scholarly journals Different strategies to retrieve aerosol properties at night-time with GRASP algorithm

2019 ◽  
Author(s):  
Jose Antonio Benavent-Oltra ◽  
Roberto Román ◽  
Juan Andrés Casquero-Vera ◽  
Daniel Pérez-Ramírez ◽  
Hassan Lyamani ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Sierra Nevada ◽  
Volume Concentration ◽  
In Situ Measurements ◽  
Saharan Dust ◽  
Scattering Coefficient ◽  
Night Time ◽  
Aerosol Properties

Abstract. This study evaluates the potential of GRASP algorithm (Generalized Retrieval of Aerosol and Surface Properties) to retrieve continuous day-to-night aerosol properties, both column-integrated and vertically-resolved. The study is focused on the evaluation of GRASP retrievals during an intense Saharan dust event that occurred during the Sierra Nevada Lidar aerOsol Profiling Experiment I (SLOPE I) field campaign. For daytime aerosol retrievals, we combined the measurements of the lidar ground-based from EARLINET (European Aerosol Research Lidar Network) station and sun/sky photometer from AERONET (Aerosol Robotic Network), both instruments co-located in Granada (Spain). However, for night-time retrievals three different combinations of active and passive remote sensing measurements are proposed. The first scheme (N0) uses lidar night-time measurements in combination with the interpolation of sun/sky daytime measurements. The other two schemes combine lidar night-time measurements with night-time aerosol optical depth obtained by lunar photometry either using intensive properties of the aerosol retrieved during sun/sky daytime measurements (N1) or using the moon aureole radiance obtained by sky camera images (N2). Evaluations of the columnar aerosol properties retrieved by GRASP are done versus standard AERONET retrievals. The coherence of day-to-night evolutions of the different aerosol properties retrieved by GRASP is also studied. The extinction coefficient vertical profiles retrieved by GRASP are compared with the profiles calculated by Raman technique at night-time with differences below 30% for all schemes at 355, 532 and 1064 nm. Finally, the volume concentration and scattering coefficient retrieved by GRASP at 2500 m a.s.l. are evaluated by in-situ measurements at this height at Sierra Nevada Station. The differences between GRASP and in-situ measurements are similar for the different schemes, with differences below 30 % for both volume concentration and scattering coefficient. In general, for the scattering coefficient, the GRASP N0 and N1 show better results than the GRASP N2 schemes, while for volume concentration, GRASP N2 shows the lowest differences against in-situ measurements, around 10 %, for high the aerosol optical depth values.

scholarly journals Different strategies to retrieve aerosol properties at night-time with the GRASP algorithm

2019 ◽  
Vol 19 (22) ◽  
pp. 14149-14171 ◽  
Author(s):  
Jose Antonio Benavent-Oltra ◽  
Roberto Román ◽  
Juan Andrés Casquero-Vera ◽  
Daniel Pérez-Ramírez ◽  
Hassan Lyamani ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Sierra Nevada ◽  
Volume Concentration ◽  
In Situ Measurements ◽  
Saharan Dust ◽  
Scattering Coefficient ◽  
Night Time ◽  
Aerosol Properties

Abstract. This study evaluates the potential of the GRASP algorithm (Generalized Retrieval of Aerosol and Surface Properties) to retrieve continuous day-to-night aerosol properties, both column-integrated and vertically resolved. The study is focused on the evaluation of GRASP retrievals during an intense Saharan dust event that occurred during the Sierra Nevada Lidar aerOsol Profiling Experiment I (SLOPE I) field campaign. For daytime aerosol retrievals, we combined the measurements of the ground-based lidar from EARLINET (European Aerosol Research Lidar Network) station and sun–sky photometer from AERONET (Aerosol Robotic Network), both instruments co-located in Granada (Spain). However, for night-time retrievals three different combinations of active and passive remote-sensing measurements are proposed. The first scheme (N0) uses lidar night-time measurements in combination with the interpolation of sun–sky daytime measurements. The other two schemes combine lidar night-time measurements with night-time aerosol optical depth obtained by lunar photometry either using intensive properties of the aerosol retrieved during sun–sky daytime measurements (N1) or using the Moon aureole radiance obtained by sky camera images (N2). Evaluations of the columnar aerosol properties retrieved by GRASP are done versus standard AERONET retrievals. The coherence of day-to-night evolutions of the different aerosol properties retrieved by GRASP is also studied. The extinction coefficient vertical profiles retrieved by GRASP are compared with the profiles calculated by the Raman technique at night-time with differences below 30 % for all schemes at 355, 532 and 1064 nm. Finally, the volume concentration and scattering coefficient retrieved by GRASP at 2500 m a.s.l. are evaluated by in situ measurements at this height at Sierra Nevada Station. The differences between GRASP and in situ measurements are similar for the different schemes, with differences below 30 % for both volume concentration and scattering coefficient. In general, for the scattering coefficient, the GRASP N0 and N1 show better results than the GRASP N2 schemes, while for volume concentration, GRASP N2 shows the lowest differences against in situ measurements (around 10 %) for high aerosol optical depth values.

scholarly journals Study of aerosol microphysical properties profiles retrieved from ground-based remote sensing and aircraft in-situ measurements during a Saharan dust event

2015 ◽  
Vol 8 (9) ◽  
pp. 9289-9338 ◽  
Author(s):  
M. J. Granados-Muñoz ◽  
J. A. Bravo-Aranda ◽  
D. Baumgardner ◽  
J. L. Guerrero-Rascado ◽  
D. Pérez-Ramírez ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Volume Concentration ◽  
Mineral Dust ◽  
In Situ Measurements ◽  
Saharan Dust ◽  
Night Time ◽  
Passive Remote Sensing ◽  
Microphysical Properties ◽  
Multi Wavelength

Abstract. In this work we present an analysis of mineral dust optical and microphysical properties obtained from different retrieval techniques applied to active and passive remote sensing measurements, including a comparison with simultaneous in-situ aircraft measurements. Data were collected in a field campaign performed during a mineral dust outbreak a Granada, Spain, experimental site (37.16° N, 3.61° W, 680 m a.s.l.) on the 27 June 2011. Column-integrated properties are provided by sun- and star-photometry which allows a continuous evaluation of the mineral dust optical properties during both day and night-time. Both the Linear Estimation and AERONET (Aerosol Robotic Network) inversion algorithms are applied for the retrieval of the column-integrated microphysical particle properties. In addition, vertically-resolved microphysical properties are obtained from a multi-wavelength Raman lidar system included in EARLINET (European Aerosol Research Lidar Network), by using both LIRIC (Lidar Radiometer Inversion Code) algorithm during daytime and an algorithm applied to the Raman measurements based on the regularization technique during night-time. LIRIC retrievals reveal several dust layers between 3 and 5 km a.s.l. with volume concentrations of the coarse spheroid mode up to 60 μm3 cm−3. The combined use of the regularization and LIRIC methods reveals the night-to-day evolution of the vertical structure of the mineral dust microphysical properties and offers complementary information to that from column-integrated variables retrieved from passive remote sensing. Additionally, lidar depolarization profiles and LIRIC retrieved volume concentration are compared with aircraft in-situ measurements. This study presents for the first time a comparison of both volume concentration and dust particle polarization ratios measured with in-situ and remote sensing techniques. Results for the depolarization measurements in the dust layer indicate reasonable agreement within the estimated uncertainties. The differences in the volume concentration profiles, although somewhat larger, are still within the expected uncertainties.

scholarly journals Overview of the SLOPE I and II campaigns: aerosol properties retrieved with lidar and sun–sky photometer measurements

2021 ◽  
Vol 21 (12) ◽  
pp. 9269-9287
Author(s):  
Jose Antonio Benavent-Oltra ◽  
Juan Andrés Casquero-Vera ◽  
Roberto Román ◽  
Hassan Lyamani ◽  
Daniel Pérez-Ramírez ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Absorption Coefficient ◽  
Sierra Nevada ◽  
Volume Concentration ◽  
In Situ Measurements ◽  
Absorption Coefficients ◽  
Desert Dust ◽  
Particle Sizer ◽  
Aerosol Properties

Abstract. The Sierra Nevada Lidar aerOsol Profiling Experiment I and II (SLOPE I and II) campaigns were intended to determine the vertical structure of aerosols by remote sensing instruments and test the various retrieval schemes for obtaining aerosol microphysical and optical properties with in situ measurements. The SLOPE I and II campaigns were developed during the summers of 2016 and 2017, respectively, combining active and passive remote sensing with in situ measurements at stations belonging to the AGORA observatory (Andalusian Global ObseRvatory of the Atmosphere) in the Granada area (Spain). In this work, we use the in situ measurements of these campaigns to evaluate aerosol properties retrieved by the GRASP code (Generalized Retrieval of Atmosphere and Surface Properties) combining lidar and sun–sky photometer measurements. We show an overview of aerosol properties retrieved by GRASP during the SLOPE I and II campaigns. In addition, we evaluate the GRASP retrievals of total aerosol volume concentration (discerning between fine and coarse modes), extinction and scattering coefficients, and for the first time we present an evaluation of the absorption coefficient. The statistical analysis of aerosol optical and microphysical properties, both column-integrated and vertically resolved, from May to July 2016 and 2017 shows a large variability in aerosol load and types. The results show a strong predominance of desert dust particles due to North African intrusions. The vertically resolved analysis denotes a decay of the atmospheric aerosols with an altitude up to 5 km a.s.l. Finally, desert dust and biomass burning events were chosen to show the high potential of GRASP to retrieve vertical profiles of aerosol properties (e.g. absorption coefficient and single scattering albedo) for different aerosol types. The aerosol properties retrieved by GRASP show good agreement with simultaneous in situ measurements (nephelometer, aethalometer, scanning mobility particle sizer, and aerodynamic particle sizer) performed at the Sierra Nevada Station (SNS) in Granada. In general, GRASP overestimates the in situ data at the SNS with a mean difference lower than 6 µm3 cm−3 for volume concentration, and 11 and 2 Mm−1 for the scattering and absorption coefficients. On the other hand, the comparison of GRASP with airborne measurements also shows an overestimation with mean absolute differences of 14 ± 10 and 1.2 ± 1.2 Mm−1 for the scattering and absorption coefficients, showing a better agreement for the absorption (scattering) coefficient with higher (lower) aerosol optical depth. The potential of GRASP shown in this study will contribute to enhancing the representativeness of the aerosol vertical distribution and provide information for satellite and global model evaluation.

scholarly journals Overview of SLOPE I and II campaigns: aerosol properties retrieved with lidar and sun-sky photometer measurements

2021 ◽  
Author(s):  
Jose Antonio Benavent-Oltra ◽  
Juan Andrés Casquero-Vera ◽  
Roberto Román ◽  
Hassan Lyamani ◽  
Daniel Pérez-Ramírez ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Absorption Coefficient ◽  
Sierra Nevada ◽  
Volume Concentration ◽  
In Situ Measurements ◽  
Dust Particles ◽  
Large Variability ◽  
Desert Dust ◽  
Aerosol Properties

Abstract. The Sierra Nevada Lidar aerOsol Profiling Experiment I and II (SLOPE I and II) campaigns were intended to determine the vertical structure of the aerosol by remote sensing instruments and test the various retrieval schemes for obtaining aerosol microphysical and optical properties with in-situ measurements. These campaigns deployed a set of in-situ and remote sensing instruments at the stations include in AGORA observatory (Andalusian Global ObseRvatory of the Atmosphere) in the Granada area (Spain) along summer in 2016 and 2017. In this work, using the in-situ measurements performed at a high-altitude station, Sierra Nevada station, and airborne flights, we evaluate the retrievals of aerosol properties by GRASP code (Generalized Retrieval of Atmosphere and Surface Properties) combining lidar and sun-sky photometer measurements. Besides, we show an overview of aerosol properties retrieved by GRASP during SLOPE I and II campaigns. We evaluate the GRASP retrievals of total aerosol volume concentration (discerning between fine and coarse modes), extinction and scattering coefficients, and for the first time we present an evaluation of absorption coefficient. The statistical analysis of the aerosol optical and microphysical properties, both column-integrated and vertically-resolved, from May to July 2016 and 2017 shows a large variability in aerosol load and types. The results show a strong predominance of desert dust particles due to the North African intrusions. The vertically-resolved analysis denotes a decay of the atmospheric aerosols with altitude up to 5 km a.s.l. Finally, two events of desert dust and biomass burning were used to show the high potential of GRASP to retrieve and study the aerosol properties profiles such as absorption coefficient and single scattering albedo for different aerosol types. The aerosol properties retrieved by GRASP show good agreement with simultaneous in situ measurements performed at Sierra Nevada Station (SNS) in Granada. In general, GRASP overestimates the in situ data at SNS with a mean difference lower than 6 µm3/cm3 for volume concentration, 11 Mm−1 and 2 Mm−1 for scattering and absorption coefficient. On the other hand, the comparison of GRASP with airborne measurements also shows an overestimation with mean absolute differences of 14 ± 10 Mm−1 and 1.2 ± 1.2 Mm−1 for scattering and absorption coefficients, showing a better agreement for absorption (scattering) coefficient with higher (lower) aerosol optical depth. The potentiality of GRASP showed in this study will contribute to enhancing the representativeness of the aerosol vertical distribution and provide information for satellite and global model evaluation.

scholarly journals Above-aircraft cirrus cloud and aerosol optical depth from hyperspectral irradiances measured by a total-diffuse radiometer

2021 ◽  
Author(s):  
Matthew S. Norgren ◽  
John Wood ◽  
K. Sebastian Schmidt ◽  
Bastiaan van Diedenhoven ◽  
Snorre A. Stamnes ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Low Cost ◽  
In Situ Measurements ◽  
Cirrus Cloud ◽  
Optical Extinction ◽  
Direct Beam ◽  
Diffuse Irradiance ◽  
Sun Photometer

Abstract. This study develops the use of spectral total and diffuse irradiance measurements, made from a prototype hyperspectral total-diffuse Sunshine Pyranometer (SPN-S), to retrieve layer fine-mode aerosol (τaer) and total optical depths from airborne platforms. Additionally, we use spectral analysis in an attempt to partition the total optical depth it into its τaer and cirrus cloud optical depth (τcld) components in the absence of coarse-mode aerosols. Two retrieval methods are developed: one leveraging information in the diffuse irradiance, and the other using spectral characteristics of the transmitted direct beam, with each approach best suited for specific cloud and aerosol conditions. SPN-S has advantages over traditional sun-photometer systems including no moving parts and a low cost. However, a significant drawback of the instrument is that it is unable to measure the direct beam irradiance as accurately as sun-photometers. To compensate for the greater measurement uncertainty of the radiometric irradiances these retrieval techniques employ ratioed inputs or spectral information to reduce output uncertainty. This analysis uses irradiance measurements from SPN-S and the Solar Spectral Flux Radiometer (SSFR) aboard the National Aeronautics and Space Administration’s (NASA) P-3 aircraft during the 2018 deployment of the ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) campaign and the 2019 Cloud, Aerosol and Monsoon Processes Philippines Experiment (CAMP2Ex) mission to quantify above-aircraft cirrus τcld and derive vertical profiles of layer τaer. Validation of the τaer retrieval is accomplished by comparison with collocated measurements of direct solar irradiance made by the Sky-Scanning Sun-Tracking Atmospheric Research (4STAR) and in situ measurements of aerosol optical depth. For the aggregated 2018 ORACLES results, regression between the SPN-S based method and sun-photometer τaer values yield a slope of 0.96 with an R2 of 0.96, while the root-mean-square error (RMSE) is 3.0 × 10−2. When comparing the retrieved τaer to profiles of integrated in situ measurements of optical extinction, the slope, R2, and RMSE values for ORACLES are 0.90, 0.96, 3.4 × 10−2, and for CAMP2Ex are 0.94, 0.97, 3.4 × 10−2 respectively. This paper is a demonstration of methods for deriving cloud and aerosol optical properties in environments where both atmospheric constituents may be present. With improvements to the low-cost SPN-S radiometer instrument, it may be possible to extend these methods to a broader set of sampling applications, such as ground-based settings.

scholarly journals Sources of discrepancy between aerosol optical depth obtained from AERONET and in-situ aircraft profiles

2012 ◽  
Vol 12 (6) ◽  
pp. 2987-3003 ◽  
Author(s):  
A. R. Esteve ◽  
J. A. Ogren ◽  
P. J. Sheridan ◽  
E. Andrews ◽  
B. N. Holben ◽  
...  
Keyword(s):  
Optical Properties ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Single Scattering ◽  
Retrieval Algorithm ◽  
Aircraft Measurements ◽  
Aerosol Optical Properties ◽  
The One ◽  
Aerosol Properties

Abstract. Aerosol optical properties were measured by NOAA's Airborne Aerosol Observatory over Bondville, Illinois, during more than two years using a light aircraft. Measured properties included total light scattering, backscattering, and absorption, while calculated parameters included aerosol optical depth (AOD), Ångström exponent, single-scattering albedo, hemispheric backscatter fraction, asymmetry parameter, and submicrometer mode fraction of scattering. The in-situ aircraft measurements are compared here with AERONET measurements and retrievals of the aerosol optical properties at the same location, although it is difficult to verify the AERONET retrieval algorithm at a site that is not highly polluted. The comparison reveals discrepancies between the aerosol properties retrieved from AERONET and from in-situ aircraft measurements. These discrepancies are smaller for the AOD, while the biggest discrepancies are for the other derived aerosol properties. Possible sources of discrepancy between the AOD measured by AERONET and the one calculated from the in-situ aircraft measurements are investigated. The largest portion of the AOD discrepancy is likely due to an incorrect adjustment to ambient RH of the scattering coefficient. Another significant part (along with uncertain nephelometer truncation corrections) may come from the possibility that there might be less aerosol below the lowest flight altitude or that the aircraft inlet excludes aerosol particles larger than 5–7 μm diameter.

scholarly journals Sun photometer retrievals of Saharan dust properties over Barbados during SALTRACE

2019 ◽  
Vol 19 (23) ◽  
pp. 14571-14583 ◽  
Author(s):  
Carlos Toledano ◽  
Benjamín Torres ◽  
Cristian Velasco-Merino ◽  
Dietrich Althausen ◽  
Silke Groß ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Saharan Dust ◽  
Caribbean Region ◽  
The Sun ◽  
Concentration Data ◽  
The Caribbean ◽  
Sun Photometer ◽  
Dust Events

Abstract. The Saharan Aerosol Long-Range Transport and Aerosol–Cloud-Interaction Experiment (SALTRACE) was devoted to the investigation of Saharan dust properties over the Caribbean. The campaign took place in June–July 2013. A wide set of ground-based and airborne aerosol instrumentation was deployed at the island of Barbados for a comprehensive experiment. Several sun photometers performed measurements during this campaign: two AERONET (Aerosol Robotic Network) Cimel sun photometers and the Sun and Sky Automatic Radiometer (SSARA). The sun photometers were co-located with the ground-based multi-wavelength lidars BERTHA (Backscatter Extinction lidar Ratio Temperature Humidity profiling Apparatus) and POLIS (Portable Lidar System). Aerosol properties derived from direct sun and sky radiance observations are analyzed, and a comparison with the co-located lidar and in situ data is provided. The time series of aerosol optical depth (AOD) allows identifying successive dust events with short periods in between in which the marine background conditions were observed. The moderate aerosol optical depth in the range of 0.3 to 0.6 was found during the dust periods. The sun photometer infrared channel at the 1640 nm wavelength was used in the retrieval to investigate possible improvements to aerosol size retrievals, and it was expected to have a larger sensitivity to coarse particles. The comparison between column (aerosol optical depth) and surface (dust concentration) data demonstrates the connection between the Saharan Air Layer and the boundary layer in the Caribbean region, as is shown by the synchronized detection of the successive dust events in both datasets. However the differences of size distributions derived from sun photometer data and in situ observations reveal the difficulties in carrying out a column closure study.

scholarly journals Measurement of aerosol optical depth and sub-visual cloud detection using the optical depth sensor (ODS)

2015 ◽  
Vol 8 (9) ◽  
pp. 9611-9648 ◽  
Author(s):  
D. Toledo ◽  
P. Rannou ◽  
J.-P. Pommereau ◽  
A. Sarkissian ◽  
T. Foujols
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Diffuse Radiation ◽  
Dust Storms ◽  
Saharan Dust ◽  
Cloud Detection ◽  
Depth Sensor ◽  
Night Time ◽  
Data Set

Abstract. A small and sophisticated optical depth sensor (ODS) has been designed to work in the atmosphere of Earth and Mars. The instrument measures alternatively the diffuse radiation from the sky and the attenuated direct radiation from the sun on the surface. The principal goals of ODS are to retrieve the daily mean aerosol optical depth (AOD) and to detect very high and optically thin clouds, crucial parameters in understanding the Martian and Earth meteorology and climatology. The detection of clouds is undertaken at twilight, allowing the detection and characterization of clouds with opacities below 0.03 (sub-visual clouds). In addition, ODS is capable to retrieve the aerosol optical depth during night-time from moonlight measurements. In order to study the performance of ODS under Mars-like conditions as well as to evaluate the retrieval algorithms for terrestrial measurements, ODS was deployed in Ouagadougou (Africa) between November 2004 and October 2005, a sahelian region characterized by its high dust aerosol load and the frequent occurrence of Saharan dust storms. The daily average AOD values retrieved by ODS were compared with those provided by a CIMEL Sun-photometer of the AERONET (Aerosol Robotic NETwork) network localized at the same location. Results represent a good agreement between both ground-based instruments, with a correlation coefficient of 0.79 for the whole data set and 0.96 considering only the cloud-free days. From the whole dataset, a total of 71 sub-visual cirrus (SVC) were detected at twilight with opacities as thin as 1.10−3 and with a maximum of occurrence at altitudes between 14 and 20 km. Although further analysis and comparisons are required, results indicate the potential of ODS measurements to detect sub-visual clouds.

scholarly journals Sun photometer retrievals of Saharan dust properties over Barbados during SALTRACE

2019 ◽  
Author(s):  
Carlos Toledano ◽  
Benjamín Torres ◽  
Cristian Velasco-Merino ◽  
Dietrich Althausen ◽  
Silke Groß ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Saharan Dust ◽  
Caribbean Region ◽  
The Sun ◽  
Concentration Data ◽  
The Caribbean ◽  
Sun Photometer ◽  
Dust Events

Abstract. The Saharan Aerosol Long-range Transport and Aerosol-Cloud-Interaction Experiment (SALTRACE) was devoted to the investigation of Saharan dust properties over the Caribbean. The campaign took place in June–July 2013. A wide set of ground-based and airborne aerosol instrumentation was deployed at Barbados island for a comprehensive experiment. Several sun photometers performed measurements during this campaign: two AERONET Cimel sun photometers and the Sun and Sky Automatic Radiometer (SSARA). The sun photometers were co-located with the ground-based multi-wavelength lidars BERTHA and POLIS. Aerosol properties derived from direct sun and sky radiance observations are analyzed, and a comparison with the co-located lidar and in-situ data is provided. The time series of aerosol optical depth allows identifying successive dust events with short periods in between in which the marine background conditions were observed. Moderate aerosol optical depth in the range 0.3 to 0.6 was found during the dust periods. The sun photometer infrared channel at 1640 nm wavelength was used in the retrieval to investigate possible improvements and expected larger sensitivity to coarse particles. The comparison between column (AOD) and surface (dust concentration) data demonstrates the connection between the Saharan Air Layer and the boundary layer in the Caribbean region, as it is shown by the synchronized detection of the successive dust events in both data sets. However the comparison of size distributions derived from sun photometer data and in-situ observations reveal the difficulties to carry out a column closure study.

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