# Rain rate with a combination of Z and KDP

**URL:** <https://openradar.discourse.group/t/rain-rate-with-a-combination-of-z-and-kdp/525>\
**Category:** General\
**Created:** [October 29, 2024, 6:38pm UTC](https://openradar.discourse.group/t/rain-rate-with-a-combination-of-z-and-kdp/525 "2024-10-29T18:38:27Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![johnnypeste](https://avatars.discourse-cdn.com/v4/letter/j/a183cd/32.png) [@johnnypeste](https://openradar.discourse.group/u/johnnypeste)\
**Post date:** [October 29, 2024, 6:38pm UTC](https://openradar.discourse.group/t/rain-rate-with-a-combination-of-z-and-kdp/525/1 "2024-10-29T18:38:27Z")

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Hi

First of all, I assume that good rain rates obtained with radar are when they compare well with udometers…

KDP method gives good rain rates when the rates are high  
Z-R (Marshal-Palmer for example) gives good rain rates when the rates are low

The question is:  
What threshold in Z (dbZ) should be used, in order to use M-P below that threshold and KDP above it?

Regards  
Joao

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**Author:** ![mgrover1](https://yyz2.discourse-cdn.com/free1/user_avatar/openradar.discourse.group/mgrover1/32/7_2.png) [@mgrover1](https://openradar.discourse.group/u/mgrover1)\
**Post date:** [October 31, 2024, 5:52pm UTC](https://openradar.discourse.group/t/rain-rate-with-a-combination-of-z-and-kdp/525/2 "2024-10-31T17:52:56Z")

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I would recommend reading through some of the recent literature, such as this paper from a few years ago!

> **[Evaluation of KDP Estimation Algorithm Performance in Rain Using a...](https://journals.ametsoc.org/view/journals/atot/38/3/JTECH-D-20-0060.1.xml)**
>
> Abstract Accurate estimation of specific differential phase (KDP) is necessary for rain rate estimation, attenuation correction, and hydrometeor classification algorithms. There are numerous published methods to process polarimetric radar...

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**Author:** ![johnnypeste](https://avatars.discourse-cdn.com/v4/letter/j/a183cd/32.png) [@johnnypeste](https://openradar.discourse.group/u/johnnypeste)\
**Post date:** [November 1, 2024, 12:14am UTC](https://openradar.discourse.group/t/rain-rate-with-a-combination-of-z-and-kdp/525/3 "2024-11-01T00:14:11Z")

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Hi  
I’ve read some things in this paper and i was trying to produce new kdp for comparison.  
However I don’t know how do I produce kdp in py- with one of the most promising methods which is PHASE\_PROC\_LP

for example with KDP\_VULPIAN i was able to produce new kdp and phidp very easily because I have examples where I see something like this:

kdp\_vulpiani = pyart.retrieve.kdp\_vulpiani(radar, band=‘C’, parallel=True)

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**Author:** ![DavidDufton](https://avatars.discourse-cdn.com/v4/letter/d/cdc98d/32.png) [@DavidDufton](https://openradar.discourse.group/u/DavidDufton)\
**Post date:** [November 6, 2024, 10:44am UTC](https://openradar.discourse.group/t/rain-rate-with-a-combination-of-z-and-kdp/525/4 "2024-11-06T10:44:16Z")

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Hi Joao,

You could try this old example notebook for using the linear programming method. [Linear programming phase processing — Py-ART Documentation (DRAFT)](https://jjhelmus.github.io/pyart/dev/auto_examples/correct/plot_lp_phase_proc.html)

For other KDP methods this more recent example is very good:  
[https://projectpythia.org/radar-cookbook/notebooks/example-workflows/kdp-comparison.html](https://projectpythia.org/radar-cookbook/notebooks/example-workflows/kdp-comparison.html)

After that you’ll have to decide if the default parameters in these functions meet your needs, which very much determines on your individual system behaviour and use case.

Kind regards  
David

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**Author:** ![johnnypeste](https://avatars.discourse-cdn.com/v4/letter/j/a183cd/32.png) [@johnnypeste](https://openradar.discourse.group/u/johnnypeste)\
**Post date:** [November 6, 2024, 11:23am UTC](https://openradar.discourse.group/t/rain-rate-with-a-combination-of-z-and-kdp/525/5 "2024-11-06T11:23:03Z")

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Hi David

thanks for the response.

the last link was where i saw the examples for using the vulpiani etc…

there is no example on how to use the linear method…

I will check the first link…

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