WO2008103697A2

WO2008103697A2 - Marine imaging system

Info

Publication number: WO2008103697A2
Application number: PCT/US2008/054366
Authority: WO
Inventors: Robert K. Cowen; Cedric M. Guigand
Original assignee: University Of Miami
Priority date: 2007-02-20
Filing date: 2008-02-20
Publication date: 2008-08-28
Also published as: WO2008103697B1; WO2008103697A3

Abstract

The present invention provides a marine imaging system, including a submersible housing including a first pod and a second pod, where the first and second pods are offset to allow water to pass therebetween; a light emitting diode disposed within the first pod, the diode emitting light along a first axis; a first mirror disposed within the first pod, the first mirror receiving light from the diode and reflecting at least a portion the light along a second axis; a second mirror disposed within the second pod, the second mirror receiving light reflected by the first mirror and reflecting at least a portion of the received light along a third axis; and a camera disposed within the second pod, the camera receiving at least a portion of the light reflected by the second mirror.

Description

MARINE IMAGING SYSTEM

FIELD OF THE INVENTION

The present invention relates to a method and system for oceanographic research imaging, and in particular, to a method and system for imaging small marine organisms in situ.

BACKGROUND OF THE INVENTION

Fisheries and research scientists across the globe need continuous information related to the marine food chain, which dominantly includes phytoplankton; zooplankton; and fish, where each becomes a food source for the next in ascending order. Zooplankton can typically be classified in two sub-categories of size: microzooplankton (typically 50 to 250 micrometers, equivalent spherical diameter ("esd")); and macrozooplankton (typically 250 micrometers to 20 mm, esd). Fish can also be sub-categorized by their size and/or stage of development: fish eggs (typically 1 mm in diameter); fish larvae (typically 1 to 3 cm in length); and juvenile and adult fish of sizes larger than that of their larval stage. Phytoplankton and zooplankton are often measured in the oceans and subsequently studied for their interrelationships and for their effect on fisheries. Information is often collected and later provided regarding the abundance and vertical distributions of phytoplankton, zooplankton, and fish in continental shelf waters, deep oceans, as well as inland waters. Acquiring such information or data accurately, continuously and with wide spatial coverage provides a significant sampling problem, especially given the limited ship-time that may be available.

In the past, the sampling of zooplankton has generally been accomplished by towing large plankton nets having mouth openings of between approximately 0.5 to 2.0 meters and lengths of approx. 3-6 meters across a body of water. On occasion, remote sensors, such as conductivity cells, have been towed behind a ship and video cameras have also been used to provide imaging of the nets and the water being strained therethrough. Researching and sampling phytoplankton presence and characteristics has generally been accomplished by one of two methods, either by collecting water bottle samples and processing the water samples by fluorometric methods, or by lowering or towing electronic instruments such as a fluorometer or a light attenuance meter into the water for analysis. The light attenuance meter is less accurate in measuring phytoplankton biomass than the fluorometer but does provide a reasonable profile of "relative biomass" when calibrated against a fluorometer at several points in sea water. The deployment of zooplankton sampler nets from ships is generally cumbersome, time consuming and provides limited spatial coverage. The nets often clog with phytoplankton material and must be recovered after short tows, e.g., having a duration of approximately 10 minutes or less. Moreover, vertical information with respect to the zooplankton in the water column is generally lost, since the collected samples are integrated in the net. Although designs using multiple stacked nets can yield improved results, the outcome is still very limited in the vertical information that can be assessed. Remote sensing of zooplankton using conductivity cells has not proven particularly successful since the cells are often small (3 to 5 nm in diameter) and unable to sample sufficient water volume. Video cameras are suitable for imaging and identifying zooplankton, but such systems typically have considerable difficulty in processing in real-time because of the large volume of data, and moreover, are often difficult to operate as they may require spatial lighting, and can only be towed at slow speeds of 1-2 knots. In addition, existing imaging systems may disturb the monitored environment with excessive illumination and/or by creating water turbulence that may significantly alter or skew the collected data.

In view of the above, it is desirable to provide a marine imaging system able to provide high-resolution imaging of small particles or organisms, such as phytoplankton, zooplankton, and fish, in a parcel of water having sufficient volume to quantify even relatively rare organisms, such as icthyoplankton, for the assessment of vertical and horizontal distribution of plankton and size classes. It is further desirable to provide a marine imaging system that does not overly disturb or alter the monitored environment with excessive illumination and/or the introduction of undesired amounts of turbulence. SUMMARY OF THE INVENTION

The present invention advantageously provides a marine imaging system, including a light source emitting light along a first axis; a first mirror receiving light from the light source, the first mirror reflecting at least a portion the light emitted from the light source along a second axis; a second mirror receiving light reflected by the first mirror, the second mirror reflecting at least a portion of the received light along a third axis; and a camera receiving at least a portion of the light reflected by the second mirror. The light source may include a light emitting diode having an emitted wavelength between approximately 400 and approximately 500 nm. The system may also include a first lens positioned between the light source and the first mirror, and a second lens positioned between the second mirror and the camera. An optical condenser may be positioned between the light source and the first mirror. The second axis may be substantially perpendicular to the first axis, and the third axis may substantially perpendicular to the second axis. In addition, the light source, first mirror, second mirror, and camera may be disposed within a submersible housing of a watercraft, where the submersible housing includes a first pod and a second pod, the first pod housing the light source and first mirror, and the second pod housing the second mirror and the camera, and where the first and second pods are offset to allow water to pass therebetween. The present invention further provides a method of imaging marine organisms, including emitting light along a first axis; reflecting the light along a second axis substantially perpendicular to the first axis, wherein the reflected light along the second axis passes through a volume of water; reflecting a portion of the light passing through the volume of water along a third axis substantially perpendicular to the second axis; and capturing an image from the light directed along the third axis. The method may further include moving the light source through a body of water. BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:

FIG. 1 is an illustration of an embodiment of a marine imaging system constructed in accordance with the principles of the present invention; and

FIG. 2 is an additional illustration of an embodiment of a marine imaging system constructed in accordance with the principles of the present invention. DETAILED DESCRIPTION OF THE INVENTION

The present invention provides an oceanographic marine imaging system capable of imaging small particles or planktonic organisms (i.e., sizes less than about lmm to 10+ cm) at a very high resolution in a parcel of water that is of sufficient volume to quantify the particles or organisms therein. The system of the present invention may be used to determine the vertical and horizontal distribution of plankton size classes to a fine detail or resolution that was previously difficult if not impossible to achieve. The system of the present invention further allows for rapid sampling as compared to traditional plankton nets or existing imaging systems, thereby reducing the time required to survey certain locations of the ocean and/or to do so in grater detail.

Now referring to FIGS. 1 and 2, an embodiment of a marine imaging system constructed in accordance with the principles of the present invention is shown and generally designated as "10." The imaging system 10 generally includes an optical assembly 12 including a camera 14 fitted into or otherwise mounted upon a water- borne vehicle or marine craft, as discussed in more detail below. In particular, the optical assembly may include one or more light sources, lenses, mirrors, and/or other optical components for manipulating a light path 15 and the properties thereof to facilitate video capture of an illuminated specimen or water volume. For example, the optical assembly of the imaging system 10 may include a combination of a light emitting diode ("LED") light source and a plurality of plano-convex lenses to create a collimated light field, where the collimated light field back-lights a parcel of a water column for image capturing by a high-resolution line scan camera. Moreover, a lighting source and technique involving shadow illumination may be employed. Focused shadowgraph techniques, as known in the art, allow for a long depth of field not achievable with other lighting techniques, such as off-axis illumination or simple backlighting. Use of a shadowgraph lighting scheme provides enhanced contoured as well as contrasted images of small, semi-transparent organisms such as zooplankton. In addition, a small, compact, vibration resistant light source such as an LED can be used without the need for overpowered or strobing operation, which results in a simplified design and an increasingly robust system 10.

Continuing to refer to FIG. 1, the optical assembly 12 of the marine imaging system 10 of the present invention may include a light source 16, such as an LED, an optical condenser 18 to manage the quality and intensity of the light, a pinhole 20, and a first lens 22. Of note, while examples of particular optical component dimensions and/or properties are provided below, such features are intended merely as examples and they may, of course, be modified to obtain a desired result within a particular application.

In particular, the light source 16 may include an LED emitting light along a first axis 24 in a substantially violet/blue wavelength (i.e. 400 to 500 nm), which produces a suitable amount of light for observing fish larvae in a relatively undisturbed environment. Of course, other light sources having varying colors or intensities may be equally applicable. The LED creates a point source of light (4 mm diameter, for instance) which is then refocused on the pinhole 20, which may measure approximately lmm for example, using the condenser lens assembly 18 (which may include lenses of 27 mm diameter and 6.9 mm focal length, for example). The light emerging from the pinhole 20 spreads to meet the first lens 22, which may be a 150 mm diameter plano-convex lens, for example. The light passing through the lens 22 may then be reflected by a first mirror 26 along a second axis 28. For example, the first mirror 26 may be oriented at an approximately 45 degree angle to the first axis 24 of the light path to direct the light emitted through the first lens 22 in a substantially perpendicular direction, that is to say, the second axis 28 may be substantially perpendicular to the first axis 24. The reflected light is then directed towards a second mirror 30, which may also be oriented at an angle of approximately 45 degree angle to direct the light along a third axis 32 substantially perpendicular to the second axis 28 (and parallel to the first axis 24). This plano-convex collimating (150 mm diameter, 586 mm focal length) lens and mirror arrangement creates a beam of light through a volume of sampled water 34 present or passing between the first and second mirrors, as discussed in more detail below. The beam of light then passes through a second collimating lens 36 and is refocused before it impinges on the camera 14.

The camera 14 may include a line-scan camera, which may be fitted with an 85 mm focal length imaging lens, for example. Such cameras function differently from traditional area-scan charge coupled device ("CCD") cameras. The line-scan camera creates a picture by adding subsequent line fractions of images as the object being imaged moves perpendicular to its axis. This creates a continuous image, which contrasts with sequential flashed photography or video images in the sense that flash/video are successive images that may overlap each other or create gaps if the object being imaged is not moving in synchronization with a camera's frame rate. Hi- speed scanning rates of the line-scan camera also allow for high resolution images. For example, a camera may be used having a vertical resolution of 2048 pixels, with a line scanning rate of 36,000 Hz. When towing or otherwise moving this instrument at an approximate speed of 5 knots (2.5 m/s) (or by placing the camera in a stationary position with water flowing past it at a similar rate), a continuous visual field of approximately 14 cm vertically and with a 20 cm depth of field may be obtained. Thus the volume of water imaged every second would be ca. 70 liters (14 cm X 20 cm X 250 cm) or -0.07 m3. As a typical 1 square meter plankton net filters ca. 0.75 m3 per s (at a tow speed of ~ 0.75 m s-1), the system 10 of the present invention using the exemplary camera described is capable of imaging close to 10% of the volume filtered by a net, which is greater than an order of magnitude improvement over existing imaging system 10s. Moreover, when towed at a speed of approximately 5 knots (2.5 m/s), the resulting pixel resolution is approximately 68X68 microns per pixel. As a typical larval fish may be 2X6 mm, then over 2600 pixels would be resolving each larva, resulting in a very high resolution image.

The described optical assembly and arrangement of components provides and economical system 10 in terms of light intensity, as all of the light entering the sampled volume between the mirrors is directed towards the camera. This avoids the use of bright light sources that could deter organisms away from the imaging area, and also results in smaller power requirements for operation of the selected light source.

Moreover, the described optical scheme makes the system 10 telecentric, meaning that magnification is independent of distance from the camera 14, thereby providing the opportunity to accurately measure the size of zooplankters within the imaged volume or sample. Finally, the shadowgraphy technique allows for a large depth of field (approximately 20-40 cm, for example), which greatly enhances the volume of water being imaged as compared to macro and micro photography.

The optical assembly 12 may be affixed, mounted, positioned or otherwise coupled to a marine craft or water-borne vehicle or platform 38. For example, the optical assembly 12 may be integrated into a submersible housing 40 to perform the subsequent marine imaging. The submersible housing may generally include two streamlined pods, where the light source 16, first lens 22, and first mirror 26 are positioned in a first pod 42, and the second mirror 30, second lens 36, and camera 14 are positioned in a second pod 44. The first and second pods may each include a transparent window or port 46, 46'opposite the first and second mirrors, respectively such that light is transmitted from the first pod 42, as directed by the first mirror 26, to the second pod 44 for direction from the second mirror 30 to the camera 14. The ports or windows may include, for example, a water-tight acrylic window. The first and second pods may be sufficiently offset to allow water to pass in between the two pods (and in particular, past the two window ports and/or the first and second mirrors) for imaging, and may include a streamlined or similarly hydrodynamic body or component to reduce turbulence around the lighted sample when in use. For example, each pod may include a conical-shaped front end to facilitate movement through a water column, and a stabilizing keel and/or wing 48 may be also be coupled to the craft to provide enhanced movement control or stability of the device. With the application of the first and second mirrors and the light beam therebetween, the imaged parcel of water passes between the forward portions of the two streamlined pods and thereby remains unaffected by turbulence. As a result, a very high-resolution image of zooplankton in their natural position and orientation may be collected. When a sufficient volume of water is imaged using the system 10 of the present invention, the enhanced quantification of density and fine scale distribution of small organisms or particles within the sampled volume is possible.

While the optical assembly may be towed behind a boat or similar water craft, it is also contemplated that the marine craft housing the optical assembly may further include a propulsion mechanism and related controls or operative components, similar to that found in Autonomous Underwater Vehicles ("AUVs"), or small Remotely Operated Vehicles ("ROVs"), to allow the system 10 of the present invention to be operated independently of a boat or other observation platform.

The marine craft/platform 38 may also include one or more sensors 50 that measure, collect, or otherwise analyze various characteristics of the operating environment surrounding the craft and/or the optical assembly. For example, temperature, flow rate, salinity, pressure and/or light sensors may be included on the body of the craft and/or the first and second pods for the collection of data ancillary to the image recording. Moreover, the craft may include depth and/or pitch sensors 52 to aid in orienting the craft, and thus the optical assembly, into a desired position with respect to the water flow. Of course, a power supply 54 (such as batteries or the like) may also be included for the operation of the components described herein.

In addition to containing the optical assembly and other components described above, the marine imaging system 10 may also include a data collection and/or transfer module (not shown) for storing and/or relaying the collected images and information to an observation platform. For example, the data collection module may include one or more electronic storage elements where the images and information obtained from the cameras and one or more sensors is stored for later retrieval. For example, a high throughput disc array (having approximately 160 GB storage space, for example) may include a plurality of hard drives controlled by a high performance computer with continuous real-time recording at 140MB/second. Should it be desirable to immediately port the recorded data to an observation platform or ship, a high through-put communication protocol may be employed to establish communication between the optical assembly of the marine craft and a ship. For example, a fiber optic coupling may directly link the camera to a fiber optic extender communicating data to a shipboard computer via a copper/ fiber optic oceanographic cable. Of course, additional and/or alternative communication methodologies and protocols may be equally usable with the system 10 of the present invention.

While the system 10 of the present invention has been described for uses involving imaging or otherwise monitoring and collecting information regarding small oceanic organisms such as plankton and the like in open water, it is also contemplated that the imaging system 10 may be used for observing, imaging or otherwise collecting information regarding other suspended particles or elements within a particular body of water. For example, the bilge contents of large oceanic vessels may be analyzed for the presence of exotic or otherwise invasive organisms prior to discharging bilge tanks into coastal ports. Moreover, the imaging system 10 of the present invention may be anchored or otherwise affixed to a stationary structure for the recording and analysis of the flux or passage of particles or organisms across a particular location for an extended duration of time.

It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope and spirit of the invention, which is limited only by the following claims.

Claims

What is claimed is:

1. A marine imaging system, comprising: a light source emitting light along a first axis; a first mirror receiving light from the light source, the first mirror reflecting at least a portion the light emitted from the light source along a second axis; a second mirror receiving light reflected by the first mirror, the second mirror reflecting at least a portion of the received light along a third axis; and a camera receiving at least a portion of the light reflected by the second mirror.

2. The marine imaging system according to Claim 1 , further comprising a first lens positioned between the light source and the first mirror.

3. The marine imaging system according to Claim 2, wherein the first lens acts as a collimator.

4. The marine imaging system according to Claim 2, further comprising a second lens positioned between the second mirror and the camera.

5. The marine imaging system according to Claim 4, wherein the second lens acts as a condenser.

6. The marine imaging system according to Claim 1, further comprising an optical condenser positioned between the light source and the first mirror.

7. The marine imaging system according to Claim 1, wherein the light source is a small point light source having an emitted wavelength between approximately 400 and approximately 500 nm.

8. The marine imaging system according to Claim 1, wherein the second axis is substantially perpendicular to the first axis.

9. The marine imaging system according to Claim 8, wherein the third axis is substantially perpendicular to the second axis.

10. The marine imaging system according to Claim 1, wherein the light source, first mirror, second mirror, and camera are disposed within a submersible housing of a watercraft.

11. The marine imaging system according to Claim 1, wherein the submersible housing includes a first pod and a second pod, the first pod housing the light source and first mirror, and the second pod housing the second mirror and the camera, and wherein the first and second pods are offset to allow water to pass therebetween.

12. The marine imaging system according to Claim 1, wherein the camera is a line- scan camera.

13. A marine imaging system, comprising: a submersible housing including a first pod and a second pod, wherein the first and second pods are offset to allow water to pass therebetween; a light emitting diode disposed within the first pod, the diode emitting light along a first axis; a first mirror disposed within the first pod, the first mirror receiving light from the diode and reflecting at least a portion the light along a second axis; a second mirror disposed within the second pod, the second mirror receiving light reflected by the first mirror and reflecting at least a portion of the received light along a third axis; and a camera disposed within the second pod, the camera receiving at least a portion of the light reflected by the second mirror.

14. The marine imaging system according to Claim 13, further comprising a first plano-convex lens positioned between the diode and the first mirror.

15. The marine imaging system according to Claim 14, further comprising a second plano-convex lens positioned between the second mirror and the camera.

16. The marine imaging system according to Claim 13, further comprising an optical condenser positioned between the light source and the first mirror.

17. The marine imaging system according to Claim 13, wherein the second axis is substantially perpendicular to the first axis, and wherein the third axis is substantially perpendicular to the second axis.

18. A method of imaging marine organisms; comprising: illuminating a volume of water passing between a light source and a camera; and capturing an image of the illuminated water with the camera.

19. The method according to Claim 18, wherein illuminating the water sample includes emitting light along a first axis; reflecting the light along a second axis substantially perpendicular to the first axis, wherein the reflected light along the second axis passes through the volume of water; reflecting a portion of the light passing through the volume of water along a third axis substantially perpendicular to the second axis; and capturing an image from the light directed along the third axis. 2O.The method according to Claim 18, further comprising moving the light source and the camera through a body of water.