Lidars at University of Hohenheim

In this contribution, we will give an update of recent lidar activities at University of Hohenheim. Two of the lidars have been developed at our institute: The scanning water vapor differential absorption lidar (WVDIAL) and the Raman lidar ARTHUS (Atmospheric Raman Temperature and HUmidity Sounder). In addition, two scanning Doppler lidars are used since a few years while a third one will be added soon. All these lidars are located at LAFO (Land Atmospheric Feedback Observatory; Branch et al., this conference). Here, also a scanning Doppler cloud radar, meteorological towers, Eddy-covariance stations, surface and sub-surface sensors are collecting routinely data. These data are combined with detailed vegetation analyses.

The WVDIAL is embedded into large truck. Its transmitter consists of an injection-seeded titanium-sapphire laser that is pumped with a diode-pumped Nd:YAG laser. The maximum laser power is 10 W at 200 Hz. This laser power can be used for vertical measurements for which the laser beam is directly emitted vertically into the atmosphere. For scanning measurements, 2 W laser power are transmitted with a fiber into the atmosphere after being expanded with a small telescope. The atmospheric backscatter signals are collected with a 80-cm telescope offering high detection efficiency. The resolution of the stored raw data is up to several Hz and a few meters. The typical resolution of the data products is 1 s and 30 m.

While the large WVDIAL needs supporting personal for its operation, our second lidar ARTHUS is an automated instrument with continuous operation (Lange et al., 2019; Wulfmeyer and Behrendt, 2022). This eyesafe Raman lidar uses a diode-pumped Nd:YAG laser as transmitter. Only the third-harmonic radiation at 355 nm is – after beam expansion – transmitted into the atmosphere. The laser power is about 15 W at 200 Hz repetition rate. The receiving telescope has a diameter of 40 cm. A polychromator extracts the elastic backscatter signal and three inelastic signals, namely the vibrational Raman signal of water vapor, and two pure rotational Raman signals. The raw data is stored with a resolution of 7.5 m and typically 10 s (while higher temporal resolution is possible). All four signals are simultaneously analyzed and stored in both photon-counting (PC) mode and voltage (so-called “analog” mode) in order to make optimum use of the large intensity range of the backscatter signals covering several orders of magnitude. Primary data products are temperature, water vapor mixing ratio, particle backscatter coefficient and particle extinction coefficient. The high resolution allows studies of boundary layer turbulence (Behrendt et al, 2015) and - in combination with the vertical pointing Doppler lidar - sensible and latent heat fluxes (Behrendt et al, 2020). Similar lidars like ARTHUS are meanwhile also available at the company Purple Pulse Lidar Systems (www.purplepulselidar.com). In 2023, a CO₂ channel was implemented into ARTHUS allowing now in addition also measurements of the CO₂ mixing ratio (Schumann et al., this conference).

 

Behrendt et al. 2015, https://doi.org/10.5194/acp-15-5485-2015

Behrendt et al. 2020, https://doi.org/10.5194/amt-13-3221-2020

Lange et al. 2019, https://doi.org/10.1029/2019GL085774

Wulfmeyer and Behrendt 2022, https://doi.org/10.1007/978-3-030-52171-4_25