Retrieval of Ozone Column Content from Airborne Sun Photometer Measurements during SOLVE II: Comparison with SAGE III, POAM III, TOMS and GOME Measurements

During the Second SAGE III Ozone Loss and Validation Experiment (SOLVE II), the 14-channel NASA Ames Airborne Tracking Sunphotometer (AATS-14) was mounted on the NASA DC-8 and successfully measured spectra of total and aerosol optical depth (TOD and AOD) during the sunlit portions of eight science flights. Values of ozone column content above the aircraft have been derived from the AATS-14 data by using a linear least squares method that iteratively finds the ozone column content that yields the best match between measured and calculated TOD spectra. The calculations assume the known Chappuis ozone absorption band shape and a three-parameter AOD shape (quadratic in log-log space). AATS-14 includes seven channels within the Chappuis band, including one with its center wavelength (604.4 nm) near the peak, and three with center wavelengths (499.4, 519.4 and 675.1 nm) where ozone absorption is ~25-35 percent of that at the peak. For the typical DC-8 SOLVE II cruising altitudes of ~8-12 km and the background stratospheric aerosol conditions that prevailed during SOLVE II, ozone absorption comprised a significant fraction of the aerosol-plus-ozone optical depth measured in the four AATS-14 channels centered between 499.4 and 675.1 nm. Typical AODs above the DC-8 ranged from 0.003-0.008 in these channels. For comparison, an ozone overburden of 0.3 atm-cm (300 DU) translates to ozone optical depths of 0.009, 0.014, 0.041, and 0.012, respectively, at these same wavelengths. In this paper, we compare AATS-14 values of ozone column content with temporally and spatially near-coincident values derived from measurements acquired by the Stratospheric Aerosol and Gas Experiment III (SAGE III) and the Polar Ozone and Aerosol Measurement III (POAM III) satellite sensors. We also compare AATS-14 ozone retrievals during selected DC-8 latitudinal and longitudinal transects with total column ozone data acquired by the Total Ozone Mapping Spectrometer (TOMS) and the Global Ozone Monitoring Experiment (GOME) satellite sensors. To enable this comparison, the amount of ozone in the column below the aircraft is estimated by combining SAGE and/or POAM data with high resolution, fast response in-situ ozone measurements acquired during the DC-8 ascent at the start of each science flight.