Design of the Atmospheric Chemistry Experiment instrument

The Atmospheric Chemistry Experiment (ACE) is the mission selected by the Canadian Space Agency for its new science satellite, SCISAT-1. Dr. Peter Bernath of the University of Waterloo is the ACE Principal Investigator, and ABB Bomem is the prime contractor for the development of the ACE main instrument, a Fourier-Transform Spectrometer (FTS). The principal goal of the ACE mission is to measure and understand the chemical and dynamical processes that control the distribution of ozone in the upper troposphere and stratosphere. A comprehensive set of simultaneous measurements of trace gases, thin clouds, aerosols and temperature will be made by solar occultation from a satellite in a low Earth orbit. A high inclination, low Earth orbit will allow coverage of tropical, mid-latitude and polar regions. A high-resolution FTS is coupled with an auxiliary 2-channel visible and near-infrared imager. The FTS, operating from 750 to 4100 cm(-1), will measure at high resolution (0.02 cm(-1)) the infrared absorption signals that contain information on different atmospheric layers to provide vertical profiles of atmospheric constituents. Its highly folded design results in a very high performance instrument with a compact size. The imager will monitor aerosols based on the extinction of solar radiation using two filtered 128x128 detector arrays at 1.02 and 0.525 microns. The instrument also includes a suntracker, which provides the Sun radiance to both the FTS and the imager during solar occultation of the Earth's atmosphere. An optional instrument is presently under investigation by the Canadian Space Agency to extend the wavelength coverage in the ultraviolet. The MAESTRO spectrograph, should it be added to the SCISAT-1 satellite, would cover the 10000 to 35100 cm(-1) spectral band. This paper presents an overview of the ACE program and its main scientific objectives, and describes the design of the ACE-FTS instrument.