Measurements of carbon monoxide and methane from space

The Measurements Of Pollution In The Troposphere (MOPITT) instrument is designed to measure carbon monoxide (CO) and methane (CH₄) in the troposphere from space and will be launched as part of the EOS AM-1 payload in mid-1998. The accuracy of the measurements is required to be 10% for CO with profile information and 1% for the CH₄ column. These targets impose strict design requirements on the instrument. MOPITT operates by measuring the upwelling radiation from the atmosphere and uses high-performance detectors, narrow spectral filters and correlation spectroscopy to achieve its objectives. The performance of the instrument and its long-term accuracy depend upon the correct implementation of the various measurement strategies, proper calibration of the entire system and validation of the experiment after launch. The major focus of an instrument of this type is the manner by which the radiances are interpreted in terms of the concentration profiles they represent. This involves aspects of instrument design, spectral modelling, retrieval techniques and validation activities. Some of the difficulties inherent in the measurement technique are the practicalities of a space instrument as opposed to a laboratory or ground-based experiment, the presence of interfering gases and the interaction of the calibration with the measurement accuracy and precision.