First of all: „Lidar“ is an acronym for „Aerosol characterization by means of lidar and sunphotometer measurements and advanced scattering models“.
MIM has a long tradition in atmospheric lidar research. The activities go back to the late 1980's when Heinrich Quenzel was head of the radiation and remote sensing working group. The scientific focus at that time was on numerical studies with respect to the accuracy of lidar data inversion schemes and feasibility studies for spaceborne lidar systems. In this context several investigations on the relevance of multiple scattering in lidar signals were provided. In cooperation with the DFVLR (now DLR) a detailed lidar concept for the German space mission D2 was developed.
In 1993/94 a mobile scanning multichannel backscatter lidar (MULIS) was implemented. The concept of MULIS allows very high flexibility in field experiments due to its small size, low power consumption and robustness. Scientific goals include cirrus clouds but primarily the characterization of aerosols. In 2005/06, MULIS was upgraded (MULIS-II) by the implementation of two Raman channels at the wavelengths of 387 nm and 607 nm, and a depolarization channel at 532 nm. The latter serves for the discrimination of spherical and non-spherical particles.
MULIS was operated in several international aerosol campaigns (see field campaings). The MIM lidar group was partners of the first German lidar network, the European Aerosol Research Lidar Network (EARLINET) and EARLINET-ASOS and ACTRIS (see projects).
In 2002 a even smaller, portable lidar (POLIS) was developed by the MIM lidar group. It is designed as a two channel lidar: either with two polarization channels at 355 nm or with channels for Raman and elastic backscattering (387 nm and 355 nm). In 2011 a three channel version was successfully developed, including 532 nm. POLIS has demonstrated its potential as stationary ground based system, as a mobile system in a van, and as a airborne system. It was flown in the framework of the BBC campaign and several programs of the ESA to validate satellite retrievals of cloud top heights. In 2006, it was operated from the FU-Berlin's CESSNA to measure aerosol distributions over Thessaloniki (SCOUT3). Groundbased campaigns include SAMUM (2006 and 2008), AMMA (2006) and the monitoring of the Eyjafjallajökull-plume in 2010. In 2013 POLIS was upgraded to a six channel Raman- and depolarization lidar (355 nm, 532 nm) and used in the framework of SALTRACE in Barbados.
Since June 2009 a Jenoptik ceilometer CHM15kx (internal name: YALIS) is installed for continuously monitoring the aerosol- and cloud-distribution, and to serve as „teaser“ for students to be involved in lidar remote sensing. Data of the ceilometer were used to investigate the spatial homogeneity of the aerosol distribution (cooperation with DWD) and to test algorithms for the assessment ot the mixing layer height. Intercomparison of different ceilometer types (Jenoptik, Vaisala) have been conducted (overlap, signal to noise ratio) and the CHM15kx was successfully calibrated (absolute calibration).
In parallel to the experimental work, numerical models to calculated the scattering properties of aerosol ensembles consisting of quite complex non-spherical particles were developed. They allowed us to understand experimental data, e.g. linear depolarization ratios from lidar measurements, and to determine the mass concentration of the Eyjafjallajökull plume over Munich (April 2010). In this context, datasets of lidar and sun photometer were exploited in synergy.
Currently we are operating two sun- and sky-radiometers SSARA-Z at the Zugspitze (Umweltforschungsstation Schneefernerhaus, UFS) and SSARA-P, the latter being under testing. Both instruments measure spectral radiances between 340 nm and 1640 nm, SSARA-P is equipped with polarimetric channels at 500 nm. Moreover, we are part of AERONET.
It should be emphasized that before operating this nice equipment, several very complex stages had to be completed. All these steps were provided by the MIM with its own personnel and infrastructure (e.g., workshop). These activities include a whole bunch of quite different steps: from the first idea over the construction and implementation to the application and the evaluation of the data. And not to forget: a lot of (non- or semi-scientific) paperwork, strong nerves and patience…