Michael Klier

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 an Airborne Doppler Lidar for Atmospheric Applications Developed in French-German Cooperation

WIND is a joint project between France (CNRS-CNES-Meteo France) and Germany (DLR) to develop an airborne wind Doppler lidar for meteorological applications. The instrument specifications are derived from the measurement objectives as well as the state-of-the-art in technology. Presently an operational airborne wind lidar can be designed around the CO2 laser technology, heterodyne detection, and a conical scanning of the lidar line-of-sight to sample the atmospheric wind field. The 10-micron spectral domain is suitable for long range measurements for it corresponds to an atmospheric window and an adequate backscatter coefficient in the troposphere. The first flights are scheduled early 1995 on board the Falcon 20 operated by DLR.

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.

Application of inverse filtering on lidar signals

Lidar is a well established remote sensing method. One gets range resolved information from remote location. Ranging, cloud ceiling, aerosol layer identification are a few examples. Using a lidar from satellites gives topographic maps of the Earths surface (Degnan 1997). For environmental purposes the aerosol smoke stack emission canbe monitored (Measures 1983, Klein und Werner 1993). The measuring principle is based onthe time measurementof a laser pulse reflected froma target. Targets canbe hard targets like the Earths surface or diffuse targets like clouds. The backscattered signal contains the information on the density characteristics of diffuse targets or the reflection characteristics of the hard target. The range resolution depends onthe pulse characteristics transmitted. In the lidar application the range resolution Lx is proportional to the laser pulse length zt: 2 Therefore, for satellite laser ranging short pulses are used to get resolution in the order of centimeters (for example t =200 ps gives 3 cm resolution for a single event). Can one get the same resolution with a longer pulse? -is one of the questions this paper focusses on. The second question is the identification of aerosol concentrations with high range resolution.

Fernmeßverfahren@@@Remote sensing of mass fluxes of trace gases in the boundary layer mit FTIR-Spektrometrie und Laser Doppler: Messung von Abgasen des Heizkraftwerks München-Nord

ZusammenfassungDie Kombination von Fernerkundungsverfahren wie Fourier-Transform-Infrarot (FTIR)-Spektrometrie und Lidar eröffner die Möglichkeit, Massenflüsse von Gasen zu erfassen. Das Doppler Lidar mißt dabei das dreidimensionale Windfeld und in der Nähe eines Kamins die Änderung des Windfeldes in der Umgebung der Austrittsöffnung. Die Fourier-Transformation des Interferogramms von einem Michelson-Interferometer berechnet aus der aufgezeichneten Intensität (Funktion des Spiegelweges im Interferometer) das spektrale Signal (Spektrum, Funktion der Wellenlänge der Strahlung). Daraus wird durch Analyse der Ausbreitung infraroter Strahlung von der Abgaswolke zum Teleskop des Interferometers die Konzentration der Gaskomponenten bestimmt. Beide Informationen, Geschwindigkeit und Konzentration, ergeben zusammen den Massenfluß des betrachteten Gases. Es wurden die Massenflüsse von CO2, CO, NO und HCl bestimmt, die in guter Übereinstimmung mit den Daten des Kraftwerkes sind. Eine Überwachung von außerhalb des Kraftwerkes ist mit optischen Fernerkundungsverfahren möglich.AbstractThe combination of remote sensing methods like Doppler lidar and FTIR allows remote determination of mass fluxes of gases. Doppler lidar measures the three-dimensional wind vector in the vicinity of diffuse sources, or the velocity of air in a chimney plume if an industrial complex is monitored. FTIR is a multicomponent remote sensing method for gas concentrations. The Fourier transformation of an interferogram of a Michelson interferometer within a FTIR system converts the recorded intensity (function of optical path length) to a spectral signal (function of wavenumber). Both information, velocity and concentration, give the mass fluxes of the tracer (gas). A first test was performed at Munich-Nord power station with FTIR and cw-Doppler lidar. Fluxes of CO2, CO, NO, and HCl were determined. The results are in good agreement with the fluxes measured byin situ instruments of the power station. The method can be used to control industrial complexes from an outside observation site.

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.