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• W75300009 abstract "The lidar for clouds and aerosols (Lidar Nuage Aerosol, LNA) is operated at Palaiseau (25km south of Paris in France) on the “Site Instrumental de Recherche par Teledetection Atmospherique” (SIRTA, http://sirta.lmd.polytechnique.fr). The instrument is developed to retrieve the optical and microphysical properties of clouds and aerosol in the boundary layer and troposphere between 0.1 and 15 kilometers. The LNA is operating since 2001 to observe routinely backscattered vertical profiles of the atmosphere. The LNA instrument is involved in many scientific programs to monitor clouds or particles microphysical properties, and to validate space observations. Measurements are acquired and automatically processed to feed a database managed by the Project SIRTA that is also accessible through internet. Many applications take advantage of lidar-radar synergy to analyze clouds microphysical properties, cloud dynamics and cloud macrophysics [01,02]. Lidarradiometers synergy helps also retrievals of cloud microphysics properties [03,04,05] and validation of observations from space [06]. A description of the instrument and its performance is provided and the algorithm developed to retrieve the microphysical structure of the atmosphere is presented. 1. DESCRIPTION OF THE LNA The lidaris shown in Fig. 1 and consists of a laser NdYAG 1064nm pulsed, doubled at 532nm and linearly polarized. A beam expander is used to extend the output beam diameter of the laser and to reduce its divergence. The backscattered signals resulting from interactions with molecules and particles of the atmosphere are collected in two telescopes, one characterized by a narrow field of view (NFOV), the other characterized by a wide field of view (WFOV). The NFOV telescope is adapted to explore the interactions in the highest layers of the atmosphere (2-15km), while the WFOV telescope is suited to detect the interactions in the lower atmospheric layers (0.1-7km). Combination of the two telescope is recommended to exploit completely the lidar signals along the vertical path from the ground to 15km. Backscattering and extinction coefficients are indeed assessed solely when the laser beam covers entirely the field of view of the telescope. Each telescope holds its own detection system composed of several optical elements to split up the signal collected at 532nm and at 1064nm. The optical system also splits up the depolarized signal at 532nm to its component linearly polarized (channel 1) and its component in the crossed polarized direction (Channel 2). Channels 1 and 2 are equipped with photomultiplier detectors and channel 3 (1064nm) uses avalanche photodiodes. The detectors are connected to amplifiers which gains allow optimizing the backscattered signal consistently with the atmospheric conditions. Procedures are in place to secure the site on the ground for the staff and in the air to account for activities in the sky during lidar operation. The lidar is coupled to a radar (9GHz) that interrupts the lidar emission automatically as soon as airplanes are detected near the site. Data acquisition and data transfer are managed by a PC that transmit data every 30 minutes. Raw data from the three channels (532//, 532 , 1064) of each telescope are transferred every hour to provide real-time visualizations on the web page http://sirta.lmd.polytechnique.fr (« donnees » menu). 24 hours after acquisition, level 1 data are processed and are accessible from the database. 2. LNA LIDAR OPERATION AND OBSERVATION CONTEXT The LNA had been operated routinely for 2 years since 2001 two days a week for the Earlinet network to study the aerosol transport over the European continent. The LNA has been operated 5 days a week since 2003 concurrently with the radar RASTA (94GHz) developed by the Centre d'etude des Environnements Terrestre et Planetaires (CETP/IPSL) operating also at Palaiseau experimental site (Fig. 2). The lidar-radar synergy provides observations of the entire vertical structure of the clouds in the atmosphere. Those instruments have contributed significantly to the European program CLOUDNET for the study of the clouds properties. In addition, the perspective of developing the SIRUS observatory at Palaiseau implies the development of the LNA to exploit: the lidar-radar synergy for the study of the clouds microphysical properties, the lidar-photometer synergy to study the optical properties of the aerosols, the lidar-radiometric synergy station to study the clouds radiative effect. Fig. 1. lidar LNA experimental site SIRTA/IPSL, Polytechnic school, Palaiseau Fig. 2. radar RASTA, experimental site SIRTA/IPSL, Polytechnic school, Palaiseau Many other instruments operate operationally at Palaiseau, in automatic mode or continuous mode or on a customary mode requiring human supervision. Some instruments operate permanently or some are deployed during specific intensive campaign of measurements. A detailed description of the entire park of instruments that equip the experimental center is presented on the web page http://sirta.lmd.polytechnique.fr « Instruments » menu. 3. DATA ANALYSIS, QUALITY CONTROL AND DATA AVAILABILITY Three levels of lidar data are yet available to users. Level 0 are raw data for which the resolution is 15 meters every 10 seconds for each channel of the telescopes. Level 1 data are the backscattered lidar profiles corrected for the range and noise and the quality flag for each channel. Level 2 data provide a classification of the atmosphere and the corrected backscattered lidar profiles. Level 0 data contributes to every of our following processing. They provide a quick representation of the temporal evolution of the backscattered lidar profiles. Fig. 3 shows an example of level 1 data retrieval for April 1 2003. Level 1 data provides additional information: the quality flag. This information allows to separate the useful signal from the noise. Among the useful signal, the total backscattering signal (flag 2) is distinguished from the partial backscattering signal (flag 1). The partial backscattering corresponds to the range for which the laser beam does not cover totally the field of view of the telescope. The data format of the Level 1 is NetCDF. Level 2 data format is also NetCDF and includes the lidar backscattered profiles and the atmosphere structure classification. The classification is realized as follow: the boundary layer height (BLH) is first identified, the particles regions (clouds, aerosols) are then detected and finally the molecular regions, useful to extract physicals data. Fig. 3. log(Pr2) measured on 01/04/2003 at 532nm, linear polarization, by the NFOV telescope on top, and by the WFOV telescope" @default.
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• W75300009 date "2004-06-01" @default.
• W75300009 modified "2023-09-26" @default.
• W75300009 title "Remote Sensing of Clouds and Aerosols Using LIDAR Groundbased Observations" @default.
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