Raman Lidar for Meteorological Observations, RALMO – Part 1: Open Access Instrument Description Climate Climate of the Past 1 1 2 2 1,3 4 of The1 Past T
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EGU Journal Logos (RGB) Open Access Open Access Open Access Advances in Annales Nonlinear Processes Geosciences Geophysicae in Geophysics Open Access Open Access Natural Hazards Natural Hazards and Earth System and Earth System Sciences Sciences Discussions Open Access Open Access Atmospheric Atmospheric Chemistry Chemistry and Physics and Physics Discussions Open Access Open Access Atmos. Meas. Tech., 6, 1329–1346, 2013 Atmospheric Atmospheric www.atmos-meas-tech.net/6/1329/2013/ doi:10.5194/amt-6-1329-2013 Measurement Measurement © Author(s) 2013. CC Attribution 3.0 License. Techniques Techniques Discussions Open Access Open Access Biogeosciences Biogeosciences Discussions Open Access Raman Lidar for Meteorological Observations, RALMO – Part 1: Open Access Instrument description Climate Climate of the Past 1 1 2 2 1,3 4 of the1 Past T. Dinoev , V. Simeonov , Y. Arshinov , S. Bobrovnikov , P. Ristori , B. Calpini , M. Parlange , and H. van den Discussions Bergh5 1 Open Access Laboratory of Environmental Fluid Mechanics and Hydrology (EFLUM), Ecole Polytechnique Fed´ erale´ de Lausanne Open Access EPFL-ENAC, Station 2, 1015 Lausanne, Switzerland Earth System 2 Earth System V.E. Zuev Institute of Atmospheric Optics SB RAS1, Academician Zuev Square, Tomsk, 634021, Russia Dynamics 3Division´ Lidar, CEILAP (UNIDEF-CITEDEF-MINDEF-CONICET), San Juan Bautista de La SalleDynamics 4397 (B1603ALO), Villa Martelli, Buenos Aires, Argentina Discussions 4Federal Office of Meteorology and Climatology MeteoSwiss, Atmospheric Data, P.O. Box 316, 1530 Payerne, Switzerland 5 Open Access Laboratory of Air and Soil Pollution, Ecole Polytechnique Fed´ erale´ de Lausanne EPFL, StationGeoscientific 6, Geoscientific Open Access 1015 Lausanne, Switzerland Instrumentation Instrumentation Correspondence to: V. B. Simeonov (valentin.simeonov@epfl.ch) Methods and Methods and Received: 2 July 2012 – Published in Atmos. Meas. Tech. Discuss.: 20 September 2012 Data Systems Data Systems Revised: 19 April 2013 – Accepted: 22 April 2013 – Published: 22 May 2013 Discussions Open Access Open Access Geoscientific Geoscientific Abstract. A new Raman lidar for unattended, round-the- 1 Introduction Model Development Model Development clock measurement of vertical water vapor profiles for op- Discussions erational use by the MeteoSwiss has been developed dur- Water vapor plays a fundamental role in the radiative en- ing the past years by the Swiss Federal Institute of Tech- ergy transfer, hydrological cycle, and atmospheric chemistry Open Access Open Access nology, Lausanne. The lidar uses narrow field-of-view, nar- processes that determineHydrology weather and climate.and It influences Hydrology and rowband configuration, a UV laser, and four 30 cm in di- the radiative budget of the planet both directly and through ameter mirrors, fiber-coupled to a grating polychromator. coupling with clouds. BecauseEarth of System its strong absorption and Earth System The optical design allows water vapor retrieval from the in- emission bands, especially in theSciences infrared, and because of its Sciences complete overlap region without instrument-specific range- abundance, water vapor is the most significant greenhouse Discussions dependent corrections. The daytime vertical range covers the gas, and in this sense the most important in establishing the Open Access Open Access mid-troposphere, whereas the nighttime range extends to the Earth’s climate. tropopause. The near range coverage is extended down to Water vapor distribution is strongly affected by atmo- Ocean Science spheric dynamics, butOcean in turn it alsoScience influences atmospheric 100 m AGL by the use of an additional fiber in one of the Discussions telescopes. This paper describes the system layout and tech- circulation and temperature structure by condensation– nical realization. Day- and nighttime lidar profiles compared evaporation processes. The water evaporation–condensation ® cycle is an important mechanism for transferring heat energy Open Access to Vaisala RS92 and Snow White profiles and a six-day Open Access continuous observation are presented as an illustration of the from the Earth’s surface to its atmosphere and in moving heat lidar measurement capability. around the Earth. The large latent energy associated with the Solid Earth Solid Earth water phase changes significantly affects the meridional en- Discussions ergy balance and the vertical stability of the atmosphere as well as the structure and evolution of storm systems, not only in the boundary layer (Normand, 1938) but alsoOpen Access in the mid- Open Access dle and upper troposphere (Peppler, 1989; Sinha and Harries, 1995; Arnold, 2008).The Cryosphere The Cryosphere Discussions Published by Copernicus Publications on behalf of the European Geosciences Union. 1330 T. Dinoev et al.: RALMO – Part 1: Instrument description Because of its essential role in the atmospheric processes, The Raman lidar technique exploits Raman scattering the water vapor spatial distribution and its temporal evolution from water vapor and nitrogen molecules to derive a profile are two of the most important parameters in global and re- of water vapor mixing ratio (Cooney, 1970; Melfy, 1972). gional numerical weather prediction (NWP) models. To im- At present, the nighttime distance range can reach up to the prove near-surface weather predictions, and to better sim- lower stratosphere but at daytime the range is limited to the ulate the evolution of local severe weather events in com- middle troposphere because the weak Raman signals are de- plex terrains (Wulfmeyer et al., 2008), the time and space tected in the presence of intensive daylight background. A resolution of the NWP models, used by the meteorological Raman lidar requires calibration either against a reference services, is currently being increased (Calpini et al., 2011). instrument or by absolute radiometric calibration of the li- The vertical water vapor profiles assimilated by these mod- dar optics, provided accurate Raman cross sections are avail- els are mainly acquired by twice-a-day radiosonde observa- able. Contrary to a DIAL, a Raman lidar does not require tions which have insufficient time resolution to resolve fast tunable laser source with specific and highly stabilized wave- running meteorological phenomena. In addition, radiosonde lengths. Furthermore, the Raman data-treatment algorithm is measurements suffer from systematic errors that are dif- significantly simpler than the DIAL algorithm, and allows ficult to correct and from essential sonde-to-sonde varia- data retrieval from the incomplete overlap region. Because tions not only between instruments from different produc- of all these advantages and because of the higher reliability, ers and operational principles, but even between instruments Raman lidars are preferred for operational use in meteorol- of the same batch (Nash et al., 2011). Ground-based mi- ogy from ground-based stations (Goldsmith et al., 1998; En- crowave radiometers (Solheim, 1998 and references therein) gelbart et al., 2006; Reichardt et al., 2012; Simeonov et al., and Fourier transform infrared radiometers (Schneider and 2010; Appituley et al., 2009). Hase, 2009 and references therein) provide humidity profiles Raman lidars have been used for high resolution verti- with sufficient time resolution, but with rather low vertical cal profiling of water vapor within the troposphere since the resolution, to resolve the spatial variability of water vapor in early 1970s. Most of the measurements were performed for the low troposphere. Therefore, national meteorological ser- research purposes and at nighttime (Whiteman, 1992; Ans- vices need a new type of autonomous, continuously operated mann et al., 1992; Vaughan et al., 1988; Balin et al., 2004). (24-7-365) instruments for near real-time, high spatial reso- First daytime measurements were possible using laser wave- lution observations of the tropospheric water vapor field. length shorter than 300 nm because at these wavelengths the Lidar (light detection and ranging) is one of the techniques solar light is absorbed by stratospheric ozone (Renault et al., able to resolve the high temporal and spatial variability of 1980; Cooney et al., 1985). The vertical range of such li- tropospheric water vapor. The advances of the last decades in dars is, however, limited to about 2 km, mainly due to tropo- the field of laser technology and improved lidar design make spheric ozone absorption. The use of a narrow field-of-view lidars suitable for operational use in meteorological services. (NFOV), narrowband (NB) receiver allows operation at vis- Two lidar techniques, DIAL and Raman, are used for water ible and near UV wavelengths, resulting in the extension of vapor measurements. the operational range up to the mid troposphere (Goldsmith The DIAL principle exploits the difference in atmospheric et al., 1998). extinction due to water vapor absorption at two closely- The successful long-term operation of the first automated spaced, near-IR wavelengths. Provided accurate knowledge NFOV NB lidar – CART (Goldsmith et al., 1998) – motivated of water vapor absorption cross section is available, DIAL the German (Engelbart et al., 2006; Reichardt et al., 2012), does not need other external references for correct measure- the Swiss (Dinoev et al., 2006; Simeonov et al., 2010) and ments and in this sense is considered “self-calibrating”. A the Dutch (Appituley et al., 2009) meteorological services to DIAL system has the potential to perform daytime obser- establish programs