- 1University of Freiburg, Faculty of Environment and Natural Resources, Chair of Environmental Meteorology, Freiburg, Germany (dana.looschelders@meteo.uni-freiburg.de)
- 2Department of Meteorology, University of Reading, United Kingdom
- 3Laboratoire de Météorologie Dynamique/Institut Pierre Simon Laplace, École Polytechnique, Palaiseau, France
- 4Chair of Climatology, Technische Universität Berlin, Germany
- 5School of Geosciences, University of Edinburgh, Edinburgh, United Kingdom
With the advances in ground-based remote sensing technology, measurement networks of automatic aerosol lidar-ceilometers are developing rapidly across Europe and worldwide. Characterising inter-instrument variability of sensors is crucial to assessing uncertainties in observational campaigns, networks, and for data assimilation. It allows the determination of thresholds that need to be exceeded for the detection of meaningful atmospheric differences between observations obtained at different locations (e.g. urban vs rural).
We co-locate six Vaisala CL61 automatic lidar-ceilometers at the SIRTA atmospheric observatory (Palaiseau, France) for a period of ten days to quantify instrument-related differences in several observed variables: profiles of attenuated backscatter and the linear depolarisation ratio (LDR), as well as derived cloud variables, such as cloud base height (CBH) and cloud cover fraction (CCF), and mixed-layer height. Analysing intervals between 5 and 60 min, median absolute differences between sensors are used to quantify inter-instrument uncertainties. For backscatter and LDR, we differentiate between conditions with rain, clear sky, and clouds, respectively.
The agreement between instruments is capable of resolving climatological differences in mesoscale conditions (5 - 50 km, e.g. across cities) for both profile variables and derived cloud variables and layer heights. However, differences exist and can be linked to signal-to-noise ratio (SNR) and atmospheric conditions. The median absolute inter-sensor differences for 15 min aggregation intervals (AD50) are 1.9 % for total CCF (excluding clear sky and fully overcast conditions) and 7.3 m for CBH. Cloud variables agree better for boundary layer clouds where the first (of five) cloud layer < 4 km agl. The mixed-layer height AD50 is 0 m. Median differences smaller than two instrument range gates (9.6 m) highlight the close inter-instrument agreement.
How to cite: Looschelders, D., Christen, A., Grimmond, S., Kotthaus, S., Dupont, J.-C., Fenner, D., Haeffelin, M., and Morrison, W.: A field intercomparison of inter-instrument variability of six co-located Vaisala CL61 lidar-ceilometers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15242, https://doi.org/10.5194/egusphere-egu25-15242, 2025.
