Oliver Reitebuch

The Airborne Demonstrator for the Direct-Detection Doppler Wind Lidar ALADIN on ADM-Aeolus. Part I: Instrument Design and Comparison to Satellite Instrument

Abstract The global observation of profiles of the atmospheric wind speed is the highest-priority unmet need for global numerical weather prediction. Satellite Doppler lidar is the most promising candidate to meet the requirements on global wind profile observations with high vertical resolution, precision, and accuracy. The European Space Agency (ESA) decided to implement a Doppler wind lidar mission called the Atmospheric Dynamics Mission Aeolus (ADM-Aeolus) to demonstrate the potential of the Doppler lidar technology and the expected impact on numerical weather forecasting. An airborne prototype of the instrument on ADM-Aeolus was developed to validate the instrument concept and retrieval algorithms with realistic atmospheric observations before the satellite launch. It is the first airborne direct-detection Doppler lidar for atmospheric observations, and it is operating at an ultraviolet wavelength of 355 nm. The optical design is described in detail, including the single-frequency pulsed laser and th...

Experimental Validation of Wind Profiling Performed by the Airborne 10-μm Heterodyne Doppler Lidar WIND

The airborne Wind Infrared Doppler Lidar (WIND) has been developed through French‐German cooperation. The system is based on a pulsed 10.6-mm laser transmitter, a heterodyne receiver, and a conical scanning device. To the authors’ knowledge, it is the first airborne Doppler lidar for atmospheric research to retrieve the whole tropospheric wind profile between the ground and the flight level looking downward. The wind vector is measured with the velocity-azimuth display (VAD) technique with a vertical sampling of 250 m. The first flights on board the DLR Falcon 20 aircraft were performed in 1999. Results of a comparison among WIND, radiosondes, windprofiler radar measurements, numerical models, and simulations are presented. It is shown that the correspondence of airborne WIND measurements with those of other instruments or models is better than 1.5 m s21 and 58 for the horizontal wind vector. These results show the excellent capability of conical scanning Doppler lidars to provide unique insights into mesoscale dynamic processes and progress made toward future spaceborne systems.

The Alpine Mountain–Plain Circulation: Airborne Doppler Lidar Measurements and Numerical Simulations

On summer days radiative heating of the Alps produces rising air above the mountains and a resulting inflow of air from the foreland. This leads to a horizontal transport of air from the foreland to the Alps, and a vertical transport from the boundary layer into the free troposphere above the mountains. The structure and the transports of this mountain–plain circulation in southern Germany (“Alpine pumping”) were investigated using an airborne 2-m scanning Doppler lidar, a wind-temperature radar, dropsondes, rawinsondes, and numerical models. The measurements were part of the Vertical Transport and Orography (VERTIKATOR) campaign in summer 2002. Comparisons of dropsonde and lidar data proved that the lidar is capable of measuring the wind direction and wind speed of this weak flow toward the Alps (1–4 ms 1 ). The flow was up to 1500 m deep, and it extended 80 km into the Alpine foreland. Lidar data are volume measurements (horizontal resolution 5 km, vertical resolution 100 m). Therefore, they are ideal for the investigation of the flow structure and the comparison to numerical models. Even the vertical velocities measured by the lidar agreed with the mass budget calculations in terms of both sign and magnitude. The numerical simulations with the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5) (mesh size 2 and 6 km) and the Local Model (LM) of the German Weather Service (mesh size 2.8 and 7 km) reproduced the general flow structure and the mass fluxes toward the Alps within 86%–144% of the observations.

Targeted Observations with an Airborne Wind Lidar

Abstract This study investigates the possibilities and limitations of airborne Doppler lidar for adaptive observations over the Atlantic Ocean. For the first time, a scanning 2-μm Doppler lidar was applied for targeted measurements during the Atlantic “The Observing System Research and Predictability Experiment” (THORPEX) Regional Campaign (A-TReC) in November and December 2003. The DLR lidar system was operated for 28.5 flight hours, and measured 1612 vertical profiles of wind direction and wind speed with a horizontal and vertical resolution of 5–10 km and 100 m, respectively. On average, there were 25 reliable wind values on every profile, which cover 2500 m in the vertical (about one-third of the mean vertical extent of the profiles). A statistical comparison of 33 dropsondes and collocated lidar winds profiles allowed individual estimates of the standard deviation to be assigned to every wind value and to determine threshold values for an objective quality control of the data. The standard deviation ...

Wind Infrared Doppler Lidar Instrument

The purpose of the project WIND (wind infrared Doppler lidar) is the development of an airborne conical scanning CO2 Doppler lidar in French-German cooperation by CNRS/CNES and DLR. The instrument and its peculiarities are described. Measurements of the Doppler shift from a moving platform with an accuracy of 1 m/s require instantaneous access to the position data of the platform. Therefore this part of the instrument is described in detail. Ground-based tests, airborne tests and a validation flight were performed. The instrument can be used for me- soscalic meteorology to test models and contribute to a spaceborne Doppler lidar in the future.

The Saharan aerosol long-range transport and aerosol-cloud-interaction experiment. Overview and Selected Highlights

AbstractNorth Africa is the world’s largest source of dust, a large part of which is transported across the Atlantic to the Caribbean and beyond where it can impact radiation and clouds. Many aspects of this transport and its climate effects remain speculative. The Saharan Aerosol Long-Range Transport and Aerosol–Cloud-Interaction Experiment (SALTRACE; www.pa.op.dlr.de/saltrace) linked ground-based and airborne measurements with remote sensing and modeling techniques to address these issues in a program that took place in 2013/14. Specific objectives were to 1) characterize the chemical, microphysical, and optical properties of dust in the Caribbean, 2) quantify the impact of physical and chemical changes (“aging”) on the radiation budget and cloud microphysical processes, 3) investigate the meteorological context of transatlantic dust transport, and 4) assess the roles of removal processes during transport.SALTRACE was a German-led initiative involving scientists from Europe, Cabo Verde, the Caribbean, a...

The Airborne Demonstrator for the Direct-Detection Doppler Wind Lidar ALADIN on ADM-Aeolus. Part II: Simulations and Rayleigh Receiver Radiometric Performance

Abstract In the frame of the Atmospheric Dynamics Mission Aeolus (ADM-Aeolus) satellite mission by the European Space Agency (ESA), a prototype of a direct-detection Doppler wind lidar was developed to measure wind from ground and aircraft at 355 nm. Wind is measured from aerosol backscatter signal with a Fizeau interferometer and from molecular backscatter signal with a Fabry–Perot interferometer. The aim of this study is to validate the satellite instrument before launch, improve the retrieval algorithms, and consolidate the expected performance. The detected backscatter signal intensities determine the instrument wind measurement performance among other factors, such as accuracy of the calibration and stability of the optical alignment. Results of measurements and simulations for a ground-based instrument are compared, analyzed, and discussed. The simulated atmospheric aerosol models were validated by use of an additional backscatter lidar. The measured Rayleigh backscatter signals of the wind lidar pr...

Spontaneous Rayleigh-Brillouin scattering of ultraviolet light in nitrogen, dry air and moist air,

Atmospheric lidar techniques for the measurement of wind, temperature, and optical properties of aerosols rely on the exact knowledge of the spectral line shape of the scattered laser light on molecules. We report on spontaneous Rayleigh-Brillouin scattering measurements in the ultraviolet at a scattering angle of 90 degrees on N(2) and on dry and moist air. The measured line shapes are compared to the Tenti S6 model, which is shown to describe the scattering line shapes in air at atmospheric pressures with small but significant deviations. We demonstrate that the line profiles of N(2) and air under equal pressure and temperature conditions differ significantly, and that this difference can be described by the S6 model. Moreover, we show that even a high water vapor content in air up to a volume fraction of 3.6vol.% has no influence on the line shape of the scattered light. The results are of relevance for the future spaceborne lidars on ADM-Aeolus (Atmospheric Dynamics Mission) and EarthCARE (Earth Clouds, Aerosols, and Radiation Explorer).

The ADM-Aeolus wind retrieval algorithms

The ADM-Aeolus is primarily a research and demonstration mission flying the first Doppler wind lidar in space. Flexible data processing tools are being developed for use in the operational ground segment and by the meteorological community. We present the algorithms developed to retrieve accurate and representative wind profiles, suitable for assimilation in numerical weather prediction. The algorithms provide a flexible framework for classification and weighting of measurement-scale (1–10 km) data into aggregated, observation-scale (50 km) wind profiles for assimilation. The algorithms account for temperature and pressure effects in the molecular backscatter signal, and so the main remaining scientific challenge is to produce representative winds in inhomogeneous atmospheric conditions, such as strong wind shear, broken clouds, and aerosol layers. The Aeolus instrument provides separate measurements in Rayleigh and Mie channels, representing molecular (clear air) and particulate (aerosol and clouds) backscatter, respectively. The combining of information from the two channels offers possibilities to detect and flag difficult, inhomogeneous conditions. The functionality of a baseline version of the developed software has been demonstrated based on simulation of idealized cases.

Daytime measurements of atmospheric temperature profiles (2-15 km) by lidar utilizing Rayleigh-Brillouin scattering

In this Letter, we report on a novel method for measuring atmospheric temperature profiles by lidar during daytime for heights of 2-15.3 km, with a vertical resolution of 0.3-2.2 km, using Rayleigh-Brillouin scattering. The measurements are performed by scanning a laser (λ=355 nm) over a 12 GHz range and using a Fabry-Pérot interferometer as discriminator. The temperature is derived by using a new analytical line shape model assuming standard atmospheric pressure conditions. Two exemplary temperature profiles resulting from measurements over 14 and 27 min are shown. A comparison with radiosonde temperature measurements shows reasonable agreement. In cloud-free conditions, the temperature difference reaches up to 5 K within the boundary layer, and is smaller than 2.5 K above. The statistical error of the derived temperatures is between 0.15 and 1.5 K.