Abstract: A method and system are provided for determining gas concentration at a region of a planetary surface. A gas filter correlation radiometry (GFCR) system, provided at a location above a planetary surface, includes a processor and a GFCR sensor having a first gas cell containing a target gas and a second gas cell that does not contain the target gas. Using the GFCR sensor, first images of a region of the planetary surface are generated via capture through the first gas cell and second images of the region are generated via capture through the second gas cell. Using the processor, ratio images are generated using the first images and the second images. Concentration of the target gas over known altitude variations of the region is determined where the concentration of the target gas is a function of the ratio images and the altitude variations of the region.

Abstract: Refraction angles in a planet's atmosphere are mapped using a database of known star locations and a field imager onboard a platform above the planet. The field imager is positioned to observe a region that includes a portion of the planet's atmospheric limb. A star field image is captured for the region. The star field image includes stars within the field imager's field-of-view. Using the field imager and the database, a modeled star field image is generated that is matched in size to the field-of-view associated with the star field image. The modeled star field image defines absolute locations of stars corresponding to stars appearing in the field imager's field-of-view. Differences between the absolute locations and locations of the images of stars are indicative of a limb refraction angle field.

Abstract: A multi-channel gas correlation sensor and sensing method are provided. A spectral partitioning filter at the sensor's aperture or a pupil image thereof partitions a beam of light energy into unique spectral regions. Each spectral region is confined to a unique spatial region of the beam and passes light energy associated with a unique spectral band. The spectrally-partitioned beam undergoes a single split into two beams traversing a first path and a second path, respectively. Each of at least one gas of interest is disposed in only one of the first path and second path. Each gas at least partially absorbs/filters the light energy in at least one of the spectral regions. A detector is positioned such that each of the two beams form a pupil image on a unique portion of the detector after they traverse the first path and second path.

Abstract: A multi-channel gas correlation sensor and sensing method are provided. A spectral partitioning filter at the sensor's aperture or a pupil image thereof partitions a beam of light energy into unique spectral regions. Each spectral region is confined to a unique spatial region of the beam and passes light energy associated with a unique spectral band. The spectrally-partitioned beam undergoes a single split into two beams traversing a first path and a second path, respectively. Each of at least one gas of interest is disposed in only one of the first path and second path. Each gas at least partially absorbs/filters the light energy in at least one of the spectral regions. A detector is positioned such that each of the two beams form a pupil image on a unique portion of the detector after they traverse the first path and second path.

Abstract: A GFCR system includes gas cells disposed to receive light energy associated with a field-of-view of an atmospheric region. Each gas cell has contents selected from the group consisting of a vacuum and a gas of unique composition. For each of the gas cells, the light energy passed therethrough is spectrally affected by the contents thereof and then output therefrom as a spectrally-affected beam of light energy associated with the field-of-view. An optical system disposed between the gas cells and an optical detector images each spectrally-affected beam on a unique region of the optical detector. One or more processors generate matched portions of each spectrally-affected beam so-imaged on the optical detector where each such matched portion corresponds to an identical portion of the field-of-view. GFCR computations can then be performed using the matched portions.

Abstract: A GFCR system includes gas cells disposed to receive light energy associated with a field-of-view of an atmospheric region. Each gas cell has contents selected from the group consisting of a vacuum and a gas of unique composition. For each of the gas cells, the light energy passed therethrough is spectrally affected by the contents thereof and then output therefrom as a spectrally-affected beam of light energy associated with the field-of-view. An optical system disposed between the gas cells and an optical detector images each spectrally-affected beam on a unique region of the optical detector. One or more processors generate matched portions of each spectrally-affected beam so-imaged on the optical detector where each such matched portion corresponds to an identical portion of the field-of-view. GFCR computations can then be performed using the matched portions.

Abstract: A Gas Filter Correlation Radiometer (GFCR) system and methods of using same are provided. The system's GFCR instrument includes a gas cell. A gas in the gas cell has a chemical composition that is different than that of a target gas in an atmospheric region being examined by the GFCR instrument. The gas included in the gas cell also possesses light absorption features with a portion thereof being at least partially correlated with light absorption features of the target gas. Measurement viewing(s) made with the GFCR instrument provide for at least one positive correlation for the portion of the at least partially correlated features so that the GFCR instrument generates a signal indicative thereof used in a gas filter correlation radiometry application.

Abstract: A method is provided for making and using measurements in gas filter correlation radiometry. A Gas Filter Correlation Radiometer (GFCR) instrument is moved in a region of space surrounding a heavenly body. An atmosphere of the heavenly body is viewed with the GFCR instrument along a first view direction with the atmosphere and the GFCR instrument experiencing a relative velocity of approximately zero. The atmosphere is also viewed with the GFCR instrument along at least one second view direction that is angularly separated from the first view direction such that atmospheric spectra associated with the second view direction appears Doppler shifted with respect to atmospheric spectra associated with the first view direction. A gas filter correlation radiometry application is performed using the measurement signals obtained from the different view directions.

Abstract: A GFCR system receives light from a scene of interest and focuses it to form an image. Light associated with a selected field-of-view of the image is confined to a spectral band absorbable by a gas of interest and is split into first and second paths. A region that does not substantially interfere with the spectral band is disposed in the first path. A first two-dimensional array of optical detection elements is disposed in the region along with a first diffuser. Disposed in the second path are a gas cell filled with the gas of interest, a second two-dimensional array of optical detection elements, and a second diffuser. The first and second optical arrays generate output signals that are summed to form corresponding first and second sums. A difference between the first and second sums is generated and normalized as a direct measure of the gas of interest.

Abstract: An entrance aperture of a GFCR system receives light from a scene of interest. The light is focused to form an image at a focal plane. Light associated with a selected field-of-view of the image at the focal plane is then confined to a spectral band at which a gas of interest absorbs. The confined light is split into first and second paths. A calibrating light is selectively produced from within the optical train at the focal plane. A portion of the calibrating light traverses each of the first and second paths. A region that is substantially non-interfering with respect to the spectral band is disposed in the first path. A gas cell filled with the gas of interest is disposed in the second path. The light passed through the region and through the gas cell is independently detected and used to generate output signals indicative of the light so-detected.

Abstract: An atmospheric refraction profile is determined using an imaging system positioned at a location that is simultaneously within line-of-sight of two celestial light sources. A variety of active or passive methods can be employed to cause the line-of-sight to vertically traverse through a refractive portion of an atmosphere. Images of the two celestial light sources are captured as the line-of-sight vertically traverses through the refractive portion of the atmosphere. Each such image indicates an apparent distance between the two celestial light sources. The apparent distances are used to determine refraction angles.

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.