scholarly journals Retrieval of aerosol backscatter, extinction, and lidar ratio from Raman lidar with optimal estimation

2014 ◽  
Vol 7 (3) ◽  
pp. 757-776 ◽  
Author(s):  
A. C. Povey ◽  
R. G. Grainger ◽  
D. M. Peters ◽  
J. L. Agnew
Keyword(s):  
Boundary Layer ◽  
Prior Knowledge ◽  
Optimal Estimation ◽  
Real Data ◽  
Raman Lidar ◽  
Ash Layer ◽  
Lidar Ratio ◽  
Aerosol Backscatter ◽  
Lidar Observations

Abstract. Optimal estimation retrieval is a form of nonlinear regression which determines the most probable circumstances that produced a given observation, weighted against any prior knowledge of the system. This paper applies the technique to the estimation of aerosol backscatter and extinction (or lidar ratio) from two-channel Raman lidar observations. It produces results from simulated and real data consistent with existing Raman lidar analyses and additionally returns a more rigorous estimate of its uncertainties while automatically selecting an appropriate resolution without the imposition of artificial constraints. Backscatter is retrieved at the instrument's native resolution with an uncertainty between 2 and 20%. Extinction is less well constrained, retrieved at a resolution of 0.1–1 km depending on the quality of the data. The uncertainty in extinction is > 15%, in part due to the consideration of short 1 min integrations, but is comparable to fair estimates of the error when using the standard Raman lidar technique. The retrieval is then applied to several hours of observation on 19 April 2010 of ash from the Eyjafjallajökull eruption. A depolarising ash layer is found with a lidar ratio of 20–30 sr, much lower values than observed by previous studies. This potentially indicates a growth of the particles after 12–24 h within the planetary boundary layer. A lower concentration of ash within a residual layer exhibited a backscatter of 10 Mm−1 sr−1 and lidar ratio of 40 sr.

scholarly journals Retrieval of aerosol backscatter, extinction, and lidar ratio from Raman lidar with optimal estimation

2013 ◽  
Vol 6 (5) ◽  
pp. 9297-9346
Author(s):  
A. C. Povey ◽  
R. G. Grainger ◽  
D. M. Peters ◽  
J. L. Agnew
Keyword(s):  
Boundary Layer ◽  
Linear Regression ◽  
Optimal Estimation ◽  
Real Data ◽  
Raman Lidar ◽  
Ash Layer ◽  
Lidar Ratio ◽  
Aerosol Backscatter ◽  
Lidar Observations

Abstract. Optimal estimation retrieval is a form of non-linear regression which determines the most probable circumstances that produced a given observation, weighted against any prior knowledge of the system. This paper applies the technique to the estimation of aerosol backscatter and extinction (or lidar ratio) from two-channel Raman lidar observations. It produces results from simulated and real data consistent with existing Raman lidar analyses and additionally returns a more rigorous estimate of its uncertainties while automatically selecting an appropriate resolution without the imposition of artificial constraints. Backscatter is retrieved at the instrument's native resolution with an uncertainty between 2 and 20%. Extinction is less well constrained, retrieved at a resolution of 0.1–1 km depending on the quality of the data. The uncertainty in extinction is >15%, in part due to the consideration of short one-minute integrations, but is comparable to fair estimates of the error when using the standard Raman lidar technique. The retrieval is then applied to several hours of observation on 19 April 2010 of ash from the Eyjafjallajökull eruption. A highly depolarizing ash layer is found with a lidar ratio of 20–30 sr, much lower values than observed by previous studies. This potentially indicates a growth of the particles after 12–24 h within the planetary boundary layer. A lower concentration of ash within a residual layer exhibited a backscatter of 10 Mm−1 sr−1 and lidar ratio of 40 sr.

scholarly journals 1064 nm rotational Raman lidar for particle extinction and lidar-ratio profiling: cirrus case study

2016 ◽  
Vol 9 (9) ◽  
pp. 4269-4278 ◽  
Author(s):  
Moritz Haarig ◽  
Ronny Engelmann ◽  
Albert Ansmann ◽  
Igor Veselovskii ◽  
David N. Whiteman ◽  
...  
Keyword(s):  
Good Accuracy ◽  
Lower Troposphere ◽  
Vertical Profiles ◽  
Raman Lidar ◽  
Extinction Coefficients ◽  
Lidar Ratio ◽  
Raman Backscatter ◽  
First Time ◽  
Lidar Observations

Abstract. For the first time, vertical profiles of the 1064 nm particle extinction coefficient obtained from Raman lidar observations at 1058 nm (nitrogen and oxygen rotational Raman backscatter) are presented. We applied the new technique in the framework of test measurements and performed several cirrus observations of particle backscatter and extinction coefficients, and corresponding extinction-to-backscatter ratios at the wavelengths of 355, 532, and 1064 nm. The cirrus backscatter coefficients were found to be equal for all three wavelengths keeping the retrieval uncertainties in mind. The multiple-scattering-corrected cirrus extinction coefficients at 355 nm were on average about 20–30 % lower than the ones for 532 and 1064 nm. The cirrus-mean extinction-to-backscatter ratio (lidar ratio) was 31 ± 5 sr (355 nm), 36 ± 5 sr (532 nm), and 38 ± 5 sr (1064 nm) in this single study. We further discussed the requirements needed to obtain aerosol extinction profiles in the lower troposphere at 1064 nm with good accuracy (20 % relative uncertainty) and appropriate temporal and vertical resolution.

scholarly journals Lidar Observations of the Vertical Aerosol Flux in the Planetary Boundary Layer

2008 ◽  
Vol 25 (8) ◽  
pp. 1296-1306 ◽  
Author(s):  
Ronny Engelmann ◽  
Ulla Wandinger ◽  
Albert Ansmann ◽  
Detlef Müller ◽  
Egidijus Žeromskis ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Vertical Wind ◽  
Particle Mass ◽  
Eddy Correlation ◽  
Correlation Technique ◽  
Atmospheric Conditions ◽  
Raman Lidar ◽  
Mass Fluxes ◽  
Lidar Observations

Abstract The vertical aerosol transport in the planetary boundary layer (PBL) is investigated with lidars. Profiles of the vertical wind velocity are measured with a 2-μm Doppler wind lidar. Aerosol parameters are derived from observations with an aerosol Raman lidar. Both instruments were operated next to each other at the Institute for Tropospheric Research (IfT) in Leipzig, Germany. The eddy correlation technique is applied to calculate turbulent particle mass fluxes on the basis of aerosol backscatter and vertical wind data obtained with a resolution of 75 m and 5 s throughout the PBL. A conversion of particle backscatter to particle mass is performed by applying the IfT inversion scheme to three-wavelength Raman lidar observations. The method, so far, is restricted to stationary and dry atmospheric conditions under which hygroscopic particle growth can be neglected. In a case study, particle mass fluxes of 0.5–2.5 μg m−2 s−1 were found in the upper part of a convective PBL on 12 September 2006.

scholarly journals Profiling of Saharan dust from the Caribbean to western Africa – Part 1: Layering structures and optical properties from shipborne polarization/Raman lidar observations

2017 ◽  
Vol 17 (21) ◽  
pp. 12963-12983 ◽  
Author(s):  
Franziska Rittmeister ◽  
Albert Ansmann ◽  
Ronny Engelmann ◽  
Annett Skupin ◽  
Holger Baars ◽  
...  
Keyword(s):  
Optical Properties ◽  
Conceptual Model ◽  
Long Range Transport ◽  
Tropical Atlantic ◽  
Raman Lidar ◽  
Western Africa ◽  
Range Transport ◽  
Lidar Ratio ◽  
The Caribbean ◽  
Lidar Observations

Abstract. We present final and quality-assured results of multiwavelength polarization/Raman lidar observations of the Saharan air layer (SAL) over the tropical Atlantic. Observations were performed aboard the German research vessel R/V Meteor during the 1-month transatlantic cruise from Guadeloupe to Cabo Verde over 4500 km from 61.5 to 20° W at 14–15° N in April–May 2013. First results of the shipborne lidar measurements, conducted in the framework of SALTRACE (Saharan Aerosol Long-range Transport and Aerosol–Cloud Interaction Experiment), were reported by Kanitz et al.(2014). Here, we present four observational cases representing key stages of the SAL evolution between Africa and the Caribbean in detail in terms of layering structures and optical properties of the mixture of predominantly dust and aged smoke in the SAL. We discuss to what extent the lidar results confirm the validity of the SAL conceptual model which describes the dust long-range transport and removal processes over the tropical Atlantic. Our observations of a clean marine aerosol layer (MAL, layer from the surface to the SAL base) confirm the conceptual model and suggest that the removal of dust from the MAL, below the SAL, is very efficient. However, the removal of dust from the SAL assumed in the conceptual model to be caused by gravitational settling in combination with large-scale subsidence is weaker than expected. To explain the observed homogenous (height-independent) dust optical properties from the SAL base to the SAL top, from the African coast to the Caribbean, we have to assume that the particle sedimentation strength is reduced and dust vertical mixing and upward transport mechanisms must be active in the SAL. Based on lidar observations on 20 nights at different longitudes in May 2013, we found, on average, MAL and SAL layer mean values (at 532 nm) of the extinction-to-backscatter ratio (lidar ratio) of 17±5 sr (MAL) and 43±8 sr (SAL), of the particle linear depolarization ratio of 0.025±0.015 (MAL) and 0.19±0.09 (SAL), and of the particle extinction coefficient of 67±45 Mm−1 (MAL) and 68±37 Mm−1 (SAL). The 532 nm optical depth of the lofted SAL was found to be, on average, 0.15±0.13 during the ship cruise. The comparably low values of the SAL mean lidar ratio and depolarization ratio (compared to typical pure dust values of 50–60 sr and 0.3, respectively) in combination with backward trajectories indicate a smoke contribution to light extinction of the order of 20 % during May 2013, at the end of the burning season in central-western Africa.

scholarly journals Strengths and limitations of the NATALI code for aerosol typing from multiwavelength Raman lidar observations

2018 ◽  
Vol 176 ◽  
pp. 05005 ◽  
Author(s):  
Doina Nicolae ◽  
Camelia Talianu ◽  
Jeni Vasilescu ◽  
Victor Nicolae ◽  
Iwona S. Stachlewska
Keyword(s):  
Neural Networks ◽  
Optical Parameters ◽  
Raman Lidar ◽  
Extinction Data ◽  
Aerosol Model ◽  
Predominant Component ◽  
Lidar Observations ◽  
Aerosol Type ◽  
Made In

A Python code was developed to automatically retrieve the aerosol type (and its predominant component in the mixture) from EARLINET’s 3 backscatter and 2 extinction data. The typing relies on Artificial Neural Networks which are trained to identify the most probable aerosol type from a set of mean-layer intensive optical parameters. This paper presents the use and limitations of the code with respect to the quality of the inputed lidar profiles, as well as with the assumptions made in the aerosol model.

scholarly journals 1064 nm Raman lidar for extinction and lidar ratio profiling: Cirrus case study

2016 ◽  
Author(s):  
Moritz Haarig ◽  
Ronny Engelmann ◽  
Albert Ansmann ◽  
Igor Veselovskii ◽  
David N. Whiteman ◽  
...  
Keyword(s):  
Extinction Coefficient ◽  
New Technique ◽  
Vertical Profiles ◽  
Raman Lidar ◽  
Extinction Coefficients ◽  
Lidar Ratio ◽  
Raman Backscatter ◽  
First Time ◽  
Lidar Observations

Abstract. For the first time, vertical profiles of the 1064 nm particle extinction coefficient obtained from Raman lidar observations at 1058 nm (nitrogen rotational Raman backscatter) are presented. We applied the new technique in the framework of test measurements and performed several cirrus observations of particle backscatter and extinction coefficients, and corresponding extinction-to-backscatter ratios at the wavelengths of 355, 532m and 1064 nm.

scholarly journals Seasonal variability of aerosol optical properties observed by means of a Raman lidar at an EARLINET site over Northeastern Spain

2011 ◽  
Vol 11 (1) ◽  
pp. 175-190 ◽  
Author(s):  
M. Sicard ◽  
F. Rocadenbosch ◽  
M. N. M. Reba ◽  
A. Comerón ◽  
S. Tomás ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Optical Properties ◽  
Planetary Boundary Layer ◽  
Optical Thickness ◽  
Seasonal Variability ◽  
Aerosol Optical Thickness ◽  
Saharan Dust ◽  
Raman Lidar ◽  
Aerosol Optical Properties ◽  
Lidar Ratio

Abstract. The annual and seasonal variability of aerosol optical properties observed by means of a Raman lidar over Northeastern Spain has been assessed. The lidar representativeness has first been checked against sun-photometer measurements in terms of aerosol optical thickness. Then the annual cycle and the seasonal variability of the planetary boundary layer aerosol optical thickness and its fraction compared to the columnar optical thickness, the lidar ratio, the backscatter-related Ångström exponent and the planetary boundary layer height are analyzed and discussed. Winter and summer mean profiles of extinction, backscatter and lidar ratio retrieved with the Raman algorithm are presented. The analysis shows the impact of most of the natural events (Saharan dust intrusions, wildfires, etc.) and meteorological situations (summer anticyclonic situation, the formation of the Iberian thermal low, winter long-range transport from North Europe and/or North America, re-circulation flows, etc.) occurring in the Barcelona area. A detailed study of a special event including a combined intrusion of Saharan dust and biomass-burning particles proves the suitability of combining the retrieval of aerosol optical properties from Raman and pure elastic lidar measurements to discriminate spatially different types of aerosols and to follow their spatial and temporal evolution.

scholarly journals Continuous monitoring of the boundary-layer top with lidar

2008 ◽  
Vol 8 (3) ◽  
pp. 10749-10790 ◽  
Author(s):  
H. Baars ◽  
A. Ansmann ◽  
R. Engelmann ◽  
D. Althausen
Keyword(s):  
Boundary Layer ◽  
Weather Forecast ◽  
Forecast Model ◽  
Raman Lidar ◽  
Data Set ◽  
Weather Forecast Model ◽  
One Year ◽  
The One ◽  
Lidar Observations

Abstract. Continuous lidar observations of the top height of the boundary layer (BL top) have been performed at Leipzig (51.3° N, 12.4° E), Germany, since August 2005. The results of measurements taken with a compact, automated Raman lidar over a one-year period (February 2006 to January 2007) are presented. Four different methods for the determination of the BL top are discussed. The most promising technique, the wavelet covariance algorithm, is improved by implementing some modifications so that an automated, robust retrieval of BL depths from lidar data is possible. Three case studies of simultaneous observations with the Raman lidar, a vertical-wind Doppler lidar, and accompanying radiosonde profiling of temperature and humidity are discussed to demonstrate the potential and the limits of the four lidar techniques at different aerosol and meteorological conditions. The lidar-derived BL top heights are compared with respective values derived from predictions of the regional weather forecast model COSMO of the German Meteorological Service. The comparison shows a general underestimation of the BL top by about 20% by the model. The statistical analysis of the one-year data set reveals that the seasonal mean of the daytime maximum BL top is 1400 m in spring, 1800 m in summer, 1200 m in autumn, and 800 m in winter at the continental, central European site. BL top typically increases by 100–300 m per hour in the morning of convective days.

scholarly journals Capabilities of an Automatic Lidar Ceilometer to Retrieve Aerosol Characteristics within the Planetary Boundary Layer

2021 ◽  
Vol 13 (18) ◽  
pp. 3626
Author(s):  
Dingdong Li ◽  
Yonghua Wu ◽  
Barry Gross ◽  
Fred Moshary
Keyword(s):  
Boundary Layer ◽  
New York ◽  
Planetary Boundary Layer ◽  
Relative Error ◽  
Satellite Observation ◽  
Calibration Error ◽  
Backscatter Coefficient ◽  
Ratio Error ◽  
Lidar Ratio ◽  
Aerosol Backscatter

Continuous observation and quantitative retrieval of aerosol backscatter coefficients are important in the study of air quality and climate in metropolitan areas such as New York City. Ceilometers are ideal for this application, but aerosol backscatter coefficient retrievals from ceilometers are challenging and require proper calibration. In this study, we calibrate the ceilometer (Lufft CHM15k, 1064 nm) system constant with the molecular backscatter coefficient and evaluate the calibrated profiles with other independent methods, including the water-phase cloud method and comparison with the NASA Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) attenuated backscatter coefficient profile. Multiple-day calibration results show a stable system constant with a relative uncertainty of about 7%. We also evaluate the overlap correction for the CHM15k ceilometer (provided by Lufft) with a Vaisala CL-31 ceilometer, and the results show good consistency between two ceilometers’ range-corrected signal (RCS) profiles above 200 m. Next, we implement a forward iterative method to retrieve aerosol backscatter coefficients from continuous ceilometer measurements. In the retrieval, the lidar ratio is constrained by the co-located NASA AERONET radiometer aerosol optical depth (AOD) retrieval and agrees with the AERONET lidar-ratio products, derived from aerosol microphysical parameters. The aerosol backscatter coefficient retrievals are validated with co-located elastic-Raman lidar retrievals and indicate a good correlation (R2≥0.95) in the planetary boundary layer (PBL). Furthermore, a case study shows that the ceilometer retrieved aerosol extinction coefficient profiles can be used to estimate the AOD of the PBL and the aloft plumes. Finally, simulations of the uncertainty of aerosol backscatter coefficient retrieval show that a calibration error of 10% results in 10–20% of relative error in the aerosol backscatter coefficient retrievals, while relative error caused by a lidar-ratio error of 10% is less than 4% in the PBL.

scholarly journals Continuous monitoring of the boundary-layer top with lidar

2008 ◽  
Vol 8 (23) ◽  
pp. 7281-7296 ◽  
Author(s):  
H. Baars ◽  
A. Ansmann ◽  
R. Engelmann ◽  
D. Althausen
Keyword(s):  
Boundary Layer ◽  
Weather Forecast ◽  
Forecast Model ◽  
Raman Lidar ◽  
Data Set ◽  
Weather Forecast Model ◽  
One Year ◽  
The One ◽  
Lidar Observations

Abstract. Continuous lidar observations of the top height of the boundary layer (BL top) have been performed at Leipzig (51.3° N, 12.4° E), Germany, since August 2005. The results of measurements taken with a compact, automated Raman lidar over a one–year period (February 2006 to January 2007) are presented. Main goals of the study are (a) to demonstrate that BL top monitoring with lidar throughout the year is possible, (b) to present the required data analysis method that permits an automated, robust retrieval of BL top at all weather situations, and (c) to use this opportunity to compare the lidar-derived BL top data with respective BL tops hourly predicted by the regional weather forecast model COSMO. Four different lidar methods for the determination of the BL top are discussed. The wavelet covariance algorithm is modified so that an automated retrieval of BL depths from lidar data is possible. Three case studies of simultaneous observations with the Raman lidar, a vertical-wind Doppler lidar, and accompanying radiosonde profiling of temperature and humidity are presented to compare the potential and the limits of the four lidar techniques. The statistical analysis of the one-year data set reveals that the seasonal mean of the daytime (about 08:00–20:00 Local Time, LT) maximum BL top is 1400 m in spring, 1800 m in summer, 1200 m in autumn, and 800 m in winter at the continental, central European site. BL top typically increases by 100–300 m per hour in the morning of convective days. The comparison between the lidar-derived BL top heights and the predictions of COSMO yields a general underestimation of the BL top by about 20% by the model.

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