Patent Publication Number: US-2015078736-A1

Title: Underwater imaging system

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to imaging systems and more particularly to imaging systems designed principally for use in underwater applications. 
     BACKGROUND OF THE INVENTION 
     Underwater imaging systems are often utilized in a variety of different applications. For instance, underwater imaging systems are often used to assist in the installation, repair and/or maintenance of underwater conduits (e.g., pipelines), oil wells, or other structures disposed in limited visibility environments (e.g., on the ocean floor). 
     Underwater imaging systems typically include a light source for generating high power light and a camera to provide still and/or video images of any objects present within the camera range (e.g., for viewing at a remote location). In use, the high power light produced by the light source travels through the water and ultimately illuminates any objects within the camera range to the extent necessary that images of the objects can be captured by the camera. 
     For example,  FIG. 1  is a simplified schematic representation of an underwater imaging system  11  of the type as described above. As can be seen, system  11  comprises a light source, or light,  13  for producing high power light and a camera  15  for capturing objects illuminated by light source  13 . 
     Although useful and well known in the art, underwater imaging systems of the type as described above have been found to suffer from a notable shortcoming. Specifically, as shown in  FIG. 1 , a relatively high concentration of suspended particles, such as silt or algae, is often present in water between light source  13  and a desired object  17 , the region with a high concentration of suspended particles being identified generally by reference numeral  19 . In use, the majority of the light emitted from light source  13 , the emitted light being represented collectively as light rays  21 , reflects off the suspended particles present within region  19  instead of object  17 , the reflected light being identified collectively as light rays  23 . At least a portion of light  23  is reflected off the suspended particles back into camera  15 , thereby resulting in an overly-reflected, blinded image that obscures viewing of desired object  17 . 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a new and improved underwater imaging system. 
     It is another object of the present invention to provide a new and improved underwater imaging system that enhances the visibility a desired object. 
     It is yet another object of the present invention to provide a new and improved underwater imaging system of the type as described above that is particularly well suited for use in underwater environments with a relatively high concentration of suspended particles, such as silt or algae. 
     It is still another object of the present invention to provide an underwater imaging system of the type as described above that allows for the capture of an image of the desired object without any obscuring from light illuminated off suspended particles. 
     It is yet still another object of the present invention to provide an underwater imaging system of the type as described above that has a limited number of parts, is inexpensive to manufacture and is simple to use. 
     Accordingly, as one feature of the present invention, there is provided an imaging system for use in a low visibility environment, the imaging system comprising (a) an object disposed in the low visibility environment, at least a portion of the object having an exterior coating that is adapted to absorb light, (b) a light source for illuminating the object, the light source being adapted to produce light with a wavelength of no greater than 750 nm, and (c) a camera for capturing at least one image of the object illuminated by the light source. 
     As another feature of the present invention, there is provided a method for capturing an image of an object in a low visibility environment using a camera, the object having an exterior, the method comprising the steps of (a) coating at least a portion of the exterior of the object with a light absorptive coating, (b) illuminating the object with a light source adapted to produce light with a wavelength of no greater than 750 nm, and (c) capturing the image of the object illuminated by the light source using the camera. 
     Various other features and advantages will appear from the description to follow. In the description, reference is made to the accompanying drawings which form a part thereof, and in which is shown by way of illustration, an embodiment for practicing the invention. The embodiment will be described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the scope of the invention. The following detailed description is therefore, not to be taken in a limiting sense, and the scope of the present invention is best defined by the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings wherein like reference numerals represent like parts: 
         FIG. 1  a simplified schematic representation of an underwater imaging system that is well known in the art; 
         FIG. 2  is a simplified schematic representation of an underwater imaging system constructed according to the teachings of the present invention; 
         FIG. 3  is a graph that represents the intensity of light in relation to wavelength, the graph depicting a shift in wavelength that occurs between light absorbed by an object with a light absorptive coating and the light subsequently emitted by the coated object; 
         FIGS. 4(   a ),  4 ( b ) and  4 ( c ) are Jablonski energy diagrams depicting photon absorption through fluorescence, phosphorescence, and delayed fluorescence, respectively; and 
         FIGS. 5(   a )-( c ) are a series of photographs that illustrate results obtained through implementation of the underwater imaging system shown in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to  FIG. 2 , there is shown a simplified schematic representation of an underwater imaging system constructed according to the teachings of the present invention, the underwater imaging system being identified generally by reference numeral  111 . As will be described in detail below, system  111  is designed to enhance the visibility of a desired object in an underwater environment by filtering light reflected by particles, such as silt or algae, which are suspended in the water. 
     It should be noted that system  111  is particularly well suited for use in underwater environments with relatively low visibility and relatively high concentrations of suspended particles. However, it is to be understood that system  111  is not limited to underwater environments. Rather, it is envisioned that system  111  could be similarly implemented in other types of environments with relatively low visibility and relatively high concentration of suspended particles, such as in a cavern, without departing from the spirit of the present invention. 
     As can be seen, imaging system  111  is similar to prior art imaging system  11  in that imaging system  111  comprises a light source  113  for illuminating a target object  115  (e.g., an underwater cable) within the underwater environment and a camera  117  for capturing images of the underwater environment, including object  115 . As will be explained in detail below, imaging system  111  is specifically designed to enhance the visibility of target object  115  by filtering light reflected by particles suspended in the immediate environment. 
     Underwater imaging system  111  differs from underwater imaging system  11  in the following three ways in order to enhance visibility of target object  115 . 
     As a first distinction, light source  113  differs from a conventional, high power, white light source, such as light source  13 , in that light source  113  is adapted to produce light of a relatively short wavelength. Specifically, as defined herein, light source  113  represents any illumination device that is adapted to produce light of a relatively short wavelength, either directly or through subsequent modulation/filtering. For example, light source  113  may be in the form of an ultraviolet (UV) light emitting diode (LED) of the type sold by Luminus Devices, Inc., of Billerica, Mass. under its CBT-120 line of LEDs. Because it has been found that underwater environments are capable of transmitting light well in the 300-750 nm range (often at underwater depths approaching 100 meters), it is preferred that source  113  emit light in the aforementioned range. 
     As a second distinction, underwater imaging system  111  includes a long wavelength pass cutoff filter  119  that is disposed directly in front of the imaging lens for camera  117 . For example, cutoff filter  119  may be in the form of a 425 nm cutoff filter of the type manufactured and sold by Thorlabs, Inc., of Newton, N.J. It is to be understood that cutoff filter  119  is an optional component that, when incorporated into imaging system  111 , filters short wavelength light generated in the immediate underwater environment. Accordingly, through filtering of reflected light using long wavelength pass cutoff filter  119  and increasing the gain of the captured image, an enhanced outline of target object  115  can be achieved, as will be explained further below. 
     As a third distinction, at least a portion of the exterior of target object  115  is preferably applied with a fluorescent, phosphorescent, or stokes-shift coating  120  (i.e., a coating adapted to absorb light). 
     For example, object  115  may be coated with fluorescent nanocrystals of the type manufactured and sold under the Trilite™ line of fluorescent nanocrystals by Cytodiagnostics Inc., of Burlington, Ontario. As can be appreciated, flourescent nanocrystals of the type referenced above, which are commonly available in both organic and aqueous formulations, are designed with a maximum emission wavelength in the range between 415-725 nm. 
     As another example, object  115  may be coated with fluorescent dyes of the type manufactured and sold under the Cyto™ line of fluorescent dyes by Cytodiagnostics, Inc., of Burlington, Ontario. As can be appreciated, fluorescent dyes of the type referenced above are available with maximum excitation and emission wavelengths that span the visible and infrared spectrum (e.g., with a maximum excitation wavelength in the range of 418-704 nm and a maximum emission wavelength in the range of 467-723 nm). 
     In use, light produced by short wavelength light source  113  (represented herein as light rays  121 ) is reflected by particles suspended in the water (e.g., sand, rock, dust-like sediment, etc.) at the same shortened wavelength as initially emitted (the reflected light being represented as light rays  123 ). By contrast, light  121  produced by short wavelength light source  113  that is absorbed by coated object  115  is re-emitted at a relatively long wavelength (the re-emitted light being represented as light rays  125 ). In this manner, by filtering the shorter wavelength light (i.e., light  121  and  123 ), camera  117  can effectively enhance the image produced from the longer wavelength light emitted from target object  115  (i.e., light  125 ) without interference from the intermediate light reflected from the suspended particles (i.e., light  123 ). 
     It is to be understood that light absorbed by coated object  115  is re-emitted at a longer wavelength (lower energy level) as a result of a principle of fluorescence known as Stokes shift. Referring now to  FIG. 3 , there is shown a graph that depicts the intensity of light in relation to wavelength, the graph being identified generally by reference numeral  211 . As can be seen, a shift in wavelength occurs between the light absorbed by coated object  115  (the absorbed light being identified generally by reference numeral  213 ) and the light subsequently emitted by coated object  115  (the emitted light being identified generally by reference numeral  215 ). 
     As can be appreciated, the fluorescence of light by an object (e.g., coated object  115 ) results in re-emission of longer wavelength photons (i.e., photons with lower energy) because the object has absorbed some of the photon energy. This shift in energy (and corresponding increase in wavelength) between the absorbed light (e.g., light  213 ) and the re-emitted light (e.g., light  215 ) is commonly referred to in the art as Stokes shift. 
     Photon absorption is sometimes depicted diagrammatically using Joblonski energy diagrams. Referring now to  FIGS. 4(   a ),  4 ( b ) and  4 ( c ), there are shown Jablonski energy diagrams depicting photon absorption through fluorescence, phosphorescence, and delayed fluorescence, respectively. As can be seen in each of  FIGS. 4(   a ),  4 ( b ) and  4 ( c ), prior to excitation, the electronic configuration of the molecule is described as being in the ground state, as represented by reference numerals  311 - 1 ,  311 - 2  and  311 - 3 , respectively. Upon absorbing a photon of excitation light, usually of short wavelengths, electrons  311 - 1 ,  311 - 2  and  311 - 3  may be raised to a higher energy and vibrational excited state, as represented by reference numerals  313 - 1 ,  313 - 2  and  313 - 3 , respectively, the aforementioned process often taking as little as a quadrillionth of a second (a time period commonly referred to as a femtosecond, 10E-15 seconds). 
     In fluorescence, as shown in  FIG. 4(   a ), during an interval of approximately a trillionth of a second (a picosecond or 10E-12 seconds), the excited electron  313 - 1  may lose some vibrational energy to the surrounding environment and return to what is called the lowest excited singlet state, as represented by reference numeral  315 - 1 . From the lowest excited singlet state  315 - 1 , the electrons are then able to “relax” back to ground state, as represented by reference numeral  317 - 1 , through the simultaneous emission of fluorescent light, as represented by reference numeral  319 - 1 . The emitted fluorescent light always has a longer wavelength than the excitation light by virtue of Stokes Law, the fluorescent light emitting for as long as the excitation illumination bathes the fluorescent specimen. Once the exciting radiation is halted, the fluorescence ceases. 
     As noted above and as shown in  FIG. 4(   a ), once an electron is in the excited state, excited electron  313 - 1  slowly relaxes through vibrational effects to lowest excited singlet state  315 - 1 . Thereafter, the electron can then drop back to ground state  317 - 1  by emitting a photon (e.g., through fluorescence). However, as shown in  FIG. 4(   b ), occasionally an excited electron  313 - 2 , instead of relaxing to the lowest singlet state through vibrational interactions, makes a forbidden transition to the exited triplet state, as represented by reference numeral  321 - 2 . From excited triplet state  321 - 2 , the electron returns to the ground state, as represented by reference numeral  317 - 2 , through a process where the emission of radiation  319 - 2  is delayed for up to several seconds or more. This phenomenon is characteristic of phosphorescence. 
     As seen most clearly in  FIG. 4(   c ), in some instances, an excited electron  313 - 3  may make a forbidden transition to the excited triplet state, as represented by reference numeral  321 - 3 , and then subsequently return back to the lowest excited singlet state  315 - 3 . Thereafter, the returned electron relaxes back to ground state  317 - 3  through the emission of fluorescent light, as represented by reference numeral  319 - 3 . Because the aforementioned sequence takes a little longer than usual fluorescence (by approximately a microsecond or two), this action is commonly referred to as delayed fluorescence in the art. 
     Referring now to  FIGS. 5(   a )-( c ), there are shown a series of photographs that illustrate a demonstration of the improved functionality of underwater imaging system  111 . In  FIG. 5(   a ), an aquarium  411  (representing the underwater environment) is shown filled with silt (i.e., granular material, such as sand or rock) suspended in water. As can be seen, the application of short wavelength light from a traditional, high brightness, white light source  413  is reflected off the silt and is scatted back to the camera, thereby obscuring view of a target object  417  located within aquarium  411 . 
     In  FIG. 5(   b ), by utilizing a short wavelength light source  415  (in place of a traditional white light source  413 ) and applying a stoke-shift (light absorptive) coating to target object  417 , which is represented herein as an elongated, cylindrical pipe, the camera is better able to view target object  417 . In  FIG. 5(   c ), an even clearer outline of target object  417  is achieved through (i) filtering of the reflected light using a long wavelength pass cutoff filter and (ii) enhancing the gain of the captured image. 
     It is to be understood that the embodiment shown in the present invention is intended to be merely exemplary and those skilled in the art shall be able to make numerous variations and modifications without departing from the spirit of the present invention. All such variations and modifications are intended to be within the scope of the present invention as defined in the appended claims. 
     As an example, it should be noted that elements of imaging system  111  could be modified to adapt to the known variances in the light absorption characteristics of different underwater environments. In particular, it is to be understood that the coefficient of light absorption varies between different ocean locations around the world. In view thereof, optimization of system  111  could be obtained for a particular environment by either (i) modifying the illumination wavelength generated by light source  113 , (ii) utilizing particular filters  119 , and/or (iii) selecting a specific type of coating to be applied to object  115 . 
     As a second example, it is envisioned that, instead of using filter  119 , light produced from light source  113  could be strobed (i.e., briefly turned off) between image capture frames. Specifically, as referenced above, since stokes shift may be delayed from picoseconds to microseconds between absorption and re-emission, it is envisioned that image capture be taken when no directly illuminated light is present, thereby increasing contrast and eliminating reflection from suspended sediment. 
     To optimize the advantages associated with strobing light source  113 , it is preferred that camera  117  be synchronized with light source  113  so as to either mechanically or electrically shutter, or block, light from its internal light detection sensor during the exact period of time when light source  113  is not producing direct light (i.e., light  121 ). In this capacity, the light detection sensor in camera  117  would only be capable of integrating photons from light produced by fluorescing objects (i.e., light  125 ). To further ensure that the light detected by camera  117  is limited to the re-emitted light (i.e., light  125 ), the aforementioned shutter mechanism is preferably designed to open only during the estimated period of fluorescence (i.e., to directly correlate with estimated delay of light re-emission from light-absorptive coating  120 ). 
     As a third example, it is envisioned that multiple coatings could be applied to target object  115  to enhance image capture. Specifically, light of multiple wavelengths (e.g., light selected from the group consisting 450 nm, 490 nm, 525 nm, 540 nm, 575 nm, 630 nm, and 665 nm wavelength light) may be absorbed and re-emitted from a target object by using a plurality of different fluorescent coatings. The multiple colors of re-emitted wavelengths are then passed through notch filters of selective wavelengths. 
     In addition, it is to be understood that multiple colors (i.e., varying wavelength light) may be generated by light source  113 , each color generated preferably falling outside of the target, or filtered, wavelength of re-emitted light. Accordingly, multiple images can be independently captured (each using a light of a different wavelength) and subsequently combined to provide a high contrast, enhanced image that is not polluted by the light from competing, or interfering, emissions. 
     As a fourth example, it is envisioned that light-absorptive coating  120  could be provided with an attractive property relative to target object  115 . In this manner, coating  120  could be subsequently applied to an object already deployed in a particular environment that would otherwise render treatment with a light-absorptive material difficult. 
     For instance, with respect to a target object  115  that is both metallic and already located in an underwater environment (e.g., an underwater pipeline), coating  120  may be in the form of a plurality of individual magnetic particles coated with a light-absorptive material (e.g., with a dust-like consistency). As such, the coated magnetic particles could be readily applied to the exterior of the underwater object and retained to its exterior surface through the principle of magnetic attraction. 
     Similarly, if target object  115  is a supply of oil present in a body of water (e.g., as the result of an oil spill), coating  120  may be in the form of an oleophylic article applied with a light-absorptive material. Accordingly, due to the attraction between the coated oleophylic article and the oil, system  111  could be used to tag and track oil flows.