Characterization of simultaneous ozone measurements by the MAESTRO and FTS space instruments

Scisat-1 is a Canadian satellite scheduled for launch in December 2002. The mission objective is to study stratospheric ozone trends, with a particular focus on the polar regions where significant ozone loss has been observed in the past two decades. Measurements of solar attenuation by ozone and other stratospheric constituents are to be taken during occultation events (sunrises and sunsets) by the two instruments on board Scisat-1, ACE-MAESTRO (Atmospheric Chemistry Experiment - Measurement of Aerosol Extinction in The Stratosphere and Troposphere Retrieved by Occultation) and the ACE-FTS (ACE Fourier Transform Spectrometer). These instruments are designed to measure absorption spectra in the visible/near-ultraviolet and infrared regions, respectively; MAESTRO is a dual concave grating spectrometer while the FTS is a Michelson interferometer. One of the principal scientific objectives for both instruments is the retrieval of vertical ozone profiles. An important question to ask when characterizing the instruments prior to launch is: Do we measure the same amount from both instruments? In order to answer this question, an experimental apparatus that allows simultaneous instrument characterization, consisting of a simulated solar source and gas cells, has been assembled. The experimental apparatus and its use in the characterization of MAESTRO and FTS are described.