Patent Publication Number: US-11022541-B2

Title: Polarimetric detection of foreign fluids on surfaces

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of and claims priority to U.S. Non-Provisional patent application Ser. No. 15/975,958, entitled “Polarimetric Detection of Foreign Fluids on Surfaces,” which was filed on May 10, 2018, and issued as U.S. Pat. No. 10,365,210, which is a continuation of and claims priority to U.S. Non-Provisional patent application Ser. No. 15/387,901, entitled “Wide-Area Real-time Method for Detecting Foreign Fluids on Water Surfaces,” and filed on Dec. 22, 2016, and issued as U.S. Pat. No. 9,970,861, which is a continuation of U.S. Non-Provisional patent application Ser. No. 14/843,835, filed on Sep. 2, 2015, and issued as U.S. Pat. No. 9,528,929, which claims priority to U.S. Provisional Patent Application Ser. No. 62/044,682, entitled “Polarimetry for the Detection of Oil on Water” and filed on Sep. 2, 2014. All of the prior applications are fully incorporated herein by reference. 
    
    
     GOVERNMENT LICENSE RIGHTS 
     This invention was made with government support under Contract Number W31P4Q-09-C-0644 awarded by the U.S. Army. The government has certain rights in the invention. 
    
    
     BACKGROUND AND SUMMARY 
     As used herein, Long Wave Infrared is referred to as “LWIR” or “thermal.” As used herein, Mid Wave Infrared is referred to as “MWIR.” As used herein, Short Wave Infrared is referred to as “SWIR.” As used herein, Infrared is referred to as “IR.” As used herein, Infrared refers to one, a combination, or all of these subsets of the Infrared spectrum. 
     A method using Infrared Imaging Polarimetry for the detection of foreign fluids on water surfaces is disclosed herein. The described method is not tied to any one specific polarimeter sensor architecture and thus the method described pertains to all Infrared sensors capable of detecting the critical polarimetric signature. The described method is not tied to any one specific portion or subset of the Infrared spectrum and thus the method described pertains to all sensors that operate in one or more of the LWIR, MWIR, or SWIR. The method comprises modeling of the foreign fluid on water or measurements of the foreign fluid on water under controlled conditions to understand the polarization response. This is done in order to select the best angles over which the detection will be most effective. The polarimeter is then mounted on a platform such that the sensor points towards the surface within the range of the acceptable angles. The polarimeter is then used to record raw image data of an area using a polarimeter to obtain polarized images of the area. The images are then corrected for non-uniformity, optical distortion, and registration in accordance with the procedure necessitated by the sensor&#39;s architecture. IR and polarization data products are computed, and the resultant data products are converted to a multi-dimensional data set for exploitation. Contrast enhancement algorithms are applied to the multi-dimensional imagery to form enhanced images. The enhanced images may then be displayed to a user, and/or an annunciator may announce the presence of the foreign fluid on the surface of the water. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawings will be provided by the Office upon request and payment of the necessary fee. 
         FIG. 1  is a diagram illustrating a system in accordance with an exemplary embodiment of the present disclosure. 
         FIG. 2  shows an exemplary cross-section of reflected and emitted radiation from a prior art system in which an IR camera measures IR contrast between oil and water. 
         FIG. 3  is a representation of reflected and emitted radiation from an exemplary cross-section of one embodiment of the current invention in which a polarimeter measures IR contrast and polarization contrast between oil and water. 
         FIG. 4  depicts a model of the dependence of the polarization signals of water as a function of the angle of incidence. 
         FIG. 5  depicts an exemplary positioning of the polarimeter to optimize the detection of a foreign fluid. 
         FIG. 6  depicts exemplary mounting of the polarimeter on a pan-tilt unit which is mounted on a tower on land. 
         FIG. 7  depicts a block diagram of a method for detecting a foreign fluid on a water surface. 
         FIG. 8  depicts an exemplary polarimeter system comprised of a polarimeter and signal processing unit according to an embodiment of the present disclosure. 
         FIG. 9  is a flowchart depicting exemplary architecture and functionality of the image processing logic in accordance with a method according to the present disclosure. 
         FIG. 10 a    is a thermal image of a foreign fluid on water at night. 
         FIG. 10 b    is a polarization image of the foreign fluid on water at night of  FIG. 10 a   , depicting exemplary improvements of fluid detection of the polarization image 
         FIG. 11 a    is an exemplary thermal image of a foreign fluid on water at night. 
         FIG. 11 b    is an exemplary polarization image of the foreign fluid of  FIG. 11 a   , also at night. 
         FIG. 11 c    is an exemplary thermal image of the foreign fluid  FIG. 11 a    on water at night, with the polarimeter at a shallower angle than the image of  FIG. 11   a.    
         FIG. 11 d    is an exemplary polarization image of the foreign fluid of  FIG. 11 c   , also at night and with the polarimeter at the same shallow angle as the thermal camera in the image of  FIG. 11   c.    
         FIG. 12 a    is a thermal image of a foreign fluid on water. 
         FIG. 12 b    is a polarization image of the foreign fluid on water of  FIG. 12   a.    
         FIG. 12 c    is a ColorFuse image of the foreign fluid on water of  FIG. 12   a.    
         FIG. 13 a    is a thermal image of the oil spill off the cost of Santa Barbara, Calif. in the summer of 2015, showing oil on the surface of the water. 
         FIG. 13 b    is a visible image of the spill of  FIG. 13   a.    
         FIG. 13 c    is a polarization image of the same spill showing the oil clearly visible. 
         FIG. 13 d    is a ColorFuse image of the same spill, showing the oil highlighted in red. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a polarimeter system  100  in accordance with an exemplary embodiment of the present disclosure. The system  100  comprises a polarimeter  1001  and a signal processing unit  1002 , which collect and analyze images of a water surface  101  for detection and annunciation of the presence of a foreign fluid  102  on the water surface. An exemplary foreign fluid  102  shown in  FIG. 1  is petroleum from natural seepage, a leak from an oil drilling or processing facility, or a leak from a vessel, or from a vessel that was intentionally dumped overboard. As used in this disclosure, the terms “oil” or “foreign fluid” may refer to any liquid that is desired to be detected. 
     The polarimeter system  100  comprises a polarimeter  1001  for recording polarized images, such as a digital camera or IR imager that collects images. The polarimeter  1001  may be mounted on a tower or platform (not shown) such that it views the water surface  101  at an angle θ  103  from a normal direction  120  to the water surface  101  and at a horizontal range “R”  104  from a general center of the field of view to the polarimeter  1001 , and a height “h”  105  defined by the vertical distance from the water surface  101  to the polarimeter  1001 . The area imaged by the polarimeter is depicted by a field of view  106 . 
     The polarimeter  1001  transmits raw image data to the signal processing unit  1002 , which processes the data as further discussed herein. The processed data is then displayed to an operator (not shown) via a display  108 . Alternatively, detection is annunciated on an annunciator  109 , as further discussed herein. Although  FIG. 1  shows the polarimeter  1001  and the signal processing unit  1002  as a combined unit, in certain embodiments the polarimeter  1001  and signal processing unit  1002  are separate units. For example, the polarimeter  1001  may be mounted remotely on a platform or tower (not shown) and the signal processing unit  1002  placed close to the operator. Similarly, the display  108  or annunciator  109  can be packaged with the system  100  or packaged with the signal processing unit  1002  or be separate from all other components and each other. 
     In the illustrated embodiment, the polarimeter  1001  sends raw image data (not shown) to the signal processing unit  1002  over a network or communication channel  107  and processed data sent to the display  108  and annunciator  109 . The signal processing unit  1002  may be any suitable computer known in the art or future-developed. The signal processing unit  1002  receives the raw image data, filters the data, and analyzes the data as discussed further herein to provide enhanced imagery and detections and annunciations. The network  107  may be of any type network or networks known in the art or future-developed, such as a simple communications cable, the internet backbone, Ethernet, Wifi, WiMax, wireless communications, broadband over power line, coaxial cable, and the like. The network  107  may be any combination of hardware, software, or both. Further, the network  107  could be resident in a sensor (not shown) housing both the polarimeter  101  and the signal processing unit  107 . 
     In the illustrated embodiment, the signal processing unit sends processed image data (not shown) to the display and annunciator over a network or communication channel  107  and processed data sent to the display  108  and annunciator  109 . 
       FIG. 2  shows an exemplary cross-section of reflected and emitted radiation from a prior art system in which an IR camera (not shown, with no polarization capability) measures IR contrast (i.e. radiance differences) between oil and water. In this embodiment, foreign fluid  102  is floating on a water surface  101 . The radiation from the water surface  101  incident on an infrared camera viewing this scene senses a “summed” radiance  200  that is the sum of emitted radiation  201  from the water surface  101  and the reflected radiation  203  from the background  202  reflected off the surface  101 . Likewise for the foreign fluid  102 , the “summed” radiance  210  is the sum of the emitted radiation  211  from the foreign fluid  102  and reflected radiation  213  from the background  212  reflected off the foreign fluid  102 . 
     The emitted radiation  201  depends on the temperature of the water  101  and the optical constant of the water, also known as the refractive index. The reflected radiation component  203  depends on the temperature of the background  202  and the optical constant of the water. Thus the summed radiance  200  depends on background temperature, water temperature, and water optical constants. 
     The emitted radiation  211  depends on the temperature of the foreign fluid  102  and the optical constant of the foreign fluid  102 . The reflected radiation component  213  depends on the temperature of the background  212  and the optical constant of the foreign fluid  102 . Thus the summed radiance  210  depends on the temperature of the foreign fluid  102 , the optical constant of the foreign fluid, and the temperature of the background  212 . 
     For detection of the foreign fluid using an IR camera, the summed radiances  200  and  210  must be different to result in radiance contrast. There are multiple possible combinations of the background and foreign fluid and water temperature values and variations in the foreign fluid optical constants such that there is very little difference in the summed radiances  200  and  210  resulting in low contrast and difficult detection of the foreign fluid. 
       FIG. 3  is a representation of reflected and emitted radiation from an exemplary cross-section of one embodiment of the current invention in which a polarimeter (not shown) measures radiance contrast and polarization contrast between oil and water. In this embodiment, foreign fluid  102  is floating on a water surface  101 . The summed radiation  300  from the water surface  101  is the sum of the emitted radiation  301  and the reflected radiation  303  from the background  302  reflected off the surface  101 . As known by persons with skill in in the relevant art, the emitted radiation  301  consists of two polarization components, a “perpendicular” polarization component  306  and a “parallel” polarization component  307 . The difference in these polarization components  306  and  307  results in a net polarization for the thermal emitted radiation  301 . 
     Likewise, the reflected component  303  consists of two polarization components, a “perpendicular” polarization component  304  and a “parallel” polarization component  305 , resulting from the reflection of the background radiation  302 . The difference in these polarization components  304  and  305  results in a net polarization for the thermal emitted radiation  303 . The total polarization signal from the water is a combination of the polarization signals from the emitted radiation  301  and reflected radiation  303 . The net polarization signal is called the Degree of Linear Polarization or “DoLP”. 
     Similarly, the summed radiation  310  from the foreign fluid surface  102  is the sum of the emitted radiation  311  and the radiation  313  from the background  312  reflected off the surface  102 . The emitted radiation  311  consists of two polarization components, the “perpendicular” polarization component  316  and the “parallel” polarization component  317 . The difference in these polarization components  316  and  317  results in a net polarization for the thermal emitted radiation  311 . Likewise, the reflected component  313  consists of two polarization components, the “perpendicular” polarization component  314  and the “parallel” polarization component  315 , resulting from the reflection of the background radiation  312 . The difference in these polarization components  313  and  314  results in a net polarization signal for the thermal emitted radiation  313 . The total polarization signal from the foreign fluid is a combination of the polarizations of  311  and  313 . The detection of the foreign fluid occurs when the polarization contrast of the foreign fluid is different from the polarization contrast of the water. 
       FIG. 4  depicts a model of the dependence of the polarization signals of water as a function of the angle of incidence  103  ( FIG. 1 ) and shows the perpendicular and parallel polarization components  304  and  305  for the reflected radiation and the perpendicular and parallel polarization components  306  and  307  of the emitted polarization. The DoLP results from the difference of perpendicular and parallel polarization components. The reflected DoLP  401  for the reflected radiation increases with increasing angle until it reaches a maximum of about 53% at an angle of about 62°. The emitted DoLP  402  for the emitted radiation monotonically decreases as a function of angle of incidence  103 . 
     It is important to note that the shape and nature of these curves depends on the optical constants of the material and thus these curves are significantly different for the foreign liquid being detected. The differences in DoLP between water and the foreign liquid are exploited by the current invention. A higher contrast difference for detecting oil on water is attained by examining these curves for the polarization performance as a function of angle. In one embodiment of the current invention, the optimal angles based upon experimental data obtained with oil are between 70° and 88° from normal (angle θ  103 ) or between 2° and 20° elevation (measured from a horizontal).  FIG. 7  is a block diagram of the process steps to achieve optimal detection that exploits these concepts. 
       FIG. 5  depicts an exemplary positioning of the polarimeter  1001  to optimize the detection where the polarimeter  1001  is positioned between angles θ 1  and θ 2 . Using the optimal range from  FIG. 4  as an example, θ 1  may be 70° and θ 2  may be 88°, and the polarimeter placed within this range. For one embodiment of the invention in which the sensor is mounted on a tower (not shown), these angles can be achieved by selecting the appropriate Range R  104  ( FIG. 1 ) and Height h  105  ( FIG. 1 ). 
       FIG. 6  depicts exemplary mounting of the polarimeter on a pan-tilt unit  110  which is mounted on a tower  111  on land. In another exemplary embodiment, the tower  111  is a mast or pole. In another exemplary embodiment, the tower  111  is a platform or other mounting point on a structure overlooking the water surface to be monitored. In other embodiments, the tower, mast, pole, platform or mounting point can be placed on a vessel, floating platform, fixed pier or platform, floating buoy, or the like. In another exemplary embodiment, the sensor system  100  and pan-tilt unit  110  is placed on a manned or unmanned aerial vehicle. The sensor system further in some embodiments is portable and can be hand-held. 
       FIG. 7  depicts a block diagram of a method  7000  to detect a foreign fluid  102  ( FIG. 1 ) on a water surface  101  ( FIG. 1 ) in the optimal conditions. In step  7001 , the polarized response of the foreign fluid is predicted through analysis of the emitted and reflected radiation of the fluid of interest, in the manner discussed with respect to  FIGS. 3 and 4  herein. Alternatively, measurements of the fluid of interest can be performed experientially, or experimentally in a controlled environment such as a laboratory where the angles can be varied. 
     In step  7002  of the method  7000 , the results of step  7001  are used to determine the range of angles θ 1  and θ 2  ( FIG. 5 ) for good performance, as discussed with respect to  FIGS. 4 and 5  herein. In step  7003 , the results of step  7002  are used to determine the best mounting location for the mounting options available, range R  104  ( FIG. 1 ) and height h  105  ( FIG. 1 ), and the polarimeter  1001  ( FIG. 1 ) is mounted. 
     In step  7004 , imagery is collected with the polarimeter  1001  as is described herein. In step  7005 , contrast enhancement algorithms are applied to the imagery to aid the detection of the foreign fluid by an operator or by autonomous detection algorithms. In step  7006 , the enhanced contrast images are displayed and/or the detection of the foreign liquid is annunciated. 
       FIG. 8  depicts an exemplary polarimeter system  100  comprised of a polarimeter  1001  and signal processing unit  1002  according to an embodiment of the present disclosure. The polarimeter  1001  comprises an objective imaging lens  1201 , a filter array  1203 , and a focal plane array  1202 . The objective imaging lens  1201  comprises a lens pointed at the water and foreign fluid surface  101  and  102  ( FIG. 1 ). The filter array  1203  filters the images received from the objective imaging lens system  1201 . The focal plane array  1202  comprises an array of light sensing pixels. 
     The signal processing unit  1002  comprises image processing logic  1302  and system data  1303 . In the exemplary signal processing unit  1002  image processing logic  1302  and system data  1303  are shown as stored in memory  1306 . The image processing logic  1302  and system data  1303  may be implemented in hardware, software, or a combination of hardware and software. 
     The signal processing unit  1002  also comprises a processor  1301 , which comprises a digital processor or other type of circuitry configured to run the image processing logic  1302  by processing the image processing logic  1302 , as applicable. The processor  1301  communicates to and drives the other elements within the signal processing unit  1002  via a local interface  1304 , which can include one or more buses. When stored in memory  1306 , the image processing logic  1302  and the system data  1303  can be stored and transported on any computer-readable medium for use by or in connection with logic circuitry, a processor, an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “computer-readable medium” can be any means that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The computer readable medium can be, for example but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium. Note that the computer-readable medium could even be paper or another suitable medium upon which the program is printed, as the program can be electronically captured, via for instance optical scanning of the paper or other medium, then compiled, interpreted or otherwise processed in a suitable manner if necessary, and then stored in a computer memory. 
     Exemplary system data  1303  is depicted comprises:
         a. Raw image data (not pictured) from the polarimeter  1001  ( FIG. 1 ) obtained from step  9001  of the method  900  ( FIG. 9 ).   b. Corrected image data (not pictured), which is the data that has been corrected for non-uniformity, optical distortion, and registration per step  9002  of the method  900  ( FIG. 8 ).   c. IR and Polarization images obtained from step  9003  of the method  900  ( FIG. 3 ).   d. Conversion of polarization and radiance data to multi-dimensional image data applied in step  9004  of the method  900  ( FIG. 9 ).   e. Contrast enhancing algorithms applied to image data in step  9005  of the method  900  ( FIG. 9 ).   f. Image data applied to the display  108  and annunciator  109  in step  9006  of the method  900  ( FIG. 9 ).   g. Radiance image data as described herein.   h. Hybrid radiance/polarization images as described herein.       

     The image processing logic  1302  executes the processes described herein with respect to  FIG. 9 . 
     Referring to  FIG. 8 , an external interface device  1305  connects to and communicates with the display  108  and annunciator  109 . The external interface device  1305  may also communicate with or comprise an input device, for example, a keyboard, a switch, a mouse, a touchscreen, and/or other type of interface, which can be used to input data from a user of the system  100 . The external interface device  1305  may also or alternatively communicate with or comprise a personal digital assistant (PDA), computer tablet device, laptop, portable or non-portable computer, cellular or mobile phone, or the like. The external interface device  1305  may also or alternatively communicate with or comprise a non-personal computer, e.g., a server, embedded computer, field programmable gate array (FPGA), microprocessor, or the like. 
     The external interface device  1305  is shown as part of the signal processing unit  1002  in the exemplary embodiment of  FIG. 8 . In other embodiments, the external interface device  1305  may be outside of the signal processing unit  1002 . 
     The display device  108  may consist of a tv, lcd screen, monitor or any electronic device that conveys image data resulting from the method  900  or is attached to a personal digital assistant (PDA), computer tablet device, laptop, portable or non-portable computer, cellular or mobile phone, or the like. The annunciator device  109  can consist of a warning buzzer, bell, flashing light, or any other auditory or visual or tactile means to warn the operator of the detection of foreign fluids. 
     In some embodiments, autonomous action may be taken based upon the foreign fluid  102  ( FIG. 1 ) detected. For example, a clean-up response may be automatically initiated. In some cases where automatic action is taken, the annunciator  109  may not be required. 
     In other embodiments, a Global Positioning System (“GPS”) device (not shown) may interface with the external interface device  1305  to provide a position of the foreign fluids  102  detected. 
     In the illustrated embodiment, the display  108  and annunciator  109  are shown as separate, but the annunciator  109  may be combined with the display  108 , and in another embodiments, annunciation could take the form of highlighted boxes or regions, colored regions, or another means used to highlight the object as part of the image data display. See, for example, the red colored region in  FIG. 12 , which provides a visual indication of a foreign fluid  102  detected. 
       FIG. 9  is a flowchart depicting exemplary architecture and functionality of the image processing logic  1302  ( FIG. 8 ) in accordance with a method  900 . In step  9001  of the method  1000 , the polarimeter  1001  captures an image of water  101  and foreign fluid  102  ( FIG. 1 ) and sends raw image data to the signal processing unit  1002  ( FIG. 1 ). 
     In step  9002 , the signal processing unit  1002  ( FIG. 1 ) corrects imager non-uniformity of the images received from the polarimeter  1001 . Examples of imager non-uniformity include fixed pattern lines in the image, noisy pixels, bad pixels, bright spots, and the like. Algorithms that are known in the art may be used for correcting the imager non-uniformity. In some embodiments, step  9002  is not performed because the imager non-uniformity does not require correction. 
     Additionally in step  9002 , the signal processing unit  1002  removes image distortion from the image data. An example of image distortion is warping at the edges of the image caused by the objective imaging lens system. Algorithms that are known in the art may be used for correcting image distortion. Registration corrections may also be performed in step  9002 , using methods known in the art. 
     In step  9003 , IR and polarization data products are computed. In this step, Stokes parameters (S 0 , S 1 , S 2 ) are calculated by weighted subtraction of the polarized image obtained in step  9002 . The IR imaging polarimeter measures both a radiance image and a polarization image. A radiance image is a standard image whereby each pixel in the image is a measure of the radiance, typically expressed in Watts/cm2-sr, reflected or emitted from that corresponding pixel area of the scene. Standard photographs and IR images are radiance images, simply mappings of the radiance distribution emitted or reflected from the scene. A polarization image is a mapping of the polarization state distribution across the image. The polarization state distribution is typically expressed in terms of a Stokes image. 
     Of the Stokes parameters, S 0  represents the conventional IR image with no polarization information. S 1  and S 2  display orthogonal polarimetric information. Thus the Stokes vector, first introduced by G. G. Stokes in 1852, is useful for describing partially polarized light and is defined as 
                     S   →     =       [           S   0               S   1               S   2               S   3           ]     =     [             I   0     +     I   90                   I   0     -     I   90                   I   45     -     I   135                   I   R     -     I   L             ]               (   1   )               
Where I 0  is the radiance that is linearly polarized in a direction making an angle of 0 degrees with the horizontal plane, I 90  is radiance linearly polarized in a direction making an angle of 90 degrees with the horizontal plane. Similarly I 45  and I 135  are radiance values of linearly polarized light making an angle of 45° and 135° with respect to the horizontal plane. Finally I R  and I L  are radiance values for right and left circularly polarized light. For this invention, right and left circularly polarized light is not necessary and the imaging polarimeter does not need to measure these states of polarization. For this reason, the Stokes vectors that we consider will be limited to the first 3 elements which express linearly polarized light only,
 
     
       
         
           
             
               
                 
                   
                     S 
                     → 
                   
                   = 
                   
                     
                       [ 
                       
                         
                           
                             
                               S 
                               0 
                             
                           
                         
                         
                           
                             
                               S 
                               1 
                             
                           
                         
                         
                           
                             
                               S 
                               2 
                             
                           
                         
                       
                       ] 
                     
                     = 
                     
                       [ 
                       
                         
                           
                             
                               
                                 I 
                                 0 
                               
                               + 
                               
                                 I 
                                 90 
                               
                             
                           
                         
                         
                           
                             
                               
                                 I 
                                 0 
                               
                               - 
                               
                                 I 
                                 90 
                               
                             
                           
                         
                         
                           
                             
                               
                                 I 
                                 45 
                               
                               - 
                               
                                 I 
                                 135 
                               
                             
                           
                         
                       
                       ] 
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     Also in step  9003 , a degree of linear polarization (DoLP) image is computed from the Stokes images. A DoLP image is useful for providing contrast for foreign fluids on a water surface, and can be calculated as follows:
 
DoLP=√{square root over (( s   1   /s   0 ) 2 +( s   2   /s   0 ) 2 )}  (3)
 
     In step  9004 , the IR and polarization data products and DoLP computed in step  9003  are converted to a multi-dimensional data set for exploitation. Note that DoLP is linear polarization. As one with skill in the art would know, in some situations polarization that is not linear (e.g., circular) may be desired. Thus in other embodiments, step  9004  may use polarization images derived from any combination of S 0 , S 1 , S 2 , or S 3  and is not limited to DoLP. 
     The DoLP image is one available image used to view polarization contrast in an image. Another alternative image to view polarization content is a “ColorFuse” image that is generated by mapping the radiance, DoLP, and orientation images to a color map. “ColorFuse” is one embodiment of multidimensional representation that can be produced in step  9004 . Those knowledgeable in the art can conceive similar mappings. For one example, the DoLP information may be emphasized when radiance values are low. 
     Persons with skill in the art makes the following mapping of polarization data to a hue-saturation-value representation for color: 
     S 0 =value 
     DoLP=saturation 
     Orientation ϕ=hue 
     This representation enables display of all optical information (radiance and polarization) in a single image and provides a means to show both radiometric and polarization contrast enhancing understanding of the scene. In many cases where polarization contrast is strong, this representation provides scene context for the surfaces or objects that are polarized. Those experienced in the art can imagine other ways of doing this. 
     Because the underlying optical radiation depends on emission, no additional light sources, illumination, or ambient light is required for polarization imaging. Further, the approach works equally well during the night time as it does during the day. 
     In step  9005 , contrast enhancing algorithms that are known in the art are applied to the multidimensional image from step  9004 . The multi-dimensional data exploits the polarization data to significantly enhance the information content in a scene. Non-restrictive examples include global mean, variance, and higher order moment analysis, Principal Component Analysis, or Linear Discriminate Analysis, computation of the statistics of the multidimensional data as a whole and then computation of local values based on a kernel convolved with the image as a whole and then normalized by global statistics of the scene. 
     In step  9006 , the contrast enhanced image of the detected oil is displayed to an operator. The detected oil is then annunciated to the user through visual or auditory means. Non-restrictive examples includes bells, buzzers or lights to draw the operator&#39;s attention to the display, or indications on the display such as distinctive colors or boxes in the region of the foreign fluid. 
     In other embodiments, steps  9003 ,  9004 ,  9005 , and  9006  are used in combinations that omit one or more of the steps. In other embodiments, the polarization image data, or the multi-dimensional (e.g. ColorFuse) data, may be viewed by humans for fluid detection, and no algorithms are applied. 
     Algorithms that exploit a combination of image features extracted from an IR imaging polarimeter can be used to detect foreign fluids. Once potential noteworthy features are detected, they can be automatically highlighted for the operator, and a warning can be given through some annunciation mechanism (buzzer or light). 
       FIGS. 10 a  and 10 b    are thermal and polarization images, respectively, of a foreign fluid (e.g., oil) on water at night depicting exemplary improvements of fluid detection of the polarization image. The values on the images show radiometric quantities for the thermal image and polarization quantities for the polarization image at various locations on the surface of the water  101  and in the area of the foreign fluid  102 . For the thermal image, the contrast between the fluid and water is very slight. For the polarization image, the contrast is significantly better. 
       FIG. 11 a    is an exemplary thermal image of a foreign fluid  102  on water  101  at night. As can be seen in  FIG. 11 a   , the foreign fluid  102  is barely detectable in the thermal image. 
       FIG. 11 b    is an exemplary polarization image of the foreign fluid  102  of  FIG. 11 a   , also at night. Importantly, no external light source is used with the method disclosed herein. The polarization image of  FIG. 11 b    was produced using the method disclosed herein. The foreign fluid  102  is easily detectable in the polarization image. The polarization image of  FIG. 11 b    shows a significant improvement over the thermal image of  FIG. 11 a   . In  FIGS. 11 a  and 11 b   , the thermal camera and polarimeter, respectively, were positioned at an oblique angle to the water&#39;s surface  101 . 
       FIG. 11 c    is an exemplary thermal image of the foreign fluid  102  of  FIG. 11 a    on water  101  at night, with the polarimeter at a shallower angle than the image of  FIG. 11 a   . The images of  FIGS. 11 a  and 11 b    were taken at roughly 15 degrees and the images of  FIGS. 11 c  and 11 d    were taken at roughly 5 degrees. As can be seen in  FIG. 11 c   , the foreign fluid  102  is really not detectable in the thermal image. 
       FIG. 11 d    is an exemplary polarization image of the foreign fluid  102  of  FIG. 11 c   , also at night and with the polarimeter at the same shallow angle as the thermal camera was in the image of  FIG. 11 c   . The foreign fluid  102  is easily detectable in the polarization image. The foreign fluid  102  is still easily detected in the polarization image of  FIG. 11 d   . In  FIGS. 11 a  and 11 b   , the thermal camera and polarimeter, respectively, were positioned at an oblique angle to the water&#39;s surface  101 . 
       FIGS. 12 a , 12 b  and 12 c    are a thermal, polarization, and ColorFuse images, respectively, of a foreign fluid  102  on water  101 . The thermal image of  FIG. 12 a    shows very little contrast, the polarization image of  FIG. 12 b    shows strong contrast, and the ColorFuse image of  FIG. 12 c    highlights in red the detection of the foreign fluid. 
       FIG. 13 a    is a thermal image of the oil spill off the cost of Santa Barbara, Calif. in the summer of 2015, showing the oil  102  on the surface of the water  101 .  FIG. 13 b    is a visible image of the spill of  FIG. 13 a   .  FIG. 13 c    is a polarization image of the same spill showing the oil  102  clearly visible.  FIG. 13 d    is a ColorFuse image of the same spill, showing the oil  102  highlighted in red.