Mission focus

The overall objective of the SciSat-1 mission is to monitor and analyse the chemical processes that control the distribution of ozone in the upper troposphere and stratosphere. In particular, ACE is focussing on one important and serious aspect of the atmospheric ozone problem - the decline of stratospheric ozone at northern mid-latitudes and in the Arctic. A comprehensive set of simultaneous measurements of trace gases, thin clouds, aerosols and temperature are being collected by solar occultation from low Earth orbit. More than 30 molecules have been detected including: O3, N2O, CH4, HNO3, H2O, HCl, HF, NO, NO2, ClNO3, CO, CO2, CCl3F, CCl2F2, and N2O5.

Science

The ACE-FTS instrument is the main payload of the SciSat-1 spacecraft. The primary scientific goal of the Atmospheric Chemistry Experiment (ACE) is to measure and understand the chemical and dynamical processes that control the distribution of ozone in the upper troposphere and stratosphere. The principle of ACE measurement is the solar occultation technique. A high inclination (74 degrees), low Earth orbit 650 km provides ACE coverage of tropical, mid-latitudes and polar regions.

The spectrometer is an adapted version of the classical Michelson interferometer using an optimised optical layout. Its highly folded double-pass optical design results in a very high performance instrument with a compact size. A signal-to-noise ratio (SNR) better than 100 is achieved, with a field-of-view (FOV) of 1.25 mrad and an aperture diameter of 100 mm. A semiconductor laser is used as the metrology source of the interferometer sub-system.

The auxiliary Visible/Near-infrared Imager (VNI) monitors aerosols based on the extinction of solar radiation using two filtered detectors at 0.525 and 1.02 micrometres. The instrument also includes a Suntracker mechanism providing fine pointing toward the radiometric center of the Sun with stability better than 3 μrad.

The Measurements of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation (MAESTRO) instrument aboard SCISAT-1 measures the vertical distribution of ozone, nitrogen dioxide, water vapour, and aerosols in Earth's atmosphere. MAESTRO consists of a UV-VIS-NIR spectrophotometer that measures the 285-1030 nm spectral region.

SciSat-1 passes through Earth's shadow 15 times per day, profiting from the occultation of the Sun to make a spectrographic analysis of the structure and chemistry of those parts of the upper atmosphere that are too high to be reached by balloons and airplanes and too low to be visited by orbiting satellites. This kind of analysis can help understand the depletion of the ozone layer and other upper atmosphere phenomena.

 
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