Advanced constituent retrieval algorithms for composition and aerosol measurement and instrument development

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Limited knowledge about the role of upper tropospheric ozone and atmospheric aerosol in the Earth's radiation balance are the two largest uncertainties of the drivers behind climate change. The global distribution of ozone and aerosol must be determined by remote sounding from space. However, ground-based remote-sounding measurements remain important references in the development of improved measurement methodologies and new instruments. The ground-based observations - AERONET for aerosol and the Dobson and Brewer networks in the case of column ozone and ozonesondes for vertical profiling of ozone - provide crude spatial distributions and reference data for space measurements. Stratospheric profile measurements of ozone are made by a number of different techniques including measurements of limb-scattered solar irradiance, occultation measurements and solar backscatter measurements. Spectrally resolved measurements from the UV to the near IR can provide information about atmospheric constituents and data about aerosol particle properties. The applicant developed two different diode array spectrometers at Environment Canada. One, a small handheld instrument called the SunPhotoSpectrometer (SPS) was constructed to fly on the Space Shuttle with Canadian astronaut Steve MacLean on his first space flight. The instrument found its scientific niche mounted in a wing pod on the NASA ER-2 high-altitude aircraft where it was used to measure ozone column and make solar radiation measurements. Limb scans of scattered solar radiation and nadir radiances were made along with a measurement of the incident solar radiation. The limb and nadir measurements were made in two polarization planes and can be used to make aerosol particle measurements. The ER-2 also carried sophisticated in situ particle counters and the analysis and comparison of these two data sets can demonstrate the performance of this approach for making aerosol property measurements from space. One M.Sc. student will be supported to re-analyze the extensive (~125 flights) data sets using state-of-the-art analysis tools leading to teh development of new instruments for use on the ground and in space. The applicant has an extensive set of MAESTRO (Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) and SPS data collected at Izana, Tenerife which were made in conjunction with an AERONET calibration exercise. The full spectral range data (~300-1000nm) collected by the MAESTRO and SPS can serve as a good model for determining whether spectrophotometers provide an improved data set compared to AERONET sunphotometers. The sunphotometers are filter instruments with a limited number of bands, long-term stability issues and poor performance in the ultraviolet. The analysis of this dataset by a M.Sc. student may answer that question and lead to a commercial instrument for composition and aerosol measurement in an operational network. The MAESTRO spectrophotometer which is on the Atmospheric Chemistry Satellite has now collected 8 years of data. Operational analysis is being done by a dated set of codes that should be replaced with something more accurate and contemporary. Work was done by a previous Ph.D. student who demonstrated that a global spectral and altitude fitting algorithm could improve the performance of the retrievals, but the code has not been translated into an operational system nor sufficiently validated. It is proposed to support a post-doctoral fellow to help set up the applicant's new laboratory, work with the graduate students and spearhead the development of an advanced global fitting retrieval algorithm. This will increase the success rate of the retrievals, extend the altitude range sampled and allow the simultaneous retrieval of temperature and water vapour profiles along with those of other absorbers such as ozone and nitrogen dioxide.