System and method for imaging through an irregular water surface
An underwater imaging system includes an underwater imaging polarimeter that captures images of the water surface. The captured images are indicative of the captured light, and are equivalent to four-component Stokes vector S=(I,Q,U,V) data. Advantageously, the passive imaging technique of the present invention utilizes polarmetric data. In contrast, conventional optical remote sensing techniques rely on light amplitude and frequency to carry information about the scattering surface. The imaging technique of the present invention exploits these properties, as well as the polarization properties of light to sense information about the scattering media. The two-dimensional slope field of surface wave can be recovered from a distance without interfering with the fluid dynamics of the air or water. By employing the physics of light scattering by a specular surface, the geometry of the surface can be found by measuring the polarimetric properties of the reflected and/or refracted light. The derived two-dimensional slope field in then used to remove the image distortion caused by light passing through the wavy surface. The undistorted images have the appearance of images taken through a flat water surface.
1. An underwater sensor for forming an image of the above-the-water environment including items located on or above the water surface, the sensor comprising:
an underwater imaging polarimeter that captures an image of the water surface and provides four-component image data equivalent to Stokes vector data and indicative of light passing through the water surface into the water; and
a processing unit that receives and processes the four-component image data to generate an image of the environment on or above the water surface.
2. The underwater sensor of claim 1 , further comprising:
a transceiver that receives the image and transmits image data indicative thereof.
3. The underwater sensor of claim 1 , where the four-component image data includes an equivalent of a first component (I) indicative of the intensity of light, second and third components (Q, U) indicative of linear polarization, and a fourth component (V) indicative of circular polarization.
4. The underwater sensor of claim 1 , where the processing unit process the four-component image data to generate two-dimensional surface slope field data.
5. The underwater sensor of claim 1 , further comprising an inertial navigation unit that provides position, attitude and velocity data of the underwater imaging polarimeter that is used by the processing unit to generate the image.
6. The underwater sensor of claim 1 , where the underwater imaging polarimeter comprises four image sensors.
7. The underwater sensor of claim 6 , where the underwater imaging polarimeter comprises a plurality of beam splitters that provide four different optical paths which are uniquely associated with one of the four image sensors, which each provide data for the four-component image data.
8. An underwater sensor for forming an image of the above-the-water environment including items located on or above the water surface, the sensor comprising:
an underwater imaging polarimeter that captures an image of the water surface and provides four-component image data indicative of light passing through the water surface into the water, where the underwater imaging polarimeter comprises an objective lens assembly that provides a ray bundle to a polarizing beamsplitter that splits the ray bundle into four different optical paths each uniquely associated with one of four image sensors that provides image data for the four-component image data; and
a processing unit that receives and processes the four-component image data from the four image sensors to generate two-dimensional water surface slope field data from which an image is generated indicative of the environment above or on the water surface, including objects located on or above the water surface.
9. The underwater sensor of claim 8 , further comprising an inertial navigation unit that provides attitude, position and velocity data of the underwater imaging polarimeter that is used by the processing unit to generate the image.
10. The underwater sensor of claim 9 , where the underwater imaging polarimeter comprises four image sensors.