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Search for Best Astronomical Observatory Sites in the MENA Region using Satellite Measurements
摘要： We perform a systematic search for astronomical observatory sites in the MENA (Middle-East and North Africa) region using space-based data for all the relevant factors, i.e. altitude (DEM), cloud fraction (CF), light pollution (NTL), precipitable water vapor (PWV), aerosol optical depth (AOD), relative humidity (RH), wind speed (WS), Richardson Number (RN), and diurnal temperature range (DTR). We look for the best locations overall even where altitudes are low (the threshold that we normally consider being 1,500 m) or where the combination of the afore-mentioned determining factors had previously excluded all locations in a given country. In this aim, we use the rich data that Earth-observing satellites provide, e.g. the Terra and Aqua multi-national NASA research satellites, with their MODIS (Moderate Resolution Imaging Spectroradiometer) and AIRS (Atmospheric Infrared Sounder) instruments, the Defense Meteorological Satellite Program’s Operational Linescan System (DMSP-OLS), and other products from climate diagnostics archives (e.g. MERRA). We present preliminary results on the best locations for the region.
关键词： diurnal temperature range,Richardson Number,MENA region,wind speed,precipitable water vapor,cloud fraction,relative humidity,aerosol optical depth,light pollution,astronomical observatory sites,satellite measurements
更新于2025-09-11 14:15:04
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Seasonal aerosol variations over a coastal city, Zhoushan, China from CALIPSO observations
摘要： This paper presents the observed seasonal aerosol variations over Zhoushan, an eastern coastal Chinese city. Data were obtained from the Cloud – Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite from the period of June 2007 to May 2017. We compared the columnar Aerosol Optical Depth (AOD) data from the CALIPSO and MODerate resolution Imaging Spectroradiometer (MODIS). Results showed good consistency, but the former was systematically lower than the latter. The temporal distribution of columnar AOD showed significant variations with the highest in spring and lowest in summer. Similarly, the seasonal scatter plots suggested that the highest correlation coefficient was 0.56 in winter and summer, followed by the autumn (0.53), and spring (0.40) seasons. In addition, the results revealed that the polluted dust and polluted continental aerosols (38.9% and 30.5%, respectively) were dominant aerosol subtypes observed in winter, whereas, the polluted dust (47.2%) aerosol subtype was found dominant in spring. The polluted continental aerosol subtype appeared dominant during the summer and autumn seasons, with the frequencies of about 56.0% and 47.4%, respectively. These findings can be reasonably explained using the air mass cluster analysis computed for the obtained backward trajectories derived from the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model. Furthermore, the aerosol vertical extinction coefficient measured at the wavelength of 532 nm was found to be highest near the surface (~0.2 km-1) in winter and autumn and decreased sharply as the altitude increased indicating that aerosols were present at an altitude <2 km. However, during spring, the values of extinction coefficient remained >0.15 km-1 at an altitude range of 0–3.5 km due to convection and strong vertical mixing lifting aerosols to slightly higher levels. Furthermore, during the spring, approximately 54% of the particulate depolarization ratio (PDR) values were ≤ 0.2, and the remaining 46% of the PDR were > 0.2, suggesting both spherical and irregular particles were present in the atmosphere.
关键词： MODIS,Aerosol Optical Depth,CALIPSO,Extinction Coefficient,East China,Aerosol subtype
更新于2025-09-10 09:29:36
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Accuracy Analysis of the Aerosol Backscatter Coefficient Profiles Derived from the CYY-2B Ceilometer
摘要： Ceilometers are originally designed for cloud base height monitoring. Since a few years, the number of ceilometers available worldwide is rapidly increasing, and these simple backscatter lidars are investigated to be used for aerosol research. This study presents an assessment of the potential of CYY-2B ceilometer for the quantitative retrieval of aerosol properties. The signal-to-noise ratio of the ceilometer is calculated, and the e?ective height of inversion is determined. It is shown that the e?ective height of the ceilometer for backscatter coe?cient pro?le inversion is 3-4 km at night and about 1.5–2 km during the day, which is lower than that of the micropulse lidar (MPL) system. The accuracy of the backscatter coe?cient pro?les derived from the CYY-2B ceilometer is analyzed by using the Vaisala CL51 ceilometer, MPL, forward scatter visibility instrument, and aerosol optical depth (AOD) dataset from aerosol robotic network (AERONET). Spectral conversions of the ceilometer’s and lidar’s data are performed using the ?Angstr¨om exponent estimated by AERONET measurements. A good agreement is found between two ceilometers and the MPL lidar in backscatter coe?cient pro?les inversion. The AODs agree well with the AERONET AODs during the observation period of small AODs. However, for the period of large AODs, the results are approximately 50%–60% of AERONET AODs. The limited range of extinction integration is the main cause of this problem.
关键词： ceilometer,AERONET,aerosol optical depth,aerosol backscatter coefficient,signal-to-noise ratio
更新于2025-09-10 09:29:36
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Improving Remote Sensing of Aerosol Optical Depth over Land by Polarimetric Measurements at 1640 nm: Airborne Test in North China
摘要： An improved aerosol retrieval algorithm based on the Advanced Multi-angular Polarized Radiometer (AMPR) is presented to illustrate the utility of additional 1640-nm observations for measuring aerosol optical depth (AOD) over land using look-up table approaches. Spectral neutrality of the polarized surface reflectance over visible to short-wavelength infrared bands is verified, and the 1640-nm measurements corrected for atmospheric effects are used to estimate the polarized surface reflectance at shorter wavelengths. The AMPR measurements over the Beijing-Tianjin-Hebei region in north China reveal that the polarized surface reflectance of 670, 865 and 1640 nm are highly correlated with correlation slopes close to one (0.985 and 1.03) when the scattering angle is less than 145°. The 1640-nm measurements are then employed to estimate polarized surface reflectance at shorter wavelengths for each single viewing direction, which are then used to improve the retrieval of AOD over land. The comparison between AMPR retrievals and ground-based Sun-sky radiometer measurements during three experimental flights illustrates that this approach retrieves AOD at 865 nm with uncertainties ranging from 0.01 to 0.06, while AOD varies from 0.05 to 0.17.
关键词： airborne Advanced Multi-angle Polarized Radiometer (AMPR),aerosol optical depth (AOD),polarized surface reflectance,1640 nm
更新于2025-09-10 09:29:36
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A Long-Term Historical Aerosol Optical Depth Data Record (1982-2011) Over China From AVHRR
摘要： A long-term historical aerosol optical depth (AOD) data (15–45° N; 75–135° E) with 0.1 spatial resolution has been produced from Advanced Very High Resolution Radiometer (AVHRR) Pathfinder Atmospheres—Extended level-2B data. The spatial distribution pattern shows that high AOD values are found in central and eastern China over the entire period with AODs larger in summer and spring than in autumn and winter. As the high-quality products from AERONET were absent for this period over mainland China, AOD data obtained using the broadband extinction method from solar radiation stations have been used to verify the quality of the AVHRR AOD data set over China. The intercomparison results show that the interannual variation of AOD has been well captured in the variation curve of the AOD monthly mean and the variation trend is also consistent over the whole period. The correlation coefficient of the monthly mean is mostly larger than 0.55, the agreement index is larger than 0.57, and the relative error is less than 21%. Both AVHRR and visibility data sets show high values in regions with rapid economic development. Using Moderate Resolution Imaging Spectroradiometer AOD data as references, it is found that AVHRR AOD from this paper has better accuracy in general than that from Deep Blue (DB) algorithm over China, especially over eastern and southern China, while DB provides more coverage especially over bright surface such as northwest China. This long-term historic AOD data set can be used together with other AOD data sets to study the climate and environmental changes, especially in the 1980s and 1990s.
关键词： Aerosol optical depth (AOD),Advanced Very High Resolution Radiometer (AVHRR),solar radiation,multiple regression method,Moderate Resolution Imaging Spectroradiometer (MODIS)
更新于2025-09-10 09:29:36
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Validation of Himawari-8 aerosol optical depth retrievals over China
摘要： High temporal resolution (every 10 min) aerosol observations are rarely provided by satellite sensors. The Advanced Himawari Imager (AHI) aboard Himawari-8 can provide aerosol optical depth (AOD) over China with this frequency. The sensor provides great opportunity to retrieve the particle matter near the ground and improve air quality modeling using the aerosol products. However, there is still lack of quality validation about AHI AOD. A comprehensive research was conducted to evaluate the performance of AHI aerosol products based on sixteen sun-photometers stations in AErosol RObotic NETwork (AERONET) and Sun–Sky Radiometer Observation Network (SONET) over China. The overall comparison of AHI AOD and ground AOD shows a high correlation (R2=0.67). However, there is only 55% of AHI AOD falling in the expected error envelops (±0.05±0.2*AOD ground). AOD bias between AHI AOD and ground AOD increases with the AOD magnitude. The accuracy of AHI AOD is also highly depend on seasons and surface land cover types. Best performance of AHI aerosol retrievals is shown in summer and for urban region. The diurnal variability validation shows that AHI AOD catch the diurnal AOD variations well, especially for summer. Large differences between AHI AOD and MODerate-resolution Imaging Spectrometer (MODIS) aerosol products are shown, especially for northwest China. The analysis indicates that the uncertainties of AHI aerosol retrievals are induced by large errors of aerosol models and surface reflectance estimation in the algorithm.
关键词： MODIS,validation,Aerosol optical depth,Himawari-8
更新于2025-09-10 09:29:36
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Evaluating VIIRS EPS Aerosol Optical Depth in China: An Intercomparison Against Ground-based Measurements and MODIS
摘要： The Visible Infrared Imaging Radiometer Suite (VIIRS) has been providing routine retrievals of aerosol properties since 2011. As a new generation advanced sensor, VIIRS has certain advantages in terms of spectral and accuracy and spatial resolution, especially with updated algorithm for the NOAA Enterprise Processing System (EPS) since July 2017. However, the VIIRS EPS aerosol products have not been extensively validated. In this study, we evaluate the VIIRS EPS AOD product over mainland China, which has been suffering from heavy aerosol pollution in the recent decade. By comparing collocated VIIRS and ground observations over 12 sites for the Aerosol Robotic Network (AERONET) and 5 sites from the Sun-sky radiometer Observation NETwork (SONET), we find that VIIRS AOD achieves overall reasonable agreement, with 50.61% falling within the expected accuracy interval and a correlation of 0.91 with ground observation. A positive bias of 0.13 is noticed with relatively larger mean bias found in the spring and summer. VIIRS AOD also has a high bias compared with MODIS. The bias is found to be slightly increasing with AOD level. The seasonal variability of VIIRS AOD are also mostly consistent with surface observation and MODIS. VIIRS aerosol model still needs improvement, especially for dust and urban aerosols. A Combined Principal Component Analysis (CPCA) to extract dominant spatial and temporal variability between VIIRS and MODIS data also shows very good agreement, an indication that VIIRS is capable of capturing the major aerosol variability over China.
关键词： MODIS,AERONET,SONET,Aerosol Optical Depth,VIIRS,China
更新于2025-09-10 09:29:36
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Assessment of Sun photometer Langley calibration at the high-elevation sites Mauna Loa and Iza?a
摘要： The aim of this paper is to analyze the suitability of the high-mountain stations Mauna Loa and Iza?a for Langley plot calibration of Sun photometers. Thus the aerosol optical depth (AOD) characteristics and seasonality, as well as the cloudiness, have been investigated in order to provide a robust estimation of the calibration uncertainty as well as the number of days that are suitable for Langley calibrations. The data used for the investigations belong to the AERONET and GAW-PFR networks, which maintain reference Sun photometers at these stations with long measurement records: 22 years at Mauna Loa and 15 years at Iza?a. In terms of clear-sky and stable aerosol conditions, Mauna Loa (3397 m a.s.l.) exhibits on average 377 Langley plots (243 morning and 134 afternoon) per year suitable for Langley plot calibration, whereas Iza?a (2373 m a.s.l.) shows 343 Langley plots (187 morning and 155 afternoon) per year. The background AOD (500 nm) values, on days that are favorable for Langley calibrations, are in the range 0.01–0.02 throughout the year, with well-defined seasonality that exhibits a spring maximum at both stations plus a slight summer increase at Iza?a. The statistical analysis of the long-term determination of extraterrestrial signals yields to a calibration uncertainty of ～ 0.25–0.5 %, this uncertainty being smaller in the visible and near-infrared wavelengths and larger in the ultraviolet wavelengths. This is due to atmospheric variability produced by changes in several factors, mainly the AOD. The uncertainty cannot be reduced based only on quality criteria of individual Langley plots and averaging over several days is shown to reduce the uncertainty to the needed levels for reference Sun photometers.
关键词： Sun photometers,aerosol optical depth,Langley calibration,Iza?a,Mauna Loa
更新于2025-09-10 09:29:36
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Monitoring and tracking the trans-Pacific transport of aerosols using multi-satellite aerosol optical depth composites
摘要： The primary goal of this study was to generate a near-real time (NRT) aerosol optical depth (AOD) product capable of providing a comprehensive understanding of the aerosol spatial distribution over the Pacific Ocean, in order to better monitor and track the trans-Pacific transport of aerosols. Therefore, we developed a NRT product that takes advantage of observations from both low-earth orbiting and geostationary satellites. In particular, we utilize AOD products from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Suomi National Polar-orbiting Partnership (NPP) Visible Infrared Imaging Radiometer Suite (VIIRS) satellites. Then, we combine these AOD products with our own retrieval algorithms developed for the NOAA Geostationary Operational Environmental Satellite (GOES-15) and Japan Meteorological Agency (JMA) Multi-functional Transport Satellite (MTSAT-2) to generate a NRT daily AOD composite product. We present examples of the daily AOD composite product for a case study of trans-Pacific transport of Asian pollution and dust aerosols in mid-March 2014. Overall, the new product successfully tracks this aerosol plume during its trans-Pacific transport to the west coast of North America as the frequent geostationary observations lead to a greater coverage of cloud-free AOD retrievals equatorward of about 35° N, while the polar-orbiting satellites provide a greater coverage of AOD poleward of 35° N. However, we note several areas across the domain of interest from Asia to North America where the GOES-15 and MTSAT-2 retrieval algorithms can introduce significant uncertainties into the new product.
关键词： trans-Pacific transport,MODIS,VIIRS,near-real time,aerosol optical depth,MTSAT-2,satellite observations,GOES-15
更新于2025-09-10 09:29:36
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Aerosol optical depth in the European Brewer Network
摘要： The high spatial and temporal variability of aerosols makes networks capable of measuring their properties in near real time of high scientific interest. In this work we present and discuss results of an aerosol optical depth algorithm to be used in the European Brewer Network, which provides data in near real time of more than 30 spectrophotometers located from Tamanrasset (Algeria) to Kangerlussuaq (Greenland). Using data from the Brewer Intercomparison Campaigns in the years 2013 and 2015, and the period in between, plus comparisons with Cimel sunphotometers and UVPFR instruments, we check the precision, stability, and uncertainty of the Brewer AOD in the ultraviolet range from 300 to 320 nm. Our results show a precision better than 0.01, an uncertainty of less than 0.05, and a stability similar to that of the ozone measurements for well-maintained instruments. We also discuss future improvements to our algorithm with respect to the input data, their processing, and the characterization of the Brewer instruments for the measurement of aerosols.
关键词： European Brewer Network,uncertainty,ultraviolet range,precision,aerosol optical depth,stability,Brewer spectrophotometer
更新于2025-09-09 09:28:46