The Leipzig Aerosol and Cloud Remote Observations System LACROS

Motivation

The large number of unsolved questions concerning the interaction between aerosol particles and clouds and corresponding indirect effects on precipitation and radiative transfer demand new measurement strategies to resolve the atmospheric processes involved. In this regard, obtaining synergistic information about cloud and aerosol properties from multi–instrument and hence multi–sensor observations is a key approach to overcome the current lack of knowledge. Motivated by these needs, the novel mobile multi–instrument platform Leipzig Aerosol and Cloud Remote Observations System — LACROS — has been set up at TROPOS.

Instrumentation

LACROS comprises a unique set of active and passive remote-sensing instruments which are to a large extent containerized and available for application in field campaigns. The instruments of LACROS are shown in Fig. 1.

The active-remote-sensing branch now spans the wavelength range from the UV to microwave radiation which is covered with

• multiwavelength-Raman-polarization lidar MARTHA (Multiwavelength Tropospheric Raman lidar for Temperature, Humidity, and Aerosol profiling - only in Leipzig)
• Backscatter Extinction Ratio Temperature, Humidity Lidar —BERTHA (only in Leipzig)
• Portable Lidar System — Polly^XT
• a ceilometer CHM 15kx
• the doppler wind lidar systems WiLi and the Streamline - device of Halo Photonics
• the 35-GHz cloud radar MIRA-35
• The Spectral Aerosol Extinction Measurement System (SAEMS) provides spectrally resolved extinction coefficients of aerosols at 15 m above ground

Passive instrumentation which helps to interpret the active remote measurements consists of an Aerosol Robotic Network (AERONET) Sun photometer, the microwave radiometer HATPRO that includes also two infrared radiometers, and an all-sky imager.

Meteorological surface data and radiosondes are available in addition. Measurements of a radiation-balance station that fullfills the criteria of the the Baseline Surface Radiation Network (BSRN) are available. For the determination of precipitation properties an optical disdrometer records the velocity and size distributionof falling hydrometeors in the size range from 0.1 to 10 mm at 4 m above ground.

In addition to the ground-based remote sensing instrumentation, TROPOS is acquiring growing expertise in the managenemt and analysis of spaceborne observationswith passive sensors as the Spinning Enhanced Visible Infrared Imager (SEVIRI) aboard the Meteosat Second Generation (MSG) satellite or the Moderate Resolution Imaging Spectroradiometer MODIS.

Fields of Application

The available lidar systems measure the optical and microphysical properties of aerosols and optically thin clouds, vertical winds within aerosol layers and at cloud base, as well as temperature and humidity profiles. The integration of the cloud radar into LACROS overcomes the limitation of the lidar systems to observe only cloud-free and thincloud (cirrus, altocumulus) scenarios. It enables extensive insights into the microphysical and dynamical processes of thick stratiform and  convective clouds, and thus the investigation of droplet activation and precipitation formation in convective cloud systems. This achievement will facilitate novel links between atmospheric measurements, laboratory studies, and modeling activities. The future application of LACROS concentrates on four main subjects:

1. Investigation of heterogeneous ice–formation processes by exploiting co–located remote–sensing observations of aerosol and cloud radiative and microphysical properties.
2. Instrument validation and development of algorithms and new measurement techniques for ground–based cloud and aerosol microphysics retrieval in the frame of the Aerosols, Clouds, and Trace gases Research InfraStructure Network (ACTRIS). Here, activities currently concentrate on the development of the dual–field–of–view lidar technique to derive cloud droplet size information and on retrievals of aerosol microphysical properties from combined lidar and Sun photometer measurements.
   In this context, the CLOUDNET algorithms have been implemented at TROPOS.
   CLOUDNET already provides a framework for the determination of cloud microphysics from remote-sensing observations, but further extensions are needed to improve reliability and availability.
3. The steadily growing number of spaceborne sensors for cloud and aerosol characterization also implies a need for ground–based observing stations that provide data sets for the validation of the derived products. Also, the combination of ground-based and spaceborne measurements may allow to reduce the uncertainties in the retrieval of cloud and aerosol microphysical
   properties.
4. Deployment during field campaigns in key regions of atmospheric research. LACROS is already scheduled for the deployment in the HOPE field campaigns in the frame of HD(CP)² and in field campaigns in Cabauw, the Netherlands as well as at Cyprus.