The Atmospheric Chemistry Experiment (ACE) is the mission selected by the Canadian Space Agency for its next science satellite, SCISAT-1. ACE consists of a suite of instruments in which the primary element is an infrared Fourier Transform Spectrometer (FTS) coupled with an auxiliary 2-channel visible (525 nm) and near infrared imager (1020 nm). A secondary instrument, MAESTRO, provides spectrographic data from the near ultraviolet to the near infrared, including the visible spectral range. In combination, the instrument payload covers the spectral range from 0.25 to 13.3 micron. A comprehensive set of simultaneous measurements of trace gases, thin clouds, aerosols and temperature will be made by solar occultation from a satellite in low earth orbit. The ACE mission will measure and analyze the chemical and dynamical processes that control the distribution of ozone in the upper troposphere and stratosphere. A high inclination (74°), low earth orbit (650 km) allows coverage of tropical, mid-latitude and polar regions.
This paper will describe level 1 algorithms that are needed on ground in order to produce meaningful data meeting all requirements of the ACE FTS instrument. Level 0 data are as downlinked from the spacecraft. Level 1A data are decoded (CCSDS, bit trim) interferograms from individual acquisition channels. Level 1B data are made of spectrally (spatial frequency) calibrated transmittances with annotated quality indicators. Some key ACE FTS L1B algorithms include, non-linearity characterization/correction, robust interferometer fringe count error handling, spectral calibration from Solar reference lines, transmittance computation with phase error correction, and correction of the instrument line shape (ILS) distortion.