Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
1999-09-08
2001-09-25
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S341500, C250S339010, C356S230000
Reexamination Certificate
active
06294785
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to the calibration of infrared sensors, and more particularly to a method of calibrating an infrared sensor positioned in orbit above a celestial body using atmospheric limb emission measurements.
BACKGROUND OF THE INVENTION
Infrared sensors are used onboard orbiting platforms (e.g., satellites) for a variety of applications. These sensors must be periodically calibrated. This is especially important when the sensors are used onboard platforms scheduled for long deployment. Currently, an onboard calibrated reference emission source must be provided and used for sensor calibration. The reference emission source must be a stable source and/or requires monitoring. Further, stable optical path(s) used by these sensors to view the reference emission source must be provided. The reference emission system must be calibrated on the ground and then mounted to withstand the severe launch stresses it will experience and in a way that allows it to exhibit the same performance in orbit as during its ground calibration.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method of calibrating an infrared sensing device.
Another object of the present invention is to provide a method of calibrating an infrared sensing device in an orbiting vehicle.
Yet another object of the present invention is to provide an accurate long-term method of calibrating an orbiting infrared sensing device.
Still another object of the present invention is to provide a method of calibrating an orbiting vehicle's infrared sensing device without the use of an onboard reference source.
Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings.
In accordance with the present invention, a method is presented for calibrating an infrared sensing device. The method uses an infrared sensing device in an orbit above a celestial body (e.g., earth) having an atmosphere and a known gravitational field. The infrared sensing device is focused at an atmospheric limb region of the atmosphere. The infrared sensing device is used to measure a signal profile (i.e., a signal as a function of the sensor's elevation angle) 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) for at least one of the spectral bandpass regions, 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 indicative of the signal profiles is determined. This temperature/pressure profile is indicative of absolute radiance emission from the atmospheric limb region, which is then used as a calibrated external source for calibrating the infrared sensing device.
REFERENCES:
patent: 4746976 (1988-05-01), Kamel et al.
patent: 5319968 (1994-06-01), Billing-Ross et al.
patent: 5325171 (1994-06-01), Shimizu
patent: 5354987 (1994-10-01), MacPherson
patent: 6023061 (2000-02-01), Bodkin
patent: 6175113 (2001-01-01), Ashley et al.
patent: 6184529 (2001-02-01), Contini
Bergen Peter J. Van
G & A Technical Software Inc.
Gagliardi Albert
Hannaher Constantine
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