Zdrcal Utility Overview

The Zdrcal utility:

  • Performs sequences of vertical scan measurements, accumulates and analyzes qualified data for monitoring the radar ZDR calibration.

    The utility is configured to trigger a message for operator attention when the sampled data allows it to conclude that the radar ZDR calibration has drifted beyond a user configurable threshold for alarm.

  • Reports calibration data at a precision which keeps the false alarm rate below 5 %.

    To establish this, the data samples are collected long enough to meet the configured precision. The run durations can be steered in part by the task parameters, while the actual total sample lengths adapt to variable atmospheric conditions. The lengths may vary from a single full sweep (in case of significant precipitation at the radar) up to a configurable upper time limit.

  • Provides a tool for responding to the utility alarm and updating the radar ZDR offset parameter from the specified previous results.

    The update action implies that the subsequent ZDR observations of isotropic scatterers are adjusted to 0 dB, which is the goal of ZDR calibration. The action has minimal inference with normal radar operation, as restart of IRIS/RDA processes is not needed.

Zdrcal distributed with RDA and IRIS, and works with RVP signal processors and any antenna controller accessible through the antenna library, at polarimetric weather radars.

Running Zdrcal

Zdrcal is designed to run either as a stand-alone non-graphic utility, or as part of IRIS scheduler (as an IRIS Exec Task).

In both modes, Zdrcal reports its progress, processing, and result quality into an output stream which is routed either to the terminal window, or into the zdrcal log history file $IRIS_LOG/zdrcal.log.

Zdrcal RAW Products

For each completed task, the Zdrcal utility outputs a RAW product, to serve as a reference for detailed quality checks and to allow for (off-site) post-processing, which is equivalent to the run-time analysis.

The Zdrcal RAW products are composed of one or up to forty full rotations of vertical sweeps.

You can use the productx utility can to view the RAW headers for the full information of the radar settings during the calibration task.

The data records contain the differential reflectivity ZDR, accompanied by the standard moments dBZ, V, spectrum width (W), and the co-polar correlation coefficient RhoHV, which are used in Zdrcal specific quality considerations and as input to sampling uncertainty estimates in analysis. Through reingest of the Zdrcal RAW products in IRIS, the data are available for graphical viewing (Quick Look Window, or standard IRIS products).

The measured data, used in Zdrcal analysis, are subject to standard RDA quality thresholding (LOG, CCR, SQI, SIG) with configurable settings for typical operational tasks.

By default, the Zdrcal RAW products are not inserted in IRIS product inventory ($IRIS_PRODUCT_RAW). You can configure them to be added by activating an input pipe.