Question about Radolan Format

[Nicolas T.]

Hello everyone,

I am currently trying to add a rain radar for my application, where you can see the rain for a specific timeline (similar to https://www.wetteronline.de/regenradar?wrp=periodCurrentHighRes ).

For the data I use the Opendata DWD (https://opendata.dwd.de/weather/radar/composit/)

The previous radar data is found in /wx and the future radar data under /wn.

As far as I know both datasets are in the Radolan format which wradlib can analyze. 

To analyze the data I wrote some python code:

f = wrl.util.get_wradlib_data_file(os.getcwd() + '/raa01-wx_10000-2012230730-dwd---bin')

data, metadata = wrl.io.read_radolan_composite(f)

maskeddata = np.ma.masked_equal(data, metadata["nodataflag"])

So far everything seems to work but my question is about the format of the analyzed data. I want to get the current precipation per hour (mm/h) but I don`t really know how to do that.

I found this section on the wradlib page (https://docs.wradlib.org/en/stable/notebooks/fileio/wradlib_radar_formats.html?highlight=divide#German-Weather-Service:-RADOLAN-(quantitative)-composit) 

Does this mean if I divide my data by 10 I get the mm/h unit or do I have to something else?
Another question is if I have to differentiate between the /wx and the /wn data.

I hope my questions are understandable and thanks in advance

[Kai Mühlbauer]

Dear Nicolas,

first of all I wish a Happy New Year to all of you out there!

To your question. It looks like the reading part is no problem so far.

WX and its forecast cousin WN are reflectivity composits with unit dBZ
(RVP6-units). For both you would need to divide by 2 and subtract -32.5
to get the correct reflectivity (dBZ) value. But there is a slight
difference between WX and WN. WX has 255 classes and WN has 4095 classes.

To transform this to mm/h you would need to apply some ZR-relation (like
Marshall-Palmer). The DWD has some material on this in [1] (page 41,
note: only in German). Please have a look also at the example in the
wradlib documentation ([2]).

Cheers,
Kai

[1]
https://www.dwd.de/DE/leistungen/radolan/radolan_info/abschlussbericht_pdf.pdf?__blob=publicationFile&v=2
[2]
https://docs.wradlib.org/en/stable/notebooks/basics/wradlib_get_rainfall.html



Am 26.12.20 um 10:16 schrieb 'Nicolas T.' via wradlib-users:

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