodiment. A interrogation signal receiver  50  located at the target device with a power source  52  receives an interrogation signal  43 . The receiver is equipped with circuitry to measure parameters of the interrogation signal and produces an interrogation signal value  53  which is supplied to power control circuitry  54  controlling the power level of the transmitter  51 . The receiver and transmitter of  FIG. 2  are equipped respectively with suitable a suitable sensor and transducer to receive and emit signals. In one contemplated embodiment depicted in this figure the parameter of the interrogation signal measured is the intensity of the received signal and the power control varies the power level of the ping signal to facilitate target device discovery by the search device while balancing this requirement with the requirement to conserve power usage to extend the life of the power source  52 . 
         [0045]    In this embodiment the circuitry to measure parameters of the interrogation signal is a means to extract seeker information. The interrogation signal value contains seeker information. In some related embodiments the circuitry consists of time measuring counters or clocks with appropriate gates to determine time relationships between different aspects of the signal. In other related embodiments the circuitry consists of measuring devices for physical aspects of the interrogation signal. 
         [0046]    In another embodiment using the components depicted in  FIG. 1  and  FIG. 2 , the ping signal is returned with a preestablished pattern of delays from the receipt of the interrogation signal. This pattern can be used by the search device to distinguish ping signals from other sources of periodic noise. Other embodiments include modulating the interrogation signal with periodic and non-periodic signals which can be detected by the interrogation signal receiver and used to modulate the ping signal with the same modulation or a modulation which is a function of that on the interrogation signal. 
         [0047]    The embodiments listed here are not intended to be inclusive and it can easily be seen that there are many possible ways to modify the ping signal as a function of seeker information extracted from the interrogation signal in order to facilitate detection of the target module by the search device. 
         [0048]    There are other embodiments similar to the one described above where a different parameter of the interrogation signal is measured or a different variation is made to the ping signal. For example, pulse duration of the ping signal may be extended to allow discovery by a search device at a greater range if the interrogation signal has a low intensity. Emission of ping signals may be suppressed or reduced to a low pulse frequency if interrogation signal intensity fails to exceed a predetermined threshold. 
         [0049]    In another embodiment depicted in  FIGS. 1 and 2  the interrogation signal receiver extracts information which is not seeker information. The receipt itself of an interrogation signal is defined above to not be seeker information or a parameter of the interrogation signal. It is defined to be interrogation signal information and is used in this embodiment to determine the timing of ping signals. This allows ping signals to be suppressed, delayed or transmitted with some other parameter chosen to conserve power until interrogation signals are received. This increases the probability that a ping signal would be received by insuring that power is available when the presence of a search device is indicated by the receipt of an interrogation signal. Other information may be combined with the interrogation signal information to make this determination by the target device. 
         [0050]      FIG. 3  is a block diagram of the search device which adds a microprocessor to the components of  FIG. 2 . In a target device  46  an interrogation signal  43  is received by the interrogation signal receiver  50 . The interrogation signal receiver passes seeker information  53  to the microprocessor  62 . The microprocessor determines the values of parameters of the ping signal as a function of the seeker information and passes control signals  63  which will implement these parameters to the ping signal transmitter  51  which emits ping signals  47 . 
         [0051]    In this embodiment the receiver may contain circuitry to measure parameters of the interrogation signal serving as a means to extract seeker information or circuitry to decode digital information encoded in the interrogation signal serving as a means to extract embedded seeker information. In some related embodiments the circuitry consists of time measuring counters or clocks with appropriate gates to determine time relationships between different aspects of the signal. In other related embodiments the circuitry consists of measuring devices for physical aspects of the interrogation signal. In still other embodiments the circuitry comprises a separator to isolate an impeded coded signal from the interrogation signal with a decoder to provide decoded embedded seeker information to the microprocessor. 
         [0052]    In one embodiment corresponding to  FIG. 3 , the interrogation signal contains an encoded request that the target device respond with ping signals of a certain frequency which has been determined by the search device to be relatively free of noise or otherwise especially suitable for ping detection. The interrogation signal receiver is equipped with circuitry to decode this request and pass it to the microprocessor. The microprocessor passes suitable control signals to the ping signal transmitter to emit pings at that frequency. In this way a ping signal parameter is modified as a function of the embedded seeker information in order to increase the probability and range of ping detection. There are contemplated other similar embodiments that receive different requests from the search device and modify different ping signal parameters such a ping signal repetition rate, ping signal duration or complex ping signal structure. These may be applied individually or in combination. In situations where there is a possibility of a signal from a source other than the target device being confused with a ping signal, the search device may request a variation in one or more parameters to eliminate or resolve that confusion. 
         [0053]      FIG. 4  is a block diagram of the target device which adds an absolute clock to the components of  FIG. 3 . In a target device  46  an interrogation signal  43  is received by the interrogation signal receiver  50 . The interrogation signal receiver passes embedded seeker information  72  to the microprocessor  62 . The microprocessor determines the values of parameters of the ping signal as a function of the seeker information and information received from the absolute clock  71  and passes control signals  63  which will implement these parameters to the ping signal transmitter  53  to the ping signal transmitter  51  which emits ping signals  47 . The absolute clock maintains the current time on the basis of a prior synchronization made directly or indirectly with a clock available to the search device. 
         [0054]    In one embodiment, corresponding to  FIG. 4 , the search device encodes the absolute time of emission of the interrogation signal into that signal. This embedded seeker information is received and passed to the microprocessor of the target device. The transit time of the interrogation signal pulse from the search device to the target device is calculated from the difference between the absolute clock times available to the two devices. A ping signal is then scheduled to be transmitted to arrive at the search device at a predetermined delay or at a predetermined absolute time calculated on the basis of equality or another assumed relationship between the transit times of interrogation and ping signals. In this way, the probability and range of ping detection is increased in this embodiment. 
         [0055]    Despite not knowing the location of the target device or the transit time of signals between the target device and the search device, the search device is enabled by the predetermined time for arrival of ping signals to establish a specific time window to expect possible ping signals. Signals arriving outside of that time window may then be rejected as spurious and not genuine ping signals. The search devise is then able to apply increased sensitivity or relaxed filtering criteria of other kinds and still maintain the same ratio of spurious to genuine candidate ping signals. 
         [0056]    Those skilled in the use of signal processing technology will see that the ability to apply a narrow time window to a signal without loss to the signal to be recognized will allow a substantial reduction in the noise obscuring the desired signal and will allow recognition of a signal of substantially less energy. Signal analysis software is here able to apply a narrow time window to the signal with a resulting reduction in signal obscuration by noise. This results in an increase in the range at which a signal has any given probability of detection. 
         [0057]      FIG. 5  adds to the components of  FIG. 1  movement of the search vessel in a way to provide interrogation signals from multiple locations. The search vessel is shown in multiple positions by means of solid lines while transmitting interrogation signals. The search vessel is shown in a projected later position with dashed lines. 
         [0058]    Referring to  FIG. 5 , in one embodiment of the current invention, a search vessel  40  with a search device  41  moves sequentially to multiple positions on the surface of the water  42  and emits at each position an interrogation signal  43 . The interrogation signals contain embedded seeker information including the time and location at which the signal is transmitted. The interrogation signals are received at the target device  46  located at the lost object  44  which is on the bottom of the water  45 . The target device calculates a projected position of the search device  80  at a time when a ping signal  47  is to be scheduled to arrive. 
         [0059]    At least four positions are required from interrogation signals received to calculate the relative location of the target device in the coordinate system used in the interrogation signal embedded information. Four equations can be determined from the four search device positions and the four times of transmission and receipt of the interrogation signals. These equations can be solved to produce the values of four unknown variables. Three of these variables are the relative location of the search and target devices in the three coordinate dimensions of space and one is the offset between the two clocks of the search and target devices. Further details of this type of calculation are given in the referenced U.S. Pat. No. 4,613,864 and are the principal method of implementating the well known global positioning system (GPS) reception technology. 
         [0060]    Referring to  FIG. 3 , this embodiment uses the microprocessor  62  to do the calculation of the positions and to further calculate transit times for the signals, a projected position for the search device and a time to transmit a ping signal to arrive at the search device at a time known to the search device. This information is used to control the transmission time of a ping signal and constitutes the modification of a parameter of the ping signal determined by embedded seeker information from the received interrogation pulses. As described in other embodiments, the ability of the search device to predict the arrival time of the ping signal in a narrow time window allows for detection of the ping signal with greater certainty and at a greater range. 
         [0061]      FIG. 6  is a block diagram of the target device of an embodiment which adds multiple sensors and transducers to the components of  FIG. 3 . Referring to  FIG. 6  an interrogation signal  43  is received by interrogation signal sensors  81  located at the target device  46 . A plurality of the interrogation signal sensors together constitute an interrogation signal multi-sensor  83  which is connected to a multiphase interrogation signal receiver  85 . This receiver extracts relative phase information from each of the sensors and passes that information to the microprocessor  62  as seeker information  53 . In a related embodiment the receiver contains electronic or computer circuitry which produces interrogation signal direction information as a function of the phase differences between the sensors and passes information to the microprocessor thereby constituting a means of extracting seeker information. 
         [0062]    Multiple ping signal transducers  82  are collectively referred to as the ping signal multi-transducer  87 . The sensors and transducers are arranged in locations whose relative coordinates are known to the microprocessor and the processor calculates phase information for use by the transducers to produce a ping signal directed toward the search device. This calculation may be made directly from one set of phase information to the other when the interrogation signal multi-sensor and the ping signal multi-transducer are similarly arrayed in space or may involve calculation of an intermediate set of direction values in the coordinate system of the target device. In a related embodiment not employing a microprocessor, the ping signal transducers may be directly supplied with information extracted from the interrogation signal sensors. The connections passing the ping timing and phase signal  86 , and sources providing phase information to the transducers constitute a means of modifying a parameter, in this case direction of emission, of the ping signal by employing seeker information. The ping signal multi-transducer emits a ping signal  47  that is directed toward the search device, which is thereby increased in intensity in that direction and can be detected at an increased distance between the search device and the target device. 
         [0063]      FIG. 7  is a block diagram of the target device of an embodiment which adds a interrogation signal multi-sensor and local sensors for acceleration and for pressure to the components of  FIG. 3 . Referring to  FIG. 7  an interrogation signal  43  is received by interrogation signal multi-sensor  83  located at the target device  46 . A plurality of the interrogation signal sensors together constitute the interrogation signal multi-sensor and are connected to a multiphase interrogation signal receiver  85 . This receiver extracts relative phase information from each of the sensors and passes that information to the microprocessor  62  as seeker information  53 . 
         [0064]    The microprocessor calculates the direction from which the interrogation signal is received in the coordinate frame of the target device from the relative phases and the known relative positions of the sensors. There is also an accelerometer  91  located at the target device that provides the microprocessor with the direction of the vertical direction established by gravity. This enables the microprocessor to calculate the direction from which the interrogations signal has arrived in a coordinate frame established by gravity. A pressure sensor  92  provides the microprocessor with information sufficient to calculate the depth at which the target device is submerged. In this embodiment the search device is assumed to be on the surface of the body of water and the distance from the search device and thereby the transit time of the signals can be calculated from the depth of the water and the angle from which the interrogation signal arrives with respect to the vertical direction. A ping signal  47  is transmitted by the ping signal transmitter  51  on the basis of control signals  63  at a time to arrive at a predictable delay from the transmission from the interrogation signal based on this transmission time. The search device is thereby enabled to receive the ping signal in a narrow and predictable time window as described in other embodiments with a similar improvement in the ability to detect the ping signal. 
         [0065]    It can be seen that there are many other ways to combine interrogation signal information, seeker information and embedded seeker information with information known at the target device from other sources to modify a ping signal and enhance the probability and range of ping signal detection. The principles and spirit of the current inventive concept are envisioned to apply to all forms of information which are produced by combing the information from the interrogation signal with information which is stored or gained from other sources and with any preestablished protocols. 
         [0066]    While the drawing and the detailed embodiments primarily illustrate the application of this inventive concept to the case of an aircraft lost in the vast spaces of the ocean, it should be appreciated that other objects of search such as persons trapped by avalanches of snow, or mudslides or in collapsed mines may be in similar situations. Devices to aid in their location may be provided working on these principles.