QUANTIFYING GAS IN PASSIVE OPTICAL GAS IMAGING

• US 20170363541A1
• Filed: 08/31/2017
• Published: 12/21/2017
• Est. Priority Date: 03/02/2015
• Status: Active Grant

• Current Assignee: Flir Systems AB (Teledyne Technologies Incorporated)
• Original Assignee: Flir Systems AB (Teledyne Technologies Incorporated)
• Inventors: Sandsten, Jonas, Kotaleski, Jonce, Ekerot, Erik
• Granted Patent: US 10,416,076 B2
• Time in Patent Office: Days
• CPC Class Codes: G01N 2021/3531 without instrumental source, i.e. radiometric
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis
• CPC Class Codes: G01N 21/3518 Devices using gas filter correlation techniques; Devices using gas pressure modulation techniques
• CPC Class Codes: G06T 2207/10048 Infrared image
• CPC Class Codes: G06T 2207/20224 Image subtraction
• CPC Class Codes: G06T 5/50 using two or more images, e.g. averaging or subtraction

Abstract

A method and a system to quantify gas in a thermal imaging device, said method comprising obtaining a gas-absorption-path-length image as a scene difference infrared image based on a gas infrared image and a scene background infrared image substantially depicting the same scene and generating a quantified scene difference infrared image based on said scene difference infrared image and a predefined gas-quantifying relation.

Claims

1. A method for quantify gas in an image of a scene having a background and a possible occurrence of gas, the method comprising:

obtaining a gas-absorption-path-length image as a scene difference infrared image, the gas-absorption-path-length image determined based on a gas infrared image and a scene background infrared image depicting a substantially same scene; and

generating a quantified scene difference infrared image based on the scene difference infrared image and a predefined gas-quantifying relation (GQR).

2. The method of claim 1, wherein the gas-quantifying relation describes a relationship between scene difference infrared image pixel values and quantified scene difference infrared image pixel values in the form of a concentration length product expressed in parts per million*meter (ppm*m).

3. The method of claim 2, wherein the gas-quantifying relation is generated by operations comprising:

measuring a first set of quantified scene difference infrared image pixel values for known gas concentrations, gas-absorption path lengths, gas temperatures, and background temperatures; and

expanding the first set to a second larger set by applying a curve fitting technique, the gas-quantifying relation comprising a relationship between a set of scene difference infrared image pixel values and the second larger set of quantified scene difference infrared image pixel values.

4. The method of claim 1, wherein:

the obtaining of the gas-absorption-path-length image comprises determining a high absorption wavelength band A and a low absorption wavelength band B to improve contrast in a generated gas-absorption-path-length image based on estimated image noise, a predetermined absorption spectrum of a gas, an estimated gas temperature, and an estimated background temperature;

the high absorption wavelength band A includes an absorption wavelength band G from the absorption spectrum; and

the low absorption wavelength band B at least partially overlaps the high absorption wavelength band A.

5. The method of claim 4, wherein the obtaining of the gas-absorption-path-length image further comprises:

generating infrared imaging system control data to control the capturing, by an infrared imaging system, of the gas infrared image of the scene comprising intensity of infrared radiation within the high absorption wavelength band A and of the background infrared image of the scene comprising intensity of infrared radiation within the low absorption wavelength band B; and

generating the gas-absorption-path-length image based on the gas infrared image and the background infrared image.

6. The method of claim 4, wherein:

the estimated image noise comprises a Noise Equivalent Temperature Difference (NETD); and

the quantified scene difference infrared image pixel values comprise temperature values.

7. The method of claim 4, wherein:

the high absorption wavelength band A is determined with a lower endpoint in a range between and including about 6 μ

m and 7.8 μ

m; and

the high absorption wavelength band A is determined with a higher endpoint in a range between and including about 8 μ

m and 9.6 μ

m.

8. The method of claim 4, further comprising:

determining a water related wavelength band C to improve contrast in the generated gas-absorption-path-length image based on a predetermined water absorption spectrum, wherein the water related wavelength band C includes at least a local maximum of the water absorption spectrum and excludes high absorption wavelength band A and low absorption wavelength band B; and

generating infrared imaging system control data to control the capturing of a water infrared image of the scene by an infrared imaging system, wherein the water infrared image comprises intensity of infrared radiation within the water related wavelength band C,

wherein the generating of the quantified scene difference infrared image is further based on the water infrared image.

9. A thermal imaging device for quantify gas in an image of a scene having a background and a possible occurrence of gas, the thermal image device comprising:

an infrared (IR) imaging system configured to capture a gas infrared image and a scene background infrared image depicting a substantially same scene;

a memory; and

a processor communicatively coupled to the IR imaging system and the memory, the processor being configured to;

obtain a gas-absorption-path-length image as a scene difference infrared image, the gas-absorption-path-length image determined based on the gas infrared image and the scene background infrared image; and

generate a quantified scene difference infrared image based on the scene difference infrared image and a predefined gas-quantifying relation (GQR).

10. The thermal imaging device of claim 9, wherein the gas-quantifying relation describes a relationship between scene difference infrared image pixel values and quantified scene difference infrared image pixel values in the form of a concentration length product expressed in parts per million*meter (ppm*m).

11. The thermal imaging device of claim 10, wherein the gas-quantifying relation is generated by operations comprising:

measuring a first set of quantified scene difference infrared image pixel values for known gas concentrations, gas-absorption path lengths, gas temperatures, and background temperatures; and

expanding the first set to a second larger set by applying a curve fitting technique, the gas-quantifying relation comprising a relationship between a set of scene difference infrared image pixel values and the second larger set of quantified scene difference infrared image pixel values.

12. The thermal imaging device of claim 9, wherein the infrared imaging system is configured and/or controllable to:

capture the gas infrared image of the scene comprising intensity of infrared radiation within a high absorption wavelength band A for a gas; and

capture the background infrared image of the scene comprising intensity of infrared radiation within a low absorption wavelength band B for the gas.

13. The thermal imaging device of claim 12, wherein the infrared imaging system comprises:

a first infrared imaging system configured and/or controllable to capture the gas infrared image; and

a second infrared imaging system configured and/or controllable to capture the scene background infrared image.

14. The thermal imaging device of claim 12, wherein:

the high absorption wavelength band A and the low absorption wavelength band B are determined so as to improve contrast in the generated gas-absorption-path-length image based on estimated image noise, a predetermined absorption spectrum of the gas, an estimated gas temperature, and an estimated background temperature;

the high absorption wavelength band A includes an absorption wavelength band G from the absorption spectrum; and

the low absorption wavelength band B at least partially overlaps the high absorption wavelength band A.

15. The thermal imaging device of claim 14, wherein the estimated image noise comprises a Noise Equivalent Temperature Difference (NETD), wherein the quantified scene difference infrared image pixel values comprise temperature values.

16. The thermal imaging device of claim 12, wherein:

the high absorption wavelength band A is determined with a lower endpoint in a range between and including about 6 μ

m and 7.8 μ

m; and

the high absorption wavelength band A is determined with a higher endpoint in a range between and including about 8 μ

m and 9.6 μ

m.

17. The thermal imaging device of claim 12, wherein the processor is further configured to obtain the gas-absorption-path-length image by operations comprising:

generating control data to control the capturing of the the gas infrared image and the background infrared image by the infrared imaging system; and

generating the gas-absorption-path-length image based on the gas infrared image and the background infrared image.

18. The thermal imaging device of claim 12, wherein:

the infrared imaging system is further configured and/or controllable to capture a water infrared image of the scene comprising intensity of infrared radiation within a water related wavelength band C;

the water related wavelength band C includes at least a local maximum of a water absorption spectrum and excludes the high absorption wavelength band A and the low absorption wavelength band B; and

the processor is further configured to generate the quantified scene difference infrared image further based on the water infrared image.

19. The thermal imaging device of claim 18, wherein the water related wavelength band C is determined based on the water absorption spectrum so as to improve contrast in the generated gas-absorption-path-length image.

20. A non-transitory computer-readable medium storing instructions which, when executed by a processor of a thermal imaging device, cause the thermal imaging device to perform a method of quantifying gas in an image of a scene having a background and a possible occurrence of gas, the method comprising:

obtaining a gas-absorption-path-length image as a scene difference infrared image, the gas-absorption-path-length image determined based on a gas infrared image and a scene background infrared image depicting a substantially same scene; and

generating a quantified scene difference infrared image based on the scene difference infrared image and a predefined gas-quantifying relation (GQR).