# US 10,371,519 B1 · Polarization optical compass

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- Number: US 10,371,519 B1
- Document ID: US10371519B1
- Status: Granted
- Kind: B1
- Application number: 15/606,761
- Filed: 2017-05-26
- Granted: 2019-08-06
- Earliest claimed: 2017-05-26
- Assignees: Lockheed Martin Corporation
- Applicants: Lockheed Martin Corporation
- Inventors: David R. Twede; James N. O'Sullivan
- Web page: https://patentgrep.com/patent/US10371519B1

## CPC

- G01C 17/34: Sun- or astro-compasses
- G01S 3/782: Systems for determining direction or deviation from predetermined direction
- G01S 3/781: Details
- G01S 3/785: using adjustment of orientation of directivity characteristics of a detector or detector system to give a desired condition of signal derived from that detector or detector system
- G02B 5/3025: {Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state (G02B5/3008, G02B5/3016 take precedence)}
- G02B 5/3033: {in the form of a thin sheet or foil, e.g. Polaroid}
- G01C: MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY (measuring liquid level G01F; radio navigation, determining distance or velocity by use of propagation effects, e.g. Doppler effects, propagation time, of radio waves, analogous arrangements using other waves G01S)
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

An optical assembly that includes at least one polarizing filter assembly and at least one sensor. The polarizing filter assembly is configured to receive electromagnetic radiation (EMR) emitted by a sun and transmit at least three different portions of EMR towards the at least one sensor, each portion filtered based on a different polarization orientation. A processor device is configured to receive sensor data generated by the at least one sensor in response to receipt of the at least three different portions of EMR, and determine an elevation angle of the sun with respect to a horizon from a geographic location of the optical assembly.

## Claims

### Claim 1

An optical assembly comprising:
at least one polarizing filter assembly;
at least one sensor comprising a grid of a plurality of detector elements; and
a processor device coupled to the at least one sensor;
wherein the at least one polarizing filter assembly is configured to:
receive electromagnetic radiation (EMR) emitted by a sun;
transmit, by the at least one polarizing filter assembly, at least three different portions of EMR towards the at least one sensor, each portion filtered based on a different polarization orientation, and at least two portions of the at least three different portions of EMR comprising different wavebands of EMR; and
wherein the processor device is configured to:
receive sensor data generated by the at least one sensor in response to receipt of the at least three different portions of EMR; and
based on the sensor data, determine an elevation angle of the sun with respect to a horizon from a geographic location of the optical assembly.

### Claim 2 (depends on 1)

The optical assembly of claim 1 wherein to determine the elevation angle of the sun with respect to the horizon from the geographic location of the optical assembly, the processor device is further configured to generate a degree of polarization image based on the sensor data, the degree of polarization image comprising a plurality of pixels, each pixel containing a degree of polarization value corresponding to one of the detector elements.

### Claim 3 (depends on 1)

The optical assembly of claim 1 wherein to determine the elevation angle of the sun, the processor device is further configured to:
generate a degree of polarization image based on the sensor data, the degree of polarization image comprising a plurality of pixels, each pixel containing a degree of polarization value corresponding to one of the detector elements;
identify a group of pixels about a center of the degree of polarization image;
determine a smallest degree of polarization value associated with any pixel in the group of pixels; and
based on the smallest degree of polarization value, determine the elevation angle of the sun with respect to the horizon from the geographic location of the optical assembly.

### Claim 4 (depends on 1)

The optical assembly of claim 1 wherein the processor device is further configured to, based on the sensor data, determine an azimuth of the sun with respect to a reference meridian.

### Claim 5 (depends on 4)

The optical assembly of claim 4 wherein to determine the azimuth of the sun, the processor device is further configured to:
generate a degree of polarization image based on the sensor data, the degree of polarization image comprising a plurality of pixels, each pixel containing a degree of polarization value corresponding to one of the detector elements;
determine at least one pixel based on a largest degree of polarization value associated with any pixel in the degree of polarization image; and
based at least in part on a location of the at least one pixel in the degree of polarization image, determine the azimuth of the sun with respect to the reference meridian.

### Claim 6 (depends on 1)

The optical assembly of claim 1 wherein the at least one polarizing filter assembly comprises a single polarizing filter assembly, and the at least one sensor comprises a single sensor, the single polarizing filter assembly comprising:
a first polarizing filter configured to receive the EMR emitted by the sun and to transmit a first subset of EMR comprising:
a first portion of EMR in a first waveband that has a first polarization orientation;
EMR in a second waveband irrespective of polarization orientation; and
EMR in a third waveband irrespective of polarization orientation;
a second polarizing filter downstream of the first polarizing filter configured to receive the first subset of EMR and to transmit a second subset of EMR comprising:
a second portion of EMR in the second waveband that has a second polarization orientation;
the EMR in the third waveband irrespective of polarization orientation; and
the first portion of EMR in the first waveband; and
a third polarizing filter downstream of the second polarizing filter configured to receive the second subset of EMR and to transmit a third subset of EMR towards the single sensor comprising:
a third portion of EMR in the third waveband that has a third polarization orientation;
the second portion of EMR in the second waveband; and
the first portion of EMR in the first waveband.

### Claim 7 (depends on 6)

The optical assembly of claim 6 wherein the first polarization orientation, second polarization orientation, and third polarization orientation are each linear polarization orientations that are each about 60 degrees from one another.

### Claim 8 (depends on 1)

The optical assembly of claim 1 wherein the at least one polarizing filter assembly comprises a first polarizing filter assembly and a second polarizing filter assembly, and wherein the at least one sensor further comprises a first sensor that receives EMR from the first polarizing filter assembly and a second sensor that receives EMR from the second polarizing filter assembly, the first polarizing filter assembly comprising:
a first polarizing filter configured to receive the EMR emitted by the sun and to transmit a first subset of EMR comprising:
a first portion of EMR in a first waveband that has a first polarization orientation; and
EMR in a second waveband that is different from the first waveband irrespective of polarization orientation;
a second polarizing filter downstream of the first polarizing filter configured to receive the first subset of EMR and to transmit a second subset of EMR towards the first sensor comprising:
a second portion of EMR in the second waveband that has a second polarization orientation; and
the first portion of EMR in the first waveband; and
the second polarizing filter assembly comprising:
a third polarizing filter configured to receive the EMR emitted by the sun and to transmit a third subset of EMR comprising:
a third portion of EMR in a third waveband that is different from the first waveband and that has a third polarization orientation; and
EMR in a fourth waveband that is different from the third waveband irrespective of polarization orientation; and
a fourth polarizing filter downstream of the third polarizing filter configured to receive the third subset of EMR and to transmit a fourth subset of EMR towards the second sensor comprising:
a fourth portion of EMR in the fourth waveband that has a fourth polarization orientation; and
the third portion of EMR in the third waveband.

### Claim 9 (depends on 8)

The optical assembly of claim 8 wherein the first polarization orientation, the second polarization orientation, the third polarization orientation, and the fourth polarization orientation are all linear polarization orientations, and wherein the first polarization orientation is 90 degrees from the second polarization orientation and the third polarization orientation is 90 degrees from the fourth polarization orientation.

### Claim 10 (depends on 8)

The optical assembly of claim 8 wherein the first waveband and the third waveband are a same waveband, and the second waveband and the fourth waveband are the same waveband.

### Claim 11 (depends on 1)

The optical assembly of claim 1 wherein the at least one polarizing filter assembly comprises a first polarizing filter assembly, a second polarizing filter assembly, and a third polarizing filter assembly, and wherein the at least one sensor further comprises a first sensor that receives EMR from the first polarizing filter assembly, a second sensor that receives EMR from the second polarizing filter assembly, and a third sensor that receives EMR from the third polarizing filter assembly, the first polarizing filter assembly comprising:
a first polarizing filter configured to receive the EMR emitted by the sun and to transmit a first portion of EMR in a first waveband that has a first polarization orientation towards the first sensor;
the second polarizing filter assembly comprising:
a second polarizing filter configured to receive the EMR emitted by the sun and to transmit a second portion of EMR in a second waveband that has a second polarization orientation towards the second sensor; and
the third polarizing filter assembly comprising:
a third polarizing filter configured to receive the EMR emitted by the sun and to transmit a third portion of EMR in a third waveband that has a third polarization orientation towards the third sensor.

### Claim 12 (depends on 11)

The optical assembly of claim 11 wherein the optical assembly further comprises a fourth polarizing filter assembly associated with a fourth sensor, the fourth polarizing filter configured to receive the EMR emitted by the sun and to transmit a fourth portion of EMR in a fourth waveband that has a fourth polarization orientation towards the fourth sensor.

### Claim 13

A method comprising:
receiving, by at least one polarizing filter assembly, electromagnetic radiation (EMR) emitted by a sun;
passing, by the at least one polarizing filter assembly, at least three different portions of EMR towards at least one sensor, each portion filtered based on a different polarization orientation and at least two portions of the at least three different portions of EMR comprising different wavebands of EMR, the at least one sensor comprising a grid of a plurality of detector elements;
generating, by the at least one sensor, sensor data in response to receipt of the at least three different portions of EMR; and
based on the sensor data, determining an elevation angle of the sun with respect to a horizon from a geographic location.

### Claim 14 (depends on 13)

The method of claim 13 wherein determining the elevation angle of the sun with respect to the horizon from the geographic location comprises generating a degree of polarization image based on the sensor data, the degree of polarization image comprising a plurality of pixels, each pixel containing a degree of polarization value corresponding to one of the detector elements.

### Claim 15 (depends on 13)

The method of claim 13 wherein determining the elevation angle of the sun further comprises:
generating a degree of polarization image based on the sensor data, the degree of polarization image comprising a plurality of pixels, each pixel containing a degree of polarization value corresponding to one of the detector elements;
identifying a group of pixels about a center of the degree of polarization image;
determining a smallest degree of polarization value associated with any pixel in the group of pixels; and
based on the smallest degree of polarization value, determining the elevation angle of the sun with respect to the horizon from the geographic location.

### Claim 16 (depends on 13)

The method of claim 13 further comprising based on the sensor data, determining an azimuth of the sun with respect to a reference meridian.

### Claim 17 (depends on 16)

The method of claim 16 wherein determining the azimuth of the sun further comprises:
generating a degree of polarization image based on the sensor data, the degree of polarization image comprising a plurality of pixels, each pixel containing a degree of polarization value corresponding to one of the detector elements;
determining at least one pixel based on a largest degree of polarization value associated with any pixel in the degree of polarization image; and
based at least in part on the location of the at least one pixel in the degree of polarization image, determining the azimuth of the sun with respect to the reference meridian.

### Claim 18 (depends on 13)

The method of claim 13 wherein passing, by the at least one polarizing filter assembly, the at least three different portions of EMR towards the at least one sensor, further comprises:
transmitting, by a first polarizing filter, a first subset of EMR comprising:
a first portion of EMR in a first waveband that has a first polarization orientation;
EMR in a second waveband irrespective of polarization orientation; and
EMR in a third waveband irrespective of polarization orientation;
receiving by a second polarizing filter downstream of the first polarizing filter the first subset of EMR;
transmitting, by the second polarizing filter, a second subset of EMR comprising:
a second portion of EMR in the second waveband that has a second polarization orientation;
the EMR in the third waveband irrespective of polarization orientation; and
the first portion of EMR in the first waveband; and
receiving, by a third polarizing filter downstream of the second polarizing filter, the second subset of EMR; and
transmitting, by the third polarizing filter, a third subset of EMR towards the at least one sensor comprising:
a third portion of EMR in the third waveband that has a third polarization orientation;
the second portion of EMR in the second waveband; and
the first portion of EMR in the first waveband.

### Claim 19 (depends on 18)

The method of claim 18 wherein the first polarization orientation, the second polarization orientation, and the third polarization orientation are each linear polarization orientations that are each about 60 degrees from one another.

### Claim 20 (depends on 13)

The method of claim 13 wherein:
receiving, by the at least one polarizing filter assembly, EMR emitted by the sun comprises:
receiving by a first polarizing filter assembly comprising a first polarizing filter and a second polarizing filter, and a second polarizing filter assembly comprising a third polarizing filter and a fourth polarizing filter, the EMR from the sun; and
passing, by the at least one polarizing filter assembly, the at least three portions of EMR towards the at least one sensor, each portion filtered based on the different polarization orientation comprises:
transmitting, by the first polarizing filter, a first subset of EMR comprising:
a first portion of EMR in a first waveband that has a first polarization orientation; and
EMR in a second waveband that is different from the first waveband irrespective of polarization orientation;
receiving, by the second polarizing filter downstream of the first polarizing filter, the first subset of EMR;
transmitting, by the second polarizing filter, a second subset of EMR towards a first sensor comprising:
a second portion of EMR in the second waveband that has a second polarization orientation; and
the first portion of EMR in the first waveband; and
transmitting, by the third polarizing filter, a third subset of EMR comprising:
a third portion of EMR in a third waveband that is different from the first waveband and that has a third polarization orientation; and
EMR in a fourth waveband that is different from the third waveband irrespective of polarization orientation;
receiving, by a fourth polarizing filter downstream of the third polarizing filter, the third subset of EMR; and
transmitting, by the fourth polarizing filter, a fourth subset of EMR towards a second sensor comprising:
a fourth portion of EMR in the fourth waveband that has a fourth polarization orientation; and
the third portion of EMR in the third waveband.

### Claim 21 (depends on 20)

The method of claim 20 wherein the first waveband and the third waveband are a same waveband, and the second waveband and the fourth waveband are the same waveband.

### Claim 22 (depends on 20)

The method of claim 20 wherein the first polarization orientation, the second polarization orientation, the third polarization orientation, and the fourth polarization orientation are all linear polarization orientations, and wherein the first polarization orientation is 90 degrees from the second polarization orientation and the third polarization orientation is 90 degrees from the fourth polarization orientation.