Processing

Please wait...

Settings

Settings

Goto Application

1. WO2016148746 - TUNABLE MULTI-BAND SPECTRO-POLARIMETER

Note: Text based on automatic Optical Character Recognition processes. Please use the PDF version for legal matters

[ EN ]

CLAIMS

1. A tunable multi-band spectro-polarimetric imaging system comprising:

an imaging detector including a two-dimensional array of pixels;

an optical sub-system configured to direct the incident electromagnetic radiation from a viewed scene along an optical path to the imaging detector;

a first tunable spectral filter positioned in the optical path between the optical subsystem and the imaging detector and configured to filter the incident electromagnetic radiation such that a first plurality of pixels of the array of pixels receives electromagnetic radiation in a first spectral band;

a second tunable spectral filter positioned in the optical path between the optical sub-system and the imaging detector and configured to filter the incident electromagnetic radiation such that a second plurality of pixels of the array of pixels receives electromagnetic radiation in a second spectral band different than the first spectral band; a plurality of polarization filters positioned in the optical path between the optical sub-system and the imaging detector, the plurality of polarization filters being configured to selectively alter a polarization state of the incident electromagnetic radiation, such that the imaging detector receives at least three different polarizations of the electromagnetic radiation in each of the first and second spectral bands, the imaging detector being configured to produce first polarimetric image data corresponding to the first spectral band and second polarimetric image data corresponding to the second spectral band; and

a controller configured to receive and process the first and second polarimetric image data to detect a target object in the viewed scene, and to provide control signals to the first and second tunable spectral filters to tune a wavelength range of each of the first and second spectral bands.

2. The system of claim 1 wherein the viewed scene includes a body of water, and wherein the controller is configured to tune the first tunable spectral filter to select the first spectral band as a guard band, wherein electromagnetic radiation in the wavelength range corresponding to the first spectral band does not penetrate below a predetermined threshold depth beneath a surface of the body of water, the processor being further configured to tune the second spectral filter to select the second spectral band as target band, wherein electromagnetic radiation in the wavelength range corresponding to the second spectral

band penetrates below the predetermined threshold depth beneath the surface of the body of water.

3. The system of claim 2 wherein, in processing the first and second polarimetric image data, the processor is configured to subtract the first polarimetric image data from the second polarimetric image data to produce composite polarimetric image data.

4. The system of claim 3 wherein the processor is further configured to apply a matched filter to the composite polarimetric image data.

5. The system of claim 1 wherein the optical sub-system includes:

an entrance slit;

foreoptics configured to direct the incident electromagnetic radiation through the entrance slit; and

imaging optics configured to receive the incident electromagnetic radiation via the entrance slit, to collimate the incident electromagnetic radiation, and to focus the incident electromagnetic radiation onto a focal plane at which the imaging detector is located.

6. The system of claim 5 further comprising a spectral filter assembly positioned in the optical path ahead of the entrance slit.

7. The system of claim 1 wherein the at least three polarizations include 0°, 60°, and 120°.

8. A tunable multi-band spectro-polarimetric imaging system comprising:

an imaging detector array;

an optical sub-system configured to direct electromagnetic radiation from a viewed scene along an optical path toward the imaging detector array;

a plurality of spectral filters positioned in the optical path between the optical subsystem and the imaging detector array and configured to filter the electromagnetic radiation into at least two spectral bands such that a first region of the imaging detector array receives electromagnetic radiation in a first spectral band and a second region of the imaging detector array simultaneously receives electromagnetic radiation in a second spectral band; a plurality of polarization filters positioned in the optical path in front of the imaging detector array and configured to filter the electromagnetic radiation in each of the first and second spectral bands into at least two different polarization states; and

a controller coupled to the imaging detector array,

wherein the first region of the imaging detector array is configured to produce first polarimetric image data for the first spectral band, and the second region of the imaging detector array is configured to produce second polarimetric image data for the second spectral band; and

wherein the controller is configured to receive and process the first and second polarimetric image data, including subtracting the first polarimetric image data from the second polarimetric image data to produce composite polarimetric data, and processing the composite polarimetric data to detect a target object in the viewed scene.

9. The system of claim 8 wherein the processor is further configured to process the composite polarimetric image data to produce at least normalized Stokes parameters So, Si, and S2.

10. The system of claim 8 wherein the plurality of polarization filters includes three polarization filters positioned in front of each of the first and second regions of the imaging detector array, and the at least two different polarization states include nominally 0°, 60°, and 120°.

11. The system of claim 8 wherein the imaging detector array includes a two-dimensional array of pixels, and wherein the plurality of polarization filters are organized into a composite polarimetric grid filter aligned with the two-dimensional array of pixels of the imaging detector array and configured to filter the electromagnetic radiation in each of the first and second spectral bands such that the first and second polarimetric image data each includes four polarization measurements.

12. The system of claim 11 wherein the four polarization measurements include irradiance (Eo), linear horizontal polarization (Ei), linear 45° polarization (E2), and circular polarization (E3).

13. The system of claim 12 wherein the controller is configured to calculate Si, a first normalized Stokes vector corresponding to the first polarimetric image data, and S2, a second normalized Stokes vector corresponding to the second polarimetric image data.

14. The system of claim 8, wherein the plurality of spectral filters are tunable and the viewed scene includes a body of water, and wherein the controller is further configured to tune a first one of the plurality of spectral filters to select the first spectral band as a guard band, wherein electromagnetic radiation in a wavelength range corresponding to the guard band does not penetrate below a predetermined threshold depth beneath a surface of the body of water, the controller being further configured to tune a second one of the plurality of spectral filters to select the second spectral band as target band, wherein electromagnetic radiation in a wavelength range corresponding to the target band penetrates below the predetermined threshold depth beneath the surface of the body of water.

15. An imaging method for detecting a submerged object in a body of water, the method comprising:

selectively tuning a spectral passband of a first spectral filter to pass electromagnetic radiation in guard spectral band;

selectively tuning a spectral passband of a second spectral filter to pass electromagnetic radiation in a target spectral band, wherein a range of an attenuation coefficient in water of the electromagnetic radiation in the guard spectral band and a range of an attenuation coefficient of the electromagnetic radiation in the target spectral band are such that the electromagnetic radiation in the target spectral band penetrates further below a surface of the body of water than the electromagnetic radiation in the guard spectral band; simultaneously filtering the electromagnetic radiation in the guard spectral band and the electromagnetic radiation in the target spectral band into a plurality of polarization states;

using an imaging detector, simultaneously obtaining first polarimetric image data from the electromagnetic radiation in the guard spectral band and second polarimetric image data from the electromagnetic radiation in the target spectral band; and

processing the first and second polarimetric image data to detect the submerged object.

16. The imaging method of claim 15 wherein processing the first and second polarimetric image data includes subtracting the first polarimetric image data from the second polarimetric image data to produce composite polarimetric image data, and performing matched filter processing on the composite polarimetric image data.

17. The imaging method of claim 16 wherein selectively tuning the spectral passbands of the first and second spectral filters is performed based at least in part on characteristics of the body of water.

18. The imaging method of claim 17 wherein selectively tuning the spectral passbands of the first and second spectral filters is further performed based at least in part on results obtained from processing the composite polarimetric image data.