Plotting negative elevation angles for RHI scans

[scollis]

Discussed in #1253

^{Originally posted by Ted-Whittock August 31, 2022}
Hello,

I have a bunch of RHI files from a mobile radar that was positioned along a mountain ridge, and so we have negative elevation angles to capture the precipitation over the surrounding lower terrain. (Iink to sample data: https://drive.google.com/drive/folders/19cQ3aS5qBt2gsQYjZu5cg14U_j7qt5J8?usp=sharing).

I have stitched 2 different azimuths together manually and added terrain heights below the radar (see attached image). However, I cannot figure out why it appears that the negative elevation angles (down to -1.4 deg) are not plotting. Is there a way to plot these negative elevations, or does Pyart always ignore them?

I am also aware that the y-axis on my attached plot is incorrect, but I wanted to address the issue of the negative elevation angles first.

Thanks,
Ted

[scollis]

@jfigui @wolfidan have you looked at negative RHI angles in PyRad?

[jfigui]

Hi @scollis,

We do have negative angles at MeteoSwiss but I never really paid attention. @wolfidan, can you have a quick look to that?

[wolfidan]

@scollis
Sorry for the delay, I'm currently in vacation, I will take a look on thursday though,
Cheers

[jfigui]

Thanks a lot!

[mgrover1]

@Ted-Whittock I took a look at your sample file, and noticed that within the data quality parameters (antenna transition), they flag the negative elevation angles... by default, we filter out these transitions in the plot_rhi function, but you can change this behavior by setting

filter_transitions=False

for example, I used the following snippet

import pyart
import matplotlib.pyplot as plt

radar = pyart.io.read("cfrad.20170203_160235.683_to_20170203_160247.799_DOW7_v245_s03_az65.00_RHI.nc")

display = pyart.graph.RadarDisplay(radar)

display = pyart.graph.RadarDisplay(radar)
display.plot_rhi("DBZHCC", cmap='pyart_HomeyerRainbow', filter_transitions=False, edges=False)
plt.ylim(-5, 10)

which resulted in the following image