Figure: MOPITT operates by sensing infrared radiation from either the thermal emission/absorption at 4.7 µm for CO profiles, or reflected sunlight at about 2.2-2.4 µm for CO and CH4 column measurements in daylight. The use of solar channels enhances the instrument sensitivity to the atmospheric boundary layer.
Figure: Signals pass through a cell containing the target gas, CO or CH4. The cell pressure or length is varied, which produces a modulation in cell opacity within the lines of the target gas, while the cell opacity at other frequencies remains constant.
Channel # | Primary Purpose | Modulator Type | Cell Pressure (mb) | Cell Temperature (K) | Cell Length (mm) | Spectral Band | Center Wavenumber (cm-1) |
---|---|---|---|---|---|---|---|
CO | LMC1 | 300 | CO thermal | 2166 (52) | |||
CO | LMC1 | 300 | CO solar | 4285 (40) | |||
CO | PMC1 | 300 | CO thermal | 2166 (52) | |||
CH4 | LMC2 | 300 | CH4 solar | 4430 (140) | |||
5 | CO | LMC3 | 300 | CO thermal | 2166 (52) | ||
6 | CO | LMC3 | 300 | CO solar | 4285 (40) | ||
7 | CO | PMC2 | 300 | CO thermal | 2166 (52) | ||
8 | CH4 | LMC4 | 300 | CH4 solar | 4430 (140) |
![]() | The high and low opacity signals from each channel are both averaged and differenced, resulting in 8 D and 8 A signals. |
![]() | Average signals are low at the line of interest, providing information about background radiance and interfering signals. Difference signals have only significant response at the line of interest, providing information about the gas of interest. |
![]() | The correlation cell pressure determines the portion of the pressure-broadened line wing that is sampled. |
![]() | Using PMRs and LMRs with different pressures thus provides information about the vertical profile. These are the weighting functions for the different cell pressures of the 6 CO channels. |
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Figure: scan pattern
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