Atmospheric Measurement Techniques | 2019
A comparative evaluation of Aura-OMI and SKYNET near-UV single-scattering albedo products
Abstract
Abstract. The aerosol single-scattering albedo (SSA) retrieved by the near-UV\nalgorithm applied to the Aura Ozone Monitoring Instrument (OMI) measurements\n(OMAERUV) is compared with an independent inversion product derived from the sky radiometer network SKYNET – a ground-based radiation observation network with sites in Asia and Europe. The present work continues previous efforts\nto evaluate the consistency between the retrieved SSA from satellite and\nground sensors. The automated spectral measurements of direct downwelling\nsolar flux and sky radiances made by the SKYNET Sun-sky radiometer are used as\ninput to an inversion algorithm that derives spectral aerosol optical depth\n(AOD) and single-scattering albedo (SSA) in the near-UV to near-IR spectral\nrange. The availability of SKYNET SSA measurements in the ultraviolet region\nof the spectrum allows, for the first time, a direct comparison with OMI SSA\nretrievals eliminating the need of extrapolating the satellite retrievals to\nthe visible wavelengths as is the case in the evaluation against the Aerosol\nRobotic Network (AERONET). An analysis of the collocated retrievals from\nover 25 SKYNET sites reveals that about 61\u2009% (84\u2009%) of OMI–SKYNET\nmatchups agree within the absolute difference of ±0.03 ( ±0.05 )\nfor carbonaceous aerosols, 50\u2009% (72\u2009%) for dust aerosols, and 45\u2009% (75\u2009%) for urban–industrial aerosol types. Regionally, the agreement\nbetween the two inversion products is robust over several sites in Japan\ninfluenced by carbonaceous and urban–industrial aerosols; at the biomass\nburning site Phimai in Thailand; and the polluted urban site in New Delhi, India. The\ncollocated dataset yields fewer matchups identified as dust aerosols mostly\nover the site Dunhuang with more than half of the matchup points confined to within\n ±0.03 limits. Altogether, the OMI–SKYNET retrievals agree within\n ±0.03 when SKYNET AOD (388 or 400\u2009nm) is larger than 0.5 and the OMI UV Aerosol Index is larger than 0.2. The remaining uncertainties in both inversion\nproducts can be attributed to specific assumptions made in the retrieval\nalgorithms, i.e., the uncertain calibration constant, assumption of spectral\nsurface albedo and particle shape, and subpixel cloud contamination. The\nassumption of fixed and spectrally neutral surface albedo (0.1) in the\nSKYNET inversion appears to be unrealistic, leading to underestimated SSA,\nespecially under lower aerosol load conditions. At higher AOD values for\ncarbonaceous and dust aerosols, however, retrieved SSA values by the two\nindependent inversion methods are generally consistent in spite of the\ndifferences in retrieval approaches.