Abstract:
A system for use with a boat to provide underwater sonar images, includes a left side scan sonar transducer for transmitting left side scan sonar pulses and for receiving left side scan sonar return signals, a right side scan sonar transducer for transmitting right side scan sonar pulses and for receiving right side scan sonar return signals, and signal processing circuitry for processing the left and right side scan sonar return signals to produce side scan image data. The system further includes a user interface including user inputs and a display and a digital processor for providing signals to the display to show an underwater image based upon the side scan image data, wherein the digital processor, in response to a user command, performs an image enhancement algorithm to enhance the underwater image.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This is a continuation of U.S. patent application Ser. No. 11/195,107, entitled “SONAR IMAGING SYSTEM FOR MOUNTING TO WATERCRAFT,” filed Aug. 2, 2005 by David A. Betts et al. and claims the benefit of U.S. Provisional Patent Application No. 60/598,326, filed Aug. 2, 2004, the teachings and disclosure of which are hereby incorporated in their entireties by reference thereto. 
     Reference is also made to application Ser. No. 12/319,594 entitled “SIDE SCAN SONAR IMAGING SYSTEM WITH BOAT POSITION ON DISPLAY” and application Ser. No. 12/319,604 entitled “SIDE SCAN SONAR IMAGING SYSTEM WITH ASSOCIATED GPS DATA”, which are filed on even date and are assigned to the same assignee as this application. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to sonar imaging systems for use in sport fishing applications such as in a fish finder, sonar depth sounder, etc., and more particularly to side scan sonar imaging systems for imaging of the underwater environment to the sides of the watercraft rather than just below the watercraft. 
     BACKGROUND OF THE INVENTION 
     Sonar devices that transmit sound waves have been used previously to obtain information about underwater articles, including fish, structures and obstructions, and the bottom. The sound waves travel from a transducer mounted to a bottom surface of the vessel through the water. The sound wave transmits from the sonar devices in diverging patterns. The sound waves contact underwater articles, which create return echoes. The transducer receives the return echoes and the sonar device analyzes the received echoes. A display device displays representations of the received echoes, for locating fish and other underwater articles. 
     Known side scan sonar devices locate the transducer in a vessel towed by the watercraft (e.g., a “tow fish”). The tow fish is coupled to the sonar display by a long cable. The length of the cable will depend on the depth of the water and other conditions. For typical applications, the length of the cable is 50 feet or more. Moreover, it is not uncommon for the cable to be hundreds or even thousands of feet long. As can be appreciated by some having ordinary skill in the art, a fisherman or recreation user desiring to have side scan images would be hindered by such an arrangement. For example, maneuvering or turning of the watercraft in different directions is difficult, as well as tangling of the sonar cable with fishing or other recreational equipment. Such known tow fish transducers are maintained at a consistent distance from the bottom of the body of water. This distance is intended to provide desired or optimized resolution and field of view. A consistent distance inhibits, if not prohibits, modifying known transducers for side scan applications (or mounting known side scan transducers to watercraft) because the distance between the transducer to the bottom of the water will vary as the watercraft travels due to the varying depth of the water. 
     Accordingly, it would be advantageous to provide a sonar imaging system that is coupled to the watercraft, rather than being coupled by a flexible cable and towed behind the watercraft. It would also be advantageous to provide sonar imaging system mountable to a motor (such as a trolling motor), a transom of the watercraft, or to the hull of the watercraft. It would also be advantageous to provide sonar imaging system operable at multiple resonant frequencies for optimized performance at varying bottom depths. It would be desirable to provide for a sonar imaging system for mounting to a watercraft having one or more of these or other advantageous features. 
     BRIEF SUMMARY OF THE INVENTION 
     In view of the above, it is an objective of the present invention to provide a new and improved sonar imaging system that is capable of being connected to a watercraft, such as a fishing boat. It is a further objective to provide a new and improved sonar imaging system that provides imaging of the underwater environment to the sides of the watercraft. It is a still further object of the invention to provide a new and improved sonar imaging system that additionally provides imaging of the underwater environment below the watercraft. 
     The system of the present invention realizes several advantages over the traditional towfish side scan sonar systems. It is more convenient because there are no deployment requirements of getting the transducer towfish into the water, no cable handling hassles and tangles, no precise speed control requirements to keep the towfish at the right depth and prevent it from hitting the bottom, no complicated large diameter turn requirements to prevent the towfish from hitting the bottom when you want to turn the boat, and no worries about getting the lines and cable tangled when fishing. The system of the present invention can even be used for imaging by a watercraft in reverse. 
     The system of the present invention is also more secure than the traditional side scan sonar systems. There is no chance of snagging the towfish or loss of transducer. Most fishing is done near bottom rises, drop-offs and underwater structures. Most natural and especially man-made lakes have rocks, stumps and standing timber that can snag a towfish and cause damage or loss of the equipment. 
     Additionally, the system of the present invention provides more area of coverage. The watercraft mounted transducer of the present invention does not limit the turning radius of the vessel, and it provides the ability to image closer to the shore and near structure. This allows for faster and more complete imaging. The system also provides more accurate target locations. Having the transducer mounted to the watercraft allows for precise target locations. With a towed side scan system the crew has to take into account how much cable is deployed and how deep the towfish is to determine how far back behind the boat the target is. With the watercraft mounted system of the present invention, this is not a factor. To provide even more accurate images, the system of the present invention provides the offset necessary to account for the X and Y distance between the side imaging transducer and the GPS antenna. The system of the present invention also has a better aspect at some targets because, in some cases, the view from the surface can “see” better over rises and into holes than the towed side scan sonar at a fixed distance from the bottom. The system of the present invention can also be mounted to smaller watercraft such as canoes, kayaks and other personal watercraft. 
     In a preferred embodiment of the present invention, the system includes features to correct for watercraft mounted nature of the transducers. Unlike using a towfish in which data collection takes place at a fixed distance from the bottom (same aspect angle at any depth of water), and in which the towfish dynamics are decoupled from vessel motion in rough seas, the system of the present invention compensates for these differences. In a preferred embodiment of the present invention, the depression angle of the side imaging elements is increased from about 20 degrees to about 30 degrees. This provides better coverage at the greater aspects. Also in a preferred embodiment, the side elements are designed to be dual frequency to provide a trade-off between area of coverage and resolution. Transducer element shielding and software filters are also provided in a preferred embodiment to eliminate vessel noise sources such as spark plug and electrical system EMI (solenoids, VHF radios, electric motors, etc.). In one embodiment of the present invention, the system includes passive yaw, tilt transducer minimization or compensation using floating oil bath self leveling. In another embodiment the system includes active yaw, tilt transducer minimization or compensation via tilt sensors and motors. 
     Additional features over traditional side scan provided by embodiments of the present invention include fish identification and alarm in side beams. Typical side scan systems consider fish as unwanted noise. Screen capture and playback functioning like a digital camera with the ability to store an image, review already stored images, erase unwanted images, and download images to a computer are also provided in embodiments of the present invention. Unlike typical data recording when a user sees an image on the screen they can simply push a capture button, instead of having to start recording before the user sees the target. Preferred embodiments also provide zoom capability that allows a user to view only the right or left side at a time and also zoom into a particular area either using the cursor or a touch screen. Further, the ability to use standard image enhancement software (algorithms) either in the unit or post processed is provided to allow for color, contrast, brightness, auto fix, edge detect, etc. 
     In a preferred embodiment of the present invention, a down beam is provided along with the side imaging. This provides for more complete around the boat information (both sides and straight down). It is not limited to a single beam. One embodiment utilizes a 200 kHz/50 kHz dual beam. Other embodiments may use a quad beam or even six beam. In preferred embodiments, at least one view shows both down beam and side imaging. This provides the ability to better relate length of shadow information to the size of the underwater target. It also provides for a quick means for verification of target location. After a target is located off to a side, the boat can be driven directly over the target and located in the down beam for precise location. 
     In a still further preferred embodiment, GPS imaging is also provided with the side imaging. In such embodiments a cursor mode allows a user to move the cursor over a target of interest on the screen image and set a waypoint for the location of the structure. The GPS history may be used to determine the distance back and the sonar may be used to determine the distance to the side. The GPS speed can be used to provide the screen scroll rate to provide more accurate front to back target dimensions. Without GPS or a speed sensor a fast scroll rate and a slow boat speed will elongate targets and a slow scroll rate and a fast boat speed will shorten targets. The corners of screen captures can be marked so that large area composite mosaic images can be generated in the unit or post processed later. Preferably, one view that shows both side imaging and navigation information is provided. This makes it easier to follow tracks and provide efficient area coverage. 
     In accordance with these objectives, an embodiment of the present invention provides a sonar imaging system for a watercraft including a transducer coupled to the watercraft. Preferably, the system includes at least one side scanning element and at least one bottom scanning element and an electronic control head unit coupled to the transducer that is configured to display sonar images. In one embodiment of the present invention, the sonar imaging system includes circular downward acoustic elements and rectangular acoustic elements. The present invention further relates to a software filter configured to remove noise generated by a spark plug or other operation of a motor for the watercraft. 
     Other aspects, objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings: 
         FIG. 1  is an isometric illustration of one embodiment of a fishing vessel mounted sonar imaging system of the present invention; 
         FIG. 2  is an exploded bottom view isometric illustration of an embodiment of a transducer module constructed in accordance with the teachings of the present invention; 
         FIG. 3  is a side view illustration of the assembled transducer module of  FIG. 2 ; 
         FIG. 4  is an end section view of the assembled transducer module of  FIG. 3  taken about section line  4 - 4 ; 
         FIG. 5  is a partial section view of the housing joint of the assembled transducer module of  FIG. 4  taken at section A; 
         FIG. 6  is a fully exploded bottom view isometric illustration to the transducer module of  FIG. 2 ; 
         FIG. 7  is a partial exploded view isometric illustration of a top housing assembly showing placement of downward looking sonar elements; 
         FIG. 8  is a partial exploded view isometric illustration of a top housing assembly showing placement of downward looking sonar elements and side scan sonar elements; 
         FIG. 9  is an exploded isometric illustration of an embodiment of a downward looking sonar element suitable for application in the sonar imaging system of the present invention; 
         FIG. 10  is an exploded isometric illustration of an embodiment of a side scan sonar element suitable for application in the sonar imaging system of the present invention; 
         FIG. 11  is an isometric illustration of one embodiment of a cable attachment for the sonar imaging system of the present invention; and 
         FIG. 12  is a simplified system block diagram of an embodiment of the sonar imaging system of the present invention. 
         FIGS. 13-18  show examples of sonar images as they appear on a display screen. 
         FIG. 19  shows a display screen showing an underwater environment using sonar images from both side scan elements and sonar returns from a downward sonar element. 
     
    
    
     While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning now to the drawings,  FIG. 1  illustrates a vessel (shown as a watercraft  10 ) on a surface  12  of a body of water  14  having a bottom  16 . A sonar imaging system  18  is mounted or coupled to the watercraft  10  (e.g., rather than being towed by a flexible cable behind the watercraft  10 ) and is configured to scan the water below and to the sides of the watercraft (i.e., a boat mounted side scan sonar system). The sonar imaging system  18  comprises a transponder or transducer  20  coupled to an electronic control head unit  22  located at the watercraft  10 . The sonar imaging system  18  repetitively scans the body of water  14  for fish and other underwater articles with transmissions of acoustic waves and receiving and displaying the sonar returns, with the duration of receiving being a function of the determined depth from a prior transmission. 
     Referring to  FIGS. 2-11 , the transducer  20  includes a housing  24 , a sonar array (in the form of a plurality of acoustic elements shown as side scan elements  26  and downward scan element  28 ), a cable  30  coupling the housing and acoustic elements to the electronic control head unit  22 . The acoustic elements are configured for acoustic wave transmitting and receiving by a transmitter and a receiver that are operated by the electronic control head unit  22  for scanning the body of water  14 , particularly for locating fish, as well as other underwater articles, and determining characteristics about the bottom  16  (see  FIG. 1 ) of the body of water. The acoustic or sonar wave beams are transmitted based on the configuration of the acoustic elements. 
     The housing  24  comprises a top housing portion  36  and a bottom housing portion  38 . The top housing portion  36  includes a pair of mounting members  40  extending from the front portion of the top housing portion  36 . Both top housing portion  36  and bottom housing portion  38  have projections extending towards the interior of the housing to provide structural support for the housing assembly, and to provide locating and positioning support for the acoustic elements. A series of projections  42  include v-shaped recesses or notches  44  to form a cradle that receives side scan elements  26 . Recesses  44  are configured (shaped and positioned) to support the rectangular shaped side scan elements  26  in a position and orientation (direction) to provide a particular, desired, predetermined acoustic beam performance. 
     The housing  24  is coupled to the watercraft  10  by any of a variety of methods. The housing  24  is coupled to the watercraft  10  so that there are no obstructions to either side of the housing (i.e., to block the operation or affect the performance of the acoustic elements). According to a preferred embodiment, the housing  24  is coupled to the watercraft  10  along the centerline of the watercraft so that the housing  24  extends about 0.25 inches below the watercraft. According to an exemplary embodiment, mounting members  40  of the top housing  36  are coupled to a mounting bracket  46  that is coupled to a trolling motor. According to an alternative embodiment, the mounting members  40  are mounted through the hull of the watercraft  10  (e.g., with a support shaft passing through a hole in the hull). According to an alternative embodiment, the mounting members are coupled to a bracket that is coupled to a transom of the watercraft  10 . Alternatively, the housing may be coupled to the watercraft at any of a variety of positions and at any of a variety of depths below the surface of the water. The top housing portion  36  may be coupled to the bottom housing portion  38  by any of a variety of conventional methods (e.g., snap fit engagement, adhesive, ultrasonic welding, fusion, heat welding, fasteners such as screws, bolts, rivets, or the like). As illustrated in  FIG. 5 , one embodiment of the housing  24  utilizes a mounting rib  25  that is received in a mounting channel  27  to locate the top and bottom housing portions  36 ,  37  together. In one embodiment, the rib  25  is welded into the channel  27  such as, e.g. via ultrasonic welding or the like. 
     The side scan elements  26  are located along the sides of the housing  24  and are configured to scan the water to the sides of the transducer  20  (and watercraft  10 ) with sonar or acoustic beams  47 . 
     The dimensions of side scan elements  26  are configured to provide the desired sonar beam pulse  47 . The size of the wave front created by the transmitted acoustic beam affects the resolution of the return echo and thus the quality of the imaging of subsurface articles displayed by the sonar device. Generally, a wide beam provides diffused return echoes that are particularly suited for indicating the presence of fish in a wide area around the watercraft. The signal displayed for fish is referred to as a “fish arch” or other indicia or icon. A narrower beam on the other hand provides a more detailed return echo or signal representative of the subsurface article. The narrow beam covers a smaller area but provides additional definition of the article. A wider beam accordingly is useful for providing indications of the presence of schools of fish in a wide area around the vessel as well as other underwater articles. The narrow beam is useful for providing details of the underwater article or the bottom. 
     A sonar beam becomes narrower (thereby providing better resolution) as the corresponding dimension of the acoustic element becomes larger, and a sonar beam becomes wider as the corresponding dimension of the acoustic element becomes smaller (e.g., a small height provides for a beam with a relatively wide vertical angle, and a large length provides for a beam with a relatively narrow horizontal angle). According to an exemplary embodiment, the side scan elements  26  are configured to provide a narrow horizontal beam width and a wide vertical beam width. According to a preferred embodiment, the side scan elements have a rectangular shape. According to a particularly preferred embodiment, the rectangular shaped side scan elements  26  are between about 3 inches to about 7 inches long by between about 0.125 inch and about 0.50 inch wide. According to a particularly preferred embodiment, the rectangular side scan elements  26  are about 4.5 inches long and about 0.25 inch wide. In such a particular preferred embodiment shown schematically in  FIG. 1 , the side scan elements  26  transmit the acoustic beam  47  with a horizontal angle  49  of about 2 degrees and a vertical angle  51  of about 50 degrees. 
     Referring to  FIGS. 1 ,  4 ,  6 , and  7 , the side scan elements  26  are supported (e.g., captured, cradled, secured, etc.) by projections  42  in housing  24  so that their exposed surface  48  is orientated at a predetermined direction and angle. According to an exemplary embodiment, the side scan elements  26  are supported by the housing so that the exposed surface is orientated outward from the transducer  20  and toward the bottom of the water (e.g., downward from the watercraft  10  and surface of the water). According to a preferred embodiment, side scan elements  26  are angled downward between about 20 degrees and about 40 degrees, depending on the resonant frequencies. According to a particularly preferred embodiment, the side scan elements  26  are orientated downward at about 30 degrees for resonant frequencies of between about 260 KHz and about 462 KHz. According to alternative embodiments, the side scan elements are mounted with any of a variety of orientations and directions, depending on types of depths the transducer is intended to be used in (e.g., lake, river, ocean, etc.) and on the configuration of the transducer sonar beams (e.g., as determined by the size and dimensions of the acoustic elements). Preferably, the side scan elements  26  are coupled to the housing  24  with an epoxy. Alternatively, the side scan elements are coupled to the housing by any of a variety of adhesives or bonding or joining materials or techniques. 
     According to a preferred embodiment, side scan elements  26  are made from a piezoelectric ceramic. According to a particularly preferred embodiment, the side scan elements are composed of lead zirconate titanate (“PZT”) commercially available from Morgan Electro Ceramics of the United Kingdom. According to alternative embodiments, the side scan elements may be made from any of a variety of piezoelectric materials capable of converting electric energy into mechanical energy and converting mechanical energy into electrical energy. 
     An acoustic shield  50  (e.g., shielding, decoupler, barrier, absorber, etc.) surrounds all but one side of side scan elements  26  to prevent sonar pulses from being transmitted, and sonar returns received by, acoustic elements in all but the desired direction of scanning. The acoustic shield  50  may be made from any of a variety of materials that are poor conductor of sonar energy, such as cork, foam, polymers, or other low density materials, and the like. 
     The downward scan element  28  is located along the bottom middle of the housing  24  and is configured to scan the water below the transducer  20  (and watercraft  10 ) with sonar or acoustic beams  53  (see  FIG. 1 ). According to a preferred embodiment, downward scan element  28  comprises a pair of transducer elements coupled together. According to alternative embodiments, the downward scan element comprises a single element or more than two elements. 
     The dimensions of downward scan element  28  are configured to provide a desired sonar beam pulse. According to an exemplary embodiment, the downward scan element  28  is configured to provide a relatively narrow sonar beam (e.g., for desired or optimum resolution). According to a preferred embodiment, the downward scan elements  28  have a cylindrical shape. According to a particularly preferred embodiment, the cylindrical shaped downward scan elements  28  have a diameter of between about 1 inch to about 2 inches and a height of between about 0.2 inches and about 0.5 inches. According to a particularly preferred embodiment, the cylindrical downward scan element  28  has a diameter of about 1.67 inches and a height of about 0.425 inch. In such a particular preferred embodiment shown in  FIG. 1 , the downward scan elements  28  transmit the acoustic beam  53  with an angle  55  of about 20 degrees. According to alternative embodiments, the side scan elements and the downward scan elements may have any of a variety of dimensions, positions, and orientations based on desired performance, manufacturing, and costs. 
     The downward scan element  28  are supported (e.g., captured, cradled, secured, etc.) by projections  52  in housing  24  so that its exposed surface  54  is orientated at a predetermined direction and angle. According to an exemplary embodiment, the downward scan elements  28  are supported by the housing so that the exposed surface is orientated vertically downward from the transducer  20  and toward the bottom of the water. Preferably, the downward scan elements  28  are coupled to the housing  24  with an epoxy. Alternatively, the downward scan elements are coupled to the housing by any of a variety of adhesives or bonding or joining materials or techniques. 
     According to a preferred embodiment, the downward scan element  28  are made from a ceramic. According to a particularly preferred embodiment, the downward scan element  28  are composed of lead zirconate titanate (“PZT”) commercially available from Morgan Electro Ceramics of the United Kingdom. According to alternative embodiments, the downward scan elements may be made from any of a variety of piezoelectric materials capable of converting electric energy into mechanical energy and converting mechanical energy into electrical energy. 
     An acoustic shield  56  (e.g., shielding, decoupler, barrier, absorber, etc.) surrounds all but one side of the downward scan elements  28  to prevent sonar pulses from being transmitted, and sonar returns received by, acoustic elements in all but the desired direction of scanning. The acoustic shield  56  may be made from any of a variety of materials that are poor conductor of sonar energy, such as cork, foam, polymers, or other low density materials, and the like. 
     The return sonar signal from the bottom reflection carries details about the bottom  16 . The return sonar signal from the side reflection carries details about the sides and bottom  16  to the side of the watercraft  10 . The sonar return data is communicated or sent to be processed by the transducer  20  to the electronic control head unit  22  for display of images or symbols representative of the received return echoes of the acoustic wave beams. The transmission of an acoustic pulse and the reception of reflected echoes is a transmit/receive cycle, which is referred to herein as a T/R cycle. The wavefront of the acoustic pulse travels from the transducer  20 , to the bottom  16  of the body of water  14 , and reflects back to the transducer which receives the reflected echoes of the acoustic wave beam. The duration of the T/R cycle depends on the depth of the water. Typically, the T/R cycles of transmission and reception are two to four times per second for deep water and more frequently, such as one-thirtieth of a second, for shallower waters. 
     According to a preferred embodiment, the transducer  20  does not include any electronics; rather the electronics are located in the electronic control head unit  22 . The images include a bottom profile, objects along the bottom or in the water (e.g., fish), and the like. The display may also display informational subject matter (e.g., depth, water temperature, velocity of the watercraft  10 , etc.). 
     Referring to  FIG. 12 , the electronic control head unit  22  is coupled to a power supply and comprises a user interface ( 58 ,  60  and  62 ), a microprocessor  64 , a co-processor  66 , a first side scan circuit  68 , a second side scan circuit  70 , and a bottom scan circuit  72 . The user interface is configured to allow for user inputs through a display menu where parameters like depth range, sensitivity, fish alarm and the like. The user interface is shown to comprise a keypad  58 , buzzer  60 , and display  62 . Alternatively, the user interface may have switches or push buttons, or the like. 
     The microprocessor  64  is coupled to the user interface and is configured to process the data from the co-processor  66  (e.g., control the displayed information, format the information for display, run the operational algorithms, and the like). The microprocessor  64  can be a microcontroller, application-specific integrated circuit (ASIC) or other digital and/or analog circuitry configured to perform various input/output, control, analysis, and other functions described herein. In one embodiment, the micro-processor  64  includes a memory (e.g., non-volatile memory) configurable with software to perform the functions disclosed herein. The microprocessor  64  of the electronic control head unit  22  implements programmed algorithms (e.g., differential amplitude filtering (eliminate engine spark noise), time variable gain optimization—for best image, fish finding algorithms, anti-ringing pulse on transmit for better resolution, and use down beam depth to correct slant angle range information). According to a preferred embodiment, a software filter algorithm is provided to filter certain noise common to operation of watercraft (and noise caused by sparkplug in particular). 
     During operation of the sonar imaging system  18  in a particularly preferred embodiment, amplitude readings are taken approximately every 0.75 inches, such that 100 feet of depth has 1600 readings. The 0.75 inch amplitude readings from the last transmit/receive cycle (T/R cycle) are saved into computer memory. For each of these 0.75 inch amplitude readings, present and previous amplitude readings the software conducts the following test: Is “present reading”−“previous reading”&gt;x. If Yes, then substitute “previous reading” for “present reading”. If no, use the present reading. The microprocessor  64  also filters the signals, sorts sonar target returns from the bottom and fish, calculates display range parameters and then feeds the processed signals to the LCD display screen. The display  62  is preferably a graphic display, for example, but not limited on the pixel order. Other displays such as LED, flasher, A-scope and digital segment may alternatively be used. The electronic control head unit  22  may be powered by batteries (e.g., its own dedicated batteries, marine battery, etc.). 
     The co-processor  66  is coupled to the microprocessor  64  and is configured to collect, process, and pass data to the microprocessor  64  (e.g. generates the transmission frequencies, converts the analog data to digital with A/D converter and sends to the microprocessor  64 ). The co-processor  66  can be a microcontroller, application-specific integrated circuit (ASIC) or other digital and/or analog circuitry configured to perform the functions disclosed herein. In one embodiment, the co-processor  66  includes a memory (e.g., non-volatile memory) configurable with soft-ware to perform the functions disclosed herein. 
     The first side scan circuit  68  is coupled to the co-processor  66  and is configured to operate one of the side scan elements. The first side scan circuit  68  comprises a receiver  74 , a transmitter  76 , and a transmit/receive switch (i.e., T/R switch  78 ). The second side scan circuit  70  is coupled to the co-processor  66  and is configured to operate the other side scan element. The second side scan circuit  70  comprises a receiver  86 , a transmitter  88 , and a transmit/receive switch (i.e., T/R switch  90 ). The bottom scan circuit  72  is coupled to the co-processor  66  and is configured to operate the bottom scan element. The bottom scan circuit  72  comprises a receiver  80 , a transmitter  82 , and a transmit/receive switch (i.e., T/R switch  84 ). 
     The receivers  74 ,  80 ,  86  are configured to amplify the signal and conducts signal filtering, base banding-rectification (e.g., remove carrier frequency), and logarithmic conversions (e.g., to obtain a wide range at output) and preferably provide variable receiver bandwidth. The transmitters  76 ,  82 ,  88  are configured to drive the acoustic elements and preferably provide variable transmit power and preferably at a high voltage. The T/R switches  78 ,  84 ,  90  are configured to switch the first side scan circuit  68  between transmit and receive modes. 
     According to a preferred embodiment, the electronic control head unit  22  is configured to operate at one or more resonant frequencies, depending on the intended depth and desired resolution. Such a multiple-frequency operation is intended to make up for shortcomings of mounting the transducer to the watercraft  10  caused by the varying distance between the transducer to the bottom  16  of the water  14 . According to a particularly preferred embodiment using a dual-resonant frequency and side scan acoustic elements that are about 4.5 by about 0.25 inch, the electronic control head unit  22  is configured to operate at 260 kHz resonant frequency (e.g., wider acoustic wave beam for deeper depth and further distances) and at 462 kHz resonant frequency (e.g., narrower acoustic wave beam for shallower depth and shorter distances). The down beam that is provided in one embodiment utilizes a 200 kHz 150 kHz dual beam. Other embodiments may use a quad beam or even six beam. In preferred embodiments, at least one view of the display shows both the down beam imaging and side imaging. This provides the ability to better relate length of shadow information to the size of the underwater target. 
       FIG. 1  shows a cross-sectional view of the body of water  14  to illustrate features of the present invention during operation of the sonar imaging system  18 . With additional reference to  FIG. 12 , the sonar imaging system  18  transmits the acoustic wave beam  47  from the side scan elements  26  and the acoustic wave beam  53  from downward scan elements  28 . The receivers  74 ,  80 ,  86  begin listening for sonar returns through the transducer  20 . The acoustic wave beams  47 ,  53  propagate to the bottom surface  16  and reflects a sonar return. The transducer  20  communicates the received sonar return to the receivers  74 ,  80 ,  86 . A prior cycle had determined the depth, and in the illustrated embodiment, the depth is displayed on the display  62  as well as provided to a controller for evaluating the duration. Using the prior determined depth, a controller determines an approximate travel time for the sound energy signal  47 ,  53  to reach the bottom  16  and return. At a predetermined proportion of the travel time, the return sonar reaches a point near the transducer. The return sonar from the bottom  16  reflection carries details about the bottom  16 . The controller directs the switch to change the receiving mode from transmit mode to receive mode. The receivers  74 ,  80 ,  86  then use the acoustic elements for the return sonar. The sonar imaging system  18  continues receiving in the narrow acoustic wave beam mode, until the start of the next T/R cycle. The received sonar returns are processed by the controller for display of representative symbols on the display  62 . The T/R cycle then repeats with the newly determined depth from the prior cycle. 
     The sonar images from the down beam and side scan elements are then displayed on the display  62 . These images may be shown in grey-scale or in color. The location of the watercraft  10  is also shown in the image. If the user chooses to only display the down beam sonar information, historic information is typically shown to the left of the location of the watercraft. As such, the display  62  shows images to the bottom of the watercraft  10  that are even with and behind the watercraft  10  when the watercraft  10  is traveling forward. The user may also display only the side scan sonar images, only those from one side scan element, or images from both sides and the bottom. The display  62  may also be configured (or configurable) to indicate information such as depth, and speed of the watercraft  10 , range, etc. 
     In a highly preferred embodiment, a GPS receiver  92  is also included to provide the microprocessor  64  location information. This information may be used to provide charting and other navigational functions. To provide even more accurate images, the system of the present invention provides the offset necessary to account for the X and Y distance between the side imaging transducer and the GPS antenna. In one embodiment a cursor mode allows a user to move a cursor on the display  62  over a target of interest on the screen image and set a waypoint for the location of the structure. The GPS history may be used to determine the distance back and the sonar may be used to determine the distance to the side. The GPS speed is used in one embodiment to provide the screen scroll rate to provide more accurate front to back target dimensions. Without GPS or a speed sensor a fast scroll rate and a slow boat speed will elongate targets and a slow scroll rate and a fast boat speed will shorten targets. The corners of screen captures can be marked so that large area composite mosaic images can be generated in the unit  22  or post processed later. Preferably, one view that shows both side imaging and navigation information is provided. This makes it easier to follow tracks and provide efficient area coverage. 
     Referring to  FIGS. 13-18 , exemplary sonar images  92  reproduced from a display  62  are shown in grey-scale. Alternatively, the display  62  may display color sonar images. The location of the watercraft  10  is shown as “0” in the images  92 . Historic information is shown to the left of “0”. As such, the display  62  shows images  92  to the bottom or side of the watercraft  10  that are even and behind the watercraft  10 . A range  105  to the side of the watercraft  10  is also provided. A dark area  106  along the top of the display  62  shows the water column above the bottom  16 . The portion  93  of the image  92  below the water column dark area  106  shows returns from the bottom  16 . As shown by the returns in the sonar images  92 , the body of water  14  includes the bottom  16  and underwater articles such as trees  94 , logs  96 , a sunken barge  98 , and a school of fish  100 . Shadows  102  from the underwater articles indicate the general distance or displacement of the underwater article (e.g., distance it extends from the bottom  1 ). Dark areas  104  typically indicate drop offs, holes, and the like. The display  62  may also be configured (or configurable) to indicate information such as depth  108 , and speed  110  of the watercraft  10 . 
     According to a preferred embodiment shown in  FIG. 19 , the display  62  is configurable to provide an image  120  that shows the underwater environment using both side scan elements (views)  26  and the downward scan element  28 . An icon  122  (in the form of a schematic watercraft) indicates the position and orientation and direction of travel of the watercraft  10 . 
     It is important to note that the terms are intended to be broad terms and not terms of limitation. These components may be used with any of a variety of products or arrangements and are not intended to be limited to use with fish finding applications. For example, mounting to a watercraft is not intended to be limiting to devices that are directly attached to the watercraft, but would include devices attached to motors (such as trolling motors) attached to the watercraft, and the like. 
     It is also important to note that the construction and arrangement of the elements of the sonar imaging system for mounting to a watercraft as shown in the preferred and other exemplary embodiments are illustrative only. Although only a few embodiments of the present invention have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter recited in the claims. For example, the transducer preferably provides dual frequency, single element side beams in the form of two opposed vertical beams optimized for range and depth and front to back beam width selected based on image resolution, fish finding and transducer length. 
     Elements shown as integrally formed may be constructed of multiple parts or elements show as multiple parts may be integrally formed, the operation of the interfaces may be modified or otherwise varied, the length or width of the structures and/or members or connector or other elements of the system may be varied, the nature or number of adjustment positions provided between the elements may be varied (e.g. by variations in the number of engagement slots or size of the engagement slots or type of engagement). It should be noted that the elements and/or assemblies of the system may be constructed from any of a wide variety of materials that provide sufficient strength or durability, in any of a wide variety of colors, textures and combinations. Accordingly, all such modifications are intended to be included within the scope of the present invention as defined in the appended claims. 
     The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. In the claims, any means-plus function clause is intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Other substitutions, modifications, changes and/or omissions may be made in the design, operating conditions and arrangement of the preferred and other exemplary embodiments without departing from the spirit of the present invention as expressed in the appended claims. 
     All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirely herein. 
     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by con-text. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
     Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.