Timing control and signal processing design of the MOPITT instrument

The MOPITT instrument operates on the principle of correlation spectroscopy where the incoming signal is modulated by gas filter and chopper mechanisms and synchronously demodulated within the signal processing system. The performance and flexibility required by the MOPITT instrument resulted in the development of a novel timing control and signal processing design. This design synchronizes modulation and demodulation from a central programmable timing control unit. The data collection system performs a highly linear sigma-delta analog-to-digital conversion prior to signal demodulation. The demodulation operation includes data averaging which reduces the sampled signal bandwidth and extends the signal to noise ratio of the data to in excess of the analog-to-digital converter's rated 16-bit dynamic range.