Merging regional and global AOD records from 15 available satellite products

Sogacheva, Larisa; Popp, Thomas; Sayer, A. M.; Dubovik, Оleg; Garay, M. J.; Heckel, A.; Hsu, N. Christina; Jethva, Hiren; Kahn, Ralph A.; Kolmonen, Pekka; Kosmale, Miriam; Leeuw, G. de; Levy, Robert C.; Litvinov, Pavel; Lyapustin, Alexei; North, Peter; Torres, Omar

doi:10.5194/acp-2019-446

Cited by 7 publications

(11 citation statements)

References 43 publications

(56 reference statements)

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“…For an earlier study of satellite AOD diversity, see Chin et al (2014) in which a different definition of diversity, a different (and smaller) set of satellite products, and a different (sub-optimal) collocation procedure lead to rather different magnitudes and spatial patterns for diversity. In contrast, the diversity presented in Sogacheva et al (2019), while using a different definition and a different (sub-optimal) collocation procedure agrees more with the one presented in Fig. 27.…”

Section: Intercomparison and Evaluation Of Collocated Morning Or Aftesupporting

confidence: 77%

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An AeroCom/AeroSat study: Intercomparison of Satellite AOD Datasets for Aerosol Model Evaluation

Schutgens¹,

Sayer²,

Heckel³

et al. 2020

Preprint

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Abstract. To better understand current uncertainties in the important observational constraint to climate models of AOD (Aerosol Optical Depth), we evaluate and intercompare fourteen satellite products, representing 9 different retrieval algorithm families using observations from 5 different sensors on 6 different platforms. The satellite products, super-observations consisting of 1° × 1° daily aggregated retrievals drawn from the years 2006, 2008 and 2010, are evaluated with AERONET (AErosol RObotic NETwork) and MAN (Maritime Aerosol Network) data. Results show that different products exhibit different regionally varying biases (both under- and overestimates) that may reach ±50 %, although a typical bias would be 15–25 % (depending on product). In addition to these biases, the products exhibit random errors that can be 1.6 to 3 times as large. Most products show similar performance, although there are a few exceptions with either larger biases or larger random errors. The intercomparison of satellite products extends this analysis and provides spatial context to it. In particular, we show that aggregated satellite AOD agrees much better than the spatial coverage (often driven by cloud masks) within the 1° × 1° grid cells. Up to 50 % of the difference between satellite AOD is attributed to cloud contamination. The diversity in AOD products shows clear spatial patterns and varies from 10 % (parts of the ocean) to 100 % (central Asia and Australia). More importantly, we show that the diversity may be used as an indication of AOD uncertainty, at least for the better performing products. This provides modellers with a global map of expected AOD uncertainty in satellite products, allows assessment of products away from AERONET sites, can provide guidance for future AERONET locations, and offers suggestions for product improvements. We account for statistical and sampling noise in our analyses. Sampling noise, variations due to the evaluation of different subsets of the data, causes important changes in error metrics. The consequences of this noise term for product evaluation are discussed.

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Section: Intercomparison and Evaluation Of Collocated Morning Or Aftesupporting

confidence: 77%

“…There is substantial overlap in the satellite products used here and in Sogacheva et al (2019), see Tables 1 and 2. Also shown is the average correlation, i.e. de average of the correlation between all possible pairs of collocated products.…”

Section: Intercomparison and Evaluation Of Collocated Morning Or Aftementioning

confidence: 99%

An AeroCom/AeroSat study: Intercomparison of Satellite AOD Datasets for Aerosol Model Evaluation

Schutgens¹,

Sayer²,

Heckel³

et al. 2020

Preprint

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“…North America in the 1990's (Bodhaine and Dutton, 1993) and by Asia some 10-15 years ago (Sogacheva et al, 2019, Zhao et al, 2019. The median slope of the ω0 trends seems to be proportional to the length of the mitigation efforts, which for some relevant pollutants (e.g., black carbon, SO2 and NOx) are still ongoing.…”

Section: Single Scattering Albedo Trendsmentioning

confidence: 97%

“…In Asia, the rapid economic growth led to increased AOD between 1980 and 2010 (Butt et al, 2017, Yoon et al, 2016, but significant decreases are now measured and modelled in the last decade in South East Asia (Sogacheva et al, 2019). In contrast, ss increasing AOD trends are found at remote and isolated sites in Asia, in high altitude Himalayan regions, in the southern 40 hemisphere ocean and in Antarctica.…”

Section: Comparison With Other Trends and Causality 20mentioning

confidence: 99%

Multidecadal trend analysis of aerosol radiative properties at a global scale

Coen¹,

Andrews²,

Alastuey³

et al. 2020

Preprint

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Abstract. In order to assess the global evolution of aerosol parameters affecting climate change, a long-term trend analyses of aerosol optical properties were performed on time series from 52 stations situated across five continents. The time series of measured scattering, backscattering and absorption coefficients as well as the derived single scattering albedo, backscattering fraction, scattering and absorption &#197;ngstr&#246;m exponents covered at least 10 years and up to 40 years for some stations. The non-parametric seasonal Mann&#8211;Kendall (MK) statistical test associated with several prewhitening methods and with the Sen's slope were used as main trend analysis methods. Comparisons with General Least Mean Square associated with Autoregressive Bootstrap (GLS/ARB) and with standard Least Mean Square analysis (LMS) enabled confirmation of the detected MK statistically significant trends and the assessment of advantages and limitations of each method. Currently, scattering and backscattering coefficients trends are mostly decreasing in Europe and North America and are not statistically significant in Asia, while polar stations exhibit a mix of increasing and decreasing trends. A few increasing trends are also found at some stations in North America and Australia. Absorption coefficients time series also exhibit primarily decreasing trends. For single scattering albedo, 52&#8201;% of the sites exhibit statistically significant positive trends, mostly in Asia, Eastern/Northern Europe and Arctic, 18&#8201;% of sites exhibit statistically significant negative trends, mostly in central Europe and central North America, while the remaining 30&#8201;% of sites have trends, which are not statistically significant. In addition to evaluating trends for the overall time series, the evolution of the trends in sequential 10 year segments was also analyzed. For scattering and backscattering, statistically significant increasing 10 year trends are primarily found for earlier periods (10 year trends ending in 2010&#8211;2015) for polar stations and Mauna Loa. For most of the stations, the present-day statistically significant decreasing 10 year trends of the single scattering albedo were preceded by not statistically significant and statistically significant increasing 10 year trends. The effect of air pollution abatement policies in continental North America is very obvious in the 10 year trends of the scattering coefficient &#8211; there is a shift to statistically significant negative trends in 2010&#8211;2011 for all stations in the eastern and central US. This long-term trend analysis of aerosol radiative properties with a broad spatial coverage enables a better global view of potential aerosol effects on climate changes.

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“…The MERGED-FMI data-set , developed by the Finnish Meteorological Institute, includes gridded L3 monthly AOD products merged from 12 available satellite products (Sogacheva et al (2019)). The merging method is based on the results of the evaluation of the individual satellite AOD products against AERONET.…”

Section: Merged Satellite Aod Datamentioning

confidence: 99%

Multi-model evaluation of aerosol optical properties in the AeroCom phase III Control experiment, using ground and space based columnar observations from AERONET, MODIS, AATSR and a merged satellite product as well as surface in-situ observations from GAW sites

Gliß

Mortier

Schulz

et al. 2020

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Abstract. Within the framework of the AeroCom (Aerosol Comparisons between Observations and Models) initiative, the present day modelling of aerosol optical properties has been assessed using simulated data representative for the year 2010, from 14 global aerosol models participating in the Phase III Control experiment. The model versions are close or equal to those used for CMIP6 and AerChemMIP and inform also on bias in state of the art ESMs. Modelled column optical depths (total, fine and coarse mode AOD) and Angstrom Exponents (AE) were compared both with ground based observations from the Aerosol Robotic Network (AERONET, version 3) as well as space based observations from AATSR-SU instruments. In addition, the modelled AODs were compared with MODIS (Aqua and Terra) data and a satellite AOD data-set (MERGED-FMI) merged from 12 different individual AOD products. Furthermore, for the first time, the modelled near surface scattering (under dry conditions) and absorption coefficients were evaluated against measurements made at low relative humidity at surface in-situ GAW sites. Statistics are based mainly on normalised mean biases and Pearson correlation coefficients from colocated model and observation data in monthly resolution. Hence, the results are mostly representative for the regions covered by each of the observation networks. Model biases established against satellite data yield insights into remote continental areas and oceans, where ground-based networks lack site coverage. The satellite data themselves are evaluated against AERONET observations, to test our aggregation and re-gridding routines, suggesting relative AOD biases of &#8722;5&#8201;%, &#8722;6&#8201;%, +9&#8201;% and +18&#8201;% for AATSR-SU, MERGED-FMI, MODIS-aqua and MODIS-terra, respectively, with high correlations exceeding 0.8. Biases of fine and coarse AOD and AE in AATSR are found to be +2&#8201;%, &#8722;16&#8201;% and +14.7&#8201;% respectively, at AERONET sites, with correlations of the order of 0.8. The AeroCom MEDIAN and most of the participating models underestimate the optical properties investigated, relative to remote sensing observations. AERONET AOD is underestimated by 21&#8201;%&#8201;&#177;&#8201;17&#8201;%. Against satellite data, the model AOD biases range from &#8722;38&#8201;% (MODIS-terra) to &#8722;17&#8201;% (MERGED-FMI). Correlation coefficients of model AODs with AERONET, MERGED-FMI and AATSR-SU are high (0.8&#8211;0.9) and slightly lower against the two MODIS data-sets (0.6&#8211;0.8). Investigation of fine and coarse AODs from the MEDIAN model reveals biases of &#8722;10%&#8201;&#177;&#8201;20&#8201;% and &#8722;41&#8201;%&#8201;&#177;&#8201;29&#8201;% against AERONET and &#8722;13&#8201;% and &#8722;24&#8201;% against AATSR-SU, respectively. The differences in bias against AERONET and AATSR-SU are in agreement with the established satellite bias against AERONET. These results indicate that most of the AOD bias is due to missing coarse AOD in the regions covered by these observations. Underestimates are also found when comparing the models against the surface GAW observations, showing AeroCom MEDIAN mean bias and inter-model variation of &#8722;44&#8201;%&#8201;&#177;&#8201;22&#8201;% and &#8722;32&#8201;%&#8201;&#177;&#8201;34&#8201;% for scattering and absorption coefficients, respectively. Dry scattering shows higher underestimation than AOD at ambient relative humidity and is in agreement with recent findings that suggest that models tend to overestimate scattering enhancement due to hygroscopic growth. Broadly consistent negative bias in AOD and scattering suggest a general underestimate in aerosol effects in current global aerosol models. The large diversity in the surface absorption results suggests differences in the model treatment of light absorption by black carbon (BC), dust (DU) and to a minor degree, organic aerosol (OA). Considerable diversity is found among the models in the simulated near surface absorption coefficients, particularly in regions associated with dust (e.g. Sahara, Tibet), biomass burning (e.g. Amazonia, Central Australia) and biogenic emissions (e.g. Amazonia). Regions associated with high anthropogenic BC emissions such as China and India exhibit comparatively good agreement for all models. Evaluation of modelled column AEs shows an underestimation of 9&#8201;%&#8201;&#177;&#8201;24&#8201;% against AERONET and &#8722;21&#8201;% against AATSR-SU. This suggests that overall, models tend to overestimate particle size, with implications for lifetime and radiative transfer calculations. An investigation of modelled emissions, burdens and lifetimes, mass-specific-extinction coefficients (MECs) and optical depths (ODs) for each species and model reveals considerable diversity in most of these parameters. These are discussed in detail for each model individually. Inter-model spread of aerosol species lifetime appears to be similar to that of mass extinction coefficients, suggesting that AOD uncertainties are still associated to a broad spectrum of parameterised aerosol processes.

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Merging regional and global AOD records from 15 available satellite products

Cited by 7 publications

References 43 publications

An AeroCom/AeroSat study: Intercomparison of Satellite AOD Datasets for Aerosol Model Evaluation

An AeroCom/AeroSat study: Intercomparison of Satellite AOD Datasets for Aerosol Model Evaluation

Multidecadal trend analysis of aerosol radiative properties at a global scale

Multi-model evaluation of aerosol optical properties in the AeroCom phase III Control experiment, using ground and space based columnar observations from AERONET, MODIS, AATSR and a merged satellite product as well as surface in-situ observations from GAW sites

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