A novel scanning water vapor differential absorption lidar (DIAL) system has been developed. This instrument is mobile
and was applied successfully in two field campaigns: COPS 2007 (Convective and Orographically-induced Precipitation
Study), a research and development project of the World Weather Research Programme, and FLUXPAT2009 within the
German Research Foundation project Patterns in Soil-Vegetation-Atmosphere Systems: monitoring, modeling and data
assimilation". In this paper, the instrument is described and its capabilities are illustrated with measurements examples.
The DIAL provides remote sensing data of the atmospheric water-vapor field with previously unachieved resolution. The
data products of the DIAL are profiles of absolute humidity with typical resolutions of 15 to 300 m with a temporal
resolution of 1 to 10 s and a maximum range of several kilometers at both day and night. But spatial and temporal
resolution can be traded off against each other. Intercomparisons with other instruments confirm high accuracy. Beside
humidity, also the backscatter field and thus aerosols and clouds are observed simultaneously.
The DIAL transmitter is based on an injection-seeded Titanium:Sapphire laser operated at 820 nm which is end-pumped
with a diode-pumped Nd:YAG laser. By use of a scanning transmitter with an 80-cm receiving telescope, the
measurements can be performed in any direction of interest and the 3-dimensional structure of the water vapor field can
Three lidar systems are currently in development at University of Hohenheim. A water vapor lidar based on the differential absorption lidar (DIAL) technology working near 815 or 935 nm, a temperature and aerosol lidar employing the rotational Raman technique at 355 nm, and an aerosol lidar working with eye-safe laser radiation near 1.5 μm. The transmitters of these three systems are based on an injection-seeded, diode laser pumped Nd:YAG laser with an average power of 100 W at 1064 nm and a repetition rate of 250 Hz. This laser emits a nearly Gaussian-shaped beam which permits frequency-doubling and tripling with high efficiencies. The frequency-doubled 532-nm radiation is employed for pumping a Ti:Sapphire ring-resonator which will be used for DIAL water vapor measurements. In a second branch, a Cr4+:YAG crystal is pumped with the 1064-nm radiation to reach 1400 to 1500 nm for eye-safe monitoring of aerosol particles and clouds. The 532 and 1064 nm radiation are also used for backscatter lidar observations. Frequency tripling gives 355-nm radiation for measurements of temperature with the rotational Raman technique and particle extinction and particle backscattering coefficients in the UV. High transmitter power and effective use of the received signals will allow scanning operation of these three lidar systems. The lidar transmitters and detectors are designed as modules which can be combined for simultaneous measurements with one scanning telescope unit in a ground-based mobile container. Alternatively, they can be connected to different Nd:YAG pump lasers and to telescope units on separate platforms.