Abstract

Abstract. This study extends the relative calibration adjustment technique for calibration of weather radars to higher-frequency radars as well as range–height indicator (RHI) scans. The calibration of weather radars represents one of the most dominant sources of error for their use in a variety of fields including quantitative precipitation estimation and model comparisons. While most weather radars are routinely calibrated, the frequency of calibration is often less than required, resulting in miscalibrated time periods. While full absolute calibration techniques often require the radar to be taken offline for a period of time, there have been online calibration techniques discussed in the literature. The relative calibration adjustment (RCA) technique uses the statistics of the ground clutter surrounding the radar as a monitoring source for the stability of calibration but has only been demonstrated to work at S- and C-band for plan-position indicator (PPI) scans at a constant elevation. In this work the RCA technique is modified to work with higher-frequency radars, including Ka-band cloud radars. At higher frequencies the properties of clutter can be much more variable. This work introduces an extended clutter selection procedure that incorporates the temporal stability of clutter and helps to improve the operational stability of RCA for relatively higher-frequency radars. The technique is also extended to utilize range–height scans from radars where the elevation is varied rather than the azimuth. These types of scans are often utilized with research radars to examine the vertical structure of clouds. The newly extended technique (eRCA) is applied to four Department of Energy Atmospheric Radiation Measurement (DOE ARM) weather radars ranging in frequency from C- to Ka-band. Cross comparisons of three co-located radars with frequencies C, X, and Ka at the ARM Cloud, Aerosol, and Complex Terrain Interactions (CACTI) site show that the technique can determine changes in calibration. Using an X-band radar at the ARM Eastern North Atlantic (ENA) site, we show how the technique can be modified to be more resilient to clutter fields that show increased variability, in this case due to sea clutter. The results show that this technique is promising for a posteriori data calibration and monitoring.

Highlights

  • The Department of Energy Atmospheric Radiation Measurement (DOE ARM) program deploys weather radars around the world to observe a variety of weather regimes

  • The X-band Scanning ARM Cloud Radar (XSACR) and Ka-band Scanning ARM Cloud Radar (KaSACR) data show that the algorithm can scale to cloud radar frequencies while demonstrating some of the limitations that are unique to higher frequencies

  • While we previously showed that the extended RCA (eRCA) technique could be run on an X-band radar (XSAPR2 at ARM Eastern North Atlantic (ENA) site), the unique setup at the Complex Terrain Interactions (CACTI) site allows for a comparison between the effectiveness of the eRCA technique and direct reflectivity cross calibration

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Summary

Introduction

Previous and existing calibration techniques rely on the detection or measurement of a known target (i.e., metallic spherical targets; Willis et al, 1964; Glover et al, 1966; Stratmann et al, 1971) or the presence of precipitation (i.e., evaluation of the drop size distribution; Marks et al, 1993; Gage et al, 2000). While these methods are effective, they require the radar to be offline or depend on weather conditions and account only for a brief

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