Abstract:
A real-time in-situ sensor system is provided for measurement of bioluminescence and determination of bioluminescence surface signature. The system measures bioluminescence in the wake of a submerged moving object as well as ambient light levels outside of the wake. Along with measurements of depth and water-quality parameters including turbidity, temperature and salinity, the surface signature of the induced underwater bioluminescence can be calculated by considering light transmission and attenuation through water. With this real-time information, the operator of the submerged moving object can employ tactical maneuvers to affect the resultant surface signature.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/705,813, filed Aug. 5, 2005, which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to optical sensing of the underwater environment, specifically bioluminescence signature created by moving submerged objects such as submersibles, swimmers and watercraft, and its observability from the surface. 
     BACKGROUND OF THE INVENTION 
     Bioluminescence is a localized phenomenon caused when organisms are stimulated by flow agitation. As a result of this effect, submerged moving objects will be highlighted with a blue-green glow and often can produce spectacular glowing wakes from ships and submerged craft. This effect is so widespread in the world&#39;s coastal regions that some level of bioluminescence is almost always present. Dinoflagellates, ubiquitous unicellular plankton also known for producing harmful blooms, are the most common sources of bioluminescence in the littoral zone. Dinoflagellates often exist in sufficient density such that ships, swimmers and submersibles can readily be detected by airborne, seaborne, or land-based observers. The intensity of bioluminescence is dependent on the local abundance of the dinoflagellates, which varies both in space and time. This makes the phenomenon difficult to predict, and when bioluminescent organisms are present, it is unavoidable by any practical means. 
     Ships, submarines and swimmers can readily be detected in the dark when strong bioluminescence activity exists, which poses a serious problem when movements need to be hidden from detection. When bioluminescence is present, there are ways to minimize the amount of signature that is detectable from the surface. In the case of submersibles and swimmers, detection vulnerability can be reduced by either decreasing the amount of flow stimulation caused by the craft (e.g., reducing speed) or by increasing operating depth, thus attenuating the surface signature caused by bioluminescence. The problem is that the operator must know in real time the bioluminescence intensity generated by the submersible&#39;s movement and how this is translated to surface signature and ultimately the vulnerability to detection. The operator must also know to what extent tactical maneuvers are effective in changing the bioluminescence signature at the surface. 
     Currently, this real-time self-monitoring capability does not exist. 
     Needs exist for a real-time, self-monitoring bioluminescence signature determination sensor. 
     SUMMARY OF THE INVENTION 
     The invention is a real-time in-situ bioluminescence detector for tactical use on submersible craft and swimmers. The miniature device can automatically provide continuous vulnerability assessment information to the vehicle operator or swimmer. 
     With this real-time quantifiable bioluminescence signature output, such a device could then recommend tactical procedures to reduce this signature by several means, for example, increasing depth, decreasing speed, combinations thereof, or any other similar evasive tactics. 
     This real-time in-situ device provides a way for operators to assess how far they can be seen based on nighttime luminescence and ambient light. It then allows the operators to modify their movement and/or change their locations continuously in response to the continuous real-time feedback they get from the device. 
     The invention provides a bioluminescence sensor for measurement of bioluminescence, for determination of bioluminescence surface signature, and for providing real-time information of the bioluminescence and the bioluminescence surface signature to the operator of a submerged moving object. The bioluminescence sensor of the invention includes one or more photodetectors, one or more ambient light detectors, one or more detectors used to measure sampled water characteristics in an enclosed space, a depth gauge, a device to measure turbidity, a speed indicator, a temperature measurement device, a pH measurement device, a salinity measurement device, a signal conditioning stage, a data acquisition system, a processor, an output, and a power source. The bioluminescence sensor further includes a dissolved oxygen measurement device. 
     The photodetectors of the bioluminescence sensor may be photodiodes, avalanche photodiodes (APD), photomultipliers, balanced photoreceivers, spectrometers, or similar photodetectors. The sensor&#39;s device to measure turbidity may be a light transmissometer, turbidity meter, or similar device to determine the effect or suspended solids in the water on light transmission. The sensor&#39;s speed indicator may be an anemometer or other similar device to measure velocity. The temperature measurement device of the bioluminescence sensor may be a thermistor, thermometer, or other similar instrument. The power source of the invention is either that of an external power source or a battery. 
     The signal conditioning stage of the invention further includes filters, pre-amplifiers, and amplifiers, and the processor consists of a digital signal processor (DSP), integrated circuit, field programmable gate array (FPGA), embedded system or other similar device. 
     The output system of the invention is a display and/or a computing device. 
     A new method of real-time bioluminescence sensing provides an apparatus including one or more photodetectors, one or more ambient light detectors, one or more detectors used to measure sampled water volumes in an enclosed space, a depth gauge, a device to measure turbidity, a speed indicator, a temperature measurement device, a pH measurement device, a salinity measurement device, a signal conditioning stage, a data acquisition system, a processor, an output system and a power source. That apparatus is then used to sense the bioluminescence signature of a body in water. 
     The apparatus of the new method of real-time bioluminescence sensing is powered by the power source. Information is then collected from the one or more photodetectors, the one or more ambient light detectors, the one or more detectors used to measure sampled water volumes in an enclosed space, the depth gauge, the device to measure turbidity, the speed indicator, the temperature measurement device, the pH measurement device, and the salinity measurement device. That collected information is passed to the signal conditioning stage where it is conditioned and passed from the conditioning stage to the data acquisition system. Information is acquired from the conditioned data, and the acquired information is passed to the processor. The acquired information is processed in the processor to determine the bioluminescence signature of the body. 
     The new method further includes predicting the potential bioluminescence signature of the body based upon changes in movement, speed, position, or other characteristics desired by the user. 
     The results of the processor are sent to a display and/or another computing device. 
     These and further and other objects and features of the invention are apparent in the disclosure, which includes the above and ongoing written specification, with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of the sensor system. 
         FIG. 2  shows details of the flow-through tube measurement detector. 
         FIGS. 3A and 3B  show examples of a system implemented onto the tail assembly of a submersible (Seal Delivery Vehicle or SDV). 
         FIG. 4  shows the sensor system used on a submersible. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a block diagram of various components of the system  1 . One or more detectors  3  including photodiodes, avalanche photodiodes (APD), photomultipliers, balanced photoreceivers, spectrometers, or similar photodetectors are used to measure the light intensity in the wake of the object. One or more ambient light detectors  5  are used to measure light levels outside of the wake. Other detectors  7  can be used to measure sampled water volumes in an enclosed space ( FIG. 2 ). A depth gauge  9  is used to measure the operating depth of the sensor system. A turbidity measurement is performed by a device  11 , for example a light transmissometer, turbidity meter or similar device to determine the effect of suspended solids in the water on light transmission. A speed indicator  13  may be, for example, an anemometer or similar device to measure velocity. Other water quality measurements are performed by sensor  15  for temperature (thermistor, thermometer, or similar instrument), pH, salinity, and/or dissolved oxygen. 
     The signals  17 ,  19 ,  21 ,  23 ,  25 ,  27 ,  29 , respectively, from the above measuring devices, go through a signal conditioning stage  31  having, for example, filters, pre-amplifiers, and amplifiers. The conditioned signals  33  are converted from analog to digital signals by a data acquisition system  35 . The converted signals  37  are sent to a processor  39  where they are processed through algorithms using, for example, a digital signal processor (DSP), integrated circuit, field programmable gate array (FPGA), embedded system, or other similar device. The algorithms calculate the light attenuation through the water to the surface based on the light levels, depth, water-quality characteristics, and/or all other parameters input from the signals. Batteries or external power source  41  supplies power  43  to the devices, electronics and instruments. The output  45  of the processor  39  algorithms may be shown on a display  47  and/or output to a computing device, for example, computer or other device  51  via USB, serial, or similar interface  49 . 
       FIG. 2  shows details of the flow-through detector apparatus  50 . A flow agitator  53  at the inlet  55  of the tube  57 , includes adjustable turning vanes, grating or similar device  59 , which induces turbulence and flow excitation that stimulates bioluminescent activity within the tube  57 +. The magnitude of flow excitation scales correspondingly as the movement speed of the craft/swimmer. Sensors  61  mounted in/on the inside surface  63  of the tube  57  measure the bioluminescence intensity in the absence of ambient external illumination. The turning vanes  59  can be adjusted by a device  64  on the tube  57 , to increase flow excitation  65  and provide predictive measurements by sensors  61  inside tube  57  of bioluminescence (i.e., light levels that would be present if the craft/swimmer changed movement speed). 
       FIGS. 3A and 3B  show examples of a system implemented onto the tail assembly of a submersible (Seal Delivery Vehicle or SDV). In  FIG. 3A  the detectors  71  and accessories  69  are installed on the submersible  67  without adversely affecting the hydrodynamics or other features of the submersible, i.e., the mounting of the inventive device is non-intrusive to the purpose of the user, whether it is a swimmer, diver, submersible or any other underwater object. Detectors  71  may include any one or more of those shown or described with reference to  FIG. 1  and accessories may include any one or more of those shown or described with reference to  FIG. 1  (for example, batteries, circuitry, transmissometer, depth gauge, other sensors, etc.).  FIG. 3B  is a detail of the device shown in  FIG. 3A . Detectors  71  and accessories  69  include ambient light detector  73 , primary detector  75 , photodiodes  77  with fields of regard  79 , all part of the device mounted on the submersible  67 . These provide the real-time continuous feedback to the operator/user of the device and allow for continuous adjustment of movement, speed, position, and other characteristics desired by the user. 
       FIG. 4  shows a conceptual rendering of the sensor system  81 , with the detector system  71  and accessories  69 , mounted on a submersible  83 .
         The technology includes, but is not limited to, the following advantageous characteristics:       

     1. Low power: the sensor can be battery powered at low levels or powered by an external source. 
     2. Low profile: the system has small form factor. The detector and accessories are compact and have little or no impact on craft hydrodynamics, maneuverability, and additional bioluminescence generation ( FIGS. 3A ,  3 B). 
     3. Simple: the system is low-cost, easy to install and remove, and does not have any negative impact on operator workflow or efficiency ( FIGS. 1-4 ). 
     4. Real time: the system provides continuous, instantaneous bioluminescence signature information for self-monitoring of detection vulnerability. 
     5. Multi-sensor configuration: the primary sensor, or sensors, directly measure bioluminescence intensity (photons/time) in the wake of the submersible. Nominally mounted at or near the tail/rudder assembly of the craft, each sensor has collection optics and a photodiode, photomultiplier, or other photodetector. One or more additional sensors may be oriented away from the primary detector to measure ambient illumination conditions. Analog circuitry, batteries and other sensors may be placed in a hydrodynamically benign location. 
     6. Internal flow-through apparatus: a cylindrical volume with an adjustable flow agitator such as turning vanes or grating excites bioluminescent activity within the enclosed volume. Photosensors inside the volume measure bioluminescence intensity due to flow excitation, which scales as the speed of movement, as shown in  FIG. 2 . 
     7. Sensor size/shape: miniature components and hydrodynamic shaping are used to minimize any effects the sensor will have on craft hydrodynamics and maneuverability. 
     8. Signal-to-noise ratio (SNR): using a multi-sensor design, the measured wake bioluminescence intensity is compared with ambient-light measurements to determine the net effect of craft/propeller-induced illumination ( FIG. 4 ). Information provided by the ambient-light sensor(s) are used in vulnerability assessment. High ambient light levels decrease bioluminescence SNR, reducing surface signature. 
     9. Other water-quality sensors: a compact beam transmissometer, or other similar turbidity meter, can be used to measure water turbidity and light attenuation, and a digital depth gauge is used to measure depth. Other water-quality parameters (including pH, salinity, temperature) can be measured, as shown in  FIG. 1 . Resulting data is used to determine a surface signature of bioluminescence illumination based on radiative transfer from depth to the surface through a turbid medium. 
     10. Display: an indicator of bioluminescence signature ranging from simple (red/yellow/green condition) to detailed (numerical readings of measured parameters and surface signature) based on light intensity, SNR, water quality and depth. When coupled to a craft hydrodynamic model, the display could specify maximum speed, minimum depth and other tactics to achieve acceptable maximum surface signature. Output can also be in digital form, interfaced to a computer or other instrument. 
     While the invention has been described with reference to specific embodiments, modifications and variations of the invention may be constructed without departing from the scope of the invention.