Browsing by Subject "Scanning"

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3-D observations of absolute humidity from the land surface to the lower troposphere with scanning differential absorption lidar
(2016) Späth, Florian Heiko; Wulfmeyer, Volker
The water vapor (WV) distribution in the atmospheric boundary layer (ABL) is spatially and temporally highly variable. To investigate this behavior, the Institute of Physics and Meteorology at the University of Hohenheim (UHOH) developed a unique scanning differential absorption lidar (DIAL). This instrument allows for water vapor measurements with high temporal and spatial resolutions of the orders of seconds and tens of meters in the range of several kilometers from the surface up to the lower troposphere. Additionally, the UHOH DIAL system can perform scanning measurements which allows for observations down to the surface as well as for observations of the horizontal moisture variability. Within this thesis, three aspects regarding high-resolution observations of moisture in the ABL with scanning DIAL are demonstrated: 1) the development of a new seeder system for the laser transmitter, 2) the presentation of three scan modes, and 3) applications of 2-D to 3-D WV DIAL data. The newly developed seeder system is based on distributed feedback (DFB) laser diodes as seed lasers and an electro-optical deflector as optical switch. The setup and its specifications are presented. Scanning measurements were performed to capture the spatial WV structures. For this purpose, three scan modes with measurement examples are presented: 1) Range-height indicator (RHI) scans provide vertical cross-section images of the atmospheric humidity distribution. The presented series of four measurements show several humidity layers with different WV content and their evolution. Clouds appear in the last scan. 2) A volume scan captures the whole three-dimensional WV structure made out of several conical scans of different elevation angles. The horizontal variation of the layer heights can be related to the terrain profile with a small hill near the DIAL site. 3) Low elevation scans observe the WV distribution directly above the surface. Thus, relationships of the ground characteristics and vegetation with the humidity content above can be investigated. It is shown that there was more moisture above a maize field and above a forest than above grassland. For the analysis of scanning measurements, new analysis and visualization routines as well as new methods for the error estimation were developed. More scientific applications of high-resolution WV data from DIAL measurements are presented in three publications. A evaluation study compared humidity profiles from model simulations with different land-surface schemes with horizontal mean profiles of scanning DIAL measurements. High-resolution humidity fluctuations from vertical measurements were used to determine higher-order moments up to the fourth-order as well as skewness and kurtosis. Furthermore, such WV profiles were combined with profiles of temperature and vertical wind velocities and used for the development of new turbulence parameterizations and for model validation.
A scanning eye-safe rotational Raman lidar in the ultraviolet for measurements of tropospheric temperature fields
(2009) Radlach, Marcus; Wulfmeyer, Volker
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.