Preprints
https://doi.org/10.5194/amt-2024-45
https://doi.org/10.5194/amt-2024-45
12 Apr 2024
 | 12 Apr 2024
Status: this preprint is currently under review for the journal AMT.

Evaluation of the effects of different lightning protection rods on the data quality of C-Band weather radars

Cornelius Hald, Maximilian Schaper, Annette Böhm, Michael Frech, Jan Petersen, Bertram Lange, and Benjamin Rohrdantz

Abstract. Lightning protection is important for weather radars to prevent critical damage or outages but can have negative effects on data quality. The existing lightning protection of the DWD polarimetric C-Band weather radar network consists of four vertical poles with a maximum diameter of 10 cm. During radar operation, these rods cause local scattering in the near field of the antenna, resulting in negative impacts on radar products. One effect is the removal of significant transmit power off the main beam axis and its addition to other areas or the side lobes. This results in wrongly localised precipitation fields in radial direction. The second effect is the loss of transmitted and received power, appearing as a decrease in system gain, and subsequently a underestimation of all power based radar moments in the vicinity of the rods. The underestimation in radar reflectivity Z then leads to a negative bias in the actual rain rate of approximately 20 % if a Z/R relationship is applied. These detrimental effects on data quality led to the requirement of developing a new lightning protection concept. The new concept must minimise the effect on data quality, but also provide sufficient protection from lightning strikes according to the existing regulations and requirements. Three possible lighting protection concepts are described in this paper: two using vertical rods of different diameters (16 and 40 mm, respectively) and one with horizontally placed rods outside the antenna aperture. Their possible influence on data quality is quantified through a dedicated measurement campaign by analysing resulting antenna patterns and precipitation sum products. Antenna patterns are analysed with respect to the side lobe levels compared to antenna patterns without lightning protection and the original lightning protection. With the newly tested lightning rods, the apparent side lobe levels are slightly increased compared to an antenna pattern taken without lightning protection, but are within the accepted antenna specifications. Compared to the original lightning protection, a decrease of up to -15 dB in apparent side lobe levels is found for all tested lightning protection options. Beam blockage is substantially reduced compared to the existing lightning protection as shown by the evaluation of QPE sums. These results and some structural considerations are a solid basis to recommend the installation of four rods with maximum 40 mm diameter for all 17 radar systems of the DWD weather radar network.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.
Cornelius Hald, Maximilian Schaper, Annette Böhm, Michael Frech, Jan Petersen, Bertram Lange, and Benjamin Rohrdantz

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2024-45', Anonymous Referee #1, 03 May 2024
  • RC2: 'Comment on amt-2024-45', Anonymous Referee #2, 14 May 2024
Cornelius Hald, Maximilian Schaper, Annette Böhm, Michael Frech, Jan Petersen, Bertram Lange, and Benjamin Rohrdantz
Cornelius Hald, Maximilian Schaper, Annette Böhm, Michael Frech, Jan Petersen, Bertram Lange, and Benjamin Rohrdantz

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Short summary
Weather radars should use lightning protection to be safe from damage, but the rods can reduce the quality of the radar measurements. This study presents three new solutions for lightning protection for weather radars and evaluates their influence on data quality. The results are compared to the current system. All tested ones have very little effects on data, and a new lightning protection system with four rods is recommended for the German Meteorological Service.