In this section we give a brief overview of our main research activities. Further details can be found under projects.
Deployment of Mobile Aerosol Lidars
The lidar "MULIS" was designed for determining geometrical, optical and microphysical properties of clouds and aerosols. The main focus is on tropospheric aerosols.
The lidar is equipped with a Nd:YAG laser simultaneously emitting radiation at 1064 nm, 532 nm, and 355 nm. The pulse repetition rate is 10 Hz. Detection channels to measure depolarization and Raman scattered radiation are operational since 2006. The line of sight of the lidar can be changed in azimuth and zenith direction to observe atmospheric cross sections or even volumes. The lidar is robust and very compact. It can be mounted in a trailer (
) so it can easily be moved to any field site.
Regular measurements are performed from the platform at the top of the institute building (48.09 N, 11.34 E, 539 m a.s.l.), since 2006 at Maisach (48.209 N, 11.258 E, 516 m a.s.l.).
Field experiments and special scientific programmes include ELITE'94, OPAP 96/97 within the framework of BayFORKLIM, ACE 2, LACE in the AFS-programme, and SLICE. The main activity are regular measurements in the framework of EARLINET, EARLINET-ASOS and ACTRIS. More details can be found here.
A second lidar, POLIS, was developed in 2001/2002. It is even smaller than MULIS and can be carried by one person. In its present configuration it has three detection channels: it can be operated as a dual wavelength backscatter lidar, as a depolarization lidar or a Raman lidar.
POLIS has been used in field campaigns, from aircrafts and from a driving van.
Application of Remote Sensing Techniques
Derivation of optical properties of aerosols - in particular the extinction coefficient - from backscatter lidar measurements requires an inversion scheme. The underlying principle, described by the so-called lidar equation, suffers from having two unknowns in one equation. Thus, additional information (assumptions) is required, introducing sources of errors.
To avoid these problems we took advantage from the scanning mechanism of our lidar. Combining measurements from two zenith angles allows an estimate of the optical depth of aerosol layers provided that the aerosols are homogeneously stratified. In 2006 we implemented two channels sensitive to in-elastically scattered radiation at 607 nm and 387 nm. Hence, we could apply the so called Raman-technique which allows us to determine extinction coefficients directly (during night).
With the upgrade of the lidar (Raman channels, depolarizazion channels) we are able to determine the aerosol bulk properties „lidar ratio“ and „linear depolarization ratio“ at two wavelengths. From these parameters an optical characterization of aerosols is possible and different aerosol types can be discriminated.
Assessment of the Potential of a Spaceborne Lidar
The European Space Agency plans to launch a backscatter lidar (ATLID) as part of an „Earth Radiation Mission“ (ERM) in the forthcoming decade.
The potentials of such a lidar for meteorological and climatological applications have been investigated by simulating future scenarios. Special emphasis was put on supporting temperature retrievals (TOVS), on the detection of (thin) clouds and aerosol layers, on the contribution to cloud climatologies, and on the determination of the optical depth of clouds. The output of these studies is part of the preparation of the ATLID mission.
Furthermore, several studies on the significance of multiple scattering for spaceborne lidar measurements were made.
In 2000, ERM was replaced by the „Earth Cloud and Aerosol Radiation Explorer“ (EarthCARE) and the co-operation between ESA and NASDA (Japan) has been intensified. The concept of ATLID was revised and updated. We are again involved in the preparation of the new lidar.