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Impact of pitch angle fluctuations on airborne lidar forward sensing along the flight direction
摘要： Airborne lidar forward sensing along the ?ight direction can serve for noti?cation of clear air turbulence (CAT) and help to prevent injuries or fatal air accidents. The validation of this concept was presented in the framework of the DELICAT (DEmonstration of LIdar-based CAT detec- tion) project. However, the strong variations in signal level, which were observed during the DELICAT measurements but not explained, sometimes indicated the need of a bet- ter understanding the observational errors due to geometrical factors. In this paper, we discuss possible error sources perti- nent to this technique, related to ?uctuations of the ?ight pa- rameters, which may lead to strong signal variations caused by the random deviations of the sensing beam from the for- ward ?ight trajectory. We analyze the variations in backscat- tered lidar signal caused by ?uctuations of the most impor- tant forward-sensing ?ight parameter, the pitch angle. The ?uctuation values considered in the paper correspond to the error limits of the compensational gyro platform used in civil aviation. The part of the pitch angle ?uctuations not com- pensated for by the beam-steering device in the presence of aerosol concentration variations can lead to noticeable signal variations that can be mistakenly attributed to wind shear, turbulence, or fast evolution of the aerosol layer. We formu- late the criteria that allow the recognition of signal variations caused by pitch angle ?uctuations. In?uence of these ?uc- tuations is shown to be stronger for aerosol variations on smaller vertical scales. An example of DELICAT observa- tions indicating a noticeable pitch angle ?uctuation impact is presented.
关键词： clear air turbulence,signal variations,pitch angle fluctuations,aerosol clusters,airborne lidar
更新于2025-09-09 09:28:46
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Constrained two-stream algorithm for calculating aerosol light absorption coefficient from the Particle Soot Absorption Photometer
摘要： We present a new correction scheme for filter-based absorption photometers based on a constrained two-stream (CTS) radiative transfer model and experimental calibrations. The two-stream model was initialized using experimentally accessible optical parameters of the filter. Experimental calibrations were taken from the literature and from dedicated experiments for the present manuscript. Uncertainties in the model and calibration experiments are discussed and uncertainties for retrieval of absorption coefficients are derived. For single-scattering albedos lower than 0.8, the new CTS method and also other correction schemes suffer from the uncertainty in calibration experiments, with an uncertainty of about 20 % in the absorption coefficient. For high single-scattering albedos, the CTS correction significantly reduces errors. At a single-scattering albedo of about 0.98 the error can be reduced to 30 %, whereas errors using the Bond correction (Bond et al., 1999) are up to 100 %. The correction scheme was tested using data from an independent experiment. The tests confirm the modeled performance of the correction scheme when comparing the CTS method to other established correction methods.
关键词： filter-based absorption photometers,radiative transfer,correction scheme,constrained two-stream model,aerosol light absorption
更新于2025-09-09 09:28:46
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MAX-DOAS retrieval of aerosol extinction properties in Madrid, Spain
摘要： Multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements were performed in the urban environment of Madrid, Spain, from March to September 2015. The O4 absorption in the ultraviolet (UV) spectral region was used to retrieve the aerosol extinction profile using an inversion algorithm. The results show a good agreement between the hourly retrieved aerosol optical depth (AOD) and the correlative Aerosol Robotic Network (AERONET) product, with a correlation coefficient of R = 0.87. Higher AODs are found in the summer season due to the more frequent occurrence of Saharan dust intrusions. The surface aerosol extinction coefficient as retrieved by the MAX-DOAS measurements was also compared to in situ PM2.5 concentrations. The level of agreement between both measurements indicates that the MAX-DOAS retrieval has the ability to characterize the extinction of aerosol particles near the surface. The retrieval algorithm was also used to study a case of severe dust intrusion on 12 May 2015. The capability of the MAX-DOAS retrieval to recognize the dust event including an elevated particle layer is investigated along with air mass back-trajectory analysis.
关键词： AOD,PM2.5,aerosol extinction,MAX-DOAS,O4 absorption,Madrid,Saharan dust
更新于2025-09-09 09:28:46
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Tuning the Porosity of TiO2 Nanoparticles via Surfactant-Templated Aerosol Process for Enhanced Photocatalytic Reactivity
摘要： In this work, we fabricated crystallite solid and porous TiO2 nanoparticles (NPs) using a surfactant-templated aerosol process. Specifically, Brij-58 surfactant was employed as a template in TiO2 matrix. The porosity of TiO2 NPs was controlled by varying the amount of Brij-58. The effect of TiO2 porosity on the photocatalytic reactivity was systematically examined. As a result, the highly porous TiO2 NPs exhibited much better photocatalytic reactivity than the low porosity TiO2 NPs. This suggests that the particle size, crystallite structure, and specific surface area play an important role in enhancing the photocatalytic reactivity of the TiO2 NPs.
关键词： surfactants,Aerosol process,photocatalysts,porous TiO2 nanoparticles,specific surface area
更新于2025-09-09 09:28:46
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Estimation of aerosol complex refractive indices for both fine and coarse modes simultaneously based on AERONET remote sensing products
摘要： Climate change assessment, especially model evaluation, requires a better understanding of complex refractive indices (CRIs) of atmospheric aerosols – separately for both fine and coarse modes. However, the widely used aerosol CRI obtained by the global Aerosol Robotic Network (AERONET) corresponds to total-column aerosol particles without separation for fine and coarse modes. This paper establishes a method to separate CRIs of fine and coarse particles based on AERONET volume particle size distribution (VPSD), aerosol optical depth (AOD) and absorbing AOD (AAOD). The method consists of two steps. First a multimodal log-normal distribution that best approximates the AERONET VPSD is found. Then the fine and coarse mode CRIs are found by iterative fitting of AERONET AODs to Mie calculations. The numerical experiment shows good performance for typical water-soluble, biomass burning and dust aerosol types, and the estimated uncertainties on the retrieved sub-mode CRIs are about 0.11 (real part) and 78 % (imaginary part). The 1-year measurements at the AERONET Beijing site are processed, and we obtain CRIs of 1.48–0.010i (imaginary part at 440 nm is 0.012) for fine mode particles and 1.49–0.004i (imaginary part at 440 nm is 0.007) for coarse mode particles, for the period of 2014–2015. Our results also suggest that both fine and coarse aerosol mode CRIs have distinct seasonal characteristics; in particular, CRIs of fine particles in winter season are significantly higher than summer due to possible anthropogenic influences.
关键词： complex refractive indices,fine and coarse modes,AERONET,remote sensing,aerosol
更新于2025-09-09 09:28:46
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Clear-air lidar dark band
摘要： This paper illustrates measurements carried out by the Raman lidar BASIL in the frame of the HD(CP)2) Observational Prototype Experiment (HOPE), revealing the presence of a clear-air dark band phenomenon (i.e. a minimum in lidar backscatter echoes) in the upper portion of the convective boundary layer. The phenomenon is clearly distinguishable in the lidar backscatter echoes at 532 and 1064 nm, as well as in the particle depolarization data. This phenomenon is attributed to the presence of lignite aerosol particles advected from the surrounding open pit mines in the vicinity of the measuring site. The paper provides evidence of the phenomenon and illustrates possible interpretations for its occurrence.
关键词： convective boundary layer,backscatter echoes,Raman lidar,clear-air dark band,lignite aerosol particles
更新于2025-09-09 09:28:46
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Aerosol retrieval from multiangle, multispectral photopolarimetric measurements: importance of spectral range and angular resolution
摘要： We investigated the importance of spectral range and angular resolution for aerosol retrieval from multiangle photopolarimetric measurements over land. For this purpose, we use an extensive set of simulated measurements for different spectral ranges and angular resolutions and subsets of real measurements of the airborne Research Scanning Polarimeter (RSP) carried out during the PODEX and SEAC4RS campaigns over the continental USA. Aerosol retrievals performed from RSP measurements show good agreement with ground-based AERONET measurements for aerosol optical depth (AOD), single scattering albedo (SSA) and refractive index. Furthermore, we found that inclusion of shortwave infrared bands (1590 and/or 2250 nm) significantly improves the retrieval of AOD, SSA and coarse mode microphysical properties. However, accuracies of the retrieved aerosol properties do not improve significantly when more than five viewing angles are used in the retrieval.
关键词： spectral range,aerosol retrieval,angular resolution,AERONET,multiangle photopolarimetric measurements,RSP
更新于2025-09-09 09:28:46
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LOAC: a small aerosol optical counter/sizer for ground-based and balloon measurements of the size distribution and nature of atmospheric particles – Part 2: First results from balloon and unmanned aerial vehicle flights
摘要： In the companion (Part I) paper, we have described and evaluated a new versatile optical particle counter/sizer named LOAC (Light Optical Aerosol Counter), based on scattering measurements at angles of 12 and 60?. That allows for some typology identification of particles (droplets, carbonaceous, salts, and mineral dust) in addition to size-segregated counting in a large diameter range from 0.2 μm up to possibly more than 100 μm depending on sampling conditions (Renard et al., 2016). Its capabilities overpass those of preceding optical particle counters (OPCs) allowing the characterization of all kind of aerosols from submicronic-sized absorbing carbonaceous particles in polluted air to very coarse particles (> 10–20 μm in diameter) in desert dust plumes or fog and clouds. LOAC’s light and compact design allows measurements under all kinds of balloons, on-board unmanned aerial vehicles (UAVs) and at ground level. We illustrate here the first LOAC airborne results obtained from a UAV and a variety of scientific balloons. The UAV was deployed in a peri-urban environment near Bordeaux in France. Balloon operations include (i) tethered balloons deployed in urban environments in Vienna (Austria) and Paris (France), (ii) pressurized balloons drifting in the lower troposphere over the western Mediterranean (during the Chemistry-Aerosol Mediterranean Experiment – ChArMEx campaigns), (iii) meteorological sounding balloons launched in the western Mediterranean region (ChArMEx) and from Aire-sur-l’Adour in south-western France (VOLTAIRE-LOAC campaign). More focus is put on measurements performed in the Mediterranean during (ChArMEx) and especially during African dust transport events to illustrate the original capability of balloon-borne LOAC to monitor in situ coarse mineral dust particles. In particular, LOAC has detected unexpected large particles in desert sand plumes.
关键词： balloon measurements,optical particle counter,desert dust,LOAC,troposphere,aerosol,UAV,stratosphere
更新于2025-09-09 09:28:46
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Characterizing the size and absorption of single nonspherical aerosol particles from angularly-resolved elastic light scattering
摘要： Measuring the absorption of a single aerosol particle is a challenging endeavor. Of the few techniques available, none are suitable for measuring the single-particle absorption of coarse-mode nonspherical aerosols. Analysis of two-dimensional angular optical scattering (TAOS) patterns provide a possible pathway to perform this measurement. Using a Multiple-Sphere T-Matrix (MSTM) code, we simulate the captured TAOS patterns with geometries similar to a previously designed instrument. By analyzing the size of the speckle and the integrated irradiance of these simulated TAOS patterns, we are able to distinguish between high-absorbing, weak-absorbing, and non-absorbing particles over the size range of 2μm to 10μm. In particular, the speckle present in the scattering patterns provides a means to estimate the size of the particle. Once the size of the particle is known, the integrated irradiance provides insight into the absorption of the particle.
关键词： Absorption,Elastic Light Scattering,Aerosol,Single Particle
更新于2025-09-09 09:28:46
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Multiple scattering correction factor estimation for aethalometer aerosol absorption coefficient measurement
摘要： We estimate the multiple scattering correction factor (????????), which is an empirical constant required to correct aerosol absorption coefficient (??????) measurements for the multiple scattering artefacts of aethalometer, using a multiplier derived from a linear regression method ( ???????? ?????? ). Estimated ???????? ?????? values during the Cheju ABC Plume Monsoon EXperiment (CAPMEX) are 3.99 (405 nm), 4.48 (532 nm), and 5.46 (781 nm) using aethalometer and 3-wavelength PhotoAcoustic Soot Spectrometer (PASS-3). The difference between these ???????? ?????? values and those of a previous study ( ???????? ??03 ; Weingartner et al. 2003) are -8.0% (405 nm), 20.1% (532 nm), and 30.2% (781 nm); the larger. ???????? difference is greater at larger wavelengths because the linear regression line intercept is ??03 varies by up to 121% with increasing aerosol absorption coefficient (??????) ?????? determined ?????? varies by only 36.8%. ???????? ??03 and ???????? ??03 ?????? ??03 and ?????? ??03 and ?????? from ?????? ?????? and ?????? ??03 and ?????? ???????? than ?????? agrees better with ?????? ????????. This suggest that square difference of ?????? ???????? are -23.1 and 25.8%; however, those of ?????? ???????? are -9.0 and 17.9%, respectively. LLN and ALT both exhibit a greater Absorption Photometer (CLAP; ?????? ??03 from ?????? ???????? than between ?????? difference between ?????? ?????? can be applied to year-round aethalometer measurements. Furthermore, ?????? ???????? during CAPMEX were applied to year-round aethalometer ?????? measurements (?????? ??????, respectively) at Gosan (GSN), Lulin (LLN), and Alert (ALT) stations. ?????? ?????? were compared to concurrent ?????? measurements from Continuous Light ????????). At GSN, the bias difference and root mean ??03 in all three environments.
关键词： CLAP,multiple scattering correction factor,aerosol absorption coefficient,PASS-3,aethalometer
更新于2025-09-09 09:28:46