Sean D. McLeod

Atmospheric Chemistry Experiment (ACE): Mission overview

SCISAT-1, also known as the Atmospheric Chemistry Experiment (ACE), is a Canadian satellite mission for remote sensing of the Earths atmosphere. It was launched into low Earth circular orbit (altitude 650 km, inclination 74°) on 12 Aug. 2003. The primary ACE instrument is a high spectral resolution (0.02 cm-1) Fourier Transform Spectrometer (FTS) operating from 2.2 to 13.3 μm (750-4400 cm-1). The satellite also features a dual spectrophotometer known as MAESTRO with wavelength coverage of 285-1030 nm and spectral resolution of 1-2 nm. A pair of filtered CMOS detector arrays records images of the Sun at 0.525 and 1.02 μm. Working primarily in solar occultation, the satellite provides altitude profile information (typically 10-100 km) for temperature, pressure, and the volume mixing ratios for several dozen molecules of atmospheric interest, as well as atmospheric extinction profiles over the latitudes 85°N to 85°S. This paper presents a mission overview and some of the first scientific results. Copyright 2005 by the American Geophysical Union.

Retrievals for the atmospheric chemistry experiment Fourier-transform spectrometer

SCISAT-1, also known as the Atmospheric Chemistry Experiment, is a satellite mission for remote sensing of the Earths atmosphere, launched on 12 August 2003. The primary instrument on the satellite is a 0.02 cm(-1) resolution Fourier-transform spectrometer operating in the mid-IR (750-4400 cm(-1)). We describe the approach developed for the retrieval of atmospheric temperature and pressure from the troposphere to the lower thermosphere as well as the strategy for the retrievals of volume-mixing ratio profiles of atmospheric species.

A global inventory of stratospheric chlorine in 2004

Total chlorine (CITOT) in the stratosphere has been determined using the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) measurements of HCl, ClONO2, CH3Cl, CCl4, CCl3F (CFC-11), CCl2F2 (CFC-12), CHClF2 (HCFC-22), CCl2FCClF2 (CFC-113), CH3CClF2 (HCFC-142b), COClF, and ClO supplemented by data from several other sources, including both measurements and models. Separate chlorine inventories were carried out in five latitude zones (60°-82°N, 30°-60°N, 30°S-30°N, 30°-60°S, and 60°-82°S), averaging the period of February 2004 to January 2005 inclusive, when possible, to deal with seasonal variations. The effect of diurnal variation was avoided by only using measurements taken at local sunset. Mean stratospheric ClTOT values of 3.65 ppbv were determined for both the northern and southern midlatitudes (with an estimated 1σ, accuracy of ±0.13 ppbv and a precision of ±.09 ppbv), accompanied by a slightly lower value in the tropics and slightly higher values at high latitudes. Stratospheric ClTOT profiles in all five latitude zones are nearly linear with a slight positive slope in ppbv /km. Both the observed slopes and pattern of latitudinal variation can be interpreted as evidence of the beginning of a decline in global stratospheric chlorine, which is qualitatively consistent with the mean stratospheric circulation pattern and time lag necessary for transport.

A global inventory of stratospheric fluorine in 2004 based on Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS) measurements

[1] Total fluorine (FTOT) in the stratosphere has been determined using Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS) measurements of HF, COF2, COClF, CF4, CCl3F (CFC-11), CCl2F2 (CFC-12), CHClF2 (HCFC-22), CCl2FCClF2 (CFC-113), CH3CClF2 (HCFC-142b), CH2FCF3 (HFC-134a), and SF6. The retrieval of HFC-134a (CH2FCF3) from spaceborne measurements had not been carried out prior to this work. Measurements of these species have been supplemented by data from models to extend the altitude range of the profiles and have also been complemented by estimates of 15 minor fluorine species. Using these data, separate fluorine budgets were determined in five latitude zones (60–82N, 30–60N, 30S–30N, 30–60S, and 60–82S) by averaging over the period of February 2004 to January 2005 inclusive, when possible. Stratospheric FTOT profiles in each latitude zone are nearly linear, with mean stratospheric FTOT values ranging from 2.50 to 2.59 ppbv (with a 1s precision of 0.04–0.07 ppbv and an estimated accuracy of 0.15 ppbv) for each zone. The highest mean FTOT value occurred in the tropics, which is qualitatively consistent with increasing levels of stratospheric fluorine and the mean stratospheric circulation pattern.

Global phosgene observations from the Atmospheric Chemistry Experiment (ACE) mission

Author Institution: Department of Chemistry, University of Waterloo, Waterloo, Ontario, Canada; NASA Jet Propulsion Laboratory/California Institute of Technology, Pasadena, CA, USA

Cloud detection in the upper troposphere‐lower stratosphere region via ACE imagers: A qualitative study

[1] Satellite-based limb occultation measurements are well suited for the detection and mapping of polar stratospheric clouds (PSCs) and cirrus clouds. Usually, cloud signatures are detected on aerosol extinction profiles. In this paper, ACE two-dimensional (2-D) imager data are used to show PSCs and cirrus clouds. Clouds can be clearly seen, with a good vertical and horizontal resolution (1 km), during sunset and sunrise. In addition, we discovered significant differences between stratospheric (PSCs) and tropospheric (cirrus) clouds. PSCs appear as ‘‘symmetric’’ layers, no horizontal or vertical ‘‘structure’’ is detected within the PSC, suggesting that PSCs are uniform clouds with a very large horizontal extent. On the other hand, cirrus cloud image geometry is not well-defined. In contrast to PSCs, cirrus clouds appear as irregular shaped clouds. These tropospheric clouds seem to have horizontal dimensions similar to the Sun on the image (25 km at the tangent point). The qualitative display of these different kinds of clouds, seen on the raw 2-D imager data, proves the ability of the imagers to be an efficient cloud detector in the upper troposphere-lower stratosphere (UTLS) region. Moreover, the structure of these clouds can be derived.

SciSat-1 retrieval results

SciSat-1, otherwise known as the Atmospheric Chemistry Experiment (ACE), is a Canadian satellite mission for remote sensing of the Earths atmosphere. It was launched into low Earth orbit (altitude 650 km, inclination 74 degrees) in August 2003. The primary instrument onboard ACE is a high resolution (maximum path difference ± 25 cm) Fourier Transform Spectrometer (FTS) operating from 2.4 to 13.3 microns (750-4100 cm-1). The satellite also features a dual spectrograph known as MAESTRO with wavelength coverage 280-1000 nm and resolution 1-2 nm. A pair of filtered CMOS detector arrays takes images of the sun at 0.525 and 1.02 nm. Working primarily in solar occultation, the satellite provides altitude profile information for temperature, pressure, and the volume mixing ratios for several dozen molecules of atmospheric interest. Scientific goals for ACE include: (1) understanding the chemical and dynamical processes that control the distribution of ozone in the stratosphere and upper troposphere; (2) exploring the relationship between atmospheric chemistry and climate change; (3) studying the effects of biomass burning in the free troposphere; and (4) measuring aerosols to reduce the uncertainties in their effects on the global energy balance.

Apodization effects in the retrieval of volume mixing ratio profiles

In remote sensing applications, spectra measured by Fourier-transform spectrometers are routinely apodized. A rigorous analysis approach would explicitly account for correlations induced in the covariance matrix by apodization, but these correlations are often ignored to simplify and speed up the processing. Using spectra measured by the Atmospheric Trace Molecule Spectroscopy missions, we investigated the effect of apodization on the retrieval of volume mixing ratio profiles for the case in which these correlations are ignored. Minor discrepancies occur between results for apodized and unapodized spectra, particularly when lines with a low signal-to-noise ratio are fitted. A set of microwindows is reported for O3 in the range of 1550-3350 cm(-1).

SCISAT-1: Retrieval algorithms, ACE-FTS testing and the ACE database

The SCISAT-1 mission, also known as the Atmospheric Chemistry Experiment (ACE), is a Canadian satellite mission to investigate the chemical and dynamical processes that control the distribution of ozone in the stratosphere and upper troposphere. The satellite is scheduled to launch in August 2003, carrying two main instruments: a high-resolution infrared Fourier transform spectrometer (ACE-FTS) and a dual grating UV-Vis-NIR spectrometer known as MAESTRO (Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) both operating primarily in solar occultation mode. Aspects of the mission pertaining to work done by ACE science team members from the University of Waterloo will be described, such as: the ACE-FTS forward model for retrieval of temperature, pressure and VMR profiles; ACE-FTS instrument testing and results; and the ACE Database along with data storage and processing hardware.

Atmospheric chemistry experiment (ACE): mission overview and early results

SciSat-1, otherwise known as the Atmospheric Chemistry Experiment (ACE), is a Canadian satellite mission for remote sensing of the Earths atmosphere. It was launched into low Earth orbit (altitude 650 km, inclination 74 degrees) in August 2003. The primary instrument onboard ACE is a high resolution (maximum path difference ± 25 cm) Fourier Transform Spectrometer (FTS) operating from 2.4 to 13.3 microns (750-4100 cm-1). The satellite also features a dual spectrograph known as MAESTRO with wavelength coverage 280-1000 nm and resolution 1-2 nm. A pair of filtered CMOS detector arrays takes images of the sun at 0.525 and 1.02 nm. Working primarily in solar occultation, the satellite provides altitude profile information for temperature, pressure, and the volume mixing ratios for several dozen molecules of atmospheric interest. Scientific goals for ACE include: (1) understanding the chemical and dynamical processes that control the distribution of ozone in the stratosphere and upper troposphere; (2) exploring the relationship between atmospheric chemistry and climate change; (3) studying the effects of biomass burning in the free troposphere; and (4) measuring aerosols to reduce the uncertainties in their effects on the global energy balance.