scholarly journals An empirical method to correct for temperature dependent variations in the overlap function of CHM15k ceilometers

2016 ◽  
Author(s):  
Maxime Hervo ◽  
Yann Poltera ◽  
Alexander Haefele
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Correction Method ◽  
Empirical Method ◽  
Cloud Base ◽  
Atmospheric Conditions ◽  
Cloud Detection ◽  
Temperature Dependent ◽  
Gradient Based ◽  
High Benefit

Abstract. Imperfections in a lidar's overlap function lead to artefacts in the background, range and overlap corrected lidar signals. These artefacts can erroneously be interpreted as an aerosol gradient or, in extreme cases, as a cloud base leading to false cloud detection. A correct specification of the overlap function is hence crucial to use automatic elastic lidars (ceilometers) for the detection of the planetary boundary layer or low clouds. In this study an algorithm is presented to correct such artefacts. It is based on the assumption of a homogeneous boundary layer and a correct specification of the overlap function down to a minimum range, which must be situated within the boundary layer. The strength of the algorithm lies in a sophisticated quality check scheme which allows to reliably identify favorable atmospheric conditions. The algorithm has been applied to 2 years of data from a CHM15k ceilometer from the company Lufft. Backscatter signals corrected for background, range and overlap have been compared using the overlap function provided by the manufacturer and the one corrected with the presented algorithm. Differences between corrected and uncorrected signals reach up to 45 % in the first 300 m above ground. The amplitude of the correction turned out to be temperature dependent being larger for higher temperatures. A linear model of the correction as a function of the instrument's internal temperature has been derived from the experimental data. Case studies and a statistical analysis of the strongest gradient derived from corrected signals reveal that the temperature model is capable to correct overlap artefacts with high quality, in particular such due to diurnal variations. The presented correction method has the potential to significantly improve the detection of the boundary layer with gradient based methods because it removes false candidates and hence simplifies the attribution of the detected gradients to the planetary boundary layer. A particularly high benefit can be expected for the detection of shallow stable layers typical for nighttime situations. The algorithm is completely automatic and does not require any intervention on site but requires the definition of an adequate instrument specific configuration. It is therefore suited for the use in large ceilometer networks.

scholarly journals An empirical method to correct for temperature-dependent variations in the overlap function of CHM15k ceilometers

2016 ◽  
Vol 9 (7) ◽  
pp. 2947-2959 ◽  
Author(s):  
Maxime Hervo ◽  
Yann Poltera ◽  
Alexander Haefele
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Correction Method ◽  
Empirical Method ◽  
Cloud Base ◽  
Atmospheric Conditions ◽  
Cloud Detection ◽  
Temperature Dependent ◽  
Night Time ◽  
Gradient Based

Abstract. Imperfections in a lidar's overlap function lead to artefacts in the background, range and overlap-corrected lidar signals. These artefacts can erroneously be interpreted as an aerosol gradient or, in extreme cases, as a cloud base leading to false cloud detection. A correct specification of the overlap function is hence crucial in the use of automatic elastic lidars (ceilometers) for the detection of the planetary boundary layer or of low cloud. In this study, an algorithm is presented to correct such artefacts. It is based on the assumption of a homogeneous boundary layer and a correct specification of the overlap function down to a minimum range, which must be situated within the boundary layer. The strength of the algorithm lies in a sophisticated quality-check scheme which allows the reliable identification of favourable atmospheric conditions. The algorithm was applied to 2 years of data from a CHM15k ceilometer from the company Lufft. Backscatter signals corrected for background, range and overlap were compared using the overlap function provided by the manufacturer and the one corrected with the presented algorithm. Differences between corrected and uncorrected signals reached up to 45 % in the first 300 m above ground. The amplitude of the correction turned out to be temperature dependent and was larger for higher temperatures. A linear model of the correction as a function of the instrument's internal temperature was derived from the experimental data. Case studies and a statistical analysis of the strongest gradient derived from corrected signals reveal that the temperature model is capable of a high-quality correction of overlap artefacts, in particular those due to diurnal variations. The presented correction method has the potential to significantly improve the detection of the boundary layer with gradient-based methods because it removes false candidates and hence simplifies the attribution of the detected gradients to the planetary boundary layer. A particularly significant benefit can be expected for the detection of shallow stable layers typical of night-time situations. The algorithm is completely automatic and does not require any on-site intervention but requires the definition of an adequate instrument-specific configuration. It is therefore suited for use in large ceilometer networks.

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 Evaluation of retrieval methods for planetary boundary layer height based on radiosonde data

2021 ◽  
Vol 14 (9) ◽  
pp. 5977-5986
Author(s):  
Hui Li ◽  
Boming Liu ◽  
Xin Ma ◽  
Shikuan Jin ◽  
Yingying Ma ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Temperature Profile ◽  
Planetary Boundary Layer ◽  
Gradient Method ◽  
Potential Temperature ◽  
Radiosonde Data ◽  
Atmospheric Conditions ◽  
Wind Speed Profile ◽  
Neutral Boundary Layer

Abstract. Radiosonde (RS) is widely used to detect the vertical structures of the planetary boundary layer (PBL), and numerous methods have been proposed for retrieving PBL height (PBLH) from RS data. However, an algorithm that is suitable under all atmospheric conditions does not exist. This study evaluates the performance of four common PBLH algorithms under different thermodynamic stability conditions based on RS data collected from nine sites in January–December 2019. The four RS algorithms are the potential temperature gradient method (GMθ), relative humidity (RH) gradient method (GMRH), parcel method (PM) and Richardson number method (RM). Atmospheric conditions are divided into convective boundary layer (CBL), neutral boundary layer (NBL) and stable boundary layer (SBL) on the basis of the potential temperature profile. Results indicate that SBL is dominant at nighttime, whilst CBL dominates at daytime. Under all and SBL classifications, PBLH retrieved by RM is typically higher than those retrieved using the other methods. On the contrary, the PBLH result retrieved by PM is the lowest. Under CBL and NBL classifications, PBLH retrieved by PM is the highest. PBLH retrieved by GMθ and GMRH is relatively low under all classifications. Moreover, the uncertainty analysis shows that the consistency of PBLH retrieved by different algorithms is more than 80 % under CBL and NBL classifications. By contrast, the consistency of PBLH is less than 60 % under SBL classification. The average profiles and standard deviations of wind speed and potential temperature under consistent and inconsistent conditions are also investigated. The results indicate that consistent cases are typically accompanied by evident atmospheric stratification, such as a large gradient in the potential temperature profile or a low-level jet in the wind speed profile. These results indicate that the reliability of the PBLH results retrieved from RS data is affected by the structure of the boundary layer. Overall, GMθ and RM are appropriate for CBL condition. GMθ and PM are recommended for NBL condition. GMθ and GMRH are robust for SBL condition. This comprehensive comparison provides a reference for selecting the appropriate algorithm when retrieving PBLH from RS data.

scholarly journals Validation of aerosol and cloud layer structures from the space-borne lidar CALIOP using a ground-based lidar in Seoul, Korea

2008 ◽  
Vol 8 (13) ◽  
pp. 3705-3720 ◽  
Author(s):  
S.-W. Kim ◽  
S. Berthier ◽  
J.-C. Raut ◽  
P. Chazette ◽  
F. Dulac ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Signal To Noise Ratio ◽  
Extinction Ratio ◽  
Cirrus Clouds ◽  
Cloud Layer ◽  
Atmospheric Conditions ◽  
Night Time ◽  
Layer Structures ◽  
Ground Based Lidar

Abstract. We present initial validation results of the space-borne lidar CALIOP onboard CALIPSO satellite using coincidental observations from a ground-based lidar in Seoul National University (SNU), Seoul, Korea (37.46° N, 126.95° E). We analyze six selected cases between September 2006 and February 2007, including 3 daytime and 3 night-time observations and covering different types of clear and cloudy atmospheric conditions. Apparent scattering ratios calculated from the two lidar measurements of total attenuated backscatter at 532 nm show similar aerosol and cloud layer structures both under cloud-free conditions and in cases of multiple aerosol layers underlying semi-transparent cirrus clouds. Agreement on top and base heights of cloud and aerosol layers is generally within 0.10 km, particularly during night-time. This result confirms that the CALIPSO science team algorithms for the discrimination of cloud and aerosol as well as for the detection of layer top and base altitude provide reliable information in such atmospheric conditions. This accuracy of the planetary boundary layer top height under cirrus cloud appears, however, limited during daytime. Under thick cloud conditions, however, information on the cloud top (bottom) height only is reliable from CALIOP (ground-based lidar) due to strong signal attenuations. However, simultaneous space-borne CALIOP and ground-based SNU lidar (SNU-L) measurements complement each other and can be combined to provide full information on the vertical distribution of aerosols and clouds. An aerosol backscatter-to-extinction ratio (BER) estimated from lidar and sunphotometer synergy at the SNU site during the CALIOP overpass is assessed to be 0.023±0.004 sr−1 (i.e. a lidar ratio of 43.2±6.2 sr) from CALIOP and 0.027±0.006 sr−1 (37.4±7.2 sr) from SNU-L. For aerosols within the planetary boundary layer under cloud-free conditions, the aerosol extinction profiles from both lidars are in agreement within about 0.02 km−1. Under semi-transparent cirrus clouds, such profiles also show good agreement for the night-time CALIOP flight, but large discrepancies are found for the daytime flights due to a small signal-to-noise ratio of the CALIOP data.

scholarly journals An Automated Common Algorithm for Planetary Boundary Layer Retrievals Using Aerosol Lidars in Support of the U.S. EPA Photochemical Assessment Monitoring Stations Program

2020 ◽  
Vol 37 (10) ◽  
pp. 1847-1864
Author(s):  
Vanessa Caicedo ◽  
Ruben Delgado ◽  
Ricardo Sakai ◽  
Travis Knepp ◽  
David Williams ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Environmental Protection Agency ◽  
Mixing Layer ◽  
Residual Layer ◽  
Cloud Base ◽  
Retrieval Algorithm ◽  
Air Quality Model ◽  
Quality Model ◽  
Monitoring Stations

AbstractA unique automated planetary boundary layer (PBL) retrieval algorithm is proposed as a common cross-platform method for use with commercially available ceilometers for implementation under the redesigned U.S. Environmental Protection Agency Photochemical Assessment Monitoring Stations program. This algorithm addresses instrument signal quality and screens for precipitation and cloud layers before the implementation of the retrieval method using the Haar wavelet covariance transform. Layer attribution for the PBL height is supported with the use of continuation and time-tracking parameters, and uncertainties are calculated for individual PBL height retrievals. Commercial ceilometer retrievals are tested against radiosonde PBL height and cloud-base height during morning and late-afternoon transition times, critical to air quality model prediction and when retrieval algorithms struggle to identify PBL heights. A total of 58 radiosonde profiles were used, and retrievals for nocturnal stable layers, residual layers, and mixing layers were assessed. Overall good agreement was found for all comparisons, with one system showing limitations for the cases of nighttime surface stable layers and daytime mixing layer. It is recommended that nighttime shallow stable-layer retrievals be performed with a recommended minimum height or with additional verification. Retrievals of residual-layer heights and mixing-layer comparisons revealed overall good correlations with radiosonde heights (square of correlation coefficients r2 ranging from 0.89 to 0.96, and bias ranging from approximately −131 to +63 m for the residual layer and r2 from 0.88 to 0.97 and bias from −119 to +101 m for the mixing layer).

scholarly journals Evaluation of retrieval methods for planetary boundary layer height based on radiosonde data

2021 ◽  
Author(s):  
Hui Li ◽  
Boming Liu ◽  
Xin Ma ◽  
Shikuan Jin ◽  
Yingying Ma ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Temperature Profile ◽  
Planetary Boundary Layer ◽  
Gradient Method ◽  
Potential Temperature ◽  
Radiosonde Data ◽  
Atmospheric Conditions ◽  
Wind Speed Profile ◽  
Neutral Boundary Layer

Abstract. Radiosonde (RS) is widely used to detect the vertical structures of the planetary boundary layer (PBL), and numerous methods have been proposed for retrieving PBL height (PBLH) from RS data. However, an algorithm that is suitable under all atmospheric conditions does not exist. This study evaluates the performance of four common PBLH algorithms under different thermodynamic stability conditions based on RS data collected from nine sites in January–December 2019. The four RS algorithms are the potential temperature gradient method (GMθ), relative humidity (RH) gradient method (GMRH), parcel method (PM) and Richardson number method (RM). Atmospheric conditions are divided into convective boundary layer (CBL), neutral boundary layer (NBL) and stable boundary layer (SBL) on the basis of the potential temperature profile. Results indicate that SBL is dominant at nighttime, whilst CBL dominates at daytime. Intercomparisons show that PBLH retrieved via RM is typically higher than those retrieved using the other methods under all and SBL conditions. PBLH retrieved using GMθ and GMRH is relatively low. PBLH from PM is the lowest under all and SBL classifications, and the highest under CBL and NBL classifications. Moreover, the uncertainty analysis shows that PBLH retrieved using different algorithms is consistent in most cases (more than 80 %) under CBL and NBL conditions. By contrast, the consistency of PBLH is less than 60 % under SBL condition. The average profiles and standard deviations of wind speed and potential temperature under consistent and inconsistent conditions indicate that consistent cases are typically accompanied by evident atmospheric stratification, such as a large gradient in the potential temperature profile or a low-level jet in the wind speed profile. These findings indicate that the reliability of the PBLH results retrieved from RS data is affected by the structure of the boundary layer. Overall, GMθ and RM are appropriate for CBL condition. GMθ and PM are recommended for NBL condition. GMθ and GMRH are robust for SBL condition. This comprehensive comparison provides a reference for selecting the appropriate algorithm when retrieving PBLH from RS data.

scholarly journals NUMERICAL MODELING OF THE PLANETARY BOUNDARY LAYER

2004 ◽  
Vol 3 (1) ◽  
pp. 74
Author(s):  
P. Oliveira ◽  
J. Soares ◽  
H. A. Karam ◽  
M. M. R. Pereira ◽  
E. P. Marques Filho
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Statistical Approach ◽  
Equations Of Motion ◽  
Simulation Models ◽  
The Other ◽  
Atmospheric Conditions ◽  
Equilibrium Conditions ◽  
Closure Models ◽  
Large Eddy

This work describes the major available techniques to simulate the time and space evolution of the planetary boundary layer. For homogeneous and equilibrium conditions the structure of the planetary boundary layer can be diagnosed from the Monin-Obukhov, Free Convection, Local and Mixed Layer Similarity theories. For the other atmospheric conditions the planetary boundary layer can be numerically simulated using first and second order closure models and large eddy models. The closure models take into consideration the traditional statistical approach. Large eddy simulation models are based on the filtered equations of motion and require the statistical approach to estimate subgrid turbulence.

scholarly journals Aerosol Properties within and above the Planetary Boundary Layer across the Korean Peninsula during December 2016

Atmosphere ◽  
2021 ◽  
Vol 12 (10) ◽  
pp. 1299
Author(s):  
Eunsil Jung ◽  
Seongkyu Seo ◽  
Ki-Ho Chang ◽  
Seong-Soo Yum ◽  
Bok-Haeng Heo
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Korean Peninsula ◽  
Geographical Location ◽  
The Yellow Sea ◽  
Size Distributions ◽  
Atmospheric Conditions ◽  
Particle Size Distributions ◽  
East West ◽  
Aerosol Properties

During December 2016, airborne aerosol measurements were taken at multiple heights across the Korean Peninsula to examine the vertical properties of aerosols. This study showed that aerosols above the planetary boundary layer (PBL) show similar concentrations and particle size distributions (PSDs), regardless of the relative locations in Korea. On the other hand, aerosols within the PBL differ depending on the geographical location, origin and path of the air mass. The concentrations are the highest in Seoul, followed by Gangneung, East Sea and the Yellow Sea. The known east–west aerosol gradient did not appear and the reasons are discussed in this paper. The study further shows that the aerosols of upwind regions affect the aerosols above the PBL, whereas aerosols in the PBL are affected by local sources and atmospheric conditions in addition to aerosols of upwind areas.

scholarly journals NUMERICAL MODELING OF THE PLANETARY BOUNDARY LAYER

2004 ◽  
Vol 3 (1) ◽  
Author(s):  
P. Oliveira ◽  
J. Soares ◽  
H. A. Karam ◽  
M. M. R. Pereira ◽  
E. P. Marques Filho
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Statistical Approach ◽  
Equations Of Motion ◽  
Simulation Models ◽  
Atmospheric Conditions ◽  
Equilibrium Conditions ◽  
Closure Models ◽  
Eddy Simulation ◽  
Large Eddy

This work describes the major available techniques to simulate the time and space evolution of the planetary boundary layer. For homogeneous and equilibrium conditions the structure of the planetary boundary layer can be diagnosed from the Monin-Obukhov, Free Convection, Local and Mixed Layer Similarity theories. For the other atmospheric conditions the planetary boundary layer can be numerically simulated using first and second order closure models and large eddy models. The closure models take into consideration the traditional statistical approach. Large eddy simulation models are based on the filtered equations of motion and require the statistical approach to estimate subgrid turbulence.

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