Satellite Retrievals of Aerosol Optical Depth over a Subtropical Urban Area: The Role of Stratification and Surface Reflectance

Escribano, Jerónimo; Gallardo, Laura; Rondanelli, Roberto; Choi, Yun-Sang

doi:10.4209/aaqr.2013.03.0082

Cited by 17 publications

(13 citation statements)

References 57 publications

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“…Several other research attempts have been made to change the surface scheme in the MDT for particular urban regions and produce better AOD retrievals for those specific cities (de Almeida Castanho et al,2007Li et al, 2005;Wong et al, 2011;Zha et al, 2011;Li et al, 2012;Escribano et al, 2014;Jäkel et al, 2015). Instead of a retrieval focused on only one city, we seek a surface parameterization that is valid for cities across the globe.…”

Section: Introductionmentioning

confidence: 99%

A surface reflectance scheme for retrieving aerosol optical depth over urban surfaces in MODIS Dark Target retrieval algorithm

et al. 2016

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Abstract. The MODerate resolution Imaging Spectroradiometer (MODIS) instruments, aboard the two Earth Observing System (EOS) satellites Terra and Aqua, provide aerosol information with nearly daily global coverage at moderate spatial resolution (10 and 3 km). Almost 15 years of aerosol data records are now available from MODIS that can be used for various climate and air-quality applications. However, the application of MODIS aerosol products for airquality concerns is limited by a reduction in retrieval accuracy over urban surfaces. This is largely because the urban surface reflectance behaves differently than that assumed for natural surfaces. In this study, we address the inaccuracies produced by the MODIS Dark Target (MDT) algorithm aerosol optical depth (AOD) retrievals over urban areas and suggest improvements by modifying the surface reflectance scheme in the algorithm. By integrating MODIS Land Surface Reflectance and Land Cover Type information into the aerosol surface parameterization scheme for urban areas, much of the issues associated with the standard algorithm have been mitigated for our test region, the continental United States (CONUS). The new surface scheme takes into account the change in underlying surface type and is only applied for MODIS pixels with urban percentage (UP) larger than 20 %. Over the urban areas where the new scheme has been applied (UP > 20 %), the number of AOD retrievals falling within expected error (EE %) has increased by 20 %, and the strong positive bias against ground-based sun photometry has been eliminated. However, we note that the new retrieval introduces a small negative bias for AOD values less than 0.1 due to the ultra-sensitivity of the AOD retrieval to the surface parameterization under low atmospheric aerosol loadings. Global application of the new urban surface parameterization appears promising, but further research and analysis are required before global implementation.

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Section: Introductionmentioning

confidence: 99%

A surface reflectance scheme for retrieving aerosol optical depth over urban surfaces in MODIS Dark Target retrieval algorithm

et al. 2016

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“…In the near-calm regime, these authors point to the importance of submesoscale motions with length scales less than 2 km (Mahrt, 2014) which in the current site may be associated to the meandering described above. These submesoscale motions may also be related to complex aerosol layers that have been documented to appear in the Santiago boundary layer during the evening transition in the cold season (Muñoz and Alcafuz, 2012;Escribano et al, 2014). The exact nature of this phenomenon, however, has not been fully elucidated yet.…”

Section: Discussionmentioning

confidence: 99%

Surface Indices of Wind, Stability, and Turbulence at a Highly Polluted Urban Site in Santiago, Chile, and their Relationship with Nocturnal Particulate Matter Concentrations

Muñoz

Corral

2017

Aerosol Air Qual. Res.

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The local meteorological factors of the cold season nocturnal particulate matter (PM) air quality problem in the western urban area of Santiago City are documented and analyzed by means of three years of multi-level temperature and turbulence measurements performed in-situ on a 30 m meteorological tower. For the 20-23 LT period in which the highest PM concentrations commonly occur, high prevalence of low wind and low vertical turbulence conditions are found. With wind speeds less than 1 m s -1 , the frequency of calms and the intensity of meandering increase, although the highest PM concentrations are associated more to meandering than to purely calm conditions. In terms of the stability of the near surface layer, while there is a general association between high PM concentrations and high stability, the most extreme PM event in the period occurred with an intermediate value of stability probably affected by the presence of mid-tropospheric clouds. Using a nocturnal vertical height scale based on the stability and the surface turbulent heat flux to compute a nocturnal ventilation factor (VF), a marked inverse relationship between VF and PM concentrations is documented. The prevalence of low winds and high meandering in this sector of Santiago is hypothesized to be related to the local topography that precludes the development of the weak but persistent drainage surface winds observed at other sites of the city. Further investigation of this very stable atmospheric boundary layer is deemed necessary for improving the numerical models used in forecasting and managing the air pollution problem of Santiago.

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“…For future investigations airborne imaging spectrometer measurements are suggested to characterize the slope parameters for urban areas also for different viewing geometries than the nadir observation. This will improve the corrections of the operational retrievals due to effect of the bidirectional reflectance distribution function (BRDF), since the anisotropy reflection of the surface is better described by the BRDF than assuming a Lambertian surface (Escribano et al, 2014).…”

Section: Discussionmentioning

confidence: 99%

“…While the resulting dark-target AOD retrieval technique shows good performance over much of the globe, the algorithm developed for dark vegetation continues to show less accurate results over surfaces with high reflectance such as arid regions (Drury et al, 2008) and urban surfaces (de Almeida Castanho et al, 2007;Oo et al, 2010;Wong et al, 2011;Zha et al, 2011;Li et al, 2012;Escribano et al, 2014). For urban surfaces in particular, de Almeida Castanho et al (2007) and Oo et al (2010) reported a positive bias of retrieved AOD over Mexico City and New York City compared to ground-based sun photometer measurements.…”

Section: Introductionmentioning

confidence: 99%

Adaption of the MODIS aerosol retrieval algorithm using airborne spectral surface reflectance measurements over urban areas: a case study

Jäkel

Mey

Levy³

et al. 2015

Atmos. Meas. Tech.

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Abstract. MODIS (MOderate-resolution Imaging Spectroradiometer) retrievals of aerosol optical depth (AOD) are biased over urban areas, primarily because the reflectance characteristics of urban surfaces are different than that assumed by the retrieval algorithm. Specifically, the operational "darktarget" retrieval is tuned towards vegetated (dark) surfaces and assumes a spectral relationship to estimate the surface reflectance in blue and red wavelengths. From airborne measurements of surface reflectance over the city of Zhongshan, China, were collected that could replace the assumptions within the MODIS retrieval algorithm. The subsequent impact was tested upon two versions of the operational algorithm, Collections 5 and 6 (C5 and C6). AOD retrieval results of the operational and modified algorithms were compared for a specific case study over Zhongshan to show minor differences between them all. However, the Zhongshanbased spectral surface relationship was applied to a much larger urban sample, specifically to the MODIS data taken over Beijing between 2010 and 2014. These results were compared directly to ground-based AERONET (AErosol RObotic NETwork) measurements of AOD. A significant reduction of the differences between the AOD retrieved by the modified algorithms and AERONET was found, whereby the mean difference decreased from 0.27 ± 0.14 for the operational C5 and 0.19±0.12 for the operational C6 to 0.10±0.15 and −0.02 ± 0.17 by using the modified C5 and C6 retrievals. Since the modified algorithms assume a higher contribution by the surface to the total measured reflectance from MODIS, consequently the overestimation of AOD by the operational methods is reduced. Furthermore, the sensitivity of the MODIS AOD retrieval with respect to different surface types was investigated. Radiative transfer simulations were performed to model reflectances at top of atmosphere for predefined aerosol properties. The reflectance data were used as input for the retrieval methods. It was shown that the operational MODIS AOD retrieval over land reproduces the AOD reference input of 0.85 for dark surface types (retrieved AOD = 0.87 (C5)). An overestimation of AOD = 0.99 is found for urban surfaces, whereas the modified C5 algorithm shows a good performance with a retrieved value of AOD = 0.86.

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Satellite Retrievals of Aerosol Optical Depth over a Subtropical Urban Area: The Role of Stratification and Surface Reflectance

Cited by 17 publications

References 57 publications

A surface reflectance scheme for retrieving aerosol optical depth over urban surfaces in MODIS Dark Target retrieval algorithm

A surface reflectance scheme for retrieving aerosol optical depth over urban surfaces in MODIS Dark Target retrieval algorithm

Surface Indices of Wind, Stability, and Turbulence at a Highly Polluted Urban Site in Santiago, Chile, and their Relationship with Nocturnal Particulate Matter Concentrations

Adaption of the MODIS aerosol retrieval algorithm using airborne spectral surface reflectance measurements over urban areas: a case study

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