The Atmospheric Chemistry Experiment (ACE) is a Canadian satellite mission for remote sensing of the Earth's atmosphere that was launched into a high-inclination (74°), circular low-earth (650 km from the surface) orbit on August 13, 2003. This orbit gives SCISAT-1 coverage of tropical, mid-latitude, and polar regions, allowing it to study a range of atmospheric processes.

Objectives

The scientific goals for the ACE mission include:

• Understanding the chemical and dynamical processes that control the distribution of ozone in the stratosphere and upper troposphere, particularly in the Arctic,
• Exploring the relationship between atmospheric chemistry and climate change,
• Studying the effects of biomass burning on the free troposphere
• Measuring aerosols and clouds to reduce the uncertainties in their effects on the global energy balance

Instrument

The primary instrument on SCISAT-1 is the ACE-FTS, a high spectral resolution infrared Fourier Transform Spectrometer (FTS). SCISAT-1 also features a UV-visible-NIR spectrophotometer known as MAESTRO. Working primarily in solar occultation mode, the satellite provides altitude profile information (typically 10-100 km) for temperature, pressure, and the volume mixing ratios (VMRs) of dozens of molecules of atmospheric interest, as well as atmospheric extinction profiles over the latitudes 85°N to 85°S.

As SCISAT-1 orbits the Earth, the FTS measures sequences of atmospheric absorption spectra during sunrise and sunset. These spectra, measured in the limb viewing geometry with different slant paths and tangent heights are inverted to obtain vertical profiles of temperature, pressure and many atmospheric trace gases with a vertical resolution of about 4 km from the cloud tops up to about 150 km. In addition, a pair of filtered imagers make high signal-to-noise ratio (SNR) measurements of atmospheric extinction for the monitoring of aerosols and clouds and provide an important diagnostic for the variation of the flux over the distorted solar disk in this region. MAESTRO (Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) is a dual optical spectrophotometer that covers the 285-1030 nm spectral region. It has a vertical resolution of 1-2 km and measures primarily ozone, nitrogen dioxide, and aerosol/cloud extinction.

The ACE-FTS mission concept is based on the ATMOS (Atmospheric Trace MOlecule Spectroscopy) instrument that NASA flew four times (1985, 1992, 1993, and 1994) on the Space Shuttle but the ACE-FTS has been miniaturized by nearly a factor of 10 in mass, power, and volume as compared to ATMOS. With fewer than 400 occultations, ATMOS has made and continues to make valuable contributions to atmospheric science. The ACE-FTS will measure well over 20,000 occultations over its mission lifetime and is augmented by measurements from the two imagers and MAESTRO.

FTS Data

Level 0: Interferograms

Level 1: Spectra

Level 2: Temperature, Pressure and Volume Mixing Ratio (VMR) profiles as a function of altitude

ACE-FTS Level 2 version 1.0, 2.0 and 2.1 datasets were each processed for a limited number of select occultations. ACE-FTS Level 2 version 2.2 is the current processing version and will be the first dataset encompassing the entire measurement period.

Level 2 Data include VMR profiles for the following trace gas molecules:

• Version 1.0: H2O, O3, N2O, CO, CH4, NO, NO2, HNO3, HF, HCl, N2O5, ClONO2, CCl2F2, CCl3F, COF2, CHF2Cl, HDO, SF6
• Version 2.0: H2O, O3, N2O, CO, CH4, NO, NO2, HNO3, HF, HCl, N2O5, ClONO2, CCl2F2, CCl3F, COF2, CHF2Cl, SF6, OCS, HCN, CF4, CH3Cl, C2H2, C2H6, N2
• Version 2.1: H2O, O3, N2O, CO, CH4, NO, NO2, HNO3, HF, HCl, N2O5, ClONO2, CCl2F2, CCl3F, COF2, CHF2Cl, SF6, OCS, HCN, CF4, CH3Cl, C2H2, C2H6, N2, ClO
• Version 2.2: H2O, O3, N2O, CO, CH4, NO, NO2, HNO3, HF, HCl, N2O5, ClONO2, CCl2F2, CCl3F, COF2, CHF2Cl, HDO, SF6, OCS, HCN, CF4, CH3Cl, C2H2, C2H6, N2, ClO, as well as isotopologues for some of these molecules

MAESTRO Data

NO2 and O3 profiles are retrieved from the UV spectrometer at the measurement tangent altitudes and interpolated at the regular tangent height grid.
O3 profiles are retrieved from the VISIBLE spectrometer at the measurement tangent altitudes and interpolated at the regular tangent height grid.

Data Access

Access to the current Level 2 ACE data (version 2.2) is only available to ACE Science Team members and other authorized users but version 1.0 is available via the Public Dataset page.

ACE Public Datasets - ACE-FTS Level 2 Data

• Version 1.0 Dataset -- ASCII Formatted (Zip)
• Version 1.0 ASCII File Format Document
• Readme

Links

• ACE main page
• ACE-FTS
• MAESTRO
• Canadian Space Agency

Contact

If you would like to know more about ACE, see the following points of contact:

• Mission Scientist, FTS Principal Investigator: Peter Bernath, University of Waterloo
• Deputy Mission Scientist: Kaley Walker, University of Toronto
• MAESTRO Prinicipal Investigator: Tom McElroy, Meterological Service of Canada (MSC)