Two of the ten instruments involved in the campaign, both Fourier transform spectrometers (FTSs), were operated simultaneously, recording atmospheric solar absorption spectra. The first instrument was an ABB Bomem DA8 high-resolution infrared FTS. The second instrument was the Portable Atmospheric Research Interferometric Spectrometer for the Infrared (PARIS-IR), the ground-based version of the satelliteborne FTS on the ACE satellite (ACE-FTS). From the measurements collected by these two ground-based instruments, total column densities of seven stratospheric trace gases (O 3 , HCl, ClONO 2 , HF, HNO 3 , NO 2 , and NO) were retrieved using the optimal estimation method and these results were compared. Since the two instruments sampled the same portions of atmosphere by synchronizing observations during the campaign and used consistent retrieval parameters, the biases in retrieved columns from the two spectrometers represent the instrumental differences. Mean differences in total column densities of O 3 , HCl, ClONO 2 , HF, HNO 3 , and NO 2 from the observations between PARIS-IR and the DA8 FTS are 2.8 %, −3.2 %, −4.3 %, −1.5 %, −1.9 %, and −0.1 %, respectively. Partial column results from the ground-based Correspondence to: K. A. Walker (kwalker@atmosp.physics.utoronto.ca) spectrometers were also compared with partial columns derived from ACE-FTS version 2.2 (including updates for O 3 ) profiles. Mean differences in partial column densities of O 3 , HCl, ClONO 2 , HF, HNO 3 , NO 2 , and NO from the measurements between ACE-FTS and the DA8 FTS are −5.9 %, −8.5 %, −11.8 %, −0.9 %, −6.6 %, −21.6 % and −7.6 % respectively. Mean differences in partial column densities of O 3 , HCl, ClONO 2 , HF, HNO 3 , NO 2 from the measurements between ACE-FTS and the PARIS-IR are −5.2 %, −4.6 %, −2.3 %, −4.7 %, 5.7 % and −11.9 %, respectively. This work provides further evidence of the reliability of ACE-FTS measurements from the first three years of on-orbit observations. Column densities of O 3 , HCl, ClONO 2 , and HNO 3 from the three FTSs were normalized with respect to HF and used to compare the time evolution of the chemical constituents in the atmosphere over Eureka during spring 2006.

It is the trace composition of the atmosphere that governs the chemistry of the lower and middle atmosphere and to a large extent the climate of our planet. Accurately determining the abundance of species such as ozone (~1 ppm), nitrogen dioxide (~1 ppb), or bromine monoxide (~1 ppt) presents a large challenge. Further determining how they vary in space and time on a global scale is even more daunting. A global view of the atmospheric trace gas and aerosol composition can only be achieved from space via remote sensing. Balloons, and later rockets, were the first  Into year 11 of a 2-yr mission, OSIRIS is redefining how limb-scattered sunlight can be used to probe the atmosphere, even into the upper troposphere.

Abstract. The 2006 Canadian Arctic ACE (Atmospheric Chemistry Experiment) Validation Campaign collected measurements at the Polar Environment Atmospheric Research Laboratory (PEARL, 80.05° N, 86.42° W, 610 m above sea level) at Eureka, Canada from 17 February to 31 March 2006. Two of the ten instruments involved in the campaign, both Fourier transform spectrometers (FTSs), were operated simultaneously, recording atmospheric solar absorption spectra. The first instrument was an ABB Bomem DA8 high-resolution infrared FTS. The second instrument was the Portable Atmospheric Research Interferometric Spectrometer for the Infrared (PARIS-IR), the ground-based version of the satellite-borne FTS on the ACE satellite (ACE-FTS). From the measurements collected by these two ground-based instruments, total column densities of seven stratospheric trace gases (O3, HNO3, NO2, HCl, HF, NO, and ClONO2 were retrieved using the optimal estimation method and these results were compared. Since the two instruments sampled the same portions of atmosphere by synchronizing observations during the campaign, the biases in retrieved columns from the two spectrometers represent the instrumental differences. These differences were consistent with those seen in previous FTS intercomparison studies. Partial column results from the ground-based spectrometers were also compared with partial columns derived from ACE-FTS version 2.2 (including updates for O3, HDO and N2O5 profiles and the differences found were consistent with the other validation comparison studies for the ACE-FTS version 2.2 data products. Column densities of O3, HCl, ClONO2, and HNO3 from the three FTSs were normalized with respect to HF and used to probe the time evolution of the chemical constituents in the atmosphere over Eureka during spring 2006.

We report on the development of a novel multi-spectral polarimetric imager for atmospheric remote sensing of aerosol and cloud properties. The instrument concept, called the Aerosol Limb Imager (ALI), is ultimately intended for satellite measurements from a low Earth orbit. It utilizes a coupling of a dual transducer acousto-optic tunable filter and a liquid crystal rotator to provide dual linear polarization observations over a wide spectral range covering 600 nm–1500 nm. In the limb, or side-viewing, geometry, these measurements provide the capability to resolve vertical and horizontal distributions of aerosol and cloud properties such as extinction coefficient, optical depth, and particle distribution parameters. Here, we present the design and performance of an ALI prototype. Lab characterization of the instrument is used to develop a mathematical instrument model to predict signal levels under various atmospheric conditions. Results from a sub-orbital flight of the ALI prototype on a stabilized high-altitude stratospheric balloon gondola are presented that show the first known polarimetric, multi-spectral images of the limb radiance. The signal levels obtained agree reasonably well with those predicted by the instrument model using radiative transfer calculations for typical atmospheric conditions.

Abstract. The Aerosol Limb Imager (ALI) is an optical remote sensing instrument designed to image scattered sunlight from the atmospheric limb. These measurements are used to retrieve spatially resolved information of the stratospheric aerosol distribution, including spectral extinction coefficient and particle size. Here we present the design, development and test results of an ALI prototype instrument. The longterm goal of this work is the eventual realization of ALI on a satellite platform in low earth orbit, where it can provide high spatial resolution observations, both in the vertical and cross-track. The instrument design uses a large-aperture acousto-optic tunable filter (AOTF) to image the sunlit stratospheric limb in a selectable narrow wavelength band ranging from the visible to the near infrared. The ALI prototype was tested on a stratospheric balloon flight from the Canadian Space Agency (CSA) launch facility in Timmins, Canada, in September 2014. Preliminary analysis of the hyperspectral images indicates that the radiance measurements are of high quality, and we have used these to retrieve vertical profiles of stratospheric aerosol extinction coefficient from 650 to 1000 nm, along with one moment of the particle size distribution. Those preliminary results are promising and development of a satellite prototype of ALI within the Canadian Space Agency is ongoing.