ACGS (Atmospheric Carbon dioxide Grating Spectrometer ) is a state-of-the-art hyperspectral grating spectrometer aimed at allowing XCO2 retrievals by measuring backscattered sunlight in three NIR/SWIR bands: the oxygen (O2) A-band (758â778 nm with ~0.04 nm spectral resolution), the CO2 weak band (1594â1624 nm with ~0.125 nm spectral resolution) and the CO2 strong band (2042â2082 nm with ~0.16 nm spectral resolution). CO2 column information is largely drawn from the weak CO2 band which includes a series of strong but not saturated CO2 lines which respond to even small variations in atmospheric CO2. The O2 A-band hyperspectral measurement contains information on aerosol and cloud scattering both in total scattering amount and scattering vertical distribution. The strong CO2 band provides information on aerosol and cloud scattering at longer wavelengths, in conjunction with information on CO2 and water vapour.
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