The onboard imagers for the Canadian ACE SCISAT‐1 mission

Abstract

[1] The Atmospheric Chemistry Experiment (ACE) onboard the Canadian Space Agency's SCISAT-1 satellite has been in orbit since August of 2003. Its broad objective is to study the problem of stratospheric ozone depletion, particularly in the Arctic. The main instruments are two spectrometers, one an infrared Fourier Transform Spectrometer and the other a dual optical spectrophotometer sensitive in the UV and visible. Also included are two filtered imagers used to measure altitude profiles of atmospheric extinction and detect thin clouds. The nominal center wavelengths of the filters are 525 nm for the visible (VIS) imager and 1020 nm for the near-infrared (NIR) imager. With the decommissioning of other satellite instruments used to monitor global aerosols [i.e., Stratospheric Aerosol and Gas Experiment II (SAGE II), SAGE III, Polar Ozone and Aerosol Measurement (POAM) III, Halogen Occultation Experiment (HALOE)], the imagers provide much needed continuity in this data record. The data product from the imagers is still, however, in a preliminary state. Funding restrictions in the prelaunch period were responsible for an incomplete characterization of the imagers' optics and electronics and prevented corrections being made for the problems found during testing. Postlaunch data analysis to correct for image artifacts is ongoing. A comparison with coincidental measurements from SAGE II shows that systematic errors from the preliminary analysis are within 5 and 20% for the VIS and NIR imagers, respectively, for uninverted profiles of optical depth. Despite the preliminary nature of the imager results, a paper describing the imagers and the initial operational data processing code is timely because the data are already being used.

Aerosol extinction profiles at 525 nm and 1020 nm derived from ACE imager data: comparisons with GOMOS, SAGE II, SAGE III, POAM III, and OSIRIS

“…At present, the processing code for the ACE imager data (version 2.2) is in a preliminary state, as was mentioned by Gilbert et al (2007). It is important to take this in account during inspection of the results shown in this work.…”

“…A detailed description of the ACE imagers and the retrieval process can be found in Gilbert et al (2007). However, for the purpose of this paper, it is necessary to repeat the essentials here.…”

Validation of HNO<sub>3</sub>, ClONO<sub>2</sub>, and N<sub>2</sub>O<sub>5</sub> from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS)

“…Both instruments record solar occultation spectra, ACE-FTS in the infrared (IR), and MAESTRO in the ultraviolet-visible(vis)-near-IR, from which vertical profiles of atmospheric trace gases, temperature, and atmospheric extinction are retrieved. In addition, a two channel near-IRvis imager (ACE-IMAGER) provides profiles of atmospheric extinction at 0.525 and 1.02 µm (Gilbert et al, 2007). The SCISAT spacecraft is in a circular orbit at 650-km altitude, with a 74 • inclination angle , providing up to 15 sunrise and 15 sunset solar occultations per day.…”

Retrieval of macrophysical cloud parameters from MIPAS: algorithm description

“…Cloud detection is achieved by monitoring the extinction of solar radiation at 1.02 µm and 0.525 µm as measured by two filtered imagers. ACE reports cloud top height, as determined from the detection process (Bernath, 2002), and extinction from values of atmospheric transmission obtained from the ratio of the incident solar radiation at the top of the atmosphere to that measured (Gilbert et al, 2007 3 and chlorofluorocarbon compounds CFC-11 and CFC-12, as well as the location of polar stratospheric clouds. HIRDLS uses finite channels to measure radiance spectra between 6 µm and 18 µm -and certain of these channels are particularly sensitive to cloud presence.…”