scholarly journals A Comparative Evaluation of Aura-OMI and SKYNET Near-UV Single-scattering Albedo Products

2019 ◽  
Author(s):  
Hiren Jethva ◽  
Omar Torres
Keyword(s):  
Surface Albedo ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Absolute Difference ◽  
Urban Site ◽  
Ultraviolet Region ◽  
Carbonaceous Aerosols ◽  
Inversion Algorithm ◽  
Ozone Monitoring Instrument ◽  
Dust Aerosols

Abstract. 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 span over Asia and Europe. The present work continues our 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 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 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 ± 0.03 (± 0.05) for carbonaceous aerosols, 50 % (72 %) for dust aerosols, 45 % (75 %) for urban-industrial aerosol types. Regionally, the agreement between the two inversion products was robust over several sites in Japan influenced by carbonaceous and urban-industrial aerosols, at the biomass burning site Phimai in Thailand, and 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 ± 0.03 limits. Combinedly, the OMI-SKYNET retrievals agree mostly within ± 0.03 for the AOD (388 or 400 nm) larger than 0.5 and UV Aerosol Index 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 sub-pixel cloud contamination. The assumption of fixed and spectrally neutral surface albedo (0.1) in the SKYNET inversion appears to be unrealistic, leading to a large underestimation of retrieved SSA, especially for low aerosol load conditions. At large 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.

scholarly journals A comparative evaluation of Aura-OMI and SKYNET near-UV single-scattering albedo products

2019 ◽  
Vol 12 (12) ◽  
pp. 6489-6503
Author(s):  
Hiren Jethva ◽  
Omar Torres
Keyword(s):  
Surface Albedo ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Absolute Difference ◽  
Urban Site ◽  
Ultraviolet Region ◽  
Carbonaceous Aerosols ◽  
Inversion Algorithm ◽  
Ozone Monitoring Instrument ◽  
Dust Aerosols

Abstract. 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 ±0.03 (±0.05) 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 ±0.03 limits. Altogether, the OMI–SKYNET retrievals agree within ±0.03 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.

Global OMI Aerosol Single Scattering Albedo evaluation using ground-based AERONET

2020 ◽  
Author(s):  
Periklis Drakousis ◽  
Marios-Bruno Korras-Carraca ◽  
Hiren Jethva ◽  
Omar Torres ◽  
Nikos Hatzianastassiou
Keyword(s):  
Optical Properties ◽  
Climate Models ◽  
Spatial Scales ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Absolute Difference ◽  
Ozone Monitoring Instrument ◽  
Seasonal Basis ◽  
Radiance Data ◽  
The Impact

<p>Aerosol measurements are carried out worldwide in order to reduce the uncertainties about the impact of aerosols on climate. Over the past two decades, different methods (ground- or satellite-based) for measuring aerosol properties have been developed, covering a variety of approaches with different temporal and spatial scales, which can be considered complementary. Aerosol optical properties are essential for assessing the effects of aerosols on radiation and climate. Aerosol single scattering albedo (SSA), along with optical depth and asymmetry parameter, is one of the three key optical properties that are necessary for radiation transfer and climate models. At the same time, SSA strongly depends on different aerosol types, thus enabling the identification of these different aerosol particles. However, despite the strong need for aerosol SSA products with global and climatological coverage, and the significant progress in retrieving SSA from satellite measurements, the satellite SSA retrievals are still subjected to uncertainties.</p><p>In this study, we perform an evaluation of the OMAERUVd (PGE Version V1.8.9.1) daily L3 (1° x 1° latitude-longitude) aerosol SSA data, which are based on the enhanced two-channel OMAERUV algorithm that essentially uses the ultraviolet radiance data from Aura/Ozone Monitoring Instrument (OMI), through comparisons against daily SSA products from 541 globally distributed Aerosol Robotic Network (AERONET) stations for a 15-year period (2005-2019). The comparison is performed between the available OMAERUVd SSA data at 354 nm, 388 nm, and 500 nm, and the AERONET SSA data at 440 nm (or 443 nm). The comparison is made on an annual and seasonal basis in order to reveal possible seasonally dependent patterns, as well as on a climatological and a year-to-year basis. The statistical metrics, such as Coefficient of Correlation (R) and Bias, are computed for individual AERONET stations as well as for all stations. The effect of availability of common OMI and AERONET data pairs on the comparison is assessed by making comparisons when at least 10, 50 and 100 common pairs are available.</p><p>The results show that about 50% (75%) of OMI-AERONET matchups agree within the absolute difference of ±0.03 (±0.05) for the 500 nm OMI SSA and the 440 nm (or 443 nm) AERONET SSA. The corresponding percentage for the 388 nm OMI SSA and the 440 nm (or 443 nm) AERONET SSA increases to 58% (81%), while the corresponding numbers for the 354 nm SSA OMI and the 440 nm (or 443 nm) AERONET are 43% (67%). It is found that in overall, OMI tends mainly to overestimate (underestimate) SSA for the 500 nm (354 nm) products in comparison to AERONET 440 nm (or 443 nm) with a total bias of 0.025 (-0.024), or 2.7% (2.6%) in relative percentage terms with respect to AERONET (mean AERONET value equal to 0.908), and an overall R value of 0.399 (0.386). At 388 nm, OMI tends to retrieve higher SSA over regions where biomass burning occurs, against lower SSA values elsewhere, with overall bias and R values equal to -0.002 (0.22%) and 0.395, respectively.</p>

scholarly journals A novel single-cavity multi-wavelength photoacoustic spectrometer for atmospheric aerosol research

2016 ◽  
Author(s):  
Claudia Linke ◽  
Inas Ibrahim ◽  
Nina Schleicher ◽  
Regina Hitzenberger ◽  
Meinrat O. Andreae ◽  
...  
Keyword(s):  
Single Scattering ◽  
Organic Content ◽  
Visible Spectral Range ◽  
Single Scattering Albedo ◽  
Urban Site ◽  
Strong Increase ◽  
Carbonaceous Aerosols ◽  
Photoacoustic Spectrometer ◽  
Multi Wavelength ◽  
Single Cavity

Abstract. The spectral light absorbing behavior of carbonaceous aerosols varies depending on the chemical composition and structure of the particles. A new single-cavity multi-wavelength photoacoustic spectrometer was developed and characterized for measuring absorption coefficients at three wavelengths across the visible spectral range. In laboratory studies, several types of soot with different organic content were generated by a diffusion flame burner and were investigated for changes in mass-specific absorption cross sections (MAC), absorption and scattering Ångström exponents (αabs and αsca), and single scattering albedo (ω). By increasing the organic carbonaceous (OC) content of the aerosol from 50 % to 90 % of the total carbonaceous mass, for 660 nm nearly no change of MAC was found with increasing OC content. In contrast, for 532 nm a significant, and for 445 nm a strong increase of MAC was found with increasing OC content of the aerosol. Depending on the OC content, the Ångström exponents of absorption and scattering as well as the single scattering albedo increased. These laboratory results were compared to a field study at a traffic dominated urban site, which was also influenced by residential wood combustion. For this site a daily average value of αabs(445–660) of 1.9 was found.

scholarly journals A novel single-cavity three-wavelength photoacoustic spectrometer for atmospheric aerosol research

2016 ◽  
Vol 9 (11) ◽  
pp. 5331-5346 ◽  
Author(s):  
Claudia Linke ◽  
Inas Ibrahim ◽  
Nina Schleicher ◽  
Regina Hitzenberger ◽  
Meinrat O. Andreae ◽  
...  
Keyword(s):  
Single Scattering ◽  
Organic Content ◽  
Visible Spectral Range ◽  
Single Scattering Albedo ◽  
Urban Site ◽  
Strong Increase ◽  
Carbonaceous Aerosols ◽  
Wood Combustion ◽  
Photoacoustic Spectrometer ◽  
Single Cavity

Abstract. The spectral light-absorbing behavior of carbonaceous aerosols varies depending on the chemical composition and structure of the particles. A new single-cavity three-wavelength photoacoustic spectrometer was developed and characterized for measuring absorption coefficients at three wavelengths across the visible spectral range. In laboratory studies, several types of soot with different organic content were generated by a diffusion flame burner and were investigated for changes in mass-specific absorption cross section (MAC) values, absorption and scattering Ångström exponents (αabs and αsca), and single scattering albedo (ω). By increasing the organic carbonaceous (OC) content of the aerosol from 50 to 90 % of the total carbonaceous mass, for 660 nm nearly no change of MAC was found with increasing OC content. In contrast, for 532 nm a significant increase, and for 445 nm a strong increase of MAC was found with increasing OC content of the aerosol. Depending on the OC content, the Ångström exponents of absorption and scattering as well as the single scattering albedo increased. These laboratory results were compared to a field study at a traffic-dominated urban site, which was also influenced by residential wood combustion. For this site a daily average value of αabs(445–660) of 1.9 was found.

CARBONACEOUS AEROSOLS-SINGLE SCATTERING ALBEDO AND EFFECT ON WEATHER HEATING

1996 ◽  
Vol 14 (1) ◽  
pp. 43-58 ◽  
Author(s):  
HAIYIN SUN ◽  
DUANE A. JACKSON ◽  
MURRAY CLARK ◽  
MALAY K. MAZUMDER
Keyword(s):  
Single Scattering ◽  
Single Scattering Albedo ◽  
Carbonaceous Aerosols

Single scattering albedo of fine mineral dust aerosols controlled by iron concentration

2012 ◽  
Vol 117 (D11) ◽  
pp. n/a-n/a ◽  
Author(s):  
Hans Moosmüller ◽  
Johann P. Engelbrecht ◽  
Michał Skiba ◽  
Garrett Frey ◽  
Rajan K. Chakrabarty ◽  
...  
Keyword(s):  
Mineral Dust ◽  
Iron Concentration ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Dust Aerosols ◽  
Mineral Dust Aerosols

scholarly journals Simulations of Contrail Optical Properties and Radiative Forcing for Various Crystal Shapes

2011 ◽  
Vol 50 (8) ◽  
pp. 1740-1755 ◽  
Author(s):  
Krzysztof M. Markowicz ◽  
Marcin L. Witek
Keyword(s):  
Optical Properties ◽  
Asymmetry Parameter ◽  
Radiative Forcing ◽  
Surface Albedo ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Crystal Shape ◽  
Crystal Shapes ◽  
The Mean ◽  
The Asymmetry

AbstractThe aim of this study is to investigate the sensitivity of radiative-forcing computations to various contrail crystal shape models. Contrail optical properties in the shortwave and longwave ranges are derived using a ray-tracing geometric method and the discrete dipole approximation method, respectively. Both methods present good correspondence of the single-scattering albedo and the asymmetry parameter in a transition range (3–8 μm). There are substantial differences in single-scattering properties among 10 crystal models investigated here (e.g., hexagonal columns and plates with different aspect ratios, and spherical particles). The single-scattering albedo and the asymmetry parameter both vary by up to 0.1 among various crystal shapes. The computed single-scattering properties are incorporated in the moderate-resolution atmospheric radiance and transmittance model (MODTRAN) radiative transfer code to simulate solar and infrared fluxes at the top of the atmosphere. Particle shapes have a strong impact on the contrail radiative forcing in both the shortwave and longwave ranges. The differences in the net radiative forcing among optical models reach 50% with respect to the mean model value. The hexagonal-column and hexagonal-plate particles show the smallest net radiative forcing, and the largest forcing is obtained for the spheres. The balance between the shortwave forcing and longwave forcing is highly sensitive with respect to the assumed crystal shape and may even change the sign of the net forcing. The optical depth at which the mean diurnal radiative forcing changes sign from positive to negative varies from 4.5 to 10 for a surface albedo of 0.2 and from 2 to 6.5 for a surface albedo of 0.05. Contrails are probably never that optically thick (except for some aged contrail cirrus), however, and so will not have a cooling effect on climate.

scholarly journals Solar UV Irradiance in a Changing Climate: Trends in Europe and the Significance of Spectral Monitoring in Italy

Environments ◽  
2019 ◽  
Vol 7 (1) ◽  
pp. 1 ◽  
Author(s):  
Ilias Fountoulakis ◽  
Henri Diémoz ◽  
Anna-Maria Siani ◽  
Gudrun Laschewski ◽  
Gianluca Filippa ◽  
...  
Keyword(s):  
Total Ozone ◽  
Surface Albedo ◽  
Forecast Model ◽  
Urban Site ◽  
Climate Trends ◽  
Ozone Monitoring Instrument ◽  
Uv Index ◽  
Uv Irradiance ◽  
Solar Uv Irradiance

Review of the existing bibliography shows that the direction and magnitude of the long-term trends of UV irradiance, and their main drivers, vary significantly throughout Europe. Analysis of total ozone and spectral UV data recorded at four European stations during 1996–2017 reveals that long-term changes in UV are mainly driven by changes in aerosols, cloudiness, and surface albedo, while changes in total ozone play a less significant role. The variability of UV irradiance is large throughout Italy due to the complex topography and large latitudinal extension of the country. Analysis of the spectral UV records of the urban site of Rome, and the alpine site of Aosta reveals that differences between the two sites follow the annual cycle of the differences in cloudiness and surface albedo. Comparisons between the noon UV index measured at the ground at the same stations and the corresponding estimates from the Deutscher Wetterdienst (DWD) forecast model and the ozone monitoring instrument (OMI)/Aura observations reveal differences of up to 6 units between individual measurements, which are likely due to the different spatial resolution of the different datasets, and average differences of 0.5–1 unit, possibly related to the use of climatological surface albedo and aerosol optical properties in the retrieval algorithms.

scholarly journals Spatial distribution of dust's optical properties over the Sahara and Asia inferred from Moderate Resolution Imaging Spectroradiometer

2013 ◽  
Vol 13 (21) ◽  
pp. 10827-10845 ◽  
Author(s):  
M. Yoshida ◽  
J. M. Haywood ◽  
T. Yokohata ◽  
H. Murakami ◽  
T. Nakajima
Keyword(s):  
Optical Properties ◽  
Spatial Distribution ◽  
Single Scattering ◽  
Surface Reflectance ◽  
Carbonaceous Aerosols ◽  
Dust Aerosols ◽  
Moderate Resolution ◽  
Resolution Imaging ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
Earth’S Climate

Abstract. There is great uncertainty regarding the role of mineral dust aerosols in Earth's climate system. One reason for this uncertainty is that the optical properties of mineral dust, such as its single scattering albedo (the ratio of scattering to total extinction), are poorly constrained because ground observations are limited to a few locations and satellite standard products are not available due to the excessively bright surface of the desert in the visible wavelength, which makes robust retrievals difficult. Here, we develop a method to estimate the spatial distributions of the aerosol single scattering albedo (ω0) and optical depth (τa), with daily 1°×1° spatial resolution using data from the Moderate Resolution Imaging Spectroradiometer (MODIS) as well as model simulations of radiative transfer. This approach is based on the "critical surface reflectance" method developed in the literature, which estimates ω0 from the top of the atmospheric radiance. We estimate the uncertainties in ω0 over the Sahara (Asia) to be approximately 0.020 and 0.010 (0.023 and 0.017) for bands 9 and 1, respectively, while the uncertainty in τa is approximately 0.235 and 0.228 (0.464 and 0.370) for bands 9 and 1, respectively. The 5–95% range of the spatial distribution of ω0 over the Sahara (Asia) is approximately 0.90–0.94 and 0.96–0.99 (0.87–0.94 and 0.89–0.97) for bands 9 and 1, respectively, and that of τa over the Sahara (Asia) is approximately 0.8–1.4 and 0.8–1.7 (0.7–2.0 and 0.7–1.9) for bands 9 and 1, respectively. The results for the Sahara indicate a good correlation between ω0 and the surface reflectance, and between ω0 and τa. However, the relationships between ω0, τa, and surface reflectance are less clear in Asia than in the Sahara, and the ω0 values are smaller than those in the Sahara. The regions with small ω0 values are consistent with the regions where coal-burning smoke and carbonaceous aerosols are reported to be transported in previous studies. Because the coal-burning and carbonaceous aerosols are known to be more absorptive and have smaller ω0 values than dust aerosols, our results indicate that the dust aerosols in Asia are contaminated by these anthropogenic aerosols. The spatial distribution of dust optical properties obtained in our work could be useful in understanding the role of dust aerosols in Earth's climate system, most likely through future collaboration with regional and global modelling studies.

scholarly journals Retrieval of aerosol single scattering albedo at ultraviolet wavelengths at the T1 site during MILAGRO

2009 ◽  
Vol 9 (15) ◽  
pp. 5813-5827 ◽  
Author(s):  
C. A. Corr ◽  
N. Krotkov ◽  
S. Madronich ◽  
J. R. Slusser ◽  
B. Holben ◽  
...  
Keyword(s):  
Mexico City ◽  
Surface Albedo ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Spectral Variation ◽  
Sensitivity Tests ◽  
Surface Measurements ◽  
Sun Photometer ◽  
Visible Wavelengths ◽  
Multifilter Rotating Shadowband Radiometer

Abstract. Surface measurements of direct and diffuse voltages at UV wavelengths were made at the T1 site during the MILAGRO (Megacity Initiative: Local and Global Research Observations) field campaign in March 2006, using a multifilter rotating shadowband radiometer (UV-MFRSR). We used the MFRSR data, together with measurements from a co-located CIMEL Sun photometer at the site operating as part of the AERONET network, to deduce aerosol single scattering albedo (ω) at 368 and 332 nm for four cloud-free days during the study. Our retrievals suggest that T1 aerosols with aerosol extinction optical depth τ368>0.1 that are influenced by Mexico City emissions, blowing dust, and biomass burning, are characterized by low ω368=0.73–0.85 and ω332=0.70–0.86, with small or no spectral variation of ω between 368 and 332 nm. Our findings are consistent with other published estimates of ω for Mexico City aerosols, including those that suggest that the absorption attributable to these aerosols is enhanced at UV wavelengths relative to visible wavelengths. We also demonstrate, via sensitivity tests, the importance of accurate τ and surface albedo measurements in ω retrievals at UV wavelengths.

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