Abstract:
A method for detecting objects in a scene using a synchronized illuminating and sensing process is provided herein. The method includes the following steps: illuminating a light beam along an illumination line within a scene; sensing reflections of said light, wherein said reflections come from objects located within a specified depth of field within said scene, along a sensing line; generating a tempo spatial synchronization between the illumination line and the sensing line, wherein said synchronization determines said depth of field; relatively shifting at least one of: the illuminating line, and the sensing line, based on said tempo spatial synchronization; and accumulating said reflections, thereby detecting said objects.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present invention relates generally to the field of spatial detection of objects using illuminating and sensing, and more particularly, to achieving same using a synchronized actuator mechanism. 
         [0003]    2. Discussion of Related Art 
         [0004]    Marine environments, which include lakes, seas, oceans, streams, rivers and other bodies of water, present particular challenges to vessels traveling in such environments under the various illumination conditions and various visibility conditions. For example, various types of semi submerged, or floating, obstacles and objects in marine environments, such as icebergs, whales, semi submerged metal ship containers which have fallen overboard, large underwater rocks slightly protruding from the surface of the water, wood logs and the like, pose potential threats to ship hulls and ship propellers. This potential threat is increased under low illumination and bad visibility conditions, such as at night, during a storm or in heavy rain. In addition, the detection of objects in a marine environment, such as buoys or sea marks, as well as the detection of persons who have fallen overboard, presents a challenge for individuals on vessels attempting to locate such objects and persons due to the small surface area of these objects and persons appearing above the surface of the water. As above, the task of locating small objects and persons in a marine environment is made more difficult in low illumination and bad visibility conditions. Furthermore, small objects and persons are usually undetected by radar or thermal imagers (e.g., Near Infrared, Medium Infrared or Far infrared imagers). The term ‘object’ or ‘target herein refers to semi submerged, or floating, obstacles, objects or persons in a marine environment. Objects can include icebergs, whales, semi submerged metal ship containers, large underwater rocks slightly protruding from the surface of the water at low tide, wood logs, buoys, persons and the like. 
         [0005]    Prior art such as U.S. Pat. No. 6,693,561 to Kaplan, entitled “System for and method of wide searching for targets in a marine environment” is directed towards a system and a method of searching for targets in a marine environment and comprises a transmitter means, a processor including a receiver means, and an indicator. The transmitter means is mounted on an object, which is above water, such as on-board a marine vessel, an aircraft, or on a seaside structure. The transmitter means emits first and second beams of optical radiation at first and second zones of water. The first beam has a first wavelength characteristic having wavelengths in the ultraviolet to blue range (300-475 nanometers), and capable of entering the first zone of water and being refracted there through as a refracted beam. The second beam has a second wavelength characteristic having wavelength in the infrared range (650-1500 nanometers) and capable of reflecting from the second zone of water as a reflected beam. The processor is operative for identifying locations of the targets in the marine environment. The receiver means is operative for separately detecting return target reflections reflected off any targets impinged by the refracted and/or the reflected beams to find an identified target. 
         [0006]    Another prior art maybe used such as U.S. Pat. No. 7,379,164 to Inbar et al., entitled “Laser gated camera imaging system and method” is directed towards a gated camera imaging system and method, utilizing a laser device for generating a beam of long duration laser pulses toward a target. A camera receives the energy of light reflexes of the pulses reflected from the target. The camera gating is synchronized to be set ‘OFF’ for at least the duration of time it takes the laser device to produce a laser pulse in its substantial entirety, including an end of the laser pulse, in addition to the time it takes the laser pulse to complete traversing a zone proximate to the system and back to the camera. The camera gating is then set ON for an ON time duration thereafter, until the laser pulse reflects back from the target and is received in the camera. The laser pulse width substantially corresponds to at least the ON time duration. 
         [0007]    Other types of environments where object detection is required may be transportation, aerial (air to air or air to ground object detection), and terrestrial (ground to air or ground to ground object detection). In these environments the objects can a pedestrian, a vehicular or any type of desired object. 
         [0008]    Both of these examples and radar and/or thermal based systems lack the simplicity and superior detection capabilities versus the proposed method. 
       BRIEF SUMMARY 
       [0009]    In accordance with the disclosed technique, there is thus provided a system for detecting objects under low illumination conditions, under low illumination with harsh weather conditions (e.g. rain, snow and fog) and under high illumination conditions (e.g. ambient light). The system includes a light source, a sensor, an actuator such as a whirling mechanism and a processor. The processor is coupled with the whirling mechanism (i.e. scanning), with the light source and with the sensor. The whirling mechanism provides a controlled movement of the light source and of the sensor as to each other. The moving light source generates continuous light toward the scenery. The sensor is sensitive at least to the wavelengths of the light generated by the light source. The sensor receives the light reflected from a specific volume of the scenery (depth of field) based on tempo spatial synchronization. The processor synchronizes the whirling mechanism, the light source and the sensor. The sensor is exposed to light for at least the duration of time it takes the reflected light, originating from the light source, to return from a specific volume of the illuminated scenery (depth of field). 
         [0010]    At least a single object, within the sensor field of view and within the specific volume of the illuminated scenery (depth of field), protruding from the surface of the body of water shall reflect a light signal larger than the water reflected light signal. 
         [0011]    These, additional, and/or other aspects and/or advantages of the present invention are: set forth in the detailed description which follows; possibly inferable from the detailed description; and/or learnable by practice of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The present invention will be more readily understood from the detailed description of embodiments thereof made in conjunction with the accompanying drawings of which: 
           [0013]      FIG. 1  is a schematic illustration of the operation of a system, constructed and operative in accordance with some embodiments of the present invention; 
           [0014]      FIGS. 2A-2E  are schematic illustrations of light propagating through space, towards, and reflecting from, an object in accordance with some embodiments of the present invention; 
           [0015]      FIGS. 3A-3C  are schematic illustrations of light propagating through space, towards, and reflecting from, objects in accordance with some embodiments of the present invention. 
           [0016]      FIG. 4  is a schematic illustration of the operation of a system, constructed and operative in accordance with some embodiments of the present invention; and 
           [0017]      FIGS. 5A-5C  are schematic illustrations of light source output orientation versus sensor unit orientation in accordance with some embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is applicable to other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting. 
         [0019]    In accordance with the present invention, the disclosed technique provides methods and systems for target or object detection, using electro-optical techniques based on the principle of sensor and active illumination synchronization. Accordingly, the terms “target” or “object” refer to any object in general, “light source” refers to any suitable source emitting of electromagnetic energy radiation (i.e. photons in any known wavelength) and “sensor” refers to any apparatus collecting of electromagnetic energy radiation (i.e. photons in any known wavelength) to provide a signal (e.g. pixel, 1D pixel array, 2D pixel array etc.). The “sensor” maybe based on; CMOS Imager Sensor, CCD, Photo-diode, Hybrid FPA, Photomultiplier (including Image Intensifier) etc. 
         [0020]    Accordingly, the disclosed technique provides for manipulation of signal capturing in a sensor, as a function of the accumulated depth of field, by changing the light source illumination parameters, by changing the state of the sensor in a manner to the distance to the target, by changing the state of the whirling mechanism in a manner to the distance to the target, and by other factors. Transmitted or emitted light source illumination refers to a Continuous-Wave (CW) or may refer to a pulsed light source. According to one embodiment, the system is mounted on a moving platform, for example, a vehicular such as; ship, yacht, car, aircraft etc. The disclosed technique is not limited to the embodiment of a moving platform. 
         [0021]    Reference is now made to  FIG. 1 , which is a schematic illustration of the operation of a system, generally referenced  10 , constructed and operative in accordance with an embodiment of the disclosed technique. 
         [0022]    System  10  includes a light source unit  11 , a sensor unit  13 , a whirling mechanism unit  12 , and a controller unit (processor)  14 . Light source unit  11  generates a light beam  17  in the form of CW (i.e. sinus wave to detect phase shift) or pulsed (single/series of continuous pulses). Light source unit  11  emits light beam  17  toward the scenery. Light beam  17  illuminates a potential target  15  in the scenery. Sensor unit  13  receives reflected light source beam  17  from target  15 . Sensor unit  13  may have a single state; a “continuous” state during which the sensor unit  13  receives incoming light continuously. A whirling (scanning) mechanism unit  12  shifts light source unit  11  and sensor unit  13  as to each other in order to accumulate in the sensor unit  13  a specific illuminated scenery volume (depth of field) by the light source unit  11 . A controller unit (processor)  14  controls and synchronizes the shifting of whirling mechanism unit  12 , the light source unit  11  and the sensor unit  13  operations. 
         [0023]    Atmospheric conditions, such as aerosols, humidity, haze, fog, smog, smoke, rain, snow and the like, represented by zone  16 , exist in the surrounding area of system  10 . Backscatter from the area in the immediate proximity to system  10  has a more significant influence on sensor unit  13  than backscatter from further distanced area. Approximate range designated as R MIN  defines the area proximate to system  10  from which the avoidance of backscattered light emitted by light source  11 . The potential target  15  is not expected to be located within range R MIN , therefore the removal of the influences of atmospheric conditions  16  in this range from the captured signal in the sensor unit  13 . These atmospheric conditions interfere with light beam  17  on its way to illuminate target  15 , and with light beam  18  reflected from target  15 . For a specific scenery (subset of a three dimensional volume space), sensor unit  13  does not accumulate light beam  17  for the duration of time that light beam  17  has completely propagated a distance R MIN  toward target  15  in the specific scenery, including the return path to sensor unit  13  from distance R MIN  the specific scenery. Distance between system  10  and potential target  15  is designated range R MAX  (i.e. potential target  15  can be located anywhere between ranges R MIN  and R MAX  being the start point and the end points, respectively). This technique utilizes the low reflected signal background versus the high reflected signal originating from a potential target  15 . In maritime environment the water is absorbing (and/or specular reflecting) most of the transmitted light signal (which is usually in the NIR). 
         [0024]    The proposed system and technique exploits the benefits of an active illumination system and exploits the tempo spatial synchronization to avoid the backscattering. In order to clearly explain how the disclosed technique provides for the senor unit  13  accumulation manipulation of a specific volume of the scenery (depth of field , i.e. between ranges R MIN  and R MAX ), it is useful to illustrate the senor unit  13  state as to the light source unit  11  state. 
         [0025]    Reference is now made to  FIG. 2A-FIG .  2 E, which are a schematic illustrations of the operation of a system, generally referenced  10 , constructed and operative in accordance with an embodiment of the disclosed technique. In order to simplify the following description single specific scenery is illustrated. 
         [0026]    At the particular instant in time (T 0 ) illustrated in  FIG. 2A , light source  11  emits a light beam  17  in the form of CW or pulsed (single/series of continuous pulses). Light source unit  11  emits light beam  17  toward specific scenery. Light duration  20  propagates towards the specific illuminated scenery with a potential target  15  located between ranges R MIN  and R MAX . Light duration  20  is formed via whirling mechanism unit  12  (not illustrated). Light source reflections  22  are due to light beam  20  propagation in a medium with aerosols. During this period (starting in time T 0 ) sensor unit  13  is not exposed to light source reflections  22 . 
         [0027]    In time (T 1 ) illustrated in  FIG. 2B , light source  11  (not illustrated) is not emitting light toward this specific scenery. Light duration  20  still propagates towards the specific illuminated scenery with a potential target  15  located between ranges R MIN  and R MAX . Light source reflections  22  are due to light beam  20  propagation in a medium with aerosols. During this period (T 0  to T 1 ) sensor unit  13  is not exposed to light source reflections  22 . 
         [0028]    In time (T 2 ) illustrated in  FIG. 2C , light source  11  (not illustrated) is not emitting light toward this specific scenery. Light duration  20  still propagates towards the specific illuminated scenery with a potential target  15  located between ranges R MIN  and R MAX . Light source reflections  22  are due to light beam  20  propagation in a medium with aerosols. Light source reflection  21 , within light beam  18 , is reflected from a target  15  originating from light beam  20 . During this period (T 1  to T 2 ) sensor unit  13  is not exposed to light source reflections  22  and not to target reflection  21 . 
         [0029]    In time (T 3 ) illustrated in  FIG. 2D , light source  11  (not illustrated) is not emitting light toward this specific scenery. Light duration  20  (not illustrated) still propagates in the direction of the specific illuminated scenery (further away from R MAX ). Light source reflection  21 , within light beam  18 , is still reflected (i.e. propagating in the atmosphere). During this period (T 2  to T 3 ) sensor unit  13  is not exposed to light source reflections  22  (not illustrated) and not to target reflection  21 . 
         [0030]    In time (T 4 ) illustrated in  FIG. 2E , light source  11  (not illustrated) is not emitting light toward this specific scenery. Light duration  20  (not illustrated) still propagates in the direction of the specific illuminated scenery (further away from R MAX ). Light source reflection  21 , within light beam  18 , is still reflected (i.e. propagating in the atmosphere) and now accumulated in sensor unit  13  for a specific time duration. 
         [0031]    In order to clearly explain how the disclosed technique provides for the senor unit  13  accumulation manipulation of a specific volume (depth of field) in a 360° scenery (i.e. between ranges R MIN  and R MAX ), it is useful to illustrate the senor unit  13  state as to the light source unit  11 . 
         [0032]    Reference is now made to  FIG. 3A-FIG .  3 C, which are a schematic illustrations of the operation of a system, generally referenced  10 , constructed and operative in accordance with an embodiment of the disclosed technique. In order to simplify the following description three specific sceneries (i.e. zones) are illustrated as A, B and C (i.e. the proposed technique may have at least a single zone). Each specific zone is divided to three regions, for example A 1 , A 2  and A 3 . Each one of the figures ( FIG. 3A-FIG .  3 C) represents a stationary condition of system  10  in T a &lt;T b &lt;T c  (time stamps). The proposed technique may have at least a single specific scenery but is not limited. 
         [0033]    At the particular instant in time (T a ) illustrated in  FIG. 3A , light source  11 , passing through region A 3 , emits light with duration of  20 A towards region A 1 . A potential target  15 A is located between ranges R MIN  and R MAX  in region A 1 . Light duration  20 A is formed via whirling mechanism unit  12  (not illustrated here. It is understood that any actuator designed for the purpose of the present invention can be used). During this period sensor unit  13 , passing through region C 3 , accumulates only reflected light  21 C origination from a reflected light signal between ranges R MIN  and R MAX  in region C 1 . In addition, a light with duration of  20 B is reflected outwards (i.e. from B 3  to B 1  direction) and a reflected light signal with duration of  21 B is reflected towards B 3 . 
         [0034]    At the particular instant in time (T b ) illustrated in  FIG. 3B , light source  11 , passing through region C 3 , emits light with duration of  20 C towards region C 1 . A potential target  15 C is located between ranges R MIN  and R MAX  in region C 1 . Light duration  20 C is formed via whirling mechanism unit  12  (not illustrated). During this period sensor unit  13 , passing through region B 3 , accumulates only reflected light  21 B origination from a reflected light signal between ranges R MIN  and R MAX  in region B 1 . In addition, a light with duration of  20 A is reflected outwards (i.e. from A 3  to A 1  direction) and a reflected light signal with duration of  21 A is reflected towards A 3 . 
         [0035]    At the particular instant in time (T c ) illustrated in  FIG. 3C , light source  11 , passing through region B 3 , emits light with duration of  20 B towards region B 1 . A potential target  15 B is located between ranges R MIN  and R MAX  in region B 1 . Light duration  20 B is formed via whirling mechanism unit 12 (not illustrated). During this period sensor unit  13 , passing through region A 3 , accumulates only reflected light  21 A origination from a reflected light signal between ranges R MIN  and R MAX  in region A 1 . In addition, a light with duration of  20 C is reflected outwards (i.e. from C 3  to C 1  direction) and a reflected light signal with duration of  21 C is reflected towards C 3 . 
         [0036]    Whirling mechanism unit  12  shifts light source unit  11  and sensor unit  13  as to each other in order to accumulate in the sensor unit  13  a specific illuminated scenery volume (depth of field) by the light source unit  11 . 
         [0037]    System  10  timing sequence is provided by the following physical parameters illustrated in  FIG. 4 . For simplicity consideration a single specific scenery (zone A) is illustrated with a potential target  15  and atmospheric conditions  16 . For speed of light (c, for a refractive index equal to 1) system  10  may have the following physical parameters (light source  11  field-of-illumination angle is not taken into account). 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       R 
                       MIN 
                     
                     = 
                     
                       R 
                       - 
                       
                         
                           Δ 
                            
                           
                               
                           
                            
                           R 
                         
                         2 
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where
 
R MIN =defines the area proximate to system  10  from which the avoidance of backscattered light emitted by light source  11 ;
 
R=defines the desired distance from system  10  to an optional target  15 ; and
 
ΔR=defines the desired specific volume of the scenery (depth of field) as to an optional target  15  located in a distance of R.
 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       R 
                       MAX 
                     
                     = 
                     
                       R 
                       + 
                       
                         
                           Δ 
                            
                           
                               
                           
                            
                           R 
                         
                         2 
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where
 
R MAX =defines the distance between system  10  and potential target  15 .
 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       t 
                       1 
                     
                     = 
                     
                       
                         2 
                          
                         
                           R 
                           MIN 
                         
                       
                       c 
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where
 
t 1 =defines the time it takes the “first” photon to propagate from light source  11  a distance R MIN  and be reflected back to system  10 .
 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       t 
                       2 
                     
                     = 
                     
                       
                         2 
                          
                         
                           R 
                           MAX 
                         
                       
                       c 
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where
 
t 2 =defines the time it takes the “first” photon to propagate from light source  11  a distance R MAX  and be reflected back to system  10 .
 
         [0000]    
       
         
           
             
               
                 
                   
                     α 
                     = 
                     
                       ω 
                        
                       
                           
                       
                        
                       
                         t 
                         1 
                       
                     
                   
                   , 
                   
                     ω 
                     = 
                     
                       
                         α 
                          
                         
                             
                         
                          
                         c 
                       
                       
                         2 
                          
                         
                           R 
                           MIN 
                         
                       
                     
                   
                   , 
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where
 
α=defines the angular shift of light source  11  as to sensor unit  13 ;
 
ω=defines the angular velocity of whirling mechanism  12 .
 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       Δ 
                        
                       
                           
                       
                        
                       t 
                     
                     = 
                     
                       
                         
                           t 
                           2 
                         
                         - 
                         
                           t 
                           1 
                         
                       
                       = 
                       
                         
                           2 
                            
                           Δ 
                            
                           
                               
                           
                            
                           R 
                         
                         c 
                       
                     
                   
                   ; 
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where
 
Δt=defines the accumulation time of sensor unit  13  as to a specific desired range and range volume.
 
         [0000]    
       
         
           
             
               
                 
                   
                     β 
                     = 
                     
                       ωΔ 
                        
                       
                           
                       
                        
                       t 
                     
                   
                   , 
                   
                     
                       β 
                       = 
                       
                         α 
                         
                           ( 
                           
                             
                               R 
                               
                                 Δ 
                                  
                                 
                                     
                                 
                                  
                                 R 
                               
                             
                             - 
                             1 
                           
                           ) 
                         
                       
                     
                     ; 
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where
 
β=defines the minimal angular FOV of sensor unit  13 .
 
         [0038]    Angular velocity of whirling mechanism  12  (ω) may be created via a MEMS such as an optical MEMS minor rotating/flipping to provide the desired angular velocity. 
         [0039]    Upon signal accumulation in sensor unit  13  a signal adaptive threshold maybe implemented in order to dissolve reflected target signal versus background signal. Adaptive threshold can be based at least partially on at least one of: a respective depth of field, ambient light conditions, type of objects, light source electro-optical parameters, and sensor unit electro-optical parameters. 
         [0040]    An adaptive depth-of-field can be provided by configuring light source unit  11  and sensor unit  13  shapes, dimensions and orientation versus each other as illustrated in  FIG. 5A-5C  (frontal view).  FIG. 5A  illustrates a frontal view of a parallel configuration where light source unit  11  output illumination  41  as to sensor unit  13  input  42 .  FIG. 5B-C  illustrate a frontal view of a diagonal configurations where light source unit  11  output illumination  41  as to sensor unit  13  input  42 . 
         [0041]    Upon object detection by system  10  additional sensors can be used to validate, investigate or rule-out these potential objects automatically using an image processing algorithm or manually by the operator. Validating or ruling out potential objects may affect the system adaptive threshold in order to reduce false rate or to increase detection sensitivity. Validating or ruling out potential objects may affect the tempo spatial synchronization in order to adapt the depth-of-field accordingly (for example if a false detection is created from a known object detected by one of the additional sensors then a different depth-of-field shape is needed) Additional sensors coupled to the object detection can be: an infrared imager (e.g., a forward Looking Infrared (FLIR) imager operating in either the 3 to 5 micrometer band using an InGaAs sensor or in the 8 12 micrometer band), an ultraviolet camera, ‘passive’ sensor (e.g. CCD, CMOS), ultrasonic sensor, RADAR, LIDAR etc. 
         [0042]    Light source unit  11  and sensor unit  13  maybe shifted separately to provide an addition flexibility of the system. The separate shift can be provided by different radial length of the units (hence, different angular velocity of whirling mechanism  12  to light source unit  11  and to sensor unit  13 ). 
         [0043]    For simplicity reasons, system  10  was described aforementioned with a single light source unit  11  and single sensor unit  13 . System  10  can comprise several sensor units  13  with a single light source  11  where each sensor unit  13  can accumulate a different depth of field based on at least one of the following; tempo spatial synchronization, wavelength and sensor unit electro-optical parameters. System  10  can comprise several light sources  11  and a single sensor unit  13  where the sensor unit  11  can accumulate a different depth of field based on at least one of the following; tempo spatial synchronization, wavelength and light source unit electro-optical parameters. System  10  can comprise several sensor units  13  with a several light sources  11  where each sensor unit  13  can accumulate a different depth of field and different detection capabilities. System  10  comprising of a dual light source  11  followed by a dual sensor unit  13  can even provide target dimension detection based on the accumulated signals from sensor units. 
         [0044]    System  10  can control/change sensor unit  13  and light source  11  tempo spatial synchronization to optimize target detection (i.e. per a specific target, system  10  may accumulates several depth of fields to optimize the detection capabilities). 
         [0045]    While the invention has been described with respect to a limited number of embodiments, these should not be construed as limitations on the scope of the invention, but rather as exemplifications of some of the preferred embodiments. Other possible variations, modifications, and applications are also within the scope of the invention. Accordingly, the scope of the invention should not be limited by what has thus far been described, but by the appended claims and their legal equivalents.