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Evaluation of differential absorption radars in the 183 GHz band for profiling water vapour in ice clouds

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journal contribution
posted on 08.07.2019, 16:44 by Alessandro Battaglia, Pavlos Kollias
Relative humidity (RH) measurements in ice clouds are essential for determining ice crystal growth processes and rates. A differential absorption radar (DAR) system with several frequency channels within the 183.3 GHz water vapour absorption band is proposed for measuring RH within ice clouds. Here, the performance of a DAR system is evaluated by applying a DAR simulator to A-Train observations in combination with co-located European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis. Observations from the CloudSat W-band radar and from the CALIPSO lidar are converted first into ice microphysical properties and then coupled with ECMWF temperature and relative humidity profiles in order to compute scattering properties at any frequency within the 183.3 GHz band. A self-similar Rayleigh–Gans approximation is used to model the ice crystal scattering properties. The radar reflectivities are computed both for a space-borne and airborne and a ground-based DAR system by using appropriate radar receiver characteristics. Sets of multi-frequency synthetic observation of attenuated reflectivities are then exploited to retrieve profiles of water vapour density by fitting the line shape at different levels. A total of 10 d of A-Train observations are used to test the measurement technique performance for different combinations of tones when sampling ice clouds globally. Results show that water vapour densities can be derived at the level that can enable ice process studies (i.e. better than 3 %), both from a ground-based system (at the minute temporal scale and with circa 100 m vertical resolution) and from a space-borne system (at 500 m vertical resolution and with circa 5 km integration lengths) with four tones in the upper wing of the absorption line. Deploying ground-based DAR system at high latitudes and high altitudes is highly recommended to test the findings of this work in the field.


The work by Alessandro Battaglia has been supported by the project Radiation and Rainfall funded by the UK National Centre for Earth Observation. This research used the ALICE High Performance Computing Facility at the University of Leicester. This work was supported by the European Space Agency under the “Multi-Frequency Radar Instrument Study” project (contract no. 4000120689/17/NL/IA).



Atmospheric Measurement Techniques, 2019, 12, 3335-3349

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/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy


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Atmospheric Measurement Techniques


European Geosciences Union (EGU), Copernicus Publications



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This research is based on CloudSat data that are publicly available at (Cloudsat data processing center, 2019).



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