The calibration of the MOPITT instrument

The MOPITT (Measurements Of Pollution In The Troposphere) instrument aboard the Terra Spacecraft was launched on Dec. 18, 1999 and has operated successfully since then. Instrument radiances are calculated from a total of 8 channels, which are combined in a retrieval scheme to measure the carbon monoxide (CO) profile and methane (CH₄) column in the troposphere. The instrument gain and offset, which are the key parameters to utilize the instrument measurements and to evaluate performance, are determined through an in-flight 2-point calibration scheme. Fluctuations and trends in the gain and offset on various time scales can be understood in terms of the instrument design, its performance, and the thermal environment. Some techniques for optimizing the noise levels as well as alternative methods of data processing, such as are required to cope with instrument anomalies, will be discussed.