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Investigating the Aerosol Optical Depth and Angstrom Exponent and Their Relationships with Meteorological Parameters Over Lahore in Pakistan
摘要： In the present work, AERONET (AErosol RObotic NETwork) data of 2006–2014 have been used to analyze the variations in aerosol optical depth (AOD) at 500 nm and Angstrom exponent (440/870) (AE). In order to have an in-depth knowledge of aerosol variability, we have analyzed the association of aerosol properties with the meteorological parameters such as temperature, mean sea level pressure, rainfall, dew point, and dust storm frequency. Long-term observations of MODIS-AOD are also validated with AERONET-AOD over Lahore. The peak monthly mean value of AOD is found in July (1.00 ± 0.34) with the corresponding AE value of 0.85 ± 0.29 pointing toward the fact that desert/soil dust aerosols dominated the atmosphere of Lahore. The lowest value of AOD is found in February (0.47 ± 0.26) with the corresponding AE value of 1.22 ± 0.29 representing the presence of urban/industrial aerosols in the atmosphere over Lahore. The monthly mean AE value is found to be maximum in January (1.36 ± 0.15), whereas lowest value of AE is found in June (0.55 ± 0.25). AOD shows positive correlations with temperature, dew point, relative humidity, visibility, rain and dust storm frequency, and negative with mean sea level pressure and wind speed. AE exhibits positive correlations with relative humidity and mean sea level pressure, while with temperature, dew point, visibility, rain and dust storm frequency, it shows negative correlations.
关键词： Aerosol optical depth,Angstrom exponent,Meteorological parameters,Lahore
更新于2025-09-23 15:23:52
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Estimation of spatiotemporal PM1.0 distributions in China by combining PM2.5 observations with satellite aerosol optical depth
摘要： Particulates smaller than 1.0 μm (PM1.0) have strong associations with public health and environment, and considerable exposure data should be obtained to understand the actual environmental burden. This study presented a PM1.0 estimation strategy based on the generalised regression neural network model. The proposed strategy combined ground-based observations of PM2.5 and satellite-derived aerosol optical depth (AOD) to estimate PM1.0 concentrations in China from July 2015 to June 2017. Results indicated that the PM1.0 estimates agreed well with the ground-based measurements with an R2 of 0.74, root mean square error of 19.0 μg/m3 and mean absolute error of 11.4 μg/m3 as calculated with the tenfold cross-validation method. The diurnal estimation performance displayed remarkable single-peak variation with the highest R2 of 0.80 at noon, and the seasonal estimation performance showed that the proposed method could effectively capture high-pollution events of PM1.0 in winter. Spatially, the most polluted areas were clustered in the North China Plain, where the average estimates presented a bimodal distribution during daytime. In addition, the quality of satellite-derived AOD, the robustness of the interpolation algorithm and the proportion of PM1.0 in PM2.5 were confirmed to affect the estimation accuracy of the proposed model.
关键词： Himawari-8,PM1.0,Neural network,Air pollution,Aerosol optical depth
更新于2025-09-23 15:23:52
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Climatological analysis of the optical properties of aerosols and their direct radiative forcing in the Middle East
摘要： In addition to climate perturbations, various problems such as air pollution, reduction in the visibility and human health hazards were caused by atmospheric aerosols in the Middle East specifically in the last two decades. With the help of the Aerosol Robotic NETwork (AERONET), the measurement of the aerosol optical and radiative properties were carried out over seven sites in the Middle East during 2013. The analysis of the optical properties of aerosols like Single Scattering Albedo (SSA), Angstrom Exponent (AE), Aerosol Optical Depth (AOD), and Asymmetry parameter (ASY) were carried out during the study period. During spring and summer, high values of AOD and low values of AE were found in all sites except CUT-TEPAK (Limassol, Cyprus), which specified the existence of coarse mode particles and dust storms in these seasons. The AE maximum values were found in the summer and fall over CUT-TEPAK and IMS-METU-ERDEMLI(Erdemli, Turkey), whereas in other sites IASBS (Zanjan, Iran), KAUST Campus (Thuwal, Saudi Arabia), Masdar Institute (Masdar, United Arab Emirates), Mezaira (Mezaira, United Arab Emirates) and Solar Village (Riyadh, Saudi Arabia) the peak values of AE occurred in the fall and winter. The maximum values of SSA and ASY were observed in the spring and summer over all sites except over CUT-TEPAK and IMS-METU-ERDEMLI. The Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model has been used for the calculations of the Aerosol Radiative Forcing (ARF) over the selected sites. We obtained negative value of ARF at the surface, which suggesting its cooling effects because of the loss of radiation back to space due to aerosols. The averaged ARF values at the SuRFace (SRF) of the earth were -43.8 Wm-2, -31 Wm-2, -56.8 Wm-2, -61.7 Wm-2, -52.5 Wm-2, -54.9 Wm-2, and -72.2 Wm-2, over CUT-TEPAK, IASABS, IMS-METU-ERDEMLI, KAUST Campus, Masdar Institute, Mezaira and Solar Village, respectively. While the positive value of atmospheric ARF showed heating of the atmosphere.
关键词： Middle East.,Aerosol Optical Depth,SBDART,Aerosol Radiative Forcing,AERONET
更新于2025-09-23 15:23:52
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Inversion of Aerosol Optical Depth Based on the CCD and IRS Sensors on the HJ-1 Satellites
摘要： To perform a high-resolution aerosol optical depth (AOD) inversion from the HJ-1 satellites, a dark pixel algorithm utilizing the HJ-1 satellite data was developed based on the Moderate-Resolution Imaging Spectroradiometer (MODIS) algorithm. By analyzing the relationship between the apparent reflectance from the 1.65 μm and 2.1 μm channels of MODIS, a method for estimating albedo using the 1.65 μm channel data of the HJ-1 satellites was established, and a high-resolution AOD inversion in the Chengdu region based on the HJ-1 satellite was completed. A comparison of the inversion results with CE318 measured data produced a correlation of 0.957, respectively, with an absolute error of 0.106. An analysis of the AOD inversion results from different aerosol models showed that the rural aerosol model was suitable as a general model for establishing an aerosol inversion look-up table for the Chengdu region.
关键词： dark pixel,albedo,aerosol optical depth,HJ-1 satellite
更新于2025-09-23 15:22:29
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CALIPSO lidar level?3 aerosol profile product: version?3 algorithm design
摘要： The CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) level 3 aerosol profile product reports globally gridded, quality-screened, monthly mean aerosol extinction profiles retrieved by CALIOP (the Cloud-Aerosol Lidar with Orthogonal Polarization). This paper describes the quality screening and averaging methods used to generate the version 3 product. The fundamental input data are CALIOP level 2 aerosol extinction profiles and layer classification information (aerosol, cloud, and clear-air). Prior to aggregation, the extinction profiles are quality-screened by a series of filters to reduce the impact of layer detection errors, layer classification errors, extinction retrieval errors, and biases due to an intermittent signal anomaly at the surface. The relative influence of these filters are compared in terms of sample rejection frequency, mean extinction, and mean aerosol optical depth (AOD). The 'extinction QC flag' filter is the most influential in preventing high-biases in level 3 mean extinction, while the 'misclassified cirrus fringe' filter is most aggressive at rejecting cirrus misclassified as aerosol. The impact of quality screening on monthly mean aerosol extinction is investigated globally and regionally. After applying quality filters, the level 3 algorithm calculates monthly mean AOD by vertically integrating the monthly mean quality-screened aerosol extinction profile. Calculating monthly mean AOD by integrating the monthly mean extinction profile prevents a low bias that would result from alternately integrating the set of extinction profiles first and then averaging the resultant AOD values together. Ultimately, the quality filters reduce level 3 mean AOD by -24 and -31 % for global ocean and global land, respectively, indicating the importance of quality screening.
关键词： version 3,aerosol,lidar,optical depth,CALIPSO,quality screening,extinction
更新于2025-09-23 15:22:29
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Extinction and optical depth retrievals for CALIPSO's Version 4 data release
摘要： The Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) on board the Cloud–Aerosol Lidar Infrared Pathfinder Satellite Observations (CALIPSO) satellite has been making near-global height-resolved measurements of cloud and aerosol layers since mid-June 2006. Version 4.10 (V4) of the CALIOP data products, released in November 2016, introduces extensive upgrades to the algorithms used to retrieve the spatial and optical properties of these layers, and thus there are both obvious and subtle differences between V4 and previous data releases. This paper describes the improvements made to the extinction retrieval algorithms and illustrates the impacts of these changes on the extinction and optical depth estimates reported in the CALIPSO lidar level 2 data products. The lidar ratios for both aerosols and ice clouds are generally higher than in previous data releases, resulting in generally higher extinction coefficients and optical depths in V4. A newly implemented algorithm for retrieving extinction coefficients in opaque layers is described and its impact examined. Precise lidar ratio estimates are also retrieved in these opaque layers. For semi-transparent cirrus clouds, comparisons between CALIOP V4 optical depths and the optical depths reported by MODIS collection 6 show substantial improvements relative to earlier comparisons between CALIOP version 3 and MODIS collection 5.
关键词： retrieval algorithms,clouds,CALIOP,lidar,optical depth,CALIPSO,aerosols,extinction,version 4
更新于2025-09-23 15:22:29
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A 10-year record of aerosol optical properties and radiative forcing over three environmentally distinct AERONET sites in Kenya, East Africa
摘要： In the framework of Aerosol Robotic Network (AERONET), the aerosol optical, microphysical and radiative properties were investigated over three sites (CRPSM_Malindi, Nairobi, and ICIPE_Mbita) in Kenya, East Africa (EA) during 2006-2015. The annual mean (±σ) aerosol optical depth at 440 nm (AOD440) was found high at Mbita (0.27±0.09) followed by Malindi (0.26±0.07), and low at Nairobi (0.19±0.04). Whereas, the seasonal mean AOD440 noticed high (low) values during the local dry (wet) seasons. The aerosol optical properties: AOD, single scattering albedo (SSA), asymmetry parameter (ASY), and complex aerosol refractive index (RI) exhibited significant temporal and spectral heterogeneities illustrating the complexity of aerosol types with an abundance of fine-mode aerosols during the local dry (JJA) season. Characterization of major aerosol types revealed the dominance of mixed-type followed by biomass burning aerosols. The aerosol volume size distribution revealed that the coarse- over fine-mode aerosols showed a significant contribution to the total volume particle concentration, especially at high (> 0.3) AOD440. Further, the aerosol columnar number size distribution (CSD) retrieved from the King’s inversion of spectral AOD exhibited a power law distribution affirming multiplicity of aerosol sources. The direct aerosol radiative forcing values simulated in the shortwave region using the Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model showed good correlation (r=>0.85) with the AERONET derived ones at the top-of-atmosphere (TOA), bottom-of-atmosphere (BOA) and within the atmosphere (ATM). The annual mean (±σ) TOA, BOA, and ATM forcing values were found in the range from -8.10±3.75 to -13.23±4.87, -34.54±4.86 to -46.11±10.27, and 26.63±6.43 to 36.24±7.26 Wm-2, respectively, with an atmospheric heating rate (AHR) of 0.74±0.12–1.02±0.20 K day-1. The SBDART-derived DARF exhibited significant temporal heterogeneity with high (low) during the local dry (wet) seasons. Results derived from the present study forms a basis for regional climate change studies and could increase the accuracy of climate models over this unexplored region of Africa.
关键词： Aerosol radiative forcing,Aerosol optical depth,Size distribution,East Africa,AERONET,Single scattering albedo
更新于2025-09-23 15:22:29
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Evaluation of the Vegetation Optical Depth Index on Monitoring Fire Risk in the Mediterranean Region
摘要： Monitoring live fuel moisture content (LFMC) in Mediterranean area is of great importance for fire risk assessment. LFMC has extensively been estimated based on optical remote sensing data. But the latter can be affected by atmospheric effects. As a complementary data source, microwave data can be used as they are relatively insensitive to atmospheric effects. Yet further evaluations are needed to investigate the potential of microwave observations to monitor LFMC. In this study, we assess the capability of long-term microwave vegetation optical depth (VOD) to capture the temporal variability of in situ measured LFMC in 14 Mediterranean shrub species in southern France during 1996-2014. Microwave-derived VOD at X band (VODX-15) displayed a high sensitivity to LFMC with correlation coefficients of 0.56. Similar evaluations were made using four optical indices computed from the Moderate Resolution Imaging Spectrometer (MODIS) data including normalized difference vegetation index (NDVI), soil adjusted vegetation index (SAVI), visible atmospheric resistant index (VARI), normalized difference water index (NDWI). The comparisons showed that VARI performs better than VODX-15 and other optical indices with highest median of correlation coefficients of 0.65. Overall, this study shows that passive microwave-derived VOD, are efficient proxies for LFMC of Mediterranean shrub species and could be used along with optical indices to evaluate fire risks in the Mediterranean region.
关键词： vegetation optical depth,fire risk,microwave remote sensing,live fuel moisture content
更新于2025-09-23 15:21:21
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Estimating Gravimetric Moisture of Vegetation Using an Attenuation-Based Multi-Sensor Approach
摘要： Estimating parameters for global climate models via combined active and passive microwave remote sensing data has been a subject of intensive research in recent years. A variety of retrieval algorithms has been proposed for the estimation of soil moisture, vegetation optical depth and other parameters. A novel attenuation-based retrieval approach is proposed here to globally estimate the gravimetric moisture of vegetation (????) and retrieve information about the amount of water [kg] per amount of wet vegetation [kg]. The parameter ???? is particularly interesting for agro-ecosystems, to assess the status of growing vegetation. The key feature of the proposed approach is that it relies on multi-sensor data from three sensor types (microwave radar, microwave radiometer, and lidar) to solve the physics equations and obtain ????-estimates. The comparability of these estimates to literature values as well as to results of a globally applied, retrieval approach of Grant [4], reveal the potential of the developed method.
关键词： lidar,radiometer,Multi-sensor,SMAP,vegetation water content,vegetation optical depth,radar
更新于2025-09-23 15:21:21
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Integrated Aerosol Extinction Profiles from Ceilometer and Sunphotometer Combination against Sunphotometer Measurements at Various Heights
摘要： The aerosol extinction profiles at Granada (Spain) have been obtained combining ceilometer and sun/sky measurements in the GRASP code. In order to see the goodness of these retrieved profiles, three photometers at different altitudes have been used. The aerosol optical depth (AOD) at different height layers have been calculated with these photometers and it has been compared against the integrated retrieved extinction at the same layers. The obtained AOD (from GRASP and from photometers at different altitudes) correlates well, showing the most of r2 values above 0.6. The differences between both AOD values indicates that the retrieved aerosol extinction profiles are within the uncertainty of the photometers but this method overestimates the extinction at low levels and underestimates at high levels.
关键词： Validation,GRASP,Aerosol Optical Depth,Aerosol Extinction,Ceilometer
更新于2025-09-23 15:21:21