Patent Publication Number: US-8976339-B2

Title: Traffic scanning LIDAR

Description:
RELATED APPLICATIONS 
     The present application is a continuation patent application and claims priority benefit, with regard to all common subject matter, of earlier-filed U.S. patent application Ser. No. 13/085,994, entitled “TRAFFIC SCANNING LIDAR,” filed Apr. 13, 2011, and issued Jan. 14, 2014, as U.S. Pat. No. 8,629,977 (“the &#39;977 Patent”). The &#39;977 Patent is a non-provisional utility application and claims priority benefit, with regard to all common subject matter, of earlier-filed U.S. Provisional Patent Applications entitled “TRAFFIC SCANNING LIDAR”, Ser. No. 61/324,083, filed Apr. 14, 2010, and “TRAFFIC SCANNING LIDAR”, Ser. No. 61/405,805, filed Oct. 22, 2010. The identified earlier-filed patent and applications are hereby incorporated by reference into the present application in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to systems for monitoring vehicle velocities. More particularly, the invention relates to systems monitoring vehicle velocities using scanning light detection and ranging. 
     2. Description of the Related Art 
     Traffic control that includes monitoring the velocities of vehicles on the roadways may be implemented by law enforcement officers using various devices and systems, such as Doppler radar and LIDAR. Doppler radar operates in the microwave frequencies, typically X, K, and Ka band, and transmits a continuous or almost continuous wave and measures the speed of vehicles by receiving the reflected signal and using the Doppler principle. Typical Doppler radars can be operated from a stationary point or can be mounted in a law enforcement vehicle and operated while the law enforcement vehicle is moving. They are able to be used in a moving situation because the beamwidth is wide, typically 20 degrees, and therefore do not have to be pointed accurately at the vehicle being measured. But this feature is also a problem because when there are multiple vehicles in the beam, the operator does not know which vehicle is being measured. In the moving mode the Doppler radar subtracts out the speed of the law enforcement vehicle on which it is mounted. 
     Light detection and ranging (LIDAR) uses a laser pulse and determines the vehicle speed by performing distance time calculations based on the travel time of the reflected light pulse. Because the LIDAR has a very narrow beam, it is very selective of the vehicle being measured even when there are several vehicles within range. But this is also a disadvantage in its usage because the operator must carefully aim the LIDAR at the vehicle, and therefore, it can only effectively be used in stationary applications. The moving application has too much motion to keep it aimed properly. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention solve the above-mentioned problems and provide a distinct advance in the art of systems for monitoring vehicle velocities. More particularly, embodiments of the invention provide a system that is operable to sweep a beam across a field of view at varying heights to detect the speed of a plurality of objects, such as motor vehicles, at the same time. 
     Embodiments of a system for detecting the speed and position of objects comprise a beam source, a transmit reflection device, a beam receiver, a receive reflection device, and a controller. The beam source may generate a beam. The transmit reflection device may reflect the beam at the objects and may include a plurality of transmit faces with at least a portion of the transmit faces oriented at a different angle and operable to reflect the beam at a different height. The beam receiver may detect the beam. The receive reflection device may include a plurality of receive faces with at least a portion of the receive faces oriented at a different angle and operable to focus the beam reflected from objects at different heights onto the beam receiver. The controller may determine the position of the objects over time and calculate the speed of the objects based on a change in the position of the objects. 
     Additional embodiments of a system for detecting the speed and position of objects comprise a beam source, a transmit device, a beam receiver, a receive device, and a controller. The beam source may generate a beam. The transmit device may sweep the beam at the objects through a known angle in the horizontal direction and a known angle in the vertical direction. The beam receiver may detect the beam. The receive device may focus the beam reflected from objects onto the beam receiver. The controller may determine the position of the objects over time and calculate the speed of the objects based on a change in the position of the objects. 
     Various embodiments of the present invention may include a transceiving reflection device for use with a light detection and ranging system. The transceiving reflection device comprises a transmit reflection device and a receive reflection device. The transmit reflection device may reflect a beam from a beam source into a space in which objects may be present and may include a transmit base, a transmit upper stage, and a plurality of transmit faces. The transmit upper stage may be spaced apart from and parallel to the transmit base. The transmit faces may be positioned in a circle between the transmit base and the transmit upper stage with at least a portion of the transmit faces oriented at a different angle therebetween. The receive reflection device may focus the beam onto a beam receiver and may include a receive base, a receive upper stage, and a plurality of receive faces. The receive base may be coupled to the transmit base. The receive upper stage may be spaced apart from and parallel to the receive base. The receive faces may be positioned in a circle between the receive base and the receive upper stage with at least a portion of the receive faces oriented at a different angle therebetween. 
     This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Other aspects and advantages of the present invention will be apparent from the following detailed description of the embodiments and the accompanying drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       Embodiments of the present invention are described in detail below with reference to the attached drawing figures, wherein: 
         FIG. 1  is a block diagram of a system for determining the speed of objects constructed in accordance with various embodiments of the present invention; 
         FIG. 2  is a diagram of a frame that is scanned by the system; 
         FIG. 3  is a diagram of the frame depicting the sweeping of a beam within the frame; 
         FIG. 4  is a perspective view of a housing operable to house at least a portion of the system; 
         FIG. 5  is a perspective view of the system with the outer walls of the housing removed; 
         FIG. 6  is a perspective view of the system of  FIG. 5  with a portion of a transceiving reflection device removed to expose its interior; 
         FIG. 7  is a perspective view of the housing with a portion of the exterior walls removed to illustrate the system transmitting and receiving the beam; 
         FIG. 8  is a front view of the transceiving reflection device including a transmit reflection device and a receive reflection device; 
         FIG. 9  is a perspective view of a transmit device including the transmit reflection device; 
         FIG. 10  is a perspective view of a receive device including the receive reflection device; 
         FIG. 11  is a sectional view of the transceiving reflection device; 
         FIG. 12  is a perspective view of an alternative embodiment of the transmit device and the receive device; 
         FIG. 13A  is an overhead view of a law enforcement vehicle utilizing the system to determine the speed of objects on a roadway; 
         FIG. 13B  is an overhead view of the law enforcement vehicle utilizing the system to determine the speed of objects on the roadway; 
         FIG. 14  is a graph of raw data from beams that are reflected by objects and received by the system; 
         FIG. 15  is a graph of a histogram of beams received versus distance from the system; 
         FIG. 16  is a graph of a histogram of beams received from a potential first object; 
         FIG. 17  is a graph of a histogram of beams received from a potential second object; 
         FIG. 18  is a graph of a histogram of beams received from a potential third object; and 
         FIG. 19  is a graph of the position of potential objects over time. 
     
    
    
     The drawing figures do not limit the present invention to the specific embodiments disclosed and described herein. The drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the invention. 
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The following detailed description of the invention references the accompanying drawings that illustrate specific embodiments in which the invention can be practiced. The embodiments are intended to describe aspects of the invention in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments can be utilized and changes can be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense. The scope of the present invention is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled. 
     In this description, references to “one embodiment”, “an embodiment”, or “embodiments” mean that the feature or features being referred to are included in at least one embodiment of the technology. Separate references to “one embodiment”, “an embodiment”, or “embodiments” in this description do not necessarily refer to the same embodiment and are also not mutually exclusive unless so stated and/or except as will be readily apparent to those skilled in the art from the description. For example, a feature, structure, act, etc. described in one embodiment may also be included in other embodiments, but is not necessarily included. Thus, the present technology can include a variety of combinations and/or integrations of the embodiments described herein. 
     Embodiments of the present invention may provide a traffic scanning light detection and ranging (LIDAR) system  10 , as shown in  FIG. 1 , that is operable to scan a field of view or a frame to determine the speeds of objects within the frame. The system  10  may broadly comprise a beam source  12 , a transmit device  14 , a receive device  16 , a beam receiver  18 , a controller  20 , and a camera  22 . The system  10  may optionally include a display  24 . The system  10  may further include a housing  26  to house the system  10  excluding the display  24 . 
     The beam source  12  generally provides a source of electromagnetic (EM) radiation that is transmitted to at least one object  28 , such as a motor vehicle as seen in  FIGS. 13A-13B , and reflected back. Typically the radiation is swept or scanned over a space or a volume, such as a roadway setting, between the system  10  and the object  28  and may take the form of a directed beam  30 . As used herein, a “sweep” may refer to the process of a beam  30  being moved, typically by rotation, through a given angle. The field of view of the scan or the data associated therewith may be referred to as a “frame”  32 , as seen in  FIG. 2 , and may include a horizontal sweep angle θ and a vertical sweep angle φ. In an exemplary frame  32 , θ may range from approximately 24 degrees to approximately 45 degrees, approximately 25.7 degrees to approximately 36 degrees or may be approximately 28 degrees. φ may range from approximately 5 degrees to approximately 9 degrees, approximately 6 degrees to approximately 8 degrees or may be approximately 7 degrees. 
     The beam source  12  may include a laser  34 , as is known in the art, operable to generate the beam  30 . In some embodiments, the beam source  12  may include a plurality of lasers that produce a plurality of beams  30 . An exemplary laser  34  may be configured to produce a pulsed output with a power that ranges from approximately 50 watts (W) to approximately 100 W, approximately 70 W to approximately 80 W, or may be 75 W. Each pulse may have a period that ranges from approximately 5 nanoseconds (ns) to approximately 20 ns, approximately 7 ns to approximately 15 ns, or may be approximately 10 ns. The pulse repetition rate may range from approximately 50 kilohertz (kHz) to approximately 100 kHz, approximately 70 kHz to approximately 90 kHz, or may be approximately 80 kHz. The output of the laser  34  may be in the infrared (IR) range with a wavelength that ranges from approximately 700 nanometers (nm) to approximately 1400 nm, approximately 850 nm to approximately 950 nm, or may be approximately 905 nm. The beam divergence may range from approximately 0.05 degrees to approximately 0.15 degrees, approximately 0.07 degrees to approximately 0.12 degrees, or may be approximately 0.1 degrees in the horizontal direction. The beam divergence may range from approximately 0.5 degrees to approximately 1.5 degrees, approximately 0.7 degrees to approximately 1.2 degrees, or may be approximately 1 degree in the vertical direction. The beam source  12  may also include a collimating element  36 , as shown in  FIG. 5 , which may collimate the output of the laser  34 . 
     The system  10  may further include a beam source input  38  from the controller  20  to the beam source  12 . The beam source input  38  may determine the operation of the beam source  12  such as energizing and de-energizing the beam  30 , the width of the pulse, the power of the output, and the like. 
     The transmit device  14  generally directs or guides the beam  30  from the beam source  12  in order to perform a sweep. The transmit device  14  may sweep the beam  30  across the field of view frame  32  in the horizontal and vertical directions. The transmit device  14  may include optical components such as lenses, mirrors, beam splitters, prisms, and the like to perform actions on the beam source  12  output such as reflecting, refracting, diffracting, collimating, focusing, steering, and the like. 
     An exemplary embodiment of the transmit device  14  is shown in  FIGS. 6-7 , and may include a transmit reflection device  40  with a plurality of transmit faces  42 . The transmit reflection device  40  may include a transmit base  44  and a spaced-apart transmit upper stage  46 . The transmit base  44  may be planar and somewhat disc shaped. The transmit upper stage  46  may also be planar and somewhat disc shaped with a smaller diameter than the transmit base  44 . The transmit base  44  and the transmit upper stage  46  may be roughly parallel with each other and have the centers aligned. Both the transmit base  44  and the transmit upper stage  46  may include central openings. 
     The transmit faces  42  may be generally rectangular in shape with a planar reflective surface. The transmit faces  42  may be located between the transmit base  44  and the transmit upper stage  46  around the circumference of the transmit base  44  and the transmit upper stage  46 . In an exemplary embodiment, there may be twelve transmit faces  42  positioned adjacent one another between the transmit base  44  and the transmit upper stage  46 . In alternative embodiments, there may be fewer or more transmit faces  42  depending on, among other things, the desired aspect ratio of the field of view frame  32 . For example, fewer transmit faces  42  may generally lead to a wider and shorter frame  32 , while more transmit faces  42  may generally lead to a narrower and taller frame  32 . 
     Generally, at least a portion of the transmit faces  42  is oriented at a different angle. In the exemplary embodiment shown in the Figures, each transmit face  42  is oriented at a different angle. For example, the transmit faces  42  may be oriented at consecutively changing angles with respect to the transmit base  44  and the transmit upper stage  46 . Specifically, the angle α between the transmit face  42  and the transmit upper stage  46 , as seen in  FIG. 11 , may change. In general, the angle α for any of the transmit faces  42  may range from approximately 25 degrees to approximately 65 degrees, from approximately 30 degrees to approximately 60 degrees, or from approximately 40 degrees to approximately 50 degrees. For individual transmit faces  42 , there may be a difference in the angle α between consecutive transmit faces  42  that ranges from approximately 0.25 degrees to approximately 0.5 degrees or may be approximately 0.375 degrees. Thus, the angle α for a first transmit face  42  may range from approximately 46.25 degrees to approximately 47.5 degrees or may be approximately 46.875 degrees. The angle α for a second transmit face  42  may range from approximately 46.0 degrees to approximately 47.0 degrees or may be approximately 46.500 degrees. The angle α for a twelfth transmit face  42  may range from approximately 42.0 degrees to approximately 43.5 degrees or may be approximately 42.750 degrees. The difference between consecutive transmit faces  42  may also influence the height of the frame  32 . For example, a greater difference may generally lead to a greater height of the frame  32 , while a lesser difference may generally lead to a shorter height of the frame  32 . 
     The transmit reflection device  40  may be positioned in proximity to the beam source  12  such that the plane of the transmit base  44  and the transmit upper stage  46  is roughly perpendicular to the axis of the beam source  12 . The beam  30  from the beam source  12  may strike the transmit faces  42  roughly in the center of each face  42 . The transmit reflection device  40  may rotate about a central axis. As the transmit reflection device  40  rotates, the beam  30  may reflect off each of the transmit faces  42  in turn, creating one sweep for each transmit face  42 . Since the transmit faces  42  are oriented at consecutively changing angles, the beam  30  is swept at a consecutively changing height within the frame  32  in order to create a raster scan. 
     Referring to  FIG. 3 , the reflection of the beam  30  off the first transmit face  42  creates a sweep at the top of the frame  32 . The reflection of the beam  30  off the second transmit face  42  creates a sweep just below the first sweep. The reflection of the beam  30  off the third transmit face  42  creates a sweep just below the second sweep. This process continues until the beam  30  is reflected off the twelfth transmit face  42 , and the transmit reflection device  40  has completed one rotation. As the transmit reflection device  40  continues to rotate, the beam  30  is reflected off the first transmit face  42  again and the beam is swept across the top of the frame  32 . The beam  30  may sweep from the bottom of the frame  32  to the top of the frame  32 , depending on the direction of rotation of the transmit reflection device  40  and the order in which the transmit faces  42  are positioned within the transmit reflection device  40 . 
     In an exemplary embodiment of the system  10 , the transmit reflection device  40  is rotated at a speed such that the beam  30  is swept to provide 20 frames per second. 
     As can be seen in  FIG. 3 , the beam  30  overlaps itself on consecutive sweeps from consecutive transmit faces  42  in the vertical direction within the frame  32 . In other words, a portion of one sweep may overlap a portion of the next sweep. For example, the lower portion of the first sweep may overlap the upper portion of the second sweep. The lower portion of the second sweep may overlap the upper portion of the third sweep. The overlap may continue until the twelfth sweep, wherein only the upper portion of the twelfth sweep overlaps the lower portion of the eleventh sweep. Then, the next transmit face  42  is the first transmit face  42 , that generates the first sweep across the top of the frame  32 . The overlap helps to ensure that the frame  32  is completely scanned and that no objects  28  are missed because of a gap between sweeps. 
     The transmit reflection device  40  may be formed from lightweight materials such as lightweight metals or plastics. The transmit faces  42  may be formed from reflective materials. Exemplary transmit faces  42  may have a reflectivity of greater than 97%. In some embodiments, the transmit reflection device  40  may be formed from separate transmit faces  42  that are joined to the transmit base  44  and the transmit upper stage  46 . However, in an exemplary embodiment, the transmit reflection device  40 , including the transmit base  44 , the transmit upper stage  46 , and the transmit faces  42 , is formed as a monolithic single unit from a plastic, perhaps injection molded, that is coated with a reflective material such as gold or silver. 
     The transmit device  14  may alternatively be implemented with a prism assembly that refracts the beam  30  instead of reflecting it. A first exemplary prism assembly is a Risley prism assembly  48  that comprises a first wedge prism  50  and a second wedge prism  52 , as seen in  FIG. 12 . With a beam  30  directed at the Risley prism assembly  48 , the first wedge prism  50  may be rotated at a greater rotational frequency than the second wedge prism  52 . This rotation scheme may result in a spiral-shaped sweeping pattern being formed. Thus, the frame  32  may have a circular shape rather than a rectangular shape. Alternatively, the Risley prism assembly  48  may be directed to sweep the beam  30  in a criss-cross pattern or a lemniscate pattern. 
     A second exemplary prism assembly is similar to the Risley prism assembly  48  of  FIG. 12  and includes a third wedge prism with a smaller deflection angle than the first and second wedge prisms  50 ,  52 . In this embodiment, the first and second wedge prisms  50 ,  52  may rotate in opposite directions to each other and at the same speed. In the absence of the third prism, the two prisms  50 ,  52  may receive the beam  30  directed at one of the prisms  50 ,  52  and refract the beam  30  to form a horizontal line sweep. The third prism may be positioned adjacent to and in line with the first and second wedge prisms  50 ,  52  such that the third prism receives the beam output from the first two prisms  50 ,  52 . The third prism may be rotated to refract the beam  30  in the vertical direction. Thus, while the first and second prisms  50 ,  52  are rotating at a constant speed, the third prism may be stationary while the beam  30  performs a full horizontal sweep at a first height. Then, the third prism may rotate through a fixed angle and stop while the beam  30  performs a full horizontal sweep at a second height, different from the first. The third prism may rotate again and stop while the beam  30  performs a full horizontal sweep at a third height, different from the second. This process may repeat while the beam  30  sweeps at different heights to scan a full frame  32 . Alternatively, the third prism may be rotated at a very slow speed compared to the rotation of the first and second prisms  50 ,  52 . 
     The system  10  may also include a motor  54  to rotate the transmit reflection device  40 . The motor  54  may include alternating current (AC), direct current (DC), stepper motors, and the like. An exemplary motor  54  may include a 36-Volt (V) brushless DC motor capable of rotating from 0 to 4,000 revolutions per minute (rpm). 
     The receive device  16  generally guides the beams  30  reflected from one or more objects  28  toward the beam receiver  18 . The receive device  16  may, in various embodiments, include optical components such as lenses, lenslets, lens arrays, focal plane arrays, mirrors, beam splitters, prisms, and the like to perform actions on the reflected beams  30  such as focusing, reflecting, refracting, diffracting, steering, and generally guiding the beams  30  to the beam receiver  18 . 
     An exemplary embodiment of the receive device  16  is shown in  FIGS. 8 and 10 , and may include a receive reflection device  55  with a plurality of receive faces  56 , a planar disc-shaped receive base  58  with a central opening, and a spaced-apart receive upper stage  60 . The receive faces  56  may be generally wedge-shaped and positioned adjacent one another between the receive base  58  and the receive upper stage  60 . In the exemplary embodiment of  FIGS. 8 and 10 , there may be twelve receive faces  56  used with the receive reflection device  55 . Generally, the number of receive faces  56  matches the number of transmit faces  42 . 
     Each receive face  56  may include an outer surface  62  with the shape of a partial circular paraboloid. As a geometric shape, the circular paraboloid has the property of reflecting rays that strike the paraboloid surface with a trajectory that is parallel to the central axis to a focal point within the paraboloid. Thus, the receive faces  56  may be used to reflect beams  30  to a focal point FP, as seen in  FIG. 11 . The beams  30  may be those that were transmitted from the beam source  12  and reflected off objects  28  such as motor vehicles. The focal point for the beams  30  may be the beam receiver  18 , discussed in more detail below. 
     Generally, at least a portion of the receive faces  56  is oriented at a different angle. In the exemplary embodiment shown in the Figures, each receive face  56  is oriented at a different angle. For example, the outer surface  62  of each receive face  56  may be oriented at consecutively changing angles with respect to the receive base  58 . Specifically, the angle β between the central axis CA of the partial circular paraboloid of each receive face  56  and a vertical axis VA that is perpendicular to the receive base  58 , as seen in  FIG. 11 , may change. In general, the angle β for any of the receive faces  56  may range from approximately 60 degrees to approximately 120 degrees, from approximately 75 degrees to approximately 105 degrees, or from approximately 80 degrees to approximately 100 degrees. For individual receive faces  56 , there may be a difference in the angle β between consecutive receive faces  56  that ranges from approximately 0.5 degrees to approximately 1 degree or may be approximately 0.75 degrees. Thus, the angle β for a first receive face  56  may range from approximately 85.0 degrees to approximately 87.5 degrees or may be approximately 86.25 degrees. The angle β for a second receive face  56  may range from approximately 86.0 degrees to approximately 88.0 degrees or may be approximately 87.00 degrees. The angle β for a twelfth receive face  56  may range from approximately 93.0 degrees to approximately 96.0 degrees or may be approximately 94.50 degrees. The change in the angle β for consecutive receive faces  56  may correspond to the change in the angle α for consecutive transmit faces  42 . In various embodiments, the change in angle β may be a multiple of the change in the angle α. 
     In operation, the receive reflection device  55  may rotate. During rotation, each receive face  56  may focus beams  30  reflected from objects  28  at varying angles of rotation. Furthermore, each consecutive receive face  56  may focus beams  30  reflected from objects  28  at varying angles with respect to the horizontal plane. For example, depending on the direction of rotation of the receive reflection device  55 , the receive faces  56  may focus beams  30  reflected from objects  28  increasingly lower in the frame  32  or increasingly higher in the frame  32 . This operation of the receive reflection device  55  creates a raster scan for the received beams  30 . 
     The receive device  16  may alternatively be implemented with a Risley prism assembly  48  shown in  FIG. 12 . Beams  30  may be reflected from objects  28  in the roadway to the second prism  52  and travel through the assembly  48  to a beam splitter (not shown). The beam  30  is then reflected from the beam splitter to the beam receiver  18 . 
     Like the transmit reflection device  40 , the receive reflection device  55  may be formed from lightweight materials such as lightweight metals or plastics, and the receive faces  56  may be formed from reflective materials. Exemplary receive faces  56  may have a reflectivity of greater than 97%. In some embodiments, the receive reflection device  55  may be formed from separate receive faces  56  that are joined to the receive base  58 . However, in an exemplary embodiment, the receive reflection device  55 , including the receive base  58  and the receive faces  56 , is formed as a monolithic single unit from a plastic, perhaps injection molded, that is coated with a reflective material such as gold or silver. 
     In some embodiments, the receive reflection device  55  may coupled to the transmit reflection device  40 , such that the receive base  58  of the receive reflection device  55  is connected to the transmit base  44  and the transmit faces  42  are positioned opposite of and vertically aligned with the receive faces  56 . The combination of the receive reflection device  55  and the transmit reflection device  40  may form a transceiving reflection device  64 . In the exemplary embodiment of  FIGS. 5-10 , the transmit reflection device  40  and the receive reflection device  55  are formed as a monolithic single unit from a metallic-coated plastic. In addition, the first receive face  56  is aligned with the first transmit face  42 , the second receive face  56  is aligned with the second transmit face  42 , and so forth, such that the twelfth receive face  56  is aligned with the twelfth transmit face  42 . 
     The motor  54  utilized for rotating the transmit reflection device  40  may also be used to rotate the receive reflection device  55 . The motor  54  may be positioned within the openings of the transmit upper stage  46  and the transmit base  44  and the opening in the base of the receive reflection device  55 . The motor  54  may include a shaft  66  that is coupled to the receive upper stage  60  of the receive reflection device  55 , such that when the shaft  66  rotates, both the transmit reflection device  40  and the receive reflection device  55  rotate as well. 
     The beam receiver  18  generally receives the reflected beams  30  that have been focused by the receive faces  56 . The beam receiver  18  may include devices or arrays of devices that are sensitive to IR radiation, such as charge-coupled devices (CCDs) or complementary metal-oxide semiconductor (CMOS) sensor arrays, photodetectors, photocells, phototransistors, photoresistors, photodiodes, or combinations thereof. In an exemplary embodiment, the beam receiver  18  includes a silicon avalanche photodiode with a peak sensitivity at 905 nm, a bandwidth of 905 nm ±40 nm, an active area of 2 mm×2 mm, and a current gain of 200. The photodiode may be coupled to a receiver circuit with a gain of 10 6 , an operational frequency range of 1 megahertz (MHz) to 100 MHz, and a comparator output. 
     The beam receiver  18  may positioned in proximity to the receive reflection device  55  at the focal point of the receive faces  56 . The beam receiver  18  may include a beam receiver output  68  that provides information corresponding to the reflected beams  30  to the controller  20 . 
     The controller  20  may execute computer programs, software, code, instructions, algorithms, applications, or firmware, and combinations thereof. The controller  20  may include processors, microprocessors, microcontrollers, field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), combinations thereof, and the like, and may be implemented using hardware description languages (HDLs), such as Verilog and VHDL. The controller  20  may further include data storage components, which may comprise “computer-readable media” capable of storing the computer programs, software, code, instructions, algorithms, applications, or firmware. The computer-readable media may include random-access memory (RAM) such as static RAM (SRAM) or dynamic RAM (DRAM), cache memory, read-only memory (ROM), flash memory, hard-disk drives, compact disc ROM (CDROM), digital video disc (DVD), or Blu-Ray™, combinations thereof, and the like. 
     In an exemplary embodiment, the controller  20  includes a Kinetis K10 microcontroller manufactured by Freescale of Austin, Tex., and an OMAP™ 4 microprocessor manufactured by Texas Instruments of Dallas, Tex. Some of the functions that the microcontroller handles include sending a control signal to the beam source  12  and sending a control signal to the motor  54 . Some of the functions that the microprocessor handles include sending video information to the display  24 , processing the received beam  30  information, and calculating the speed of objects  28  within the frame  32 . 
     The controller  20  may further include a timer circuit that is operable to measure the time of flight of the beam  30  or pulses of the beam  30 . The timer may start when a pulse of the beam  30  is transmitted from the beam source  12  and may stop when the pulse of the beam  30  is received by the beam receiver  18 . 
     In addition, the controller  20  may include an accelerometer or may receive the output of an external accelerometer to determine the motion of a vehicle in which the system  10  is implemented. The controller  20  may also receive the pulse train output of the transmission of the vehicle. 
     In various embodiments, the controller  20  may be aware of the angle at which the transceiving reflection device  40  is rotating. Thus, the controller  20  may be aware of which transmit face  42  is reflecting the beam  30  and which receive face  56  is focusing beams  30  onto the beam receiver  18 . Furthermore, the controller  20  may be aware of the horizontal sweep angle θ and the vertical sweep angle φ the beam  30  is being reflected from the transmit reflection device  40 . 
     In some embodiments, the controller  20  may also receive MPEG4-encoded data from the camera  22  and may determine velocity vector information regarding objects  28  within the frame  32  based on the MPEG4 data. 
     The system  10  may further include components not shown in the figures such as inputs, outputs, and communication ports. Inputs may include knobs, dials, switches, keypads, keyboards, mice, joysticks, combinations thereof, and the like. Outputs may include audio speakers, lights, dials, meters, printers, combinations thereof, and the like. Communication ports may be wired or wireless, electronic, optical, radio frequency (RF), combinations thereof, and the like. 
     The camera  22  generally provides an image of the space or volume that the system  10  is scanning. An exemplary camera  22  may be a 1080p high-definition camera capable of capturing 30 fps. The camera  22  may include a camera output  70  that communicates video data to the display  24 . In some embodiments, the camera  22  may include an MPEG4 codec, as is known in the art, to generate MPEG4-encoded data that may be communicated to the controller  20  via a camera data output  72 . 
     The display  24  generally displays the video image from the camera  22  as well as information from the controller  20  regarding objects in the image. The display  24  may include video monitors as are known in the art capable of displaying moving or still video images in addition to text or graphical data within the same frame. Examples of the display  24  may include cathode ray tubes (CRTs), plasma monitors, liquid crystal display (LCD) monitors, light-emitting diode (LED) monitors, LED-LCD monitors, combinations thereof, and the like. 
     In embodiments wherein the system  10  does not include the display  24 , the system  10  may send data on a display output  74  to an external display or monitor. 
     The housing  26  may be of cubic or rectangular box shape with six walls: a top wall  76 , a bottom wall  78 , a left side wall  80 , a right side wall  82 , a front wall  84 , and a rear wall  86  that are coupled together in a typical box construction. The housing  26  may further include an internal frame  88  and an optical isolation plate  90 . The housing  26  may be constructed from plastics or lightweight metals, such as aluminum. 
     The camera  22  may be positioned on the exterior of the housing  26 , such as mounted on the exterior of the front wall  84  or the exterior of the top wall  76 . In other embodiments, the camera  22  may be positioned within the housing  26  adjacent a window or opening through which the camera  22  captures video images. In still other embodiments, the camera  22  may be positioned external to the housing  26 . 
     The motor  54  may be mounted on the bottom wall  78  close to the center thereof. Thus, the transmit reflection device  40  may face the bottom wall  78 , while the receive reflection device  55  faces the top wall  76 . The beam source  12  may also be mounted on the bottom wall  78  in proximity to the front wall  84 , such that the collimating element  36  is aligned with one of the transmit faces  42 . 
     The front wall  84  may include a receive window  92  and a transmit window  94 , both of which may be filled with a material, such as glass or glass-like material, that is transparent to electromagnetic radiation at a wavelength that ranges from approximately 700 nm to approximately 1400 nm, approximately 850 nm to approximately 950 nm, or may be approximately 905 nm. The receive window  92  may be positioned in proximity to the receive reflection device  55  such that it is aligned with the receive faces  56 . Beams  30  may reflect off objects  28  into the receive window  92  and may be focused by the receive faces  56  onto the beam receiver  18 , as shown in  FIGS. 7 and 11 . The transmit window  94  may be positioned in proximity to the transmit reflection device  40  such that it is aligned with the transmit faces  42 . The beam source  12  may generate the beam  30  that reflects off the transmit faces  42  and travels through the transmit window  94 . 
     The internal frame  88  may include a first upright wall member  96  in proximity to the left side wall  80  and a second upright wall member  98  in proximity to the right side wall  82 , both of which are coupled to the bottom wall  78 . The frame  32  may also include a cross beam  100  coupled to the upper edges of the first and second upright wall members  96 ,  98 . The frame  32  may further include a mounting assembly  102  coupled to the cross beam  100  and to which the beam receiver  18  is mounted. The mounting assembly  102  may be adjustable about one or more axes in order to position the beam receiver  18  at the focal point of the partial circular paraboloid of the receive faces  56 . 
     The optical isolation plate  90  may be positioned within the housing along a horizontal plane at a level just above the receive base  58  of the receive reflection device  55 . First, second, and third sides of the optical isolation plate  90  may couple to the left side wall  80 , the front wall  84 , and the right side wall  82 , respectively. A fourth side includes a circular cutout that is slightly smaller than the circumference of the receive base  58  of the receive reflection device  55 . Thus, the cutout of the optical isolation plate  90  is positioned between the edge of the receive base  58  and the receive faces  56 . Since the optical isolation plate  90  overlaps the receive base  58 , the plate  90  acts as a shield to prevent stray radiation from the beam source  12  being detected by the beam receiver  18 . 
     The system  10  is generally implemented in a law enforcement vehicle  104 , and the housing  26  may be mounted on the dashboard with access to an open field of view. In various embodiments, the housing  26  may be mounted on the exterior of the vehicle  104 , such as on the roof. In some embodiments, the camera  22  may be mounted on the exterior of the vehicle  104  as well. 
     The system  10  may operate as follows. Referring to  FIG. 13A , the system  10 , mounted in the law enforcement vehicle  104 , may scan the field generally toward the front of the vehicle  104  for objects  28 , such as other vehicles. The controller  20  may send a signal to the beam source  12  and the motor  54  to initiate a scan of the field of view frame  32 . Generally, once the system  10  is energized, the frame  32  is scanned repeatedly, such that when one frame  32  is scanned, another frame  32  begins scanning automatically. 
     Given a command from the controller  20 , the beam source  12  generates a beam  30  that may have the power and pulse characteristics as described above. Also given a command from the controller  20 , the motor  54  rotates the transmit reflection device  40 . The beam  30  from the beam source  12  may reflect off one of the transmit faces  42  and travel through the transmit window  94  to the roadway or landscape in front of the law enforcement vehicle  104 . As the transmit reflection device  40  rotates, the transmit faces  42  rotate as well. Rotation of a transmit face  42  while it is reflecting a beam  30  causes the beam  30  to sweep in the horizontal direction across the field of view frame  32 . The beam  30  may sweep from right to left or left to right depending on the direction of rotation of the transmit reflection device  40 . Once the edge of one transmit face  42  rotates beyond the beam  30  from the beam source  12 , the next transmit face  42  reflects the beam  30  horizontally in the same direction as the previous transmit face  42  did. The current transmit face  42  may sweep the beam  30  across the frame  32  at a different height from the previous transmit face  42 . Depending on the order in which the transmit faces  42  are positioned on the transmit reflection device  40  or the direction of rotation of the transmit reflection device  40 , the beam  30  reflected from the current transmit face  42  may sweep higher or lower in the frame  32  than the beam  30  from the previous transmit face  42 . 
     While the beams  30  are transmitted from the system  10  to the roadway in front of the law enforcement vehicle  104 , one or more beams  30  may be reflected off of objects  28 , as seen in  FIG. 13B . The objects  28  may be moving or stationary, on the road and off of the road. In addition, the law enforcement vehicle  104  and, in turn, the system  10  may be stationary or in motion. 
     As the beams  30  are reflected back to the system  10 , the beams  30  may be focused by the receive reflection device  55  to the beam receiver  18 . Since the receive base  58  of the receive reflection device  55  is coupled to the transmit base  44 , the two devices  16 ,  40  rotate at the same speed. In addition, the angle at which each receive face  56  is oriented corresponds to the angle at which the vertically-aligned transmit face  42  is oriented. For example, the transmit face  42  that sweeps the beam  30  along the lowest horizontal path of the frame  32  is aligned with the receive face  56  that is oriented to focus beams  30  reflected from objects located along the lowest horizontal path of the frame  32 . Likewise, the transmit face  42  that sweeps the beam  30  along the highest horizontal path of the frame  32  is aligned with the receive face  56  that is oriented to focus beams  30  reflected from objects located along the highest horizontal path of the frame  32 . 
     The controller may use the timer circuit to determine the time of flight of pulses of the reflected beams  30  received by the beam receiver  18 . Given the time of flight of the pulse and the speed of the pulse (roughly the speed of light), the distance to the object  28  from which the pulse of the beam  30  was reflected can be calculated. Furthermore, the controller  20  may determine the horizontal sweep angle θ at which the pulse of the beam  30  was transmitted from the transmit reflection device  40 . The controller  20  may assume that the pulse is reflected off an object  28  at the same angle it was transmitted. As a result, for each pulse of the beam  30  received by the beam receiver  18 , the controller  20  determines the distance that the pulse traveled and the angle θ at which the pulse was reflected. Thus, the controller  20  may record the data for each received pulse in terms of polar coordinates where the radius is the distance to the object  28  from which the pulse was reflected and the angle is the angle θ at which the pulse was reflected. The controller  20  may ignore data relating to pulses that are received near the horizontal edges of the frame  32 , because that is where the beam  30  was transitioning from one transmit face  42  to the next transmit face  42  and the pulses may not be received properly at the edges of the frame  32 . 
     The controller  20  may perform a plurality of calculations in order to calculate the speed of objects  28  moving in the roadway in front of the law enforcement vehicle  104 . The results of the calculations may be represented in  FIGS. 14-19 . The controller  20  may not necessarily communicate the results of the calculations to the display  24  or other monitor. However, the results are shown as graphs in the Figures to help illustrate the operation of the controller  20 . 
     The controller  20  may convert the data relating to received pulses of the beam  30  from polar coordinates to rectangular Cartesian coordinates, as shown in graph  106  of  FIG. 14 . Graph  106  depicts an overhead view of the roadway and the field of view of the system  10 . The housing  26  of the system  10  may be located at coordinates (0, 0) of graph  106 . Plotted along the y-axis is the distance to the left (positive y direction) and to the right (negative y direction) from the housing  26  given in units of feet. Plotted along the x-axis is the distance away from the housing  26  in front of the law enforcement vehicle  104  given in units of feet. The V-shaped lines  108  represent the boundaries of the sweep of the beam  30 . Received pulses of the beam  30  are raw data points  110  plotted on graph  106  with a lower case x. In graph  106 , a plurality of pulses are plotted that were received over a short period of time—perhaps one second. 
     Also shown in graph  106  are boxes  112  and circles  114  around clusters of points  110  detected to be objects  28 , as described in greater detail below. The sides of the box  112  may be drawn at the extents of the object  28 . The circle  114  may be drawn with its center located at the median or the mean of the points  110  of the object  28 . 
     In order to determine where objects  28  are in the plot of graph  106 , the controller  20  may sort the points  110  by distance from the housing  26 , as shown in the histogram plot of graph  116  in  FIG. 15 . Along the y-axis of graph  116  is plotted the number of points  110  received. Along the x-axis is plotted the distance from the housing  26 . As seen from graph  106  of  FIG. 15 , there is a large number of points  110  from the distance of about 45 feet to the distance of about 70 feet. There is a smaller number of points  110  from the distance of about 75 feet to about 90 feet. There are very small amounts of points  110  occurring at greater distances from the housing  26 . All the points  110  shown in graph  106  are plotted in graph  116  as the number of points  110  occurring at each distance away from the housing  26 . 
     To enhance the detection of objects  28 , a second set of points  118  may also be calculated and plotted. The second set of points  118  is, for each distance, the sum of the number of points  110  for two feet on either side of the distance. The value of two feet may be variable for other embodiments. For example, if the number of points  110  at consecutive distances is given by: 8 feet=4 points, 9 feet=3 points, 10 feet=6 points, 11 feet=5 points, and 12 feet=4 points. A second point  118  for the distance of 10 feet would be the sum of the points  110  for 8 feet to 12 feet=4+3+6+5+4. Thus, a second point  118  for 10 feet=22. 
     A threshold  120  is also applied to the second set of points  118 , as seen in graph  116 . The threshold  120  may have a constant value at a given number of points. In the example of graph  116 , the constant value occurs at approximately 410. The threshold  120  may also include an exponential decay that approaches an asymptote of zero points. For every group of points  118  that crosses the threshold  120 , there may be one or more objects  28 . 
     To determine the number of objects  28  and the width of each object  28  at a certain distance, the controller  20  may sort the points  118  by distance from the center at the certain distance from the housing  26 . Thus, everywhere that there is a peak of the points  118  that crosses the threshold  120 , the controller  20  may sort the points  118  at the peak. In the example plot of graph  116 , there are two peaks (a first at about 55 feet and a second at about 80 feet) where the points  118  cross the threshold  120 . There is a third peak at about 135 feet where the threshold  120  is almost crossed. The distribution of points  118  at the three peaks are plotted as histograms in graphs  122 ,  124 ,  126  shown in  FIGS. 16 ,  17 , and  18  respectively. 
     The distribution of both sets of points  110 ,  118  at a distance of approximately 55 feet from the housing  26  is plotted in graph  122 . For reference, it can be seen in graph  106  that at a distance along the x-axis of about 55 feet, there is a plurality of points  110  positioned from about 4 feet to about 10 feet in the y direction. The raw data points  110  are plotted in graph  122  from 4 feet to 10 feet along the x-axis. The second set of enhanced data points  118  is also plotted in graph  122 . The threshold  120 , with a value of approximately 35, is plotted as well. Thus, it appears from graph  122  that there is only one object at the distance of about 55 feet. 
     The distribution of both sets of points  110 ,  118  at a distance of approximately 80 feet from the housing  26  is plotted in graph  124 . Similar to graph  122  discussed above, for reference, it can be seen in graph  106  that at a distance along the x-axis of about 80 feet, there is a first plurality of points  110  positioned from about 14 feet to about 20 feet in the y direction. There is a second plurality of points  110  from about 12 feet to about 18 feet in the negative y direction. These points  110  are plotted in graph  124 , showing one set of points  110  between −18 and −12 and a second set of points  110  between 14 and 20. The second set of enhanced data points  118  is also plotted in graph  124 . In addition, the threshold  120 , with a value of approximately 15, is plotted. Thus, it can be seen that there are two objects  28  spaced about 25 feet apart at a distance of about 80 feet from the housing  26 . 
     The third peak from graph  116  is plotted in graph  126 . As can be seen in graph  106 , at approximately 135 feet from the housing, there is a small number of points  110  at about 10 feet and about 22 feet in the negative y direction. The raw data points  110  are plotted in graph  126  along with the second set of enhanced points  118 . As can be seen, the points  118  fail to cross the threshold  120  of about 5.5. Thus, there is likely not an object  28  of any interest at a distance of about 135 feet from the housing  26 . 
     Once objects  28  are detected, the controller  20  may track them. For every object  28  that is detected, the controller  20  may create a track  128 . The track  128  represents the xy position of the median of points  110  that were determined to be an object  28  from graphs  122 ,  124  discussed above. A plot of tracks  128  is shown in graph  130  of  FIG. 19 . Graph  130  is similar to graph  106  in that it shows an overhead view of the roadway in front of the housing  26  which may be mounted in a law enforcement vehicle  104 . The lines  108  show the boundaries of the sweep of the beam  30 . Three tracks  128  are shown in graph  130  that correspond to the three objects  28  of graph  106 . The tracks  128  that are shown were recorded over a period of time of a few seconds. Since the tracks  128  represent the distance traveled by each object  28  and the period of time is known, then the speed of each object  28  can be calculated as the distance divided by the time. As can be seen, the upper and lower tracks  128  of graph  130  do not cover much distance, and thus their speeds are near zero. But, the middle track  128  travels a certain distance and has a non-zero speed. 
     To determine the actual speed of the objects  28 , the controller  20  may receive data from an accelerometer or from the pulse train of the transmission of the law enforcement vehicle  104  to detect whether the vehicle  104  is moving. If the law enforcement vehicle  104  is moving, then the controller  20  may add or subtract the speed of the vehicle  104 , as appropriate, to determine the actual speed of each object  28 . If the law enforcement vehicle  104  is stationary, then the speed calculated from the steps above is the actual speed. 
     Once the controller  20  has determined the speed of the objects  28  in the frame  32 , the controller  20  may communicate the speed information to the display  24 . The display  24  may show an image from the camera  22  that depicts the field of view of the camera  22 , which is generally the same as the frame  32  that is being scanned by the system  10 . The display  24  may also show the speed data from the controller  20 , such that objects  28  on the display  24  have an associated speed. For example, a car may be seen on the display  24  with a box, a crosshair, or similar icon superimposed over the car with the speed of the car displayed nearby. The speed and the position of the icon may be updated as the object  28  moves. Alternatively or in addition, the display  24  may have a split screen wherein the image from the camera  22  occupies one portion of the screen and a data information area occupies another portion of the screen. The image portion may still include an indicator of the speed of each car in motion. The data information portion may also list the speeds of objects  28  as well as additional information on the objects  28  or the system  10 . The display  24  may further include touchscreen capabilities that allow the user to touch the screen to issue commands to the system  10  or retrieve more information. 
     The traffic scanning LIDAR system  10  described herein offers a distinct advantage over prior art LIDAR systems. Prior art LIDAR systems aim a beam at a single target and measure the difference between the time of flight of consecutive pulses. This approach measures the relative speed at which the target is moving toward or away from the LIDAR source. The relative speed measured is the actual speed of the target if the target is traveling on a path directly to or from the LIDAR source. If the target is traveling on a path away from the LIDAR source then the measured speed is less than the actual speed of the target. This inaccuracy is known as the “cosine effect” or the “cosine error”. The current system  10  avoids the cosine error because the controller  20  is aware of the angle at which pulses are being reflected from objects  28  (targets). Thus, the current system  10  can track the actual path of the object  28 , not just the path relative to the beam source  12 . Determining the actual path of the object  28  results in calculating the actual speed of the object  28 . 
     An additional advantage of the current system  10  over prior art systems is that the current system  10  sweeps a beam  30  repeatedly over a field of view frame  32  and can therefore track a plurality of objects  28  simultaneously. Prior art systems are generally not capable of sweeping a beam and are thus limited to tracking a single object  28 . 
     The current system  10  is also capable of being used in other applications. The system  10  could be utilized in marine environments for speed detection or navigation. The system  10  could also be utilized in robotic applications for intelligent guidance and navigation of self-propelled robots or robotic machinery. Furthermore, the system  10  could be in the automotive or other vehicle industries for intelligent collision-avoidance systems. 
     Although the invention has been described with reference to the embodiments illustrated in the attached drawing figures, it is noted that equivalents may be employed and substitutions made herein without departing from the scope of the invention as recited in the claims. 
     Having thus described various embodiments of the invention, what is claimed as new and desired to be protected by Letters Patent includes the following: