Abstract:
The present invention relates to a sonar method and apparatus of tracking objects underwater. Specifically, the method and apparatus can be used to acoustically track a multitude of objects in a hemispherical volume 360° azimuth and 180° elevation relative to the location of the apparatus. The method and apparatus of the present invention provide four-dimensional, real-time tracking of underwater objects.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a non-provisional of U.S. provisional patent application 60/868,590, filed Dec. 5, 2006, which is incorporated by reference as if fully recited herein. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a sonar method and apparatus for tracking objects underwater. Specifically, the method and apparatus can be used to acoustically track multiple objects in a 360° horizontal and 180° vertical directional zone, with reference to the location of the apparatus. The method and apparatus of the present invention provide four-dimensional, real-time tracking of underwater objects. 
       BACKGROUND OF THE ART 
       [0003]    Conventional methods of tracking underwater objects utilizing sonar technology suffer from several limitations. One method utilizes motorized rotating sonar transducers. This method is limited to two-dimensional tracking of objects in small areas of the water column. Moreover, the utilization of moving parts makes the apparatus expensive and prone to failure. 
         [0004]    An improvement over this method utilizes two orthogonally mounted transducers, producing two intersecting beams. This method is limited to pinpointing of objects in three-dimensions in the small volume of water where the two beams intersect. Moreover, since this method utilizes two sound transmitters of the same frequency, unwanted interference between the two sound waves occurs. 
         [0005]    An improved method utilizes a multi-beam sonar comprised of a multitude of parallel beams in one direction together with a multitude of parallel beams in a different, orthogonal direction. This method can track objects in three-dimensions, as the objects move through the intersection of the orthogonal beams. The method utilizes only one sound transmitter at one particular frequency. This method is limited in several ways. 
         [0006]    First, the method utilizes two sonar heads to generate the orthogonal beams. This makes the application costly. Second, although the method permits a larger volume of water to be observed at any one time, this can only occur in the direction of the transmitted wave and the direction of the beams. Third, as the method utilizes a sound wave of only one frequency, a large amount of computing power is required to periodically sample each beam for possible targets. 
       SUMMARY OF THE INVENTION 
       [0007]    Accordingly, it is an object of the present invention to utilize a single sonar head with a multitude of sonar transmit and receive piezoelectric elements, hereinafter called sonar elements. This configuration has several advantages, including lower cost, easier handling and simpler installation. The sonar head of the present invention utilizes a special arrangement of sonar elements to achieve the objects of the invention. 
         [0008]    Another object of the present invention is to provide a method of continuous tracking of objects in the entire body of water surrounding the sonar head. The present invention is capable of continuous and simultaneous observation of the hemispherical body of water surrounding the sonar head, 360° azimuth and 180° elevation relative to the sonar head apparatus, typically oriented in a downward direction. 
         [0009]    This is accomplished by utilizing a multitude of fixed intersecting angled beams. The beams are oriented in four horizontal directions, or quadrants, covering the entire 360° area surrounding the sonar head. The beams are also angled downward from the sonar head. The angled beams are adjacent to each other, such that the entire 180° vertical space in a downward direction from the sonar head is being continuously monitored. This configuration of the beams provides for the continuous intersection of the beams in the entire volume of observed water. 
         [0010]    The sonar elements used in this invention both transmit sound waves and receive waves reflected from target objects. Each sonar element emits a simultaneous sound/sonar wave, thus permitting simultaneous reception by all sonar elements of sound waves. Each sonar element also detects reflected sound waves of only a particular frequency. The elements may be arranged in such a configuration to utilize multiple frequencies. This innovative feature is essential in permitting the current invention to continuously monitor the entire body of water surrounding the sonar head. 
         [0011]    The sonar elements of the present invention are preferably arranged in four quadrants in a horizontal direction, and are angled so as to cover the entire vertical space from the sonar head downward. In addition, one or more central sonar element(s) can be used to transmit sound waves in a vertical downward direction from the apparatus. These vertical sonar elements produce intersecting beams directly beneath the sonar head, in the volume of water where the angled beams previously described are not present. 
         [0012]    A further object of the current invention is to analyze the reflected sound waves of each sonar element and display the data in real-time on a monitor for easy viewing by a user. This is accomplished with the use of a computer or microprocessor and any desired type of display monitor. 
         [0013]    As previously mentioned, each sonar element transmits and receives sound waves of a particular frequency. This permits simultaneous transmission by all sonar elements in order to achieve sound waves that intersect each other. Once a sonar element detects sound waves reflected from a target object, data is transmitted to the on-board computer for analysis. This data contains the strength of the returned signal, as well as the time of detection and the direction to the target object. Similar data is transmitted from one or more adjacent sonar elements producing sound waves that intersect the previous sound wave, and which detect the same target. 
         [0014]    The computer analyzes the data from the sonar elements and determines the exact location of the object in three-dimensions: distance, angle and depth. Moreover, the computer can track the time of detection of each target by each transmitted wave, thus adding time as a fourth dimension that can be utilized therein to continuously track the object. 
         [0015]    The present invention has the advantage that the processing power of the on-board computer/microprocessor is reduced in comparison to the previously described conventional methods of underwater object tracking. This is due to the fact that the computer and the software running therewith can unambiguously identify which sonar element detected a target object and, therefore, can make appropriate determinations as to the direction and angle to the target object, without continuous comparative calculations. 
         [0016]    Further features of the invention will be described or will become apparent in the course of the following detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    In order that the invention may be more clearly understood, embodiments thereof will now be described in detail by way of example, with reference to the accompanying drawings, in which: 
           [0018]      FIG. 1  is a top view of the sonar element arrangement utilized by an embodiment of the sonar head of the present invention; 
           [0019]      FIG. 2  is an example embodiment side view of the multibeam arrangement of the present invention, corresponding to the sonar element arrangement of  FIG. 1 ; 
           [0020]      FIG. 3  is a diagram showing intersecting beams; and 
           [0021]      FIG. 4  is another diagram showing intersecting beams. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    Referring now to  FIG. 1  the sonar element arrangement inside the sonar head of a preferred embodiment of the present invention is shown. The sonar head of the present invention comprises four groups of peripheral sonar elements  1 ,  2 ,  3  and  4 , one in each quadrant of a horizontal plane, hereafter referred to as quadrant sonar elements. 
         [0023]    Each of the four groups of quadrant sonar elements  1 ,  2 ,  3  and  4  is comprised of multiple sets of two or more sonar elements. In this preferred embodiment there are four sets, each is comprised of two rectangular sonar elements. Although one long rectangular sonar element in each set is sufficient, it is preferable to use two or more such sonar elements in order to increase the output power and the receiving sensitivity of the sonar head. 
         [0024]    Referring again to  FIG. 1 , the quadrant sonar elements in each set of group  1  are of the same size and orientation. The outer set is comprised of quadrant sonar elements  11   a  and  11   b , each of which produces beams that are 12° wide, projected to cover the first  120  downward from the horizontal surface, that is, the span between 90° from a downward vertical line to 78° from such a line, as best illustrated in  FIG. 2 . The next set is comprised of quadrant sonar elements  12   a  and  12   b , which produce beams that are 130 wide, covering the range of from 78° to 65° from the downward vertical line, as best illustrated in  FIG. 2 . The next set is comprised of quadrant sonar elements  13   a  and  13   b , which produce beams that are 18° wide, covering the range of from about 65° to about 47° from the vertical, as best illustrated in  FIG. 2 . The inner most set is comprised of quadrant sonar elements  14   a  and  14   b , which produce beams that are 27° wide, covering the range of from 47° to 20° from the vertical, as best illustrated by  FIG. 2 . 
         [0025]    Each beam produced by a quadrant sonar element is 90° in length, extending in a horizontal outward direction. The two elements of each set are cambered at 90 degrees with respect to each other. This feature combined with the fact that sonar elements in the same set transmit and receive sound waves of the same frequency, effectively creates one 180° long beam corresponding to each set of quadrant sonar elements. 
         [0026]    Referring again to  FIG. 1 , quadrant sonar element groups  2 ,  3  and  4  contain sonar elements of the same size and configuration as those described previously for group  1 . As the beams corresponding to each set are effectively 180° long, four sound waves can be transmitted and received in each of the four orthogonal directions from the location of the sonar head. In this fashion beams originating from each group of quadrant sonar elements intersect the beams of the two neighboring groups of quadrant sonar elements. For example beams originating from group  1  intersect the beams originating from groups  2  and  4 ; beams from group  2  intersect the beams originating from groups  1  and  3 ; beams from group  3  intersect the beams originating from groups  2  and  4 ; beams from group  4  intersect the beams originating from groups  1  and  3 . 
         [0027]    The centre sonar elements  50  and  60  are square, circular or annular in shape and produce beams oriented in a vertical downward direction from the apparatus. In this preferred embodiment sonar element  50  produces a conical beam that subtends a 40° angle and sonar element  60  produces a conical beam with a 10° angle. The purpose of sonar elements  50  and  60  is to transmit and receive sound waves in the volume of water directly beneath the sonar head, where the beams of the four quadrant sonar elements are not present. Since the angle of the centre sonar beams is perpendicular to the water surface, the beams produced have a direct path to the seafloor. This direct path allows for the maximum rate of transmission of sonar waves per second. This feature is especially useful for the maximum definition of targets directly beneath the sonar head. 
         [0028]    Referring now to  FIG. 2 , a cross-section of the beams produced by the sonar elements of groups  1  and  3  through the AA section of  FIG. 1  is shown. Horizontal line  100  represents the water surface. As shown in  FIG. 2 , beam  11  is produced by quadrant sonar elements  11   a  and  11   b  of  FIG. 1 . Beam  11  is 12° wide and oriented at 78° from the downward vertical line. Beam  31  in the opposite quadrant is produced by quadrant sonar elements  31   a  and  31   b  of  FIG. 1  and is identical to beam  11 , with the exception of being oriented in the opposite direction. The same is true of beams  12  and  32 , produced by quadrant sonar elements  12   a ,  12   b  and  32   a ,  32   b , respectively. Beams  12  and  32  are 13° wide and oriented at 65° from the downward vertical in opposite quadrants. Beams  13  and  33 , produced by quadrant sonar elements  13   a ,  13   b  and  33   a ,  33   b , respectively, are 18° wide and oriented at 47° from the downward vertical line. Beams  14  and  34 , produced by quadrant sonar elements  14   a ,  14   b  and  34   a ,  34   b , respectively, are 27° wide and oriented at 20° from the downward vertical line. Finally the centre beams  51  and  61  are produced by sonar elements  50  and  60  respectively and are conical and 40 degrees and 10 degrees wide respectively and oriented directly downward from the sonar head. 
         [0029]    As can be appreciated, an identical set of beams is produced by the quadrant sonar elements of groups  2  and  4 , however in an orthogonal direction to the beams produced by the quadrant sonar elements of groups  1  and  3 . As the beams are 180° long, they intersect as shown in  FIG. 3 . 
         [0030]      FIG. 3  is a cross-section through the same AA section shown in  FIG. 2 . In  FIG. 3  the beams  11 ,  12 ,  13  and  14  produced by the quadrant sonar elements of group  1  of  FIG. 1  are shown, together with beam  21  produced by quadrant sonar elements  21   a  and  21   b  of group  2 . It can be appreciated that beam  21  has a direction perpendicular to the plane of the page. Thus beam  21  intersects beam  11  in the area labeled  1121 , beam  12  in the area labeled  1221 , beam  13  in the area labeled  1321  and beam  14  in the area  1421 . 
         [0031]    In the same fashion, beams  22 ,  23  and  24  of group  2  intersect beams  11 ,  12 ,  13  and  14  of group  1 . Similarly beams  21 ,  22 ,  23  and  24  of group  2  intersect beams  31 ,  32 ,  33  and  34  of group  3 . It can also be appreciated that beams  41 ,  42 ,  43  and  44  intersect in the same fashion the beams of group  1  and  3 . 
         [0032]    As an illustration,  FIG. 4  is a cross-section through the same AA section shown in  FIG. 2 , showing the intersection of beam  22  of group  2  with beams  31 ,  32 ,  33  and  34  of group  3  in areas  3122 ,  3222 ,  3322  and  3422 , respectively. 
         [0033]    As can be appreciated, a multitude of beam intersections throughout the entire body of water is created by the sonar element configuration of the present invention. The beam intersections extend indefinitely in all directions. A moving underwater object passes continuously through areas of intersecting beams. 
         [0034]    In operation, each sonar element is capable of both transmitting and receiving sound waves at a particular frequency. The rate of transmission of the sound waves is adjusted during the operation of the apparatus. In particular, when the apparatus is first turned on a determination of the depth of the body of water will be performed by each sonar element and the rate of transmission of each transducer sonar element will be adjusted accordingly. This determination by each sonar element is necessary because each sonar element&#39;s corresponding beam is angled differently and therefore the distance to the bottom of the water body will be different. Alternatively the user can define the outside perimeter, radius and depth to be utilized, as explained in more detail below. 
         [0035]    Once the depth determination is made by each sonar element and the rate of transmission is properly set, the sonar elements will continuously transmit sound waves at particular frequencies and listen for returned sound waves that are reflected by any underwater objects. When a sonar element receives a reflected wave, the distance to the target object can be determined in accordance with well known sonar techniques. 
         [0036]    Due to the fact that each sonar element provides a unique received signal, the computer can easily determine the beam in which the target object was detected. Moreover, since the computer/microprocessor is pre-programmed with each sonar element&#39;s exact orientation, it can precisely determine the downward angle to the target object. Once the distance and downward angle to the target object are known the computer can easily calculate the depth and horizontal distance to the target object. A person skilled in the art can appreciate that the processing power required for these calculations is much less than that required for existing single frequency multibeam sonar systems, in which all beams must be continuously compared using complex calculations to determine a potential target locations. 
         [0037]    In addition, an essential feature and advantage of the present invention is that a target object is always present at the intersection of two different beams and therefore the object will always be detected by an additional beam. This feature enables the computer/microprocessor of the present invention to calculate with improved precision the position of the target object in the 360° space surrounding the sonar head. 
         [0038]    As an object moving through the water is continuously present in an area of intersection of two different beams, the present invention is capable of precisely tracking the movement of any underwater object. The time of each detection of a target object is recorded and monitored. Thus, the present invention is capable of tracking and monitoring underwater objects in real-time. The time element is essentially a fourth-dimension of the present invention&#39;s tracking capabilities, in addition to distance, downward elevation angle and azimuthal direction to the target object. 
         [0039]    As can be appreciated from the heretofore description, the areas of intersection of two beams become progressively larger as the distance from the sonar head increases. Therefore, to a certain extent, the accuracy of the system is dependent on the distance of the target object from the sonar head. Should increased accuracy be required, the number of beams in each quadrant can be increased in order to increase the number of beam intersections, as described in more detail infra at paragraph 44. 
         [0040]    The data processed by the computer is immediately displayed on any suitable display, such as LCD, CRT or any other desired display type. A user will be able to continuously monitor underwater objects in real-time. 
         [0041]    Another useful feature of the present invention is the capability for a user to set limits to the monitoring distance from the sonar head. For example, in an application such as recreational fish-finding, a user may want to limit the target detection to a particular horizontal circular area of a few hundred meters and a depth of a few tens of meters, as practicable. In another application, such as commercial fishing, the monitoring area can be increased, as required. A user can easily accomplish this by inputting the dimensions of the perimeter, radius and depth to be monitored into the on-board computer connected to the sonar-head. 
         [0042]    The present invention can be utilized in many different applications, such as recreational or commercial fish-finding, military applications and many other applications where underwater target detection is desired. Depending on the application, the present invention can be easily interfaced with a GPS or mapping unit in order to precisely pinpoint the exact coordinates of a target object. 
         [0043]    Another advantage of the present invention is the effective target detection in shallow water columns. The angled beams of the present invention can overcome the inherent problems of conventional sonar techniques associated with shallow water depths. In contrast to conventional sonar methods, which can monitor only a small conical sample of the water column directly beneath the sonar head, the present invention offers the user a complete view of the entire body of water. This not only provides a greater scope of view for target objects, but it also provides an increase in navigational safety, such as allowing forward detection of obstacles and bottom depth. 
         [0044]    Yet another advantage of the present invention occurs in fishing applications, where utilizing conventional sonar techniques require the fishing vessel to be directly above the fish. In shallow water fish are likely to scatter away from an area where a vessel navigates directly above. By utilizing the present invention, the fishing vessel is not required to be directly above the fish for adequate detection. 
         [0045]    The preferred embodiment described heretofore is only an example embodiment of the present invention. Depending on the application, the sonar head used may contain many more sonar elements at many other orientations. An application requiring more accuracy can employ more than four sets of sonar elements in each quadrant. The areas of intersection of the beams produced will be smaller, thus increasing the accuracy of detection and tracking. In addition, where more accuracy is required directly beneath the sonar head, the number of centre sonar elements can be reduced or eliminated in order to accommodate more quadrant sonar elements. 
         [0046]    In addition, the sonar heads of the present invention are field replaceable, such that a user need only purchase one computer and display unit, which can be used with many different sonar heads, according to the application at hand. At the same time the invention is not predicated upon a particular type of sonar element, such that in the future more efficient sonar elements may be used, as they become available. 
         [0047]    Moreover, one computer/microprocessor unit may be connected to two or more sonar heads. This is particularly useful when a vessel&#39;s hull contains large protrusions which may block the transmission and receival of sound waves in all desired directions. In such applications sonar heads may be placed at different locations on the vessel&#39;s hull in order to enable unobstructed transmittal and receival in a complete 360° horizontal and 180° vertical directions. This may be accomplished using multiple complete sonar heads as described herein or by using multiple partial sonar heads such that the aggregate provides the capabilities described herein. 
         [0048]    Other advantages which are inherent to the structure are obvious to one skilled in the art. The embodiments are described herein illustratively and are not meant to limit the scope of the invention as claimed. Variations of the foregoing embodiments will be evident to a person of ordinary skill.