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.
This paper is presented to give a general description of the ORACLE project and of the technology development results obtained to date. ORACLE is a feasibility study of a fully automated differential absorption lidar for global measurements of tropospheric and stratospheric ozone and aerosols with high vertical and horizontal resolution. The proposed program includes both novel technology demonstrations and obtaining scientific data from spacecraft. These data are needed to address key issues in atmospheric research including the depletion of stratospheric ozone, global warming, atmospheric transport and dynamics, tropospheric ozone budgets, atmospheric chemistry, and the atmospheric impact of hazards. Only a space-based lidar system can provide the required spatial resolution for ozone and aerosols in both the stratosphere and the troposphere on a global scale at all required altitudes. To deliver these data, the most novel technologies such as all-solid-state lasers, photon-counting detectors and ultra-lightweight deployable telescopes must be employed in the mission payload.
During the ASHOE/MAESA campaign a series of observations of the UV-visible radiation field were obtained from the ER-2 aircraft with the composition and photodissociative flux measurement (CPFM) instrument. Observations were made at the limb and in the zenith and nadir directions over the spectral range 300 - 775 nm at 1 nm spectral resolution. Analysis of these data yield surface and cloud effects on the radiation field as well as the effects of polar stratospheric clouds and changes in column ozone. We have conducted model-data comparisons of the direct and scattered radiation field and compared these results to TOMS satellite overflights. The radiation field models used in the data analysis include the integral equation solution described by Anderson et al., DISORT and MODTRAN3. In addition, the resultant radiation field observations are utilized in photochemical models for comparison to the in situ trace constituent measurements. Finally, we have found that the CPFM oxygen atmospheric band observations can be used to detect effective cloud heights.