The Experts below are selected from a list of 207030 Experts worldwide ranked by ideXlab platform
Jakob Mann - One of the best experts on this subject based on the ideXlab platform.
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Cross-contamination effect on turbulence spectra from Doppler beam swinging wind Lidar
Wind Energy Science, 2020Co-Authors: Felix Kelberlau, Jakob MannAbstract:Abstract. Turbulence velocity spectra are of high importance for the estimation of loads on wind turbines and other built structures, as well as for fitting measured turbulence values to turbulence models. Spectra generated from reconstructed wind vectors of Doppler beam swinging (DBS) wind Lidars differ from spectra based on one-point measurements. Profiling wind Lidars have several characteristics that cause these deviations, namely cross-contamination between the three velocity components, averaging along the lines of sight and the limited sampling frequency. This study focuses on analyzing the cross-contamination effect. We sample wind data in a computer-generated turbulence box to predict Lidar-derived turbulence spectra for three wind directions and four measurement heights. The data are then processed with the conventional method and with the method of squeezing that reduces the longitudinal separation distances between the measurement locations of the different Lidar beams by introducing a time lag into the data processing. The results are analyzed and compared to turbulence velocity spectra from field measurements with a Windcube V2 wind Lidar and ultrasonic anemometers as reference. We successfully predict Lidar-derived spectra for all test cases and found that their shape is dependent on the angle between the wind direction and the Lidar beams. With conventional processing, cross-contamination affects all spectra of the horizontal wind velocity components. The method of squeezing improves the spectra to an acceptable level only for the case of the longitudinal wind velocity component and when the wind blows parallel to one of the lines of sight. The analysis of the simulated spectra described here improves our understanding of the limitations of turbulence measurements with DBS profiling wind Lidar.
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Taking the Motion out of Floating Lidar: Turbulence Intensity Estimates with a Continuous-Wave Wind Lidar
Remote Sensing, 2020Co-Authors: Felix Kelberlau, Vegar Neshaug, Lasse Lønseth, Tania Bracchi, Jakob MannAbstract:Due to their motion, floating wind Lidars overestimate turbulence intensity ( T I ) compared to fixed Lidars. We show how the motion of a floating continuous-wave velocity–azimuth display (VAD) scanning Lidar in all six degrees of freedom influences the T I estimates, and present a method to compensate for it. The approach presented here uses line-of-sight measurements of the Lidar and high-frequency motion data. The compensation algorithm takes into account the changing radial velocity, scanning geometry, and measurement height of the Lidar beam as the Lidar moves and rotates. It also incorporates a strategy to synchronize Lidar and motion data. We test this method with measurement data from a ZX300 mounted on a Fugro SEAWATCH Wind Lidar Buoy deployed offshore and compare its T I estimates with and without motion compensation to measurements taken by a fixed land-based reference wind Lidar of the same type located nearby. Results show that the T I values of the floating Lidar without motion compensation are around 50 % higher than the reference values. The motion compensation algorithm detects the amount of motion-induced T I and removes it from the measurement data successfully. Motion compensation leads to good agreement between the T I estimates of floating and fixed Lidar under all investigated wind conditions and sea states.
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an inter comparison study of multi and dbs Lidar measurements in complex terrain
Remote Sensing, 2016Co-Authors: Lukas Pauscher, Jakob Mann, Nikola Vasiljevic, Doron Callies, Tobias Klaas, Julian Hieronimus, Julia Gottschall, Annedore Schwesig, Martin Kuhn, Michael CourtneyAbstract:Wind measurements using classical profiling Lidars suffer from systematic measurement errors in complex terrain. Moreover, their ability to measure turbulence quantities is unsatisfactory for wind-energy applications. This paper presents results from a measurement campaign during which multiple WindScanners were focused on one point next to a reference mast in complex terrain. This multi-Lidar (ML) technique is also compared to a profiling Lidar using the Doppler beam swinging (DBS) method. First- and second-order statistics of the radial wind velocities from the individual instruments and the horizontal wind components of several ML combinations are analysed in comparison to sonic anemometry and DBS measurements. The results for the wind speed show significantly reduced scatter and directional error for the ML method in comparison to the DBS Lidar. The analysis of the second-order statistics also reveals a significantly better correlation for the ML technique than for the DBS Lidar, when compared to the sonic. However, the probe volume averaging of the Lidars leads to an attenuation of the turbulence at high wave numbers. Also the configuration (i.e., angles) of the WindScanners in the ML method seems to be more important for turbulence measurements. In summary, the results clearly show the advantages of the ML technique in complex terrain and indicate that it has the potential to achieve significantly higher accuracy in measuring turbulence quantities for wind-energy applications than classical profiling Lidars.
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Assessment of wind conditions at a fjord inlet by complementary use of sonic anemometers and Lidars
Energy Procedia, 2015Co-Authors: Jasna Bogunović Jakobsen, Torben Mikkelsen, Mikael Sjoholm, Jakob Mann, Etienne Cheynet, Jónas Thór Snæbjörnsson, Nicolas Angelou, Per Juel Hansen, Benny Svardal, Valerie-marie KumerAbstract:Abstract Wind velocity measurement devices based on the remote optical sensing, Lidars, are extensively applied in wind energy research and wind farm operation. The present paper demonstrates the relevance and potential of Lidar measurements for other wind- sensitive structures such as long-span bridges. In a pilot study in Lysefjord, Norway, a pulsed long-range Lidar and two short-range WindScanners were installed at the bridge site, together with a long-term monitoring system based on sonic anemometers. The deployment of the two types of Lidars is described in more details and the complementary value of the data from all three types of the instruments is illustrated. The emphasis is on the Lidars’ potential to map the wind conditions along the whole span of a bridge in a complex terrain, as opposed to “point” measurements achievable by sonic anemometers. The challenging balance between the spatial and temporal resolution of the data is discussed.
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comparison of 3d turbulence measurements using three staring wind Lidars and a sonic anemometer
Meteorologische Zeitschrift, 2009Co-Authors: Jakob Mann, Torben Mikkelsen, Rozenn Wagner, Mikael Sjoholm, Michael Courtney, Jean-pierre Cariou, Remy Parmentier, Per Jonas Petter Lindelow, Karen EnevoldsenAbstract:The goals are to compare Lidar volume averaged wind measurement with point measurement reference sensors and to demonstrate the feasibility of performing 3D turbulence measurements with Lidars. For that purpose three pulsed Lidars were used in staring mode, placed so that their beams crossed close to a 3D sonic anemometer mounted at 78 m above the ground. The results show generally very good correlation between the Lidar and the sonic times series, except that the variance of the velocity measured by the Lidar is attenuated due to spatial filtering. The amount of attenuation can however be predicted theoretically by use of a spectral tensor model of the atmospheric surface-layer turbulence.
Yibing Shen - One of the best experts on this subject based on the ideXlab platform.
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relationship between the effective attenuation coefficient of spaceborne Lidar signal and the iops of seawater
Optics Express, 2018Co-Authors: Qun Liu, Dong Liu, Jian Bai, Yudi Zhou, Zhipeng Liu, Yupeng Zhang, Sijie Chen, Haochi Che, Yibing Shen, Chong LiuAbstract:Multiple scattering is an inevitable effect in spaceborne oceanic Lidar because of the large footprint size and the high optical density of seawater. The effective attenuation coefficient kLidar in the oceanic Lidar equation, which indicates the influence of the multiple scattering effect on the formation of Lidar returns, is an important parameter in the retrieval of inherent optical properties (IOPs) of seawater. In this paper, the relationships between kLidar of the spaceborne Lidar signal and the IOPs of seawater are investigated by solving the radiative transfer equation with an improved semianalytic Monte Carlo model. Apart from the geometric loss factors, kLidar is found to decrease exponentially with the increase of depth in homogeneous waters. kLidar is given as an exponential function of depth and IOPs of seawater. The mean percentage errors between kLidar calculated by the exponential function and the simulated ones in three typical stratified waters are within 0.5%, proving the effectiveness and applicability of this kLidar-IOPs function. The results in this paper can help researchers have a better understanding of the multiple scattering effect of spaceborne Lidar and improve the retrieval accuracy of the IOPs and the chlorophyll concentration of case 1 water from spaceborne Lidar measurements.
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retrieval and analysis of a polarized high spectral resolution Lidar for profiling aerosol optical properties
Optics Express, 2013Co-Authors: Dong Liu, Zhongtao Cheng, Yongying Yang, Hanlu Huang, Bo Zhang, Tong Ling, Yibing ShenAbstract:Taking advantage of the broad spectrum of the Cabannes-Brillouin scatter from atmospheric molecules, the high spectral resolution Lidar (HSRL) technique employs a narrow spectral filter to separate the aerosol and molecular scattering components in the Lidar return signals and therefore can obtain the aerosol optical properties as well as the Lidar ratio (i.e., the extinction-to-backscatter ratio) which is normally selected or modeled in traditional backscatter Lidars. A polarized HSRL instrument, which employs an interferometric spectral filter, is under development at the Zhejiang University (ZJU), China. In this paper, the theoretical basis to retrieve the aerosol Lidar ratio, depolarization ratio and extinction and backscatter coefficients, is presented. Error analyses and sensitivity studies have been carried out on the spectral transmittance characteristics of the spectral filter. The result shows that a filter that has as small aerosol transmittance (i.e., large aerosol rejection rate) and large molecular transmittance as possible is desirable. To achieve accurate retrieval, the transmittance of the spectral filter for molecular and aerosol scattering signals should be well characterized.
Dong Liu - One of the best experts on this subject based on the ideXlab platform.
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the nonlinear effective attenuation coefficient of spaceborne oceanic Lidar signal
European Physical Journal Web of Conferences, 2020Co-Authors: Qun Liu, Dong Liu, Jian Bai, Xiaoyu Cui, Yudi Zhou, Zhipeng Liu, Xiaobin WangAbstract:Multiple scattering is an inevitable effect in spaceborne oceanic Lidar because of the large footprint size and the high optical density of seawater. The effective attenuation coefficient kLidar in oceanic Lidar equation, which indicates the influence of the multiple scattering effect on the formation of Lidar returns, is an important parameter in the retrieval of inherent optical properties (IOPs) of seawater. In this paper, the nonlinearity of kLidar and the relationships between kLidar and the IOPs of seawater are investigated by solving the radiative transfer equation with an improved semianalytic Monte Carlo model. kLidar is found to decrease exponentially with the increase of depth in homogeneous waters. kLidar is given as an exponential function of depth and IOPs of seawater. The results in this paper can help to have a better understanding of the multiple scattering effect of spaceborne Lidar and improve the retrieval accuracy of the IOPs of seawater using spaceborne Lidar.
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relationship between the effective attenuation coefficient of spaceborne Lidar signal and the iops of seawater
Optics Express, 2018Co-Authors: Qun Liu, Dong Liu, Jian Bai, Yudi Zhou, Zhipeng Liu, Yupeng Zhang, Sijie Chen, Haochi Che, Yibing Shen, Chong LiuAbstract:Multiple scattering is an inevitable effect in spaceborne oceanic Lidar because of the large footprint size and the high optical density of seawater. The effective attenuation coefficient kLidar in the oceanic Lidar equation, which indicates the influence of the multiple scattering effect on the formation of Lidar returns, is an important parameter in the retrieval of inherent optical properties (IOPs) of seawater. In this paper, the relationships between kLidar of the spaceborne Lidar signal and the IOPs of seawater are investigated by solving the radiative transfer equation with an improved semianalytic Monte Carlo model. Apart from the geometric loss factors, kLidar is found to decrease exponentially with the increase of depth in homogeneous waters. kLidar is given as an exponential function of depth and IOPs of seawater. The mean percentage errors between kLidar calculated by the exponential function and the simulated ones in three typical stratified waters are within 0.5%, proving the effectiveness and applicability of this kLidar-IOPs function. The results in this paper can help researchers have a better understanding of the multiple scattering effect of spaceborne Lidar and improve the retrieval accuracy of the IOPs and the chlorophyll concentration of case 1 water from spaceborne Lidar measurements.
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measurements of aerosol phase function and vertical backscattering coefficient using a charge coupled device side scatter Lidar
Optics Express, 2014Co-Authors: Zongming Tao, Dong Liu, Zhenzhu Wang, Chenbo Xie, Qingze Zhang, Yingjian WangAbstract:By using a charge-coupled device (CCD) as the detector, side-scatter Lidar has great potential applications in the near range atmospheric detection. A new inversion method is proposed for CCD side-scatter Lidar (CLidar) to retrieve aerosol phase function and vertical backscattering coefficient. Case studies show the retrieved results from CLidar are in good agreements with those obtained from other instruments. It indicates that the new proposed inversion method is reliable and feasible and that the CLidar is practicable.
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retrieval and analysis of a polarized high spectral resolution Lidar for profiling aerosol optical properties
Optics Express, 2013Co-Authors: Dong Liu, Zhongtao Cheng, Yongying Yang, Hanlu Huang, Bo Zhang, Tong Ling, Yibing ShenAbstract:Taking advantage of the broad spectrum of the Cabannes-Brillouin scatter from atmospheric molecules, the high spectral resolution Lidar (HSRL) technique employs a narrow spectral filter to separate the aerosol and molecular scattering components in the Lidar return signals and therefore can obtain the aerosol optical properties as well as the Lidar ratio (i.e., the extinction-to-backscatter ratio) which is normally selected or modeled in traditional backscatter Lidars. A polarized HSRL instrument, which employs an interferometric spectral filter, is under development at the Zhejiang University (ZJU), China. In this paper, the theoretical basis to retrieve the aerosol Lidar ratio, depolarization ratio and extinction and backscatter coefficients, is presented. Error analyses and sensitivity studies have been carried out on the spectral transmittance characteristics of the spectral filter. The result shows that a filter that has as small aerosol transmittance (i.e., large aerosol rejection rate) and large molecular transmittance as possible is desirable. To achieve accurate retrieval, the transmittance of the spectral filter for molecular and aerosol scattering signals should be well characterized.
Michael Courtney - One of the best experts on this subject based on the ideXlab platform.
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the rune experiment a database of remote sensing observations of near shore winds
2016Co-Authors: Rogier Floors, Nikola Vasiljevic, Alfredo Pena, Guillaume Lea, Elliot Simon, Michael CourtneyAbstract:We present a comprehensive database of near-shore wind observations that were carried out during the experimental campaign of the RUNE project. RUNE aims at reducing the uncertainty of the near-shore wind resource estimates from model outputs by using Lidar, ocean, and satellite observations. Here, we concentrate on describing the Lidar measurements. The campaign was conducted from November 2015 to February 2016 on the west coast of Denmark and comprises measurements from eight Lidars, an ocean buoy and three types of satellites. The wind speed was estimated based on measurements from a scanning Lidar performing PPIs, two scanning Lidars performing dual synchronized scans, and five vertical profiling Lidars, of which one was operating offshore on a floating platform. The availability of measurements is highest for the profiling Lidars, followed by the Lidar performing PPIs, those performing the dual setup, and the Lidar buoy. Analysis of the Lidar measurements reveals good agreement between the estimated 10-min wind speeds, although the instruments used different scanning strategies and measured different volumes in the atmosphere. The campaign is characterized by strong westerlies with occasional storms.
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an inter comparison study of multi and dbs Lidar measurements in complex terrain
Remote Sensing, 2016Co-Authors: Lukas Pauscher, Jakob Mann, Nikola Vasiljevic, Doron Callies, Tobias Klaas, Julian Hieronimus, Julia Gottschall, Annedore Schwesig, Martin Kuhn, Michael CourtneyAbstract:Wind measurements using classical profiling Lidars suffer from systematic measurement errors in complex terrain. Moreover, their ability to measure turbulence quantities is unsatisfactory for wind-energy applications. This paper presents results from a measurement campaign during which multiple WindScanners were focused on one point next to a reference mast in complex terrain. This multi-Lidar (ML) technique is also compared to a profiling Lidar using the Doppler beam swinging (DBS) method. First- and second-order statistics of the radial wind velocities from the individual instruments and the horizontal wind components of several ML combinations are analysed in comparison to sonic anemometry and DBS measurements. The results for the wind speed show significantly reduced scatter and directional error for the ML method in comparison to the DBS Lidar. The analysis of the second-order statistics also reveals a significantly better correlation for the ML technique than for the DBS Lidar, when compared to the sonic. However, the probe volume averaging of the Lidars leads to an attenuation of the turbulence at high wave numbers. Also the configuration (i.e., angles) of the WindScanners in the ML method seems to be more important for turbulence measurements. In summary, the results clearly show the advantages of the ML technique in complex terrain and indicate that it has the potential to achieve significantly higher accuracy in measuring turbulence quantities for wind-energy applications than classical profiling Lidars.
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comparison of 3d turbulence measurements using three staring wind Lidars and a sonic anemometer
Meteorologische Zeitschrift, 2009Co-Authors: Jakob Mann, Torben Mikkelsen, Rozenn Wagner, Mikael Sjoholm, Michael Courtney, Jean-pierre Cariou, Remy Parmentier, Per Jonas Petter Lindelow, Karen EnevoldsenAbstract:The goals are to compare Lidar volume averaged wind measurement with point measurement reference sensors and to demonstrate the feasibility of performing 3D turbulence measurements with Lidars. For that purpose three pulsed Lidars were used in staring mode, placed so that their beams crossed close to a 3D sonic anemometer mounted at 78 m above the ground. The results show generally very good correlation between the Lidar and the sonic times series, except that the variance of the velocity measured by the Lidar is attenuated due to spatial filtering. The amount of attenuation can however be predicted theoretically by use of a spectral tensor model of the atmospheric surface-layer turbulence.
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comparison of 3d turbulence measurements using three staring wind Lidars and a sonic anemometer
IOP Conference Series: Earth and Environmental Science, 2008Co-Authors: Jakob Mann, Torben Mikkelsen, Rozenn Wagner, Mikael Sjoholm, Michael Courtney, Jean-pierre Cariou, Remy Parmentier, Per Jonas Petter Lindelow, Karen EnevoldsenAbstract:Three pulsed Lidars were used in staring, non-scanning mode, placed so that their beams crossed close to a 3D sonic anemometer. The goal is to compare Lidar volume averaged wind measurement with point measurement reference sensors and to demonstrate the feasibility of performing 3D turbulence measurements with Lidars. The results show a very good correlation between the Lidar and the sonic times series. The variance of the velocity measured by the Lidar is attenuated due to spatial filtering, and the amount of attenuation can be predicted theoretically.
Alain Hauchecorne - One of the best experts on this subject based on the ideXlab platform.
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Atmospheric Density and Temperature Vertical Profile Retrieval for Flight-Tests with a Rayleigh Lidar On-Board the French Advanced Test Range Ship Monge
Atmosphere, 2020Co-Authors: Robin Wing, Laurent Yung, Patrick Retailleau, Yann Courcoux, Milena Martic, Jacques Porteneuve, Philippe Keckhut, Alain Hauchecorne, Dorothee CocuronAbstract:The Advanced Test Range Ship Monge (ATRSM) is dedicated to in-flight measurements during the re-entry phase of ballistic missiles test flights. Atmospheric density measurements from 15 to 110 km are provided using one of the world’s largest Rayleigh Lidars. This Lidar is the culmination of three decades of French research experience in Lidar technologies, developed within the framework of the global Network for Detection of Atmospheric and Climate Changes (NDACC), and opens opportunities for high resolution Rayleigh Lidar studies above 90 km. The military objective of the ATRSM project is to provide near real time estimates of the atmospheric relative density profile, with an error budget of less than 10% at 90 km altitude, given a temporal integration of 15 min and a vertical resolution of 500 m. To achieve this aim we have developed a unique Lidar system which exploits six laser transmitters and a constellation of eight receiving telescopes which maximises the Lidar power-aperture product. This system includes a mix of standard commercially available optical components and electronics as well as some innovative technical solutions. We have provided a detailed assessment of some of the more unique aspects of the ATRSM Lidar.
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Lidar temperature series in the middle atmosphere as a reference data set part 1 improved retrievals and a 20 year cross validation of two co located french Lidars
Atmospheric Measurement Techniques, 2018Co-Authors: Robin Wing, Philippe Keckhut, Alain Hauchecorne, Sophie Godinbeekmann, Sergey Khaykin, E Mccullough, Jeanfrancois Mariscal, Eric DalmeidaAbstract:Abstract. The objective of this paper and its companion ( Wing et al. , 2018 ) is to show that ground-based Lidar temperatures are a stable, accurate, and precise data set for use in validating satellite temperatures at high vertical resolution. Long-term Lidar observations of the middle atmosphere have been conducted at the Observatoire de Haute-Provence (OHP), located in southern France (43.93 ∘ N, 5.71 ∘ E), since 1978. Making use of 20 years of high-quality co-located Lidar measurements, we have shown that Lidar temperatures calculated using the Rayleigh technique at 532 nm are statistically identical to Lidar temperatures calculated from the non-absorbing 355 nm channel of a differential absorption Lidar (DIAL) system. This result is of interest to members of the Network for the Detection of Atmospheric Composition Change (NDACC) ozone Lidar community seeking to produce validated temperature products. Additionally, we have addressed previously published concerns of Lidar–satellite relative warm bias in comparisons of upper-mesospheric and lower-thermospheric (UMLT) temperature profiles. We detail a data treatment algorithm which minimizes known errors due to data selection procedures, a priori choices, and initialization parameters inherent in the Lidar retrieval. Our algorithm results in a median cooling of the Lidar-calculated absolute temperature profile by 20 K at 90 km altitude with respect to the standard OHP NDACC Lidar temperature algorithm. The confidence engendered by the long-term cross-validation of two independent Lidars and the improved Lidar temperature data set is exploited in Wing et al. ( 2018 ) for use in multi-year satellite validations.
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Investigations of stratospheric temperature regional variability with Lidar and Advanced Microwave Sounding Unit
Journal of Geophysical Research Atmospheres, 2011Co-Authors: Beatriz M. Funatsu, Chantal Claud, Wolfgang Steinbrecht, Philippe Keckhut, Alain HauchecorneAbstract:Seasonal and interannual stratospheric temperature variability at two\nrelatively close-by Lidar stations, the Observatoire de Haute-Provence\n(France) and the Hohenpeissenberg Observatory (Germany), are\ninvestigated using Lidars and the Advanced Microwave Sounding Unit\n(AMSU) satellite data to examine possible causes of temperature trend\ndiscrepancies between these two sites. We first examined data measured\nby Lidar and AMSU at each station and found that temperature anomalies\nobserved with Lidar have larger spread than those with AMSU probably as\na result of distinct vertical sampling. Lidar and AMSU measurements have\ncorrelation typically higher than 0.7; however, correlation is decreased\nto 0.4-0.5 in summer at the French station. Lidar measurements have good\ncorrelation between the two stations, around 0.9 in winter and 0.45 in\nsummer, while AMSU data show correlations between both stations of about\n0.94 year-round. Data from coincident measurement dates at both sites\nhave then been taken from the integral series in order to isolate local\ngeophysical effects. A comparison between Lidar and AMSU measurements of\ncoincident dates suggests that in wintertime measurement discrepancies\nare to a great extent a result of different local atmospheric dynamics.\nThese are important on the estimation of stratospheric trends and can\npartially explain discrepancies observed in trends estimates based on\nLidars in distinct locations or on satellite data. The present results\nhave implications on the planning of measurement strategies using Lidars\ninvolved in the Network for the Detection of Atmospheric Composition\nChanges (NDACC), as well as on methodologies for satellite data use for\nstratospheric monitoring purposes.
