A comparative evaluation of Aura-OMI and SKYNET near-UV single-scattering albedo products
<p>The aerosol single-scattering albedo (SSA) retrieved by the near-UV algorithm applied to the Aura Ozone Monitoring Instrument (OMI) measurements (OMAERUV) is compared with an independent inversion product derived from the sky radiometer network SKYNET – a ground-based radiation observation...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-12-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://www.atmos-meas-tech.net/12/6489/2019/amt-12-6489-2019.pdf |
| Summary: | <p>The aerosol single-scattering albedo (SSA) retrieved by the near-UV
algorithm applied to the Aura Ozone Monitoring Instrument (OMI) measurements
(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
to evaluate the consistency between the retrieved SSA from satellite and
ground sensors. The automated spectral measurements of direct downwelling
solar flux and sky radiances made by the SKYNET Sun-sky radiometer are used as
input to an inversion algorithm that derives spectral aerosol optical depth
(AOD) and single-scattering albedo (SSA) in the near-UV to near-IR spectral
range. The availability of SKYNET SSA measurements in the ultraviolet region
of the spectrum allows, for the first time, a direct comparison with OMI SSA
retrievals eliminating the need of extrapolating the satellite retrievals to
the visible wavelengths as is the case in the evaluation against the Aerosol
Robotic Network (AERONET). An analysis of the collocated retrievals from
over 25 SKYNET sites reveals that about 61 % (84 %) of OMI–SKYNET
matchups agree within the absolute difference of <span class="inline-formula">±0.03</span> (<span class="inline-formula">±0.05</span>)
for carbonaceous aerosols, 50 % (72 %) for dust aerosols, and 45 % (75 %) for urban–industrial aerosol types. Regionally, the agreement
between the two inversion products is robust over several sites in Japan
influenced by carbonaceous and urban–industrial aerosols; at the biomass
burning site Phimai in Thailand; and the polluted urban site in New Delhi, India. The
collocated dataset yields fewer matchups identified as dust aerosols mostly
over the site Dunhuang with more than half of the matchup points confined to within
<span class="inline-formula">±0.03</span> limits. Altogether, the OMI–SKYNET retrievals agree within
<span class="inline-formula">±0.03</span> when SKYNET AOD (388 or 400 nm) is larger than 0.5 and the OMI UV Aerosol Index is larger than 0.2. The remaining uncertainties in both inversion
products can be attributed to specific assumptions made in the retrieval
algorithms, i.e., the uncertain calibration constant, assumption of spectral
surface albedo and particle shape, and subpixel cloud contamination. The
assumption of fixed and spectrally neutral surface albedo (0.1) in the
SKYNET inversion appears to be unrealistic, leading to underestimated SSA,
especially under lower aerosol load conditions. At higher AOD values for
carbonaceous and dust aerosols, however, retrieved SSA values by the two
independent inversion methods are generally consistent in spite of the
differences in retrieval approaches.</p> |
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| ISSN: | 1867-1381 1867-8548 |