# Radar Grid Weighting - PyDDA

**URL:** <https://openradar.discourse.group/t/radar-grid-weighting-pydda/274>\
**Category:** Retrievals\
**Created:** [July 24, 2023, 8:06pm UTC](https://openradar.discourse.group/t/radar-grid-weighting-pydda/274 "2023-07-24T20:06:57Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![sdm5607](https://yyz2.discourse-cdn.com/free1/user_avatar/openradar.discourse.group/sdm5607/32/188_2.png) [@sdm5607](https://openradar.discourse.group/u/sdm5607)\
**Post date:** [July 24, 2023, 8:06pm UTC](https://openradar.discourse.group/t/radar-grid-weighting-pydda/274/1 "2023-07-24T20:06:57Z")

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Hi all,  
I’m currently working on creating a dual-doppler analysis using PyDDA between a mobile C-band and NEXRAD radar but am having some issues with the resulting 3D wind field. I know the get\_dd\_wind\_field() function takes in a list of radar grids to create the 3D wind field, but it seems as though the list order is determining the final result. Specifically, if the C-band radar’s grid is listed first, the resulting horizontal wind pattern nearly matches that of the C-band’s original radial velocity field and if the NEXRAD radar’s grid is listed first, the resulting horizontal wind pattern nearly matches that of the NEXRAD’s original velocity field. I have extensively looked through the documentation but can’t seem to find the right parameters to tune that would give each radar grid an equal weighting. Any advice would be greatly appreciated.

In the get\_dd\_wind\_field() function I have set Co=1.0, Cm=256.0, Cx=0.0, Cy=0.0, Cz=0.0 and my gridding is done with a resolution of 1 km.

I have attached an image of what I am seeing in the final result when the NEXRAD radar is first in the radar grid list input to get\_dd\_wind\_field.

 ![DD_xy](https://global.discourse-cdn.com/free1/uploads/openradar/original/1X/ee33974b77927d7dbcb01dd44ec6857b0aab42d8.png)

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**Author:** ![rcjackson](https://yyz2.discourse-cdn.com/free1/user_avatar/openradar.discourse.group/rcjackson/32/14_2.png) [@rcjackson](https://openradar.discourse.group/u/rcjackson)\
**Post date:** [July 27, 2023, 9:29am UTC](https://openradar.discourse.group/t/radar-grid-weighting-pydda/274/2 "2023-07-27T09:29:34Z")

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Hello!

An issue was raised on the GitHub page regarding your very problem just last month. I’ve cut a new release of PyDDA to 1.3.0 that fixes this issue, among others. For more information, see here:

> <https://github.com/openradar/PyDDA/issues/89>
>
> Hi devs !
> 
> First of all, many thanks for making \`pydda\` available, it's a very… interesting tool !
> 
> For information, during my different explorations and trials, I noticed that the \[current implementation\](https://github.com/openradar/PyDDA/blob/main/pydda/retrieval/wind\_retrieve.py#L725-L769) of \`retrieval.wind\_retrieve.\_get\_dd\_wind\_field\_tensorflow()\` always affect zero weights to the observation data associated to the last radar provided, when more than one radar are provided.
> 
> Note: the same seems to occur with the equivalent scipy implementation.

Much regards,  
Bobby

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**Author:** ![sdm5607](https://yyz2.discourse-cdn.com/free1/user_avatar/openradar.discourse.group/sdm5607/32/188_2.png) [@sdm5607](https://openradar.discourse.group/u/sdm5607)\
**Post date:** [July 27, 2023, 6:24pm UTC](https://openradar.discourse.group/t/radar-grid-weighting-pydda/274/3 "2023-07-27T18:24:43Z")

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Thank you so much! That was the key to the problem!