Bandpass optimization for total column measurements of atmospheric CO and CH4 using a length modulated gas filter correlation radiometer

MOPITT, which will be carried aboard Platform-A of the Earth Observing System, will measure total column amounts of carbon monoxide and methane in the atmosphere by using length modulated gas filter correlation radiometers to measure the absorption of reflected solar infrared radiation. The carbon monoxide measurements will be made using the first overtone band, which is centered near 4260 cm^-1. The methane measurements will be made using overtone and combination bands near 4400 cm^-1. The center, width, and shape of the bandpass filters used to isolate the spectral bands must in each case satisfy the often conflicting requirements of maximizing the signal level and sensitivity to the gas of interest while minimizing the interference from other absorbing gases (notably water vapor). The filter parameters must simultaneously remain within the bounds of current manufacturing capabilities. The author used a general line-by-line radiative transfer code along with the HITRAN data base to calculate the sensitivity to the gases of interest and the interference from other gases as a function of filter center and width for a range of gas amounts. The results are presented in graphical form and interpreted.