A scanning eye-safe rotational Raman lidar in the ultraviolet for measurements of tropospheric temperature fields

Within the frame of the virtual Institute COSI-TRACKS the first scanning rotational Raman lidar has been developed and deployed successfully in two large field campaigns. This has allowed new investigations of the convective boundary layer and contributed to studies on the initiation of convection during the PRINCE campaign (PRediction, Identification and trackiNg of Convective cElls) in July 2006 and the COPS experiment (Convective and Orographically-induced Precipitation Study) from June to August 2007. The University of Hohenheim rotational Raman lidar was deployed in both these campaigns on Hornisgrinde (48.61 °N, 8.20 °E, 1161 m above sea level), the highest peak in the Northern Black Forest in southwest Germany. The lidar provides measurements of atmospheric temperature fields in the troposphere with high spatial and temporal resolution at day and night. Daytime scanning temperature measurements within a range of 3 km using a temporal resolution of 169 s and a moving average of 300 m in range show statistical temperature uncertainties of less than 1 K while pointing at 21 directions. Temperature uncertainties of less than 1 K are achieved during nighttime up to a range of 8 km using a temporal resolution of 3 minutes and a range resolution of 300 m. The lidar resolves also turbulence in the convective boundary layer, e.g., at 470 m height with a temporal resolution of 10 s and statistical uncertainties of only 0.41 K. In addition to temperature, also the particle backscatter coefficient and the particle extinction coefficient are measured independently. The instrument operates with a primary wavelength of 355 nm. This has instrumental advantages compared to 532 nm but also yields eye-safety beyond a range of 500 m which facilitates the deployment. Highly efficient spectral separation of the atmospheric backscatter signals is performed by a polychromator with narrow-band interference filters in a sequential setup. The spectral characteristics of these filters were optimized with respect to high measurement performance in the daytime planetary boundary layer and the lower free troposphere. Pioneering measurements of the 2-dimensional temperature distribution in the lower troposphere in the vicinity of a mountain ridge are presented.Im Rahmen des virtuellen Institutes COSI-TRACKS wurde das erste abtastende Rotations-Raman-Lidar entwickelt und in zwei großen Feldmesskampagnen erfolgreich eingesetzt. Dies ermöglichte neue Untersuchungen in der konvektiven Grenzschicht und trug während der Messkampagne PRINCE (PRediction, Identification and trackiNg of Convective cElls) im Juli 2006 und dem COPS Experiment (Convective and Orographically-induced Precipitation Study) von Juni bis August 2007 zu Studien der Auslösung von Konvektion bei. Das Rotations-Raman-Lidar der Universität Hohenheim wurde während beider Messkampagnen auf der Hornisgrinde (48.61 °N, 8.20 °O, 1161 m ü. NN), der höchsten Erhebung im Nordschwarzwald im Südwesten Deutschlands, stationiert. Das Lidar erlaubt Messungen atmosphärischer Temperaturfelder in der Troposphäre mit zeitlich und räumlich hoher Auflösung am Tag und in der Nacht. Abtastende Temperaturmessungen in 21 unterschiedlichen Richtungen am Tage bis zu einer Entfernung von 3 km, mit einer zeitlichen Auflösung von 169 s und einer räumlichen Glättungslänge von 300 m zeigen statistische Messunsicherheiten der Temperatur von weniger als 1 K. Messunsicherheiten von weniger als 1 K werden in der Nacht mit einer zeitliche Auflösung von 3 Minuten und einer Entfernungsauflösung von 300 m bis zu einer Entfernung von 8 km erreicht. Das Lidar löst ebenso die Turbulenz in einer konvektiven Grenzschicht auf, z.B. in einer Höhe von 470 m mit einer zeitlichen Auflöung von 10 s und statistischen Unsicherheiten von nur 0.41 K. Zusätzlich zur Temperatur werden unabhängig voneinander auch der Partikel-Rückstreukoeffizient und der Partikel-Extinktionskoeffizient gemessen. Das Gerät wird bei einer Primärwellenlänge von 355 nm betrieben, dies bietet im Vergleich zu 532 nm instrumentelle Vorteile, aber auch die Augensicherheit wird in einer Entfernung von 500 m erreicht, was den Einsatz sehr erleichtert. Eine sehr effiziente spektrale Aufteilung des atmosphärischen Rückstreusignals erfolgt in der Strahlseparationseinheit mit schmalbandigen Interferenzfiltern in einem sequentiellen Aufbau. Die spektralen Eigenschaften der Filter wurden im Hinblick auf hohe Effizienz für Tageslichtmessungen in der planetaren Grenzschicht und der unteren freien Troposphäre optimiert. Erstmals werden Messungen der 2-dimensionalen Temperaturverteilung in der unteren Troposphäre in der Umgebung eines Berges gezeigt

Water vapour intercomparison effort in the frame of the Convective and Orographically-induced Precipitation Study

International audienceThe main objective of this work is to provide accurate error estimates for the different water vapour profiling sensors based on an intensive inter-comparison effort. The inter-comparison, performed in the framework of COPS--Convective and Orographically-induced Precipitation Study (01 June-31 August 2007), involves airborne and ground-based water vapour lidar systems, radiosondes with different humidity sensors, GPS and Microwave radiometers (MWR). Simultaneous and co-located data from different sensors are used to compute relative bias and root-mean square (RMS) deviations as a function of altitud

Water vapour intercomparison effort in the frame of the Convective and Orographically-induced Precipitation Study

International audienceThe main objective of this work is to provide accurate error estimates for the different water vapour profiling sensors based on an intensive inter-comparison effort. The inter-comparison, performed in the framework of COPS--Convective and Orographically-induced Precipitation Study (01 June-31 August 2007), involves airborne and ground-based water vapour lidar systems, radiosondes with different humidity sensors, GPS and Microwave radiometers (MWR). Simultaneous and co-located data from different sensors are used to compute relative bias and root-mean square (RMS) deviations as a function of altitud

Water vapour intercomparison effort in the frame of the Convective and Orographically-induced Precipitation Study

The main objective of this work is to provide accurate error estimates for the different water vapour profiling sensors based on an intensive inter-comparison effort. The inter-comparison, performed in the framework of COPS - Convective and Orographically-induced Precipitation Study (01 June-31 August 2007), involves airborne and ground-based water vapour lidar systems, radiosondes with different humidity sensors, GPS and Microwave radiometers (MWR). Simultaneous and co-located data from different sensors are used to compute relative bias and root-mean square (RMS) deviations as a function of altitude. Comparisons between airborne CNRS DIAL and ground-based Raman lidar BASIL from three dedicated flights performed in the frame of the H2Olidar EUFAR project indicate a mean relative bias between the two sensors of 3.9% (0.11 g/kg) and a mean RMS deviation of 13.7% (0.97 g/kg) in the altitude region 0-4.5 kin above ground level. A specific inter-comparison between radiosondes with different humidity sensors (Vaisala RS80-A, RS80-H and RS92) was also performed during COPS. Results from the radiosonde inter-comparison indicate that RS80-A and RS80-H are affected by several systematic sources of error (contamination error, time-lag error, etc.), which have been corrected through established algorithms [1, 2, 3]. After correction for these error sources, mean bias between RS80 (A&H) and RS92 is found to be reduced to -4.5%. Based on the 3 comparisons between BASIL vs airborne DLR DIAL, the mean relative bias is about -3.5% in the altitude region 0-3 Km, while the RMS is approx. 13%. There are also ongoing comparisons between BASIL vs GPS, MWR and radiosondes and between the water vapor sensors located at different sites and the airborne DIALs which will be discussed at the symposium. Thus on the present statistics of comparisons between BASIL vs both the airborne DIALs and GPS and putting equal weight on the data reliability of each instrument, it results in the bias values of. BASIL Raman Lidar-0.3%, DLR DIAL 3.2%, CNRS DIAL-3.6% and GPS 0.6%. More ongoing comparisons between water vapor profiling sensors, especially benefiting from the extraordinary performances of the ground-based UHOH DIAL system, will be discussed at the symposium