Infrared mapping spectrometer to provide vertical information on atmospheric CH<sub>4</sub>

Jack B. Kumer; John L. Mergenthaler; Aidan E. Roche; David J. Crain; Larrabee L. Strow; Robert Chatfield

doi:10.1117/12.627729

21 October 2005 Infrared mapping spectrometer to provide vertical information on atmospheric CH₄

Jack B. Kumer, John L. Mergenthaler, Aidan E. Roche, David J. Crain, Larrabee L. Strow, Robert Chatfield

Proceedings Volume 5978, Sensors, Systems, and Next-Generation Satellites IX; 59781X (2005) https://doi.org/10.1117/12.627729
Event: SPIE Remote Sensing, 2005, Bruges, Belgium

Abstract

Precise measurements of CH₄ in a column of near surface air, and in partial columns above this, would be very valuable in identifying sources/sinks of atmospheric CH₄, and its transport. For this purpose we have proposed a grating mapping spectrometer (GMS) for deployment as an Instrument of Opportunity (IOO) on the NPOESS that acquires data in the 2990 to 3050 cm^-1 spectral region. It will provide measurements of CH₄ absorption of sunlight in the weaker CH₄ features in the region, and of thermal emission in the stronger CH₄ features in the region. It is the combination of the two that provides the vertical information. The IOO will acquire spectra on a crosstrack swath centered on nadir, and with 1/2 width of 55 degrees on each side of nadir (about 2800 km full width swath on the ground for a nominal 828 km satellite altitude). This with footprints that are about 3.1 km on a side at nadir. The small footprint facilitates cloud screening, and identification of CH₄ source hotspots. A capability to project the slit to nadir along the direction from satellite to sun will be utilized for over the ocean viewing in order to facilitate measurements in solar glitter. It will obtain spectra with resolution n < 0.58 cm^-1 and sample spacing < 0.17 cm^-1. Based on the spectral characteristics and currently achievable very low-noise we do a linear error analysis (Rodgers, [1]) for the simultaneous retrieval of multi-column CH₄, humidity, and surface parameters and ¹³CH₄ total column. We show that useful multi-column CH₄ retrievals can be obtained, with good near surface sensitivity in sunlit conditions. We also show the ¹³CH₄ column can be retrieved with precision better than 3%. Retrieval of ¹³CH₄ column in the earth's atmosphere is analogous in difficulty to retrieval of the major CH₄ isotope column in the Martian atmosphere by a similar GMS deployed on a Mars orbiter. We show that H₂O vertical information can be retrieved from these measurements and discuss the potential for ethane column retrieval.

Citation Download Citation

Jack B. Kumer, John L. Mergenthaler, Aidan E. Roche, David J. Crain, Larrabee L. Strow, and Robert Chatfield "Infrared mapping spectrometer to provide vertical information on atmospheric CH₄", Proc. SPIE 5978, Sensors, Systems, and Next-Generation Satellites IX, 59781X (21 October 2005); https://doi.org/10.1117/12.627729

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