Clive Midwinter

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.

The ACE-MAESTRO instrument on SCISAT: description, performance, and preliminary results

The Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation (MAESTRO) instrument on the SCISAT satellite is a simple, compact spectrophotometer for the measurement of atmospheric extinction, ozone, nitrogen dioxide, and other trace gases in the stratosphere and upper troposphere as part of the Atmospheric Chemistry Experiment (ACE) mission. We provide an overview of the instrument from requirements to realization, including optical design, prelaunch and on-orbit performance, and a preliminary examination of retrievals of ozone and NO(2).

A comparison of J‐values from the composition and photodissociative flux measurement with model calculations

The first measurements of the spectral flux on a horizontal surface, limb brightness and apparent surface brightness beneath the NASA ER-2 research aircraft were made during the Stratospheric Photochemistry, Aerosol and Dynamics Expedition (SPADE) of the NASA High-Speed Research Program. Results from the May, 1993 campaign are presented. J-values for the production of O(¹D) from the photodissociation of ozone and the photodissociation rate of NO2 to form NO have been determined and are compared to the currently used, modelled values.

A sensitivity study of photolysis rate coefficients during POLARIS

Recent improvements in the agreement between observation-derived and modeled photolysis rate coefficients (j-values) have allowed for the close examination of the sensitivity of j-values to variations in physical parameters influencing their magnitude and temporal(spatial variability. Altitude and solar zenith angle profiles of j-values for two photolytic processes, NO2 → NO + O(3P) and O3 → O2 + O(1D), are modeled, varying surface albedo, atmospheric baseheight, total column ozone, and ozone and temperature altitude profiles over the ranges observed during the NASA Photochemistry of Ozone Loss in the Arctic Region In Summer (POLARIS) high-altitude ER-2 aircraft campaign. The effect of atmospheric refraction at high solar zenith angles is also addressed. Modeled j-values using measured ozone/albedo input from the Composition and Photodissociative Flux Measurement (CPFM) spectroradiometer on board the ER-2 exceed those derived from CPFM flux measurements by 6% for jNO2 and 14% for jO3, within experimental uncertainties. The individual effects of albedo, baseheight, and ozone on j-values along specific ER-2 flight tracks are modeled and related to the temporal and spatial variability observed. For jNO2, surface albedo has the greatest effect; for jO3, the ozone above the aircraft and surface albedo are the most important.

Intercomparison of total ozone observations at Fairbanks, Alaska, during POLARIS

The pattern of seasonal ozone loss over Fairbanks, Alaska (AK), during the NASA Photochemistry of Ozone Loss in the Arctic Region In Summer (POLARIS) campaign in the spring and summer of 1997 is defined. Five independent data sets of total ozone observations at Fairbanks are presented, from the Earth Probe and ADEOS Total Ozone Mapping Spectrometer (TOMS) satellite instruments, balloon-borne electrochemical concentration cell ozonesondes, and ground-based (Brewer spectroradiometer, Dobson spectrophotometer, and the Jet Propulsion Laboratory MkIV infrared interferometer) instruments. The excellent agreement between different observational techniques lends confidence to the observed rate of summertime loss of total ozone at high latitudes. In addition, the small offsets between the data sets are well understood.

University of Toronto’s balloon-borne Fourier transform spectrometer

A commercial ABB-Bomem DA5 Fourier transform spectrometer (FTS) was refitted with new software and electronics to create a FTS that is appropriate for both ground-based and balloon-based measurements. Nearly all the electronics were replaced, and new control software was written that allows the instrument to run remotely, provides access to all housekeeping information, and permits considerable freedom in data processing approaches. A “delta” tracker was used for fine tracking of the sun over a small tracking range, using the main gondola pointing system for coarse azimuth tracking. This facilitated a simple, effective method of instrument integration onto the payload. The new design reduced the mass of the FTS from 90to55kg and reduced the power consumption from 145to65W.

The concentration profile of nitric acid and other species over Saskatchewan in August 1998: Retrieval from data recorded by thermal-emission radiometry

Abstract We present vertical mixing ratio profiles for nitric acid (HNO3) recorded during the Middle Atmosphere Nitrogen TRend Assessment (MANTRA) 1998 balloon flight over Saskatchewan, Canada. The profiles are based on radiance spectra containing HNO3 thermal‐emission features and were collected during balloon ascent and over a latitude and longitude interval (52°± 0.2°N, 106.6° ± 0.5°W) between 3:30 and 6:30 am local time (9:30 and 12:30 UTC), 24 August 1998. The spectra were simultaneously recorded by two radiometer instruments in the 715–1250 cm−1 atmospheric window at an approximate instrument resolution of 20 cm−1. Profiles of CFC‐11, CFC‐12, ozone (O3), methane (CH4) and nitrous oxide (N2O) based on emission features in the same observation window are also presented. Raw radiance measurements are analysed using a forward estimation technique to recover multiple gas profiles from very low‐spectral resolution measurements of atmospheric radiance. The technique uses detailed atmosphere and instrument models and a least‐mean‐squares estimator to iterate maximum‐likelihood volume mixing ratio (VMR) from 7 to 30 km on a 2‐km grid. The analysis approach described is adaptable to other retrievals of multiple constituents from low‐resolution spectra recorded by lower‐cost, robust instrumentation developed for balloon and space flight. Averaging kernels and an error analysis are included in order to illustrate instrument sensitivity to vertical composition and expected accuracy. Results from each instrument compare favourably and show close agreement with HNO3 climatology results based on satellite observations made by the Microwave Limb Sounding (MLS) instrument, 1992–94.

Science commissioning of the atmospheric chemistry experiment (ACE)

The Atmospheric Chemistry Experiment (ACE) was launched in August 2003 on board the Canadian scientific satellite SciSat-1. The ACE payload consists of two instruments: ACE-FTS, a high resolution (0.02 cm-1) Fourier transform infrared spectrometer and MAESTRO (Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation), a dual UV-visible-NIR spectrograph. Primarily, the two instruments use a solar occultation technique to make measurements of trace gases, temperature, pressure and atmospheric extinction. It will also be possible to make near-nadir observations with the ACE instruments. The on-orbit commissioning of the instruments and spacecraft were undertaken in the months following launch. At the end of this period, a series of science-oriented commissioning activities were undertaken. These activities had two aims: the first was to verify and extend the measurement results obtained during the pre-launch Science Calibration Test campaign and the second was to confirm appropriate parameters and establish procedures for operational measurements (occultation and near-nadir observations and exo-atmospheric calibration measurements). One of the most important activities was to determine the relative location of each instrument field of view and optimize the pointing of the sun-tracker to provide the best viewing for both instruments.

Measurements of Stratospheric Trace Gases Column Density and J-values Using UV-Visible Photodiode Array Spectroscopy during the MANTRA 2002 Balloon Campaign

Three spectrophotometers were used to measure stratospheric constituents during the MANTRA2002 balloon campaign. The instrument, calibration, and observations are described. The raw data are now being analyzed, and the results will be compared with previous balloon flights.

First Results from a MAESTRO Instrument: Field-Testing MAESTRO-B During the MANTRA 2002 Balloon Campaign

The first atmospheric spectra recorded by a MAESTRO instrument were collected during the MANTRA 2002 field campaign. These spectra will be used in the development and testing of retrieval algorithms for the MAESTRO satellite instrument.