WDSS-II contains ports of several NWS open radar product generator (ORPG) dual-pol algorithms. Through the use of these ports, it is possible to do a multitude of things, including running the hydrometeor classification algorithm (HCA) and computing instantaneous rain fall rates from the dual-pol variables and the HCA. Previously, the only way to do this in WDSS-II required the use of multiple algorithms. This workflow for computing rain rates from dual-pol observations is:

w2dp_preproc → w2dp_hca → w2dp_rainrates

w2dp_preproc takes the base dual-pol outputs from ldm2netcdf, which tend to be noisy and difficult to interpret or use in algorithms, and recombines them from a 0.5 degree azimuthal resolution to a 1.0 degree azimuthal resolution. Through this recombination, the noise of the dual-pol products is reduced. Additionally, this algorithm creates quality flags for each product, which are required by the HCA algorithm.

Next w2dp_hca reads in all of the output from w2dp_preproc, and, you guessed it, runs the HCA. The hydrometeor classifications, as well as some of the output from w2dp_preproc, are then be passed into w2dp_rainrates to determine instantaneous rainfall rates for each dual-pol variable and the HCA. Unfortunately, this workflow is not quite fast enough to run in real-time, so we sought a way to speed it up.

This speed up is achieved by combining w2dp_preproc, w2dp_hca, and w2dp_rainrates into 1 algorithm: w2dualpol. With w2dualpol, you can process as much or as little data as you want. By default, w2dualpol will run all the way through the computational stream discussed above. However, you can specify where in the computational stream you want w2dualpol to stop with the -O flag, where;

0: Preproc — stop after the preprocessor calculations
1: HCA – stop after the HCA calculations
2: RainRates – stop after the rain rate calculations (default)

Additionally, you can specify the products you want written out with the –outputProducts flag. So, for example, if you’re only interested in the HCA, your command line would look like:

w2dualpol -i /data/KTLX/code_index.fam -o /data/KTLX -s KTLX -O 1 --outputProducts=DHCA

Or, if you’re interested in the HCA and the rain rates computed from the HCA, you can run:

w2dualpol -i /data/KTLX/code_index.fam -o /data/KTLX -s KTLX --outputProducts=DHCA,RREC