Infrared sensor response calibration using atmospheric limb emission measurements

• US 6,294,785 B1
• Filed: 09/08/1999
• Issued: 09/25/2001
• Est. Priority Date: 09/08/1999
• Status: Expired due to Fees

• Current Assignee: G&A Technical Software, Inc.
• Original Assignee: G&A Technical Software, Inc.
• Inventors: Gordley, Larry L.
• Primary Examiner(s): Hannaher, Constantine
• Assistant Examiner(s): GAGLIARDI, ALBERT J
• Application Number:
  US09/392,212
• Time in Patent Office: 748 Days
• Field of Search: 250/339.09, 250/339.01, 250/340, 250/341.5, 250/252.1, 356/230
• US Class Current: 250/339.09
• CPC Class Codes: G01J 5/53 Reference sources, e.g. standard lamps; Black bodies

Abstract

A method is presented for calibrating an infrared sensing device while in an orbit above a celestial body. The infrared sensing device measures a signal profile proportional to radiance emission from the atmospheric limb region in each of a plurality of spectral bandpass regions. The radiance emission from each of the spectral bandpass regions is primarily due to a gas in the atmospheric limb region. The gas must 1) have a known mixing ratio as a function of pressure, 2) cause spectral opacity to be different for each spectral bandpass region, and 3) cause spectral opacity to be non-linearly proportional to concentration of the gas in the atmospheric limb region over at least a portion of the signal profile. A temperature/pressure profile that is indicative of the signal profiles is determined. The temperature/pressure profile is indicative of absolute radiance emission which is then used to calibrate the infrared sensing device.

Claims

1. A method of calibrating an infrared sensing device, comprising the steps of:

providing an infrared sensing device in an orbit above a celestial body having an atmosphere and a known gravitational field;

focusing said infrared sensing device at an atmospheric limb region of said atmosphere;

measuring, using said infrared sensing device, a signal profile proportional to radiance emission from said atmospheric limb region in each of a plurality of spectral bandpass regions, wherein said radiance emission from each of said plurality of spectral bandpass regions is primarily due to a gas in said atmospheric limb region, said gas having a known mixing ratio as a function of pressure, wherein spectral opacity due to said gas is different for each of said plurality of spectral bandpass regions, and wherein, for at least one of said plurality of spectral bandpass regions, said spectral opacity is non-linearly proportional to concentration of said gas in said atmospheric limb region over at least a portion of said signal profile;

determining a temperature/pressure profile that is indicative of said signal profiles, wherein said temperature/pressure profile is indicative of absolute radiance emission from said atmospheric limb region; and

using said absolute radiance emission to calibrate said infrared sensing device.

2. A method according to claim 1 wherein said infrared sensing device has a known field-of-view, and wherein said step of measuring includes the step of scanning said infrared sensing device through a vertical elevation angle such that said known field-of-view traverses said atmospheric limb region.

3. A method according to claim 2 wherein said known field-of-view has a vertical resolution that is less than approximately 10 kilometers when said known field-of-view is projected to said atmospheric limb region.

4. A method according to claim 1 wherein said celestial body is the earth.

5. A method according to claim 4 wherein said gas is selected from the group consisting of carbon dioxide, oxygen, nitrous oxide and methane.

6. A method according to claim 1 wherein said atmospheric limb region exhibits spherical uniformity at pressure levels within said atmospheric limb region.

7. A method according to claim 1 wherein said celestial body is the earth and said atmospheric limb region is selected from the group consisting of the stratosphere, troposphere and mesosphere.

8. A method according to claim 1 wherein said step of determining comprises the steps of:

taking the logarithm of said signal profiles to form a corresponding plurality of logarithmic signal profiles;

differentiating, with respect to altitude in said atmospheric limb region, each of said plurality of logarithmic signal profiles to form a corresponding plurality of differential logarithmic signal profiles; and

using said plurality of differential logarithmic signal profiles to determine said temperature/pressure profile that is uniquely indicative of said signal profiles.

9. A method of calibrating an infrared sensing device, comprising the steps of:

providing an infrared sensing device above the earth;

focusing said infrared sensing device at an atmospheric limb region in the stratosphere that exhibits spherical uniformity at all pressure levels thereof;

measuring, using said infrared sensing device, a signal profile proportional to radiance emission from said atmospheric limb region in each of a plurality of spectral bandpass regions, wherein said radiance emission from each of said plurality of spectral bandpass regions is primarily due to a gas in said atmospheric limb region, said gas having a known mixing ratio as a function of pressure, wherein spectral opacity due to said gas is different for each of said plurality of spectral bandpass regions, and wherein, for at least one of said plurality of spectral bandpass regions, said spectral opacity is non-linearly proportional to concentration of said gas in said atmospheric limb region over at least a portion of said signal profile;

determining a temperature/pressure profile that is indicative of said signal profiles, wherein said temperature/pressure profile is indicative of absolute radiance emission from said atmospheric limb region; and

using said absolute radiance emission to calibrate said infrared sensing device.

10. A method according to claim 9 wherein said infrared sensing device has a known field-of-view, and wherein said step of measuring includes the step of scanning said infrared sensing device through a vertical elevation angle such that said known field-of-view traverses said atmospheric limb region.

11. A method according to claim 10 wherein said known field-of-view has a vertical resolution that is less than approximately 10 kilometers when said known field-of-view is projected to said atmospheric limb region.

12. A method according to claim 9 wherein said gas is selected from the group consisting of carbon dioxide and oxygen.

13. A method according to claim 9 wherein said step of determining comprises the steps of:

taking the logarithm of said signal profiles to form a corresponding plurality of logarithmic signal profiles;

differentiating, with respect to altitude in said atmospheric limb region, each of said plurality of logarithmic signal profiles to form a corresponding plurality of differential logarithmic signal profiles; and

using said plurality of differential logarithmic signal profiles to determine said temperature/pressure profile that is uniquely indicative of said signal profiles.

14. A method of calibrating an infrared sensing device, comprising the steps of:

providing an infrared sensing device above the earth, wherein said infrared sensing device has a known field-of-view;

scanning said infrared sensing device through a vertical angle such that said known field-of-view traverses an atmospheric limb region above the earth;

measuring, using said infrared sensing device, a signal profile proportional to radiance emission from said atmospheric limb region in each of a plurality of spectral bandpass regions, wherein said radiance emission from each of said plurality of spectral bandpass regions is primarily due to a gas in said atmospheric limb region, said gas having a known mixing ratio as a function of pressure, wherein spectral opacity due to said gas is different for each of said plurality of spectral bandpass regions, and wherein, for at least one of said plurality of spectral bandpass regions, said. spectral opacity is non-linearly proportional to concentration of said gas in said atmospheric limb region over at least a portion of said signal profile;

taking the logarithm of said signal profiles to form a corresponding plurality of logarithmic signal profiles;

differentiating, with respect to altitude in said atmospheric limb region, each of said plurality of logarithmic signal profiles to form a corresponding plurality of differential logarithmic signal profiles;

determining a temperature/pressure profile that is indicative of said signal profiles based on said plurality of differential logarithmic signal profiles, wherein said temperature/pressure profile is indicative of absolute radiance emission from said atmospheric limb region; and

using said absolute radiance emission to calibrate said infrared sensing device.

15. A method according to claim 14 wherein said known field-of-view has a vertical resolution that is less than approximately 10 kilometers when said known field-of-view is projected to said atmospheric limb region.

16. A method according to claim 14 wherein said gas is selected from the group consisting of carbon dioxide, oxygen, nitrous oxide and methane.

17. A method according to claim 14 wherein said atmospheric limb region exhibits spherical uniformity at pressure levels within said atmospheric limb region.

18. A method according to claim 14 wherein said atmospheric limb region is selected from the group consisting of the stratosphere, troposphere and mesosphere.