UNDERWATER HYPERSPECTRAL IMAGING

• US 20110205536A1
• Filed: 05/21/2009
• Published: 08/25/2011
• Est. Priority Date: 05/21/2008
• Status: Active Grant

• Current Assignee: Ecotone AS
• Original Assignee: NTNU Technology Transfer AS (Norwegian University of Science and Technology)
• Inventors: Johnsen, Geir
• Granted Patent: US 8,502,974 B2
• Time in Patent Office: Days
• US Class Current: 356/326
• CPC Class Codes: G01J 3/0208 using focussing or collimating elements, e.g. lenses or mirrors; performing aberration correction
• CPC Class Codes: G01J 3/027 Control of working procedures of a spectrometer; Failure detection; Bandwidth calculation
• CPC Class Codes: G01J 3/0289 Field-of-view determination; Aiming or pointing of a spectrometer; Adjusting alignment; Encoding angular position; Size of measurement area; Position tracking
• CPC Class Codes: G01J 3/0291 Housings; Spectrometer accessories; Spatial arrangement of elements, e.g. folded path arrangements
• CPC Class Codes: G01J 3/06 Scanning arrangements arrangements for order-selection
• CPC Class Codes: G01J 3/10 Arrangements of light sources specially adapted for spectrometry or colorimetry
• CPC Class Codes: G01J 3/28 Investigating the spectrum using colour filters G01J3/51
• CPC Class Codes: G01J 3/2823 Imaging spectrometer
• CPC Class Codes: G01J 3/42 Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry beam switching arrangements G01J3/08
• CPC Class Codes: G01N 21/255 Details, e.g. use of specially adapted sources, lighting or optical systems
• CPC Class Codes: G01N 2201/0218 Submersible, submarine
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G02B 21/33 Immersion oils , or microscope systems or objectives for use with immersion fluids

Abstract

An apparatus for placement on or in a body of water for hyperspectral imaging of material in the water comprises an artificial light source and a hyperspectral imager. These are arranged so that in use light exits the apparatus beneath the surface of the water and is reflected by said material before re-entering the apparatus beneath the surface of the water and entering the hyperspectral imager. The hyperspectral imager is adapted to produce hyperspectral image data having at least two spatial dimensions.

Claims

1. An apparatus for placement on or in a body of water for hyperspectral imaging of material in the water comprising an artificial light source and a hyperspectral imager which are arranged so that in use light exits the apparatus beneath the surface of the water and is reflected by said material before re-entering the apparatus beneath the surface of the water and entering said hyperspectral imager, wherein said hyperspectral imager is adapted to produce hyperspectral image data having at least two spatial dimensions, and wherein the apparatus is arranged to estimate a spectral attenuation coefficient of the ambient water and to adjust the spectral output of the artificial light source so that a predetermined light spectrum arrives at said material.

3. An apparatus as claimed in claim 1 comprising one or more optical filters selectably placeable in the path of the emitted light so as to adjust the spectral output of the artificial light source.

4. An apparatus as claimed in claim 3 comprising a plurality of optical filters selectably placeable in the path of the emitted light, each having a unique spectral-filtering characteristic.

5. An apparatus as claimed in claim 1 wherein the light source comprises a plurality of light-emitting elements each with differing emission spectra, and wherein the apparatus is configured to alter the power supplied to respective light-emitting elements in order to give a required overall output spectrum.

6. An apparatus as claimed in claim 5 wherein the light-emitting elements comprise light emitting diodes.

7. An apparatus as claimed in claim 1 comprising an optical sensor and logic for estimating a spectral attenuation coefficient of the ambient water using an output from said optical sensor.

8. An apparatus as claimed in claim 1 wherein the hyperspectral imager operates using dispersive spectrography.

9. An apparatus as claimed in claim 1 wherein the hyperspectral imager has no independently moving parts.

10. An apparatus as claimed in claim 1 arranged so that movement of the apparatus through the body of water enables an area of interest to be continuously imaged.

11. An apparatus as claimed in claim 1 comprising a tether for connecting to a ship or other vessel.

12. An apparatus as claimed in claim 11 wherein the tether comprises an umbilical power supply.

13. An apparatus as claimed in claim 1 comprising a portable power supply and wherein the apparatus is capable of independent movement.

14. An apparatus as claimed in claim 13 wherein the portable power supply comprises a battery.

15. An apparatus as claimed in claim 1 further comprising an image capturer for capturing frames from the hyperspectral imager.

16. An apparatus as claimed in claim 15 further comprising image processing logic arranged to process captured images from the hyperspectral imager.

17. An apparatus as claimed in claim 1 adapted to be fully submersible.

18. An apparatus as claimed in claim 17 comprising a housing designed to withstand external pressures of at least 10 bars.

19. An apparatus as claimed in claim 1 wherein the hyperspectral imager is arranged to provide a spectral resolution of finer than 1 nm.

20. An apparatus as claimed in claim 1 wherein the hyperspectral imager is arranged to image over the whole spectrum of visible light.

21. An apparatus as claimed in claim 1 wherein the hyperspectral imager has a maximum physical dimension of less than 50 cm.

22. An apparatus as claimed in claim 1 wherein the hyperspectral imager weighs less than 1 kg.

23. An apparatus as claimed in claim 1 wherein the hyperspectral imager consumes less than 2 Watts.

2. (canceled)

24. A method of imaging material beneath the surface of a body of water comprising:

illuminating said material with an artificial light source from beneath the surface of the water;

receiving from beneath the surface of the water light reflected from said material into a hyperspectral imager;

said hyperspectral imager generating hyperspectral image data from said material, said image data having at least two spatial dimensions;

estimating a spectral attenuation coefficient of the ambient water; and

adjusting the spectral output of the artificial light source so that a predetermined light spectrum arrives at said material.

25. A method as claimed in claim 24 wherein the artificial light source is provided in the same unit as the imager.

26. A method as claimed in claim 24 comprising use of apparatus for placement on or in a body of water for hyperspectral imaging of material in the water, comprising an artificial light source and a hyperspectral imager which are arranged so that in use light exits the apparatus beneath the surface of the water and is reflected by said material before re-entering the apparatus beneath the surface of the water and entering said hyperspectral imager, wherein said hyperspectral imager is adapted to produce hyperspectral image data having at least two spatial dimensions, and wherein the apparatus is arranged to estimate a spectral attenuation coefficient of the ambient water and to adjust the spectral output of the artificial light source so that a predetermined light spectrum arrives at said material.

28. A method as claimed in claim 24 comprising the further step of using the hyperspectral imager to determine whether a predetermined spectrum for the artificial light is achieved.

29. A method as claimed in claim 24 comprising the further step of using an optical sensor to determine whether a predetermined spectrum for the artificial light is achieved.

31. A method as claimed in claim 24 wherein said estimating is continuous.

32. A method as claimed in claim 24 comprising the further step of locating a spectral filter in the path of the artificial light.

33. A method as claimed in claim 24 comprising the further step of selectively illuminating elements from among a set of spectrally-distinct light-emitting elements.

35. A method as claimed in claim 3124 wherein the predetermined light spectrum comprises substantially uniform energy across the visible spectrum.

36. A method as claimed in claim 24 further comprising:

deploying a calibration surface having known reflectance characteristics; and

using feedback control to alter the spectrum of light emitted by the light source depending on the spectrum of the light reflected from the calibration surface until a predetermined spectrum is achieved.

37. A method as claimed in claim 36 wherein the calibration surface is a white Teflon disc and wherein the disc is deployed in front of the hyperspectral imager at a given distance.

38. A method as claimed in claim 24 comprising the further step of locating or mapping the extent of one or more organisms or other material by the characteristic spectral fingerprint(s) thereof.

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60. An apparatus for placement on or in a body of water for hyperspectral imaging of material in the water comprising an artificial light source and a hyperspectral imager which are arranged so that in use light exits the apparatus beneath the surface of the water and is reflected by said material before re-entering the apparatus beneath the surface of the water and entering said hyperspectral imager, wherein said hyperspectral imager is adapted to produce hyperspectral image data having at least two spatial dimensions, and wherein the apparatus is arranged to estimate a spectral attenuation coefficient of the ambient water and to compensate for the attenuation of reflected or emitted light returning to the apparatus.

61. A method of imaging material beneath the surface of a body of water comprising:

illuminating said material with an artificial light source from beneath the surface of the water;

receiving from beneath the surface of the water light reflected from said material into a hyperspectral imager;

said hyperspectral imager generating hyperspectral image data from said material, said image data having at least two spatial dimensions;

estimating a spectral attenuation coefficient of the ambient water; and

compensating for the attenuation of reflected or emitted light returning to the apparatus.