Development of a Portable Aerosol-Lidar
To become even more flexible (concerning experiments) a portable lidar was developed. It is called POLIS. This activity was done in the framework of the GTCO.
The concept study began in late 2000 as a joint project of the GTCO and the lidar group of the Meteorological Institute. As a conclusion of this study - due to the very strict requirements concerning aerosol detection in the whole troposphere - the optical system was completely developed by ourselves, because no commercial systems could fulfill our specifications. The design of the lidar allows groundbased and aircraft operation. First field experiments were conducted in July 2002.
Developments for Lidar Quality Assurance
A major problem in running a lidar system is the precise characterization of the system. Only if all components are specified and their accuracy is known, high quality measurements can be performed. For testing the performance of the lidar, several subsystems have been developed in our group.
CCD-Camera Assembly
This device has been developed to accurately align the optical axes of the laser and the telescope. If the alignment is not perfect, problems arise in the near field as well as in the far field of the observations: in particular, the calibration of the lidar signals to Rayleigh-conditions in the upper troposhere is not possible. Unfortunately, due to the small signals at that ranges it is difficult to identify misaligned signals from „good“ signals. Thus, extreme care is required to align the system. Otherwise, the retrieved optical properties are wrong.
For this purpose, we have developed an CCD-Camera assembly (image 1).
It can be mounted within a few minutes in the optical path of the lidar in such a way that the image of the laser beam in the telescope can be seen on a monitor. By moving the laser by micro-screws at its front-end (image 2) and the possible rotation at the back-end (image 3), the direction of the emitted beam can be changed to perfectly fit into the center of the image.
Optical Pulse Generator
For testing the response of the electronics of the system, clearly specified rectangular shaped optical pulses are emitted by the Optical Pulse Gemerator.
Electrical Pulse Generator
For testing the response of the electronics of the system, defined electrical pulses are emitted by the Electrical Pulse Gemerator.
