This study evaluates the effects of precipitation scavenging on aerosol loading and its subsequent impact on air quality in Shanghai, one of the world’s largest and fastest-growing megacities. The study employs advanced statistical techniques and machine learning models to assess which variables influence pollution levels, providing valuable information on periodic patterns and unexpected fluctuations in air quality. The use of Random Forest (RF) models demonstrated robust capabilities in predicting pollution trends over longer time scales, underscoring the importance of feature interpretability in environmental forecasting models. In addition, the study underscores the need to integrate data-driven approaches, such as machine learning, into environmental monitoring systems to improve predictive accuracy and policy effectiveness. The findings support the argument that the use of advanced computational models and large datasets can lead to more targeted interventions and better decision-making frameworks for urban planners and policy makers.
We propose a two-step spatial enhancement procedure for the two 100m thermal infra red (TIR) bands of LandSat 8/9, captured by its TIR spectrometer (TIRS), approached as a problem of fusion of heterogeneous data, or multimodal fusion. The fusion algorithm is guided by the statistical similarity between the TIR and visible and near infra red (VNIR) and short wave infra red (SWIR) bands provided at 30m by the operational land imager (OLI). In the first step, hyper-sharpening is applied from 100m scale to 30m scale (3:10 scale ratio): the two TIRS bands are spatially enhanced by means of two linear combination of the 30m VNIR+SWIR bands, devised to maximize the correlation with each thermal band at its native 100m scale. In the second step, the thermal bands, previously hyper-sharpened at 30m, are pansharpened through the 15m Panchromatic (PAN) band of OLI. The proposed approach is compared to plain 100m-to-15m pansharpening carried out uniquely by means of the Pan image of OLI. Both visual evaluations and statistical indexes measuring the radiometric and spatial consistency at the three scales are provided and discussed. The superiority of the two-step approach is undoubtedly highlighted.
Guest editors Kaixu Bai, Simone Lolli, and Yuanjian Yang introduce the Special Section on Integrating Remote Sensing, Machine Learning, and Data Science for Air Quality Management.
In this paper, we wish to explain the contradiction of quality assessments of pansharpening carried out at full and reduced spatial scales. It seems that at full scale, methods based on Component Substitution (CS) are quantitatively poorer than the other methods, but this depends on the intrinsic space varying misregistration between the two datasets. At reduced scale, the local shifts are divided by the MS-to-Pan scale ratio and thus they tend to vanish. The problem of full-scale quality indexes is that they were originally validated on aerial Multispectral (MS) data, with synthetic panchromatic (Pan) and thus total absence of misregistration. In the presence of local misregistration due to inaccurate information of the height of the imaged surface, CS methods locally align the lowpass MS components towards the sharpening Pan, thereby preserving the geometry of the scene; all the other methods produce fading contours because of shifts. The favorable property of CS, however, impacts against the (spectral) consistency property of Wald’s protocol, developed when the misalignments between MS and Pan was a small fraction of the pixel size, and hence negligible. In this perspective, methods that do not shift the original MS information are better, even though the visual quality of fading contours is worse. After exposing and explaining the contradiction between full- and reduced-scale assessments, we perform an in-depth analysis of the spectral and spatial consistency indexes of three widespread full-scale protocols: QNR, KQNR and HQNR. We investigate the robustness to shifts of all consistency indexes and propose to couple the spectral index and the spatial index that are least sensitive to shifts. In this way, the ranking of methods of reduced-scale assessments is preserved in full-scale assessments.
Aerosols are significant atmospheric constituents that modulate radiation and cloud processes. We evaluated 17-year aerosol profile trends in Barcelona, Spain, from lidar measurements. In summer aerosol reaches 5 km, while in the other seasons it exhibits clear exponential decay. Sahara dust transport affects all seasons, with winter layers above and others penetrating the boundary layer. This study informs the formation of haze and urban preservation strategies in the Mediterranean. The analysis puts in evidence that the averaged net radiative effect is of cooling at both surface level and top of the atmosphere.
In this paper, we propose a processing chain jointly employing Sentinel-1 and Sentinel-2 data aimed at monitoring changes in the status of the vegetation cover by integrating the four visible and near infrared (VNIR) bands with the three red-edge (RE) bands of Sentinel-2, approximately spanning the gap between Red and NIR bands (700 nm – 800 nm) with bandwidths of 15/20 nm and 20 m pixel spacing. The RE bands will be sharpened to 10 m and the resulting 7-bands, 10 m fusion product will be integrated with polarimetric features calculated from the Interferometric Wide (IW) Ground Range Detected (GRD) product of Sentinel-1, available at 10 m pixel spacing. Key point of the fusion of optical bands is the correction of atmospheric path radiance before fusion is accomplished through modulation of the interpolated band by a sharpening term achieved through the hyper-sharpening paradigm. Whenever surface reflectance data are available, haze estimation and correction can be skipped. Hyper-sharpening of Sentinel-2 multispectral (MS) bands and modulation-based integration of Sentinel-1 polarimetric synthetic aperture radar (SAR) features are applied on a multitemporal dataset acquired before and after a recent fire event.
Natural and anthropogenic aerosol atmospheric emissions play a fundamental role in directly modulating the incoming solar radiation and affecting the air quality. Likewise, aerosols indirectly impact cloud lifetime, atmospheric column thermodynamics and precipitation patterns. For this reason, it is crucial to assess aerosol spatial and temporal variability to reduce the associated uncertainty of global climate models in correctly forecasting future scenarios and it will enable application of mitigation strategies. In this manuscript, for the first time, we developed a simple aerosol optical depth (AOD) retrieval algorithm in the blue wavelength range that does not use either look-up-tables or radiative transfer models.
The water cycle strongly influences life on Earth. In particular, the precipitation modifies the atmospheric column thermodynamics through the process of evaporation and serves as a proxy for latent heat modulation. For this reason, a correct precipitation parameterization (especially low-intensity precipitation) at global scale, bedsides improving our understanding of the hydrological cycle, it is crucial to reduce the associated uncertainty of the global climate models to correctly forecast future scenarios, i.e. to apply fast mitigation strategies. In this study we developed an algorithm to automatically detect precipitation from lidar measurements obtained by the National and Aeronautics Space Administration (NASA) Micropulse lidar network (MPLNET) permanent observational site in Goddard. The algorithm, once full operational, will deliver in Near Real Time (latency 1.5h) a new rain mask product that will be publicly available on MPLNET website as part of the new Version 3 Level 1.5 data. The methodology, based on an image processing technique, can detect only light precipitation events (defined by intensity and duration) as the morphological filters used through the detection process are applied on the lidar volume depolarization ratio range corrected composite images, i.e. heavy rain events are unusable as the lidar signal is completely extinguished after few meters in the precipitation or no signal detected because of the water accumulated on the receiver optics. Results from the algorithm, besides filling a gap in precipitation and virga detection by radars, are of particular interest for the scientific community because will help to better understand long-term aerosol-cloud interactions and aerosol atmospheric removal (scavenging effect) by rain as multi-year database being available for several MPLNET permanent observational sites across the globe. Moreover, we developed the automatic algorithm at Universitat Politecnica de Catalunya (UPC) Barcelona, the unique permanent observation station member of MPLNET and the European Aerosol Lidar Network (EARLINET) In the future the algorithm can be then easily applied to any other lidar and/or ceilometer network infrastructure in the frame of World Meteorological Organization (WMO) Global Aerosol Watch (GAW) aerosol lidar observation network (GALION)
In this paper, we present a modified version of a popular component-substitution (CS) pansharpening method, namely the hyperspherical color space (HCS) fusion technique. Unlike other improvements of HCS, the proposed method is insensitive to the format of the data, either calibrated spectral radiance values or uncalibrated digital numbers (DNs), thanks to the use of a multivariate linear regression between the squares of the interpolated MS bands and the squared lowpass filtered Pan, in order to find out the intensity component peculiar of CS methods. The regression of squared MS, instead of the Euclidean radius used by HCS, makes the color space hyper-ellipsoidal instead of hyper-spherical and the intensity component more similar to the lowpass-filtered Pan, such that the extracted detail, namely Pan minus intensity, is more accurate. Furthermore, before the regression is calculated, the interpolated MS bands are diminished by their minima, in order to build a multiplicative injection model with approximately de-hazed components, thereby benefiting from the haze correction, as for all methods exploiting the multiplicative model. Experiments on true GeoEye-1 images show consistent advantages over the baseline HCS and its improvements achieved over time, and a performance comparable with some of the most advanced methods.
Natural and anthropogenic aerosol emissions play a fundamental role both in directly modulating the incoming solar radiation and affecting air quality in the planetary boundary layer. Likewise, their indirect effects impact cloud lifetime, atmospheric column thermodynamics and precipitation patterns. For this reason, it is of crucial importance to assess aerosol spatial and temporal variability to reduce the uncertainty in forecasting future scenarios by the climatological models. In this study we developed an image based robust methodology that permits to retrieve the atmospheric path radiance and then the Aerosol Optical Depth (AOD) using satellite high-resolution spatial images paired with the Fu-Liou-Gu radiative transfer model. We applied our methodology to study aerosol variability in the PO valley (Northern Italy), one of the most polluted region in Europe.
Aerosol, together with cirrus clouds, play a fundamental role in the earth-atmosphere system radiation budget, especially at tropical latitudes, where the Earth surface coverage by cirrus cloud can easily reach 70%. In this study we evaluate the combined aerosol and cirrus cloud net radiative effects in a wild and barren region like South East Asia. This part of the world is extremely vulnerable to climate change and it is source of important anthropogenic and natural aerosol emissions. The analysis has been carried out by computing cirrus cloud and aerosol net radiative effects through the Fu-Liou-Gu atmospheric radiative transfer model, adequately adapted to input lidar measurements, at surface and top-of-the atmosphere. The aerosol radiative effects were computed respectively using the retrieved lidar extinction from Cloud-Aerosol Lidar with Orthogonal Polarization in 2011 and 2012 and the lidar on-board of Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations for the South East Asia Region (27N-12S, 77E-132E) with 5° x 5° spatial resolution. To assess the cirrus cloud radiative effect, we used the ground-based Micro Pulse Lidar Network measurements at Singapore permanent observational site. Results put in evidence that strong aerosol emission areas are related on average to a net surface cooling. On the contrary, cirrus cloud radiative effect shows a net daytime positive warming of the system earth-atmosphere. This effect is weak over the ocean where the albedo is lower and never counter-balances the net cooling produced by aerosols. The net cooling is stronger in 2011, with an associated reduction in precipitations by the four of the five rain-gauges stations deployed in three regions as Sumatra, Kalimantan and Java with respect to 2012. We can speculate that aerosol emissions may be associated with lower rainfall, however some very important phenomena as El Nino Southern Oscillation , Madden-Julian Oscillation, Monsoon and Indian Dipole are not considered in the analysis.
In this letter, we show that pansharpening of visible/near-infrared (VNIR) bands takes advantage from a correction of the atmospheric path-radiance term during the fusion process. This holds whenever the fusion mechanism emulates the radiative transfer model ruling the acquisition of the Earth’s surface from space, that is, for methods exploiting a contrastbased injection model of spatial details extracted from the panchromatic (Pan) image into the interpolated multispectral (MS) bands. Such methods are high-pass modulation (HPM), Brovey transform (BT), synthetic variable ratio (SVR), UNB pansharp, smoothing filter-based intensity modulation (SFIM) and spectral distortion minimization (SDM). The path radiance should be estimated and subtracted from each band before the product by Pan is accomplished and added back after. Both empirical and model-based estimation techniques of MS path radiances are compared within the framework of optimized SVR and HPM algorithms. Simulations carried out on QuickBird and IKONOS data highlight that the atmospheric correction of MS before fusion is always beneficial, especially on vegetated areas and in terms of spectral quality.
The atmosphere over Penang Island is monitored for one year using a ground based Lidar. The Lidar signals are processed to obtain the AOD, extinction coefficients and the PBL heights to provide an overview of the atmospheric conditions in Penang. The data are averaged daily and plotted for the year of 2014. The AOD and extinction coefficients display seasonal trends that increase during the monsoon seasons (Southwest monsoon and Northeast monsoon) and decrease during the inter-monsoon seasons. During the monsoon seasons, a mixture of clear and hazy atmospheric conditions is found due to the presence of rain which removes the particulates or aerosols from the atmosphere. If no rain occurs, aerosols transported over Penang will stay in the atmosphere and be removed after a certain period. The average AOD is 0.4034 for year 2014 with a maximum of 1.0787 on a hazy day and a minimum of 0.0354 on a clear day. The extinction coefficient range is quite wide especially during the monsoonal months owing to the intervention of aerosol layers in the atmosphere of Penang. A clear day will have a smaller range of extinction coefficients. The planetary boundary layer has an average height of 0.878 km. Thicker PBLs are found after monsoon seasons as the aerosols has sunk to the earth surface from higher altitudes. The PBL has an opposing trend to the AOD and extinction coefficients. The atmosphere over Penang Island consists of a mixture of marine particles and fine particles that are mainly transported to Penang by the monsoon winds from the surrounding sea and biomass burnings in the neighboring SEA countries. An overview of the atmospheric conditions in Penang for a whole year is meaningful for further research.
Atmospheric profiles of the optical aerosol properties through the retrieved backscattering or extinction coefficients by lidar measurements can improve drastically the MACC-II aerosol model performances on vertical dimension. Currently the MODIS Aerosol Optical Depth data (both from Terra and Aqua) are assimilated into the model. Being a columnintegrated quantity, these data do not modify the model aerosol vertical profile, especially if the aerosols are not interactive with the meteorology. Since 1999, the MPLNET lidar network provides continuously lidar data measurements from worldwide permanent stations (currently 21), deployed from the Arctic to the Antarctic regions and in tropical and equatorial zones. The purpose of this study is to show the first preliminary results of the intercomparison of MPLNET lidar data against the ECWMF MACC-II aerosol model, for a selected MPLNET permanent observational site at National Central University of Taiwan. Assessing the model performances it is the first step for future near-real time lidar data assimilation into MACC-II aerosol model forecast.
From August 2012 to February 2013 a High Resolution Spectral Lidar (HSRL; 532 nm) was deployed at that National University of Singapore near a NASA Micro Pulse Lidar NETwork (MPLNET; 527 nm) site. A primary objective of the MPLNET lidar project is the production and dissemination of reliable Level 1 measurements and Level 2 retrieval products. This paper characterizes and quantifies error in Level 2 aerosol optical property retrievals conducted through inversion techniques that derive backscattering and extinction coefficients from MPLNET elastic single-wavelength datasets. MPLNET Level 2 retrievals for aerosol optical depth and extinction/backscatter coefficient profiles are compared with corresponding HSRL datasets, for which the instrument collects direct measurements of each using a unique optical configuration that segregates aerosol and cloud backscattered signal from molecular signal. The intercomparison is performed, and error matrices reported, for lower (0-5km) and the upper (>5km) troposphere, respectively, to distinguish uncertainties observed within and above the MPLNET instrument optical overlap regime.
The determination of the depth of daytime and nighttime Planetary Boundary Layer Height (PBLH) must be
known very accurately to relate boundary layer concentrations of gases or particles to upstream fluxes. Moreover, the air
quality forecasts rely upon semi-empirical parameterizations within numerical models for the description of dispersion,
formation and fate of pollutants influenced by the spatial and temporal distribution of emissions in cities, topography,
and weather. The particulate matter (PM) mass measured at the ground level is a common way to quantify the amount of
aerosol particles in the atmosphere and is the standard used to evaluate air quality. Remote sensing of atmospheric
aerosols in the lower troposphere that affect air quality is done at the University of Maryland, Baltimore County
(UMBC) by the Atmospheric Lidar Group, that supported the joint NOAA/ARL and NCEP ad hoc field study. These
campaigns launched radiosondes from Howard University (HU) (26.6km south of UMBC) and RFK Stadium (29.15 km
south of UMBC) during September 14-22, 2009 to develop a database to investigate the evolution and spatial variability
of the PBLH. In this paper, we examined the potential for continual observation of PBLH by performing a statistical
comparison of the spatial and temporal resolution of PBLH from lidars, wind profiler, and radiosonde measurements
Eyjafjallajökull volcano eruptions of ash plumes starting on April 2010 paralyzed completely air traffic in
Europe for several days. During the crisis, Leosphere collected 24/7 real time measurements of the backscatter
profiles, taken by ALS polarizations lidars spread from Denmark to South of France in order to provide quick
looks of the sky at regular intervals for different met agencies and for the Volcanic Ash Advisory Centres
(VAAC) coordinated by UK MetOffice. Moreover, Meteo France supported by other institutions such as CNRS
(Centre National de la Recherche Scientifique), CEA (Commissariat à l'Energie Atomique), CNES (Centre
National d'Études Spatiales) and Leosphere performed several test flights over France and North Atlantic with an
airborne Lidar. These unique data allowed detection and identification of ash plume and provided a guidance
regarding the decision-making chain. The ash mass concentration and its calculation were also discussed.
Urbanized cities in the world are exposed to atmospheric pollution events. To understand the chemical and
physical processes it is necessary to describe correctly the Planetary Boundary Layer (PBL) dynamics and height
evolution. For these proposals, a compact and rugged eye safe UV Lidar, the EZLIDAR™, was developed
together by CEA/LMD and LEOSPHERE (France) to study and investigate structural and optical properties of
clouds and aerosols and PBL time evolution. A new 2D method of PBL detection, developed by Leosphere and
based on image processing, is working on a large set of temporal profiles, typically 6 to 24 hours. It allows the
use of the temporal correlation between the profiles and the integration of atmospheric parameters about PBL
evolution in the detection algorithms. This method, based on the gradient, is using a unique automatic threshold
algorithm that will adapt to any atmospheric conditions. No specific parametrisation is required before
measurements and the final result is more robust than a profile per profile method.
We validated our algorithm during the two campaigns of the ICOS (Integrated Carbon Observation System)
project. These campaigns took place at Trainou (France) on October 2008 and at Mace Head (Ireland) on June
2009 under very different and complicated atmospheric situations, with all different meteorological conditions
(frequent showers, windy situations, no significant inversion layer). Furthermore, this algorithm is able to detect
accurately clouds and rain episode.
Duststorms and sandstorms regularly devastate Northeast Asia and cause considerable damage to transportation system
and public health; further, these events are conceived to be one of the very important indices for estimating the global
warming and desertification. Previously, yellow sand events were considered natural phenomena that originate in deserts
and arid areas. However, the greater scale and frequency of these events in recent years are considered to be the result of
human activities such as overgrazing and over-cultivation. Japan, Korea, Cina and Mongolia are directly concerned to
prevent and control these storms and have been able to some extent to provide forecasts and early warnings. In this
framework, to improve the accuracy of forecasting , a compact and rugged eye safe lidar, the EZ LIDATM, developed
together by Laboratoire des Sciences du Climat et l'Environnement (LSCE) (CEA-CNRS) and LEOSPHERE (France) to
study and investigate structural and optical properties of clouds and aerosols, thanks to the strong know-how of CEA and
CNRS in the field of air quality measurements and cloud observation and analysis, was deployed in Seoul, Korea in
order to detect and study yellow sand events, thanks to its depolarization channel and scan capabilities. The preliminary
results, showed in this paper, of this measurement campaign put in evidence that EZ Lidar, for its capabilities of
operating unattended day and night under each atmospheric condition, is mature to be deployed in a global network to
study long-range transport, crucial in the forecasting model.
To fully understand atmospheric dynamics, climate studies, energy transfer, and weather prediction the wind field is one
of the most important atmospheric state variables. Studies indicate that a global determination of the tropospheric wind
field to an accuracy of 0.5 m/s is critical for improved numerical weather forecasting. LEOSPHERE recently developed
a new generation long range compact, eye safe and transportable wind Lidar, named WLS70, capable to fully determine
locally the wind field in real time in the planetary boundary layer (PBL). First results of the measurement campaign put
in evidence both wind velocity vertical profiles and atmosphere structure derived from Lidar data.
Lidar investigation of temporal and vertical optical atmospheric properties will play a key role in the future for a
continuous monitoring over the whole planet through world ground based networks. The EZ LidarTM, manufactured by
LEOSPHERE, has been validated in several campaigns as that one in Southern Great Plains (ARM) or at Goddard Space
Flight Center (NASA). An EZ LIDARTM with
cross-polarization capabilities was deployed in Kanpur, India in the frame
of TIGER-Z campaign organized by NASA/AERONET in order to measure aerosol microphysical and optical properties
in the Gange basin. In addition, 12 sun-photometers were deployed during this campaign and CALIPSO (The
Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) data were also acquired. In this work we present the results
in retrieving aerosol extinction and backscattering from EZ
LidarTM measurements, and the validation of the space borne
instrument CALIPSO under the satellite track.
EZ LidarTM is also coupled with the photometers to provide the
measurements of the Aerosol Optical Depth over the selected region.
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