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Discussion papers | Copyright
https://doi.org/10.5194/amt-2018-101
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 10 Apr 2018

Research article | 10 Apr 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).

Enhancing the consistency of spaceborne and ground-based radar comparisons by using quality filters

Irene Crisologo1, Robert Warren2, Kai Mühlbauer3, and Maik Heistermann1 Irene Crisologo et al.
  • 1Institute of Earth and Environmental Sciences, University of Potsdam, Germany
  • 2School of Earth, Atmosphere and Environment, Monash University, Australia
  • 3Meteorological Institute, University of Bonn, Germany

Abstract. Coinciding monsoon and typhoon seasons in the Philippines cause torrential rainfall, and associated hazards such as flooding and landslides. While early warning systems require accurate radar-based rainfall estimates, low-density rain gauge networks in the Philippines make it challenging to monitor the calibration of the ground-based radars (GRs). As an alternative, we explore the potential of spaceborne radar (SR) observations from the Ku-band precipitation radars on board the TRMM and GPM satellites as a reference to quantify the calibration bias of an S-band GR in the Philippines. To this end, the 3D volume-matching algorithm proposed by Schwaller and Morris (2009) is implemented and applied to five years (2012–2016) of observations. We further extend the procedure by a framework to take into account the data quality of each ground radar bin. Through these methods, we are able to assign a quality index to each matching SR-GR volume, and thus compute the GR calibration bias as a quality-weighted average of reflectivity differences in any sample of matching GR-SR volumes. We exemplify the idea of quality-weighted averaging by using the beam blockage fraction as a basis of a quality index. As a result, we can increase the consistency of SR and GR observations, and thus the precision of calibration bias estimates. The remaining scatter between GR and SR reflectivity, as well as the variability of bias estimates between overpass events indicate, however, that other error sources are not yet fully addressed. Still, our study provides a framework to introduce any other quality variables that are considered relevant in a specific context. The code that implements our analysis is based on the open source software library wradlib, and is, together with the data, publicly available to monitor radar calibration, or to scrutinize long series of archived radar data back to December 1997, when TRMM became operational.

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Irene Crisologo et al.
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Short summary
The calibration of ground-based weather radar (GR) can be improved a-posterio by comparing observed GR reflectivity to well-established spaceborne radar platforms (SR), such as TRMM or GPM. Our study shows that the consistency between GR and SR reflectivity measurements can be enhanced by considering the quality of GR data from areas where signals may have been blocked due to the surrounding terrain, and provides an open source toolset to carry out corresponding analyses.
The calibration of ground-based weather radar (GR) can be improved a-posterio by comparing...
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