Sky polarization and sun sensor system and method

• US 9,423,484 B2
• Filed: 10/22/2014
• Issued: 08/23/2016
• Est. Priority Date: 10/22/2013
• Status: Active Grant

• Current Assignee: Polaris Sensor Technologies, Inc
• Original Assignee: Polaris Sensor Technologies, Inc
• Inventors: Pezzaniti, J. Larry, Aycock, Todd Michael, Chenault, David, Lompado, Arthur
• Primary Examiner(s): Allison, Andrae S
• Application Number:
  US14/521,401
• Publication Number:
  US 20150226827A1
• Time in Patent Office: 671 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: G01C 17/00 Compasses; Devices for ascertaining true or magnetic north for navigation or surveying purposes using gyroscopic effect G01C19/00
• CPC Class Codes: G01C 21/02 by astronomical means G01C21/24, G01C21/26 take precedence
• CPC Class Codes: G01S 3/783 using amplitude comparison of signals derived from static detectors or detector systems
• CPC Class Codes: G01S 3/7861 Solar tracking systems
• CPC Class Codes: G01S 3/7862 mounted on a moving platform, e.g. space vehicle
• CPC Class Codes: G01S 5/16 using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 5/163 Determination of attitude using inertial means G01C9/00; control of attitude G05D1/49
• CPC Class Codes: G06T 2207/20061 Hough transform
• CPC Class Codes: G06T 2207/30181 Earth observation
• CPC Class Codes: G06T 7/70 Determining position or orientation of objects or cameras camera calibration G06T7/80
• CPC Class Codes: G06V 10/147 Details of sensors, e.g. sensor lenses fingerprint or palmprint sensors G06V40/13; vascular sensors G06V40/145; eye sensors G06V40/19
• CPC Class Codes: G06V 20/00 Scenes; Scene-specific elements control of digital cameras H04N23/60
• CPC Class Codes: G06V 20/20 in augmented reality scenes
• CPC Class Codes: H04N 7/183 for receiving images from a single remote source

Abstract

A system for determining a new orientation and/or position of an object comprises a sky polarimeter configured to record image data of the sky, a signal processing unit, and logic configured to receive and store in memory the image data received from the sky polarimeter. The logic calculates the Stokes parameters (S₀, S₁, S₂,), DoLP, and AoP from the image data, detects obscurants and filters the obscurants (such as clouds and trees) from the image data to produce a filtered image. The logic is further configured to find the Sun and zenith in the filtered image, and to determine the roll, pitch, yaw, latitude and longitude of the object using the filtered image. A method for determining a new position/orientation of an object comprises recording raw image data using a sky polarimeter, calculating S₀, S₁, S₂, DoLP, and AoP from the image data, detecting obscurants and filtering the obscurants from the image data to produce a filtered image, obtaining last known position/orientation data of the object, finding the Sun and zenith in the filtered image, and determining the roll, pitch, yaw, latitude and longitude of the object using the filtered image.

Claims

1. A method of determining orientation of an object, the method comprising:

recording raw image data of the sky using a sky polarimeter;

calculating Stokes parameters (S₀, S₁, S₂), degree of linear polarization (DoLP) and angle of polarization (AoP) from the image data;

detecting obscurants and filtering the obscurants from the image data to produce a filtered image;

obtaining position/orientation data of the object;

finding the Sun azimuth and elevation in the filtered image by performing a coordinate transform on a measured polarization pattern to generate a scanning AoP image;

determining one or more of the roll, pitch, yaw, latitude and longitude of the object using the filtered image;

when yaw is determined using the filtered image, calculating platform yaw based on the angle between the line intersecting the Sun and the zenith and expected Sun/azimuth position for a given date and time;

performing minimum detection and extracting a region of the image containing the Sun and zenith;

applying morphological erosion on a binary image to reduce the detected minimum region to a single line; and

extracting a sun-zenith line.

2. The method of claim 1, further comprising fusing a position estimate and a position prediction of the object to determine the new position/orientation of the object.

3. The method of claim 1, wherein the step of finding the Sun azimuth and elevation in the filtered image comprises finding the Sun azimuth from a zenith value in a fixed AoP image.

4. The method of claim 1, wherein, the step of finding the Sun azimuth and elevation in the filtered image comprises performing a coordinate transform on a measured polarization pattern to generate a scanning AoP image.

5. The method of claim 1, wherein the step of extracting the sun-zenith line comprises performing a Hough transform.

6. The method of claim 1, wherein the sky polarimeter comprises three or more polarization optical channels, each polarization optical channel comprising a uniquely-oriented polarization filter.

7. The method of claim 6, wherein the sky polarimeter further comprises an open optical channel that attenuates image data received from an objective lens without polarization.

8. The method of claim 7, wherein the step of finding the Sun azimuth and elevation in the filtered image further comprises detecting the sun in the open optical channel.

9. The system of claim 8, wherein the step of finding the Sun azimuth and elevation in the filtered image further comprises finding the centroid of the sun in S0 and calculating the distance between the Sun and the zenith, which distance is the Sun elevation.