scholarly journals Helicopter-borne observations of the continental background aerosol in combination with remote sensing and ground-based measurements

2018 ◽  
Vol 18 (2) ◽  
pp. 1263-1290 ◽  
Author(s):  
Sebastian Düsing ◽  
Birgit Wehner ◽  
Patric Seifert ◽  
Albert Ansmann ◽  
Holger Baars ◽  
...  
Keyword(s):  
Aerosol Particle ◽  
Extinction Coefficient ◽  
In Situ Measurements ◽  
Light Extinction ◽  
Backscatter Coefficient ◽  
New Approach ◽  
Light Extinction Coefficient ◽  
Lidar Measurements ◽  
Lidar Ratio

Abstract. This paper examines the representativeness of ground-based in situ measurements for the planetary boundary layer (PBL) and conducts a closure study between airborne in situ and ground-based lidar measurements up to an altitude of 2300 m. The related measurements were carried out in a field campaign within the framework of the High-Definition Clouds and Precipitation for Advancing Climate Prediction (HD(CP)2) Observational Prototype Experiment (HOPE) in September 2013 in a rural background area of central Europe.The helicopter-borne probe ACTOS (Airborne Cloud and Turbulence Observation System) provided measurements of the aerosol particle number size distribution (PNSD), the aerosol particle number concentration (PNC), the number concentration of cloud condensation nuclei (CCN-NC), and meteorological atmospheric parameters (e.g., temperature and relative humidity). These measurements were supported by the ground-based 3+2 wavelength polarization lidar system PollyXT, which provided profiles of the particle backscatter coefficient (σbsc) for three wavelengths (355, 532, and 1064 nm). Particle extinction coefficient (σext) profiles were obtained by using a fixed backscatter-to-extinction ratio (also lidar ratio, LR). A new approach was used to determine profiles of CCN-NC for continental aerosol. The results of this new approach were consistent with the airborne in situ measurements within the uncertainties.In terms of representativeness, the PNSD measurements on the ground showed a good agreement with the measurements provided with ACTOS for lower altitudes. The ground-based measurements of PNC and CCN-NC are representative of the PBL when the PBL is well mixed. Locally isolated new particle formation events on the ground or at the top of the PBL led to vertical variability in the cases presented here and ground-based measurements are not entirely representative of the PBL. Based on Mie theory (Mie, 1908), optical aerosol properties under ambient conditions for different altitudes were determined using the airborne in situ measurements and were compared with the lidar measurements. The investigation of the optical properties shows that on average the airborne-based particle light backscatter coefficient is 50.1 % smaller for 1064 nm, 27.4 % smaller for 532 nm, and 29.5 % smaller for 355 nm than the measurements of the lidar system. These results are quite promising, since in situ measurement-based Mie calculations of the particle light backscattering are scarce and the modeling is quite challenging. In contrast, for the particle light extinction coefficient we found a good agreement. The airborne-based particle light extinction coefficient was just 8.2 % larger for 532 nm and 3 % smaller for 355 nm, for an assumed LR of 55 sr. The particle light extinction coefficient for 1064 nm was derived with a LR of 30 sr. For this wavelength, the airborne-based particle light extinction coefficient is 5.2 % smaller than the lidar measurements. For the first time, the lidar ratio of 30 sr for 1064 nm was determined on the basis of in situ measurements and the LR of 55 sr for 355 and 532 nm wavelength was reproduced for European continental aerosol on the basis of this comparison. Lidar observations and the in situ based aerosol optical properties agree within the uncertainties. However, our observations indicate that a determination of the PNSD for a large size range is important for a reliable modeling of aerosol particle backscattering.

scholarly journals Helicopter-borne observations of the continental background aerosol in combination with remote sensing and ground-based measurements

2017 ◽  
Author(s):  
Sebastian Düsing ◽  
Birgit Wehner ◽  
Patric Seifert ◽  
Albert Ansmann ◽  
Holger Baars ◽  
...  
Keyword(s):  
Optical Properties ◽  
Aerosol Particle ◽  
Extinction Coefficient ◽  
Cloud Condensation Nuclei ◽  
In Situ Measurements ◽  
Light Extinction ◽  
Backscatter Coefficient ◽  
Light Extinction Coefficient ◽  
Lidar Measurements

Abstract. This study presents vertical profiles up to a height of 2300 m a.s.l. of aerosol microphysical and optical properties and cloud condensation nuclei (CCN). Corresponding data have been measured during a field campaign as part of the High-Definition Clouds and Precipitation for Advancing Climate Prediction (HD(CP)2) Observational Prototype Experiments (HOPE), which took place at Melpitz, Germany from September 9 to 29, 2013. The helicopter-borne payload ACTOS (Airborne Cloud and Turbulence Observation System) was used to determine the aerosol particle number size distribution (PNSD), the number concentrations of aerosol particles (PNC) and cloud condensation nuclei (CCN) (CCN-NC), the ambient relative humidity (RH), and temperature (T). Simultaneous measurements on ground provided a holistic view on aerosol microphysical properties such as the PNSD, the chemical composition and the CCN-NC. Additional measurements of a 3 + 2 wavelength polarization lidar system (PollyXT) provided profiles of the aerosol particle light backscatter coefficient (σbsc) for three wavelengths (355, 532 and 1064 nm). From profiles of σbsc profiles of the aerosol particle light extinction coefficient (σext) were determined using the extinction-to-backscatter ratio. Furthermore, CCN-NC profiles were estimated on basis of the lidar-measurements. Ambient state optical properties of aerosol particles were derived on the basis of airborne in situ measurements of ACTOS (PNSD) and in situ measurements on ground (chemical aerosol characterization) using Mie-theory. On the basis of ground-based and airborne measurements, this work investigates the representativeness of ground-based aerosol microphysical properties for the boundary layer for two case-studies. The PNSD measurements on ground showed a good agreement with the measurements provided with ACTOS for lower altitudes. The ground-based measurements of PNC and CCN-NC are representative for the PBL when the PBL is well mixed. Locally isolated new particle formation events on ground or at the top of the PBL led to vertical variability in the here presented cases and ground-based measurements are not representative for the PBL. Furthermore, the lidar-based estimates of CCN-NC profiles were compared with the airborne in situ measurements of ACTOS. This comparison showed good agreements within the uncertainty range. Finally, this work provides a closure study between the optical aerosol particle properties in ambient state based on the airborne ACTOS measurements and derived with the lidar measurements. The investigation of the optical properties shows for 14 measurement-points that the airborne-based particle light backscatter coefficient is for 1064 nm 50 % smaller than the measurements of the lidar system, 27.6 % smaller for 532 nm and 29.9 % smaller for 355 nm. These results are quite promising, since in-situ measurement based Mie-calculations of the particle light backscattering are scarce and the modelling is quite challenging. In contradiction for the particle light extinction coefficient retrieved from the airborne in situ measurements were found a good agreement. The airborne-based particle light extinction coefficient was just 7.9 % larger for 532 nm and 3.5 % smaller for 355 nm, for an assumed lidar ratio (LR) of 55 sr. The particle light extinction coefficient for 1064 nm was derived with a LR of 30 sr. For this wavelength, the airborne-based particle light extinction coefficient is 5.2 % smaller than the lidar-measurements. Also, the correlation for the particle light extinction coefficient in combination with Mie-based LR's are in agreement for typical LR's of European background aerosol.

scholarly journals Measurement report: Comparison of airborne, in situ measured, lidar-based, and modeled aerosol optical properties in the central European background – identifying sources of deviations

2021 ◽  
Vol 21 (22) ◽  
pp. 16745-16773
Author(s):  
Sebastian Düsing ◽  
Albert Ansmann ◽  
Holger Baars ◽  
Joel C. Corbin ◽  
Cyrielle Denjean ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Optical Properties ◽  
Aerosol Particle ◽  
In Situ Measurements ◽  
Light Extinction ◽  
Aerosol Optical Properties ◽  
Central European ◽  
Lidar Ratio ◽  
Aerosol Mixing State

Abstract. A unique data set derived from remote sensing, airborne, and ground-based in situ measurements is presented. This measurement report highlights the known complexity of comparing multiple aerosol optical parameters examined with different approaches considering different states of humidification and atmospheric aerosol concentrations. Mie-theory-based modeled aerosol optical properties are compared with the respective results of airborne and ground-based in situ measurements and remote sensing (lidar and photometer) performed at the rural central European observatory at Melpitz, Germany. Calculated extinction-to-backscatter ratios (lidar ratios) were in the range of previously reported values. However, the lidar ratio is a function of the aerosol type and the relative humidity. The particle lidar ratio (LR) dependence on relative humidity was quantified and followed the trend found in previous studies. We present a fit function for the lidar wavelengths of 355, 532, and 1064 nm with an underlying equation of fLR(RH, γ(λ))=fLR(RH=0,λ)×(1-RH)-γ(λ), with the derived estimates of γ(355 nm) = 0.29 (±0.01), γ(532 nm) = 0.48 (±0.01), and γ(1064 nm) = 0.31 (±0.01) for central European aerosol. This parameterization might be used in the data analysis of elastic-backscatter lidar observations or lidar-ratio-based aerosol typing efforts. Our study shows that the used aerosol model could reproduce the in situ measurements of the aerosol particle light extinction coefficients (measured at dry conditions) within 13 %. Although the model reproduced the in situ measured aerosol particle light absorption coefficients within a reasonable range, we identified many sources for significant uncertainties in the simulations, such as the unknown aerosol mixing state, brown carbon (organic material) fraction, and the unknown aerosol mixing state wavelength-dependent refractive index. The modeled ambient-state aerosol particle light extinction and backscatter coefficients were smaller than the measured ones. However, depending on the prevailing aerosol conditions, an overlap of the uncertainty ranges of both approaches was achieved.

scholarly journals Closure of In-Situ Measured Aerosol Backscattering and Extinction Coefficients with Lidar Accounting for Relative Humidity

2021 ◽  
Author(s):  
Sebastian Düsing ◽  
Albert Ansmann ◽  
Holger Baars ◽  
Joel C. Corbin ◽  
Cyrielle Denjean ◽  
...  
Keyword(s):  
Optical Properties ◽  
Relative Humidity ◽  
Aerosol Particle ◽  
Light Absorption ◽  
Aerosol Particles ◽  
Light Extinction ◽  
Mixing State ◽  
Carbon Mass ◽  
Lidar Ratio

Abstract. Aerosol particles contribute to the climate forcing through their optical properties. Measuring these optical aerosol particle properties is still challenging, especially considering the hygroscopic growth of aerosol particles, which alters their optical properties. Lidar and in-situ techniques can derive a variety of aerosol optical properties, like aerosol particle light extinction, backscattering, and absorption. But these techniques are subject to some limitations and uncertainties. Within this study, we compared airborne in-situ based and, on Mie-theory based, modeled optical properties at dry state. At ambient state, modeled optical properties were compared with lidar-based estimates. Also, we examined the dependence of the aerosol particle light extinction-to-backscatter ratio, also lidar ratio, to relative humidity. The used model was fed with measured physicochemical aerosol properties and ambient atmospheric conditions. The model considered aerosol particles in an internal core-shell mixing state with constant volume fractions of the aerosol components over the entire observed aerosol particle size-range. The underlying set of measurements was conducted near the measurement site Melpitz, Germany, during two campaigns in summer, 2015, and winter, 2017, and represent Central European background aerosol conditions. Two airborne payloads deployed on a helicopter and a balloon provided measurements of microphysical and optical aerosol particle properties and were complemented by the polarization Raman lidar system PollyXT as well as by a holistic set of microphysical, chemical and optical aerosol measurements derived at ground level. Comparisons of calculated optical aerosol properties with ground-based in-situ measured aerosol optical properties at dry state showed an agreement of the model within 13 % (3 %) in terms of scattering at 450 nm wavelength during the winter (summer) campaign. The model also represented the aerosol particle light absorption at 637 nm within 8 % (18 %) during the winter (summer) campaign and agreed within 13 % with the airborne in-situ aerosol particle light extinction measurements during summer. During winter, in a comparatively clean case with equivalent black carbon mass-concentrations of around 0.2 µg m−3 the modeled airborne measurement-based aerosol particle light absorption, was up to 32–37 % larger than the measured values during a relatively clean period. However, during a high polluted case, with an equivalent black carbon mass concentration of around 4 µg m−3, the modeled aerosol particle light absorption coefficient was, depending on the wavelength, 13–32 % lower than the measured values. Spread and magnitude of the disagreement highlighted the importance of the aerosol mixing state used within the model, the requirement of the inclusion of brown carbon, and a wavelength-dependent complex refractive index of black and brown carbon when such kind of model is used to validate aerosol particle light absorption coefficient estimates of, e.g., lidar systems. Besides dry state comparisons, ambient modeled aerosol particle light extinction, as well as aerosol particle light backscattering, were compared with lidar estimates of these measures. During summer, on average, for four of the twelve conducted measurement flights, the model calculated lower aerosol particle light extinction (up to 29 % lower) as well as backscattering (up to 32 % lower) than derived with the lidar. In winter, the modeled aerosol particle light extinction coefficient was 17 %–41 % lower, the aerosol particle light backscattering coefficient 14 %–42 % lower than the lidar estimates. For both, the winter and summer cases, the Mie-model estimated reasonable extinction-to-backscatter (LR) ratios. Measurement-based Mie-modeling showed evidence of the dependence of the lidar ratio on relative humidity (RH). With this result, we presented a fit for lidar wavelengths of 355, 532, and 1064 nm with an underlying equation of fLR (RH,γ(λ)) = fLR (RH = 0,λ) × (1 − RH)(−γ(λ)) and estimates of γ(355 nm) = 0.29 (±0.01), γ(532 nm) = 0.48 (±0.01), and γ(1064 nm) = 0.31 (±0.01). However, further measurements are required to entangle the behavior of the lidar ratio with respect to different aerosol types, to set up a climatology, and to assess the influence of the aerosol mixing state. This comprehensive study combining airborne and ground-based in-situ and remote sensing measurements, which simulated multiple aerosol optical coefficients in the ambient and dry state, is with its complexity unique of its kind.

scholarly journals The Retrieval of Ice-Cloud Properties from Cloud Radar and Lidar Synergy

2005 ◽  
Vol 44 (6) ◽  
pp. 860-875 ◽  
Author(s):  
Claire Tinel ◽  
Jacques Testud ◽  
Jacques Pelon ◽  
Robin J. Hogan ◽  
Alain Protat ◽  
...  
Keyword(s):  
Extinction Coefficient ◽  
Radar Data ◽  
Mie Scattering ◽  
In Situ Measurements ◽  
Physical Parameters ◽  
Backscatter Coefficient ◽  
Blind Test ◽  
Cloud Radar ◽  
Microphysical Properties

Abstract Clouds are an important component of the earth’s climate system. A better description of their microphysical properties is needed to improve radiative transfer calculations. In the framework of the Earth, Clouds, Aerosols, and Radiation Explorer (EarthCARE) mission preparation, the radar–lidar (RALI) airborne system, developed at L’Institut Pierre Simon Laplace (France), can be used as an airborne demonstrator. This paper presents an original method that combines cloud radar (94–95 GHz) and lidar data to derive the radiative and microphysical properties of clouds. It combines the apparent backscatter reflectivity from the radar and the apparent backscatter coefficient from the lidar. The principle of this algorithm relies on the use of a relationship between the extinction coefficient and the radar specific attenuation, derived from airborne microphysical data and Mie scattering calculations. To solve radar and lidar equations in the cloud region where signals can be obtained from both instruments, the extinction coefficients at some reference range z0 must be known. Because the algorithms are stable for inversion performed from range z0 toward the emitter, z0 is chosen at the farther cloud boundary as observed by the lidar. Then, making an assumption of a relationship between extinction coefficient and backscattering coefficient, the whole extinction coefficient, the apparent reflectivity, cloud physical parameters, the effective radius, and ice water content profiles are derived. This algorithm is applied to a blind test for downward-looking instruments where the original profiles are derived from in situ measurements. It is also applied to real lidar and radar data, obtained during the 1998 Cloud Lidar and Radar Experiment (CLARE’98) field project when a prototype airborne RALI system was flown pointing at nadir. The results from the synergetic algorithm agree reasonably well with the in situ measurements.

scholarly journals Low hygroscopic scattering enhancement of boreal aerosol and the implications for a columnar optical closure study

2015 ◽  
Vol 15 (13) ◽  
pp. 7247-7267 ◽  
Author(s):  
P. Zieger ◽  
P. P. Aalto ◽  
V. Aaltonen ◽  
M. Äijälä ◽  
J. Backman ◽  
...  
Keyword(s):  
Light Scattering ◽  
Extinction Coefficient ◽  
Radiative Forcing ◽  
Mass Fraction ◽  
In Situ Measurements ◽  
Light Extinction ◽  
Minor Importance ◽  
Airborne Measurements ◽  
Sun Photometer

Abstract. Ambient aerosol particles can take up water and thus change their optical properties depending on the hygroscopicity and the relative humidity (RH) of the surrounding air. Knowledge of the hygroscopicity effect is of crucial importance for radiative forcing calculations and is also needed for the comparison or validation of remote sensing or model results with in situ measurements. Specifically, particle light scattering depends on RH and can be described by the scattering enhancement factor f(RH), which is defined as the particle light scattering coefficient at defined RH divided by its dry value (RH <30–40 %). Here, we present results of an intensive field campaign carried out in summer 2013 at the SMEAR II station at Hyytiälä, Finland. Ground-based and airborne measurements of aerosol optical, chemical and microphysical properties were conducted. The f(RH) measured at ground level by a humidified nephelometer is found to be generally lower (e.g. 1.63±0.22 at RH = 85 % and λ = 525 nm) than observed at other European sites. One reason is the high organic mass fraction of the aerosol encountered at Hyytiälä to which f(RH) is clearly anti-correlated (R2&amp;approx;0.8). A simplified parametrization of f(RH) based on the measured chemical mass fraction can therefore be derived for this aerosol type. A trajectory analysis revealed that elevated values of f(RH) and the corresponding elevated inorganic mass fraction are partially caused by transported hygroscopic sea spray particles. An optical closure study shows the consistency of the ground-based in situ measurements. Our measurements allow to determine the ambient particle light extinction coefficient using the measured f(RH). By combining the ground-based measurements with intensive aircraft measurements of the particle number size distribution and ambient RH, columnar values of the particle extinction coefficient are determined and compared to columnar measurements of a co-located AERONET sun photometer. The water uptake is found to be of minor importance for the column-averaged properties due to the low particle hygroscopicity and the low RH during the daytime of the summer months. The in situ derived aerosol optical depths (AOD) clearly correlate with directly measured values of the sun photometer but are substantially lower compared to the directly measured values (factor of ~ 2–3). The comparison degrades for longer wavelengths. The disagreement between in situ derived and directly measured AOD is hypothesized to originate from losses of coarse and fine mode particles through dry deposition within the canopy and losses in the in situ sampling lines. In addition, elevated aerosol layers (above 3 km) from long-range transport were observed using an aerosol lidar at Kuopio, Finland, about 200 km east-north-east of Hyytiälä. These elevated layers further explain parts of the disagreement.

scholarly journals Low hygroscopic scattering enhancement of boreal aerosol and the implications for a columnar optical closure study

2015 ◽  
Vol 15 (3) ◽  
pp. 3327-3379
Author(s):  
P. Zieger ◽  
P. P. Aalto ◽  
V. Aaltonen ◽  
M. Äijälä ◽  
J. Backman ◽  
...  
Keyword(s):  
Light Scattering ◽  
Extinction Coefficient ◽  
Radiative Forcing ◽  
Mass Fraction ◽  
In Situ Measurements ◽  
Light Extinction ◽  
Minor Importance ◽  
Airborne Measurements ◽  
Sun Photometer

Abstract. Ambient aerosol particles can take up water and thus change their optical properties depending on the hygroscopicity and the relative humidity (RH) of the surrounding air. Knowledge of the hygroscopicity effect is of crucial importance for radiative forcing calculations and is also needed for the comparison or validation of remote sensing or model results with in-situ measurements. Specifically, particle light scattering depends on RH and can be described by the scattering enhancement factor f(RH), which is defined as the particle light scattering coefficient at defined RH divided by its dry value (RH <30–40%). Here, we present results of an intensive field campaign carried out in summer 2013 at the SMEAR II station at Hyytiälä, Finland. Ground-based and airborne measurements of aerosol optical, chemical and microphysical properties were conducted. The f(RH) measured at ground by a humidified nephelometer is found to be significantly lower (1.53±0.24 at RH = 85% and λ=450 nm) than observed at other European sites. One reason is the high organic mass fraction of the aerosol encountered at Hyytiälä to which f(RH) is clearly anti-correlated (R2&amp;approx;0.8). A trajectory analysis revealed that elevated values of f(RH) and the corresponding elevated inorganic mass fraction are partially caused by transported hygroscopic sea spray particles. An optical closure study shows the consistency of the ground based in-situ measurements. Our measurements allow to determine the ambient particle light extinction coefficient using the measured f(RH). By combining the ground-based measurements with intensive aircraft measurements of the particle number size distribution and ambient RH, columnar values of the particle extinction coefficient are determined and compared to direct measurements of a co-located AERONET Sun photometer. The water uptake is found to be of minor importance for the column averaged properties due to the low particle hygroscopicity and the low RH during the daytime of the summer months. The in-situ derived aerosol optical depth (AOD) clearly correlates with directly measured values (R2&amp;approx;0.9 for λ = 400 nm to R2&amp;approx;0.6 for λ,=1000 nm), but is significantly lower compared to the Sun photometer AOD (slope ≈ 0.5). The comparison degrades for longer wavelengths. The disagreement between in-situ derived and directly measured AOD is hypothesized to originate from losses of coarse and fine mode particles through dry deposition within the canopy and losses in the in-situ sampling lines. In addition, elevated aerosol layers (above 3 km) from long-range transport were observed using an aerosol lidar at Kuopio, Finland, about 200 km east-northeast of Hyytiälä. These elevated layers further explain parts of the disagreement.

scholarly journals Aerosol optical and microphysical retrievals from a hybrid multiwavelength lidar data set – DISCOVER-AQ 2011

2014 ◽  
Vol 7 (9) ◽  
pp. 3095-3112 ◽  
Author(s):  
P. Sawamura ◽  
D. Müller ◽  
R. M. Hoff ◽  
C. A. Hostetler ◽  
R. A. Ferrare ◽  
...  
Keyword(s):  
Remote Sensing ◽  
In Situ Measurements ◽  
Index Of Refraction ◽  
High Spectral Resolution ◽  
Lidar Data ◽  
Data Set ◽  
Microphysical Properties ◽  
Lidar Measurements ◽  
Multiwavelength Lidar

Abstract. Retrievals of aerosol microphysical properties (effective radius, volume and surface-area concentrations) and aerosol optical properties (complex index of refraction and single-scattering albedo) were obtained from a hybrid multiwavelength lidar data set for the first time. In July 2011, in the Baltimore–Washington DC region, synergistic profiling of optical and microphysical properties of aerosols with both airborne (in situ and remote sensing) and ground-based remote sensing systems was performed during the first deployment of DISCOVER-AQ. The hybrid multiwavelength lidar data set combines ground-based elastic backscatter lidar measurements at 355 nm with airborne High-Spectral-Resolution Lidar (HSRL) measurements at 532 nm and elastic backscatter lidar measurements at 1064 nm that were obtained less than 5 km apart from each other. This was the first study in which optical and microphysical retrievals from lidar were obtained during the day and directly compared to AERONET and in situ measurements for 11 cases. Good agreement was observed between lidar and AERONET retrievals. Larger discrepancies were observed between lidar retrievals and in situ measurements obtained by the aircraft and aerosol hygroscopic effects are believed to be the main factor in such discrepancies.

scholarly journals Comparison of in situ and columnar aerosol spectral measurements during TexAQS-GoMACCS 2006: testing parameterizations for estimating aerosol fine mode properties

2009 ◽  
Vol 9 (4) ◽  
pp. 17465-17494
Author(s):  
D. B. Atkinson ◽  
P. Massoli ◽  
N. T. O'Neill ◽  
P. K. Quinn ◽  
S. Brooks ◽  
...  
Keyword(s):  
Gulf Of Mexico ◽  
Atmospheric Aerosols ◽  
Regional Scale ◽  
Atmospheric Composition ◽  
Light Extinction ◽  
Large Area ◽  
Light Extinction Coefficient ◽  
Spectral Models ◽  
Fine Mode

Abstract. During the 2006 Texas Air Quality Study and Gulf of Mexico Atmospheric Composition and Climate Study (TexAQS-GoMACCS 2006), the optical, chemical and microphysical properties of atmospheric aerosols were measured on multiple mobile platforms and at ground based stations. In situ measurements of the aerosol light extinction coefficient (σep) were performed by two multi-wavelength cavity ring-down (CRD) instruments, one located on board the NOAA R/V Ronald H. Brown (RHB) and the other located at the University of Houston, Moody Tower (UHMT). An AERONET sunphotometer was also located at the UHMT to measure the columnar aerosol optical depth (AOD). The σep data were used to extract the extinction Ångström exponent (åep), a measure of the wavelength dependence of σep. There was general agreement between the åep (and to a lesser degree σep measurements by the two spatially separated CRD instruments during multi-day periods, suggesting a regional scale consistency of the sampled aerosols. Two spectral models are applied to the σep and AOD data to extract the fine mode fraction of extinction (η) and the fine mode effective radius (Reff f). These two parameters are robust measures of the fine mode contribution to total extinction and the fine mode size distribution respectively. The results of the analysis are compared to Reff f values extracted using AERONET V2 retrievals and calculated from in situ particle size measurements on the RHB and at UHMT. During a time period when fine mode aerosols dominated the extinction over a large area extending from Houston/Galveston Bay and out into the Gulf of Mexico, the various methods for obtaining Reff f agree qualitatively (showing the same temporal trend) and quantitatively (pooled standard deviation=28 nm).

scholarly journals Validation of aerosol backscatter profiles from Raman lidar and ceilometer using balloon-borne measurements

2021 ◽  
Vol 21 (3) ◽  
pp. 2267-2285
Author(s):  
Simone Brunamonti ◽  
Giovanni Martucci ◽  
Gonzague Romanens ◽  
Yann Poltera ◽  
Frank G. Wienhold ◽  
...  
Keyword(s):  
Remote Sensing ◽  
In Situ Measurements ◽  
Aerosol Size Distribution ◽  
Spatial And Temporal Variability ◽  
Raman Lidar ◽  
Backscatter Coefficient ◽  
Custom Made ◽  
Aerosol Backscatter ◽  
Good Agreement

Abstract. Remote-sensing measurements by light detection and ranging (lidar) instruments are fundamental for the monitoring of altitude-resolved aerosol optical properties. Here we validate vertical profiles of aerosol backscatter coefficient (βaer) measured by two independent lidar systems using co-located balloon-borne measurements performed by Compact Optical Backscatter Aerosol Detector (COBALD) sondes. COBALD provides high-precision in situ measurements of βaer at two wavelengths (455 and 940 nm). The two analyzed lidar systems are the research Raman Lidar for Meteorological Observations (RALMO) and the commercial CHM15K ceilometer (Lufft, Germany). We consider in total 17 RALMO and 31 CHM15K profiles, co-located with simultaneous COBALD soundings performed throughout the years 2014–2019 at the MeteoSwiss observatory of Payerne (Switzerland). The RALMO (355 nm) and CHM15K (1064 nm) measurements are converted to 455 and 940 nm, respectively, using the Ångström exponent profiles retrieved from COBALD data. To account for the different receiver field-of-view (FOV) angles between the two lidars (0.01–0.02∘) and COBALD (6∘), we derive a custom-made correction using Mie-theory scattering simulations. Our analysis shows that both lidar instruments achieve on average a good agreement with COBALD measurements in the boundary layer and free troposphere, up to 6 km altitude. For medium-high-aerosol-content measurements at altitudes below 3 km, the mean ± standard deviation difference in βaer calculated from all considered soundings is −2 % ± 37 % (−0.018 ± 0.237 Mm−1 sr−1 at 455 nm) for RALMO−COBALD and +5 % ± 43 % (+0.009 ± 0.185 Mm−1 sr−1 at 940 mm) for CHM15K−COBALD. Above 3 km altitude, absolute deviations generally decrease, while relative deviations increase due to the prevalence of air masses with low aerosol content. Uncertainties related to the FOV correction and spatial- and temporal-variability effects (associated with the balloon's drift with altitude and different integration times) contribute to the large standard deviations observed at low altitudes. The lack of information on the aerosol size distribution and the high atmospheric variability prevent an accurate quantification of these effects. Nevertheless, the excellent agreement observed in individual profiles, including fine and complex structures in the βaer vertical distribution, shows that under optimal conditions, the discrepancies with the in situ measurements are typically comparable to the estimated statistical uncertainties in the remote-sensing measurements. Therefore, we conclude that βaer profiles measured by the RALMO and CHM15K lidar systems are in good agreement with in situ measurements by COBALD sondes up to 6 km altitude.

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