Engelbert Nagel

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...

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.

WIND: the joint French-German airborne Doppler lidar

An airborne coherent Doppler Lidar to retrieve mesoscale wind fields has been developed in the frame of the Franco- German WIND project. The instrument is based on a pulsed CO2 laser transmitter, heterodyne detection and wedge scanner. The performance of the instrument operating on the ground and in the aircraft is reported.

High spectral brightness UV laser for airborne wind-lidar observations

Laser sources employed in light detection and ranging (lidar) systems for the quantification of atmospheric parameters such as wind velocity, temperature or trace gas concentration need to fulfill a large set of strict requirements regarding their power performance as well as their spatial and spectral properties. In particular, the generation of high-energy output pulses in the UV spectral region with excellent spectral purity is mandatory for the precise measurement of wind velocities by means of direct-detection Doppler wind lidar systems. Here, the frequency stability of the laser transmitter must be better than 5 MHz to ensure low systematic errors in wind velocity of about 1 m/s. The realization of reliable, high spectral brightness laser sources is further complicated when operating in severe vibration environments such as on ships or aircraft.

Airborne Doppler lidar wind measurement: housekeeping data as critical parameters

For the airborne measurement of the wind field, exact data of velocity and orientation of the platform are mandatory. Any small deviation in these parameter will cause a systematic error in the estimation of the wind field. In practice all navigation systems like inertial reference systems (IRS) and also GPS have some errors in their data which may lead to a significant error in the estimated wind field. However a conical scanning Doppler lidar like ADOLAR will also offer some information from the ground return which can be used to select and correct most of the housekeeping data from the other systems. This paper describes briefly the Doppler lidar used for the wind measurements and then extends on the different processing steps necessary to retrieve the 3D wind field with an accuracy better than 1 m/s. The campaign with the airborne Doppler Lidar ADOLAR on board the DLR research aircraft Falcon F20 at November 96 will be used to illustrate this topic. At this campaign three flights were performed at Bavaria, the North sea , and the Baltic Sea. Especially at the first flight in Bavaria approximately one . hour of lidar data with ground return have been obtained. This allows an extended comparison of the different sources of housekeeping data like IRS, GPS, and the Doppler Udar itself.

Calibration of an inertial reference system (IRS) using the ground return of a Doppler lidar

For the measurement of the wind field from a moving platform one big challenge is the elimination of the Doppler shift due to platform motion. If the housekeeping data (platform velocity and attitude) are not accurate enough, a calibration to the ground return of the lidar is a possible solution. This presentation deals with the advantages and problems of such a procedure at the example of measurements obtained with the airborne Doppler lidar ADOLAR. Here a rectangular flight pattern from October 13, 1994 over the Nordsee is discussed together with the possibility of using this technique at a satellite.

Airborne cw Doppler lidar (ADOLAR)

During the last 10 years the DLR container LDA (Laser Doppler Anemometer) was used for many wind related measurements in the atmospheric boundary layer. The experience out of this were used to construct an airborne Doppler lidar ADOLAR. Based on the available Doppler lidars it is now proposed to perform a campaign to demonstrate the concept of the spaceborne sensor ALADIN, and to answer some questions concerning the signal quality from clouds, water and land. For the continuous wave CO2 laser, the energy is focused by the telescope into the region of investigation. Some of the radiation is back scattered by small aerosol particles drifting with the wind speed through the sensing volume. The back scattered radiation is collected by the telescope and detected by coherent technique. With the laser Doppler method one gets the radial wind component. To determine the magnitude and direction of the horizontal wind, some form of scanning in azimuth and elevation is required. To keep the airborne system compact, the transceiver optics is directly coupled to a wedge scanner which provides the conical scan with the axis in Nadir direction from the aircraft. The system ADOLAR was tested in 1994. Results of the flight over the lake Ammersee are presented and are compared with the data of the inertial reference system of the aircraft.