# Separating multiple scans from same Lidar

**URL:** <https://openradar.discourse.group/t/separating-multiple-scans-from-same-lidar/604>\
**Category:** Retrievals\
**Created:** [May 20, 2025, 4:49am UTC](https://openradar.discourse.group/t/separating-multiple-scans-from-same-lidar/604 "2025-05-20T04:49:30Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![SunnysChan](https://yyz2.discourse-cdn.com/free1/user_avatar/openradar.discourse.group/sunnyschan/32/421_2.png) [@SunnysChan](https://openradar.discourse.group/u/SunnysChan)\
**Post date:** [May 20, 2025, 4:49am UTC](https://openradar.discourse.group/t/separating-multiple-scans-from-same-lidar/604/1 "2025-05-20T04:49:30Z")

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Hi, I am running PyDDA with doppler Lidars. One thing I notice iss that " pydda.retrieval.get\_dd\_wind\_field" always requires reflectivity. Looking at the source code shows the reflectivity is used for correcting vertical velocity of rain fall. In my case where Lidar scans dust particles/ aerosols, whose vertical velocity should be rather small. I set reflectivity as very small number around -200dBz. Would like to confirm such work-around should be appropriate?

Also, the Lidars can have different scan modes (e.g. ppi, rhi, along a fixed line), would like to know the differences between first combining various scans from same Lidar with “pyart.util.join\_radar” as one radar object before passing them to PyDDA, versus directly passing individual scan to PyDDA as single radar object? From my test result, the second approach seems to output weird results. What will be the recommended aproach? Thanks.

Sunny

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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:** [June 3, 2025, 2:10pm UTC](https://openradar.discourse.group/t/separating-multiple-scans-from-same-lidar/604/2 "2025-06-03T14:10:34Z")

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Hello! Have you considered using other wind retrieval techniques? Please see this wind retrieval using PPI scans available in the Atmospheric Data Community Toolkit, developed by the U.S. Department of Energy Atmospheric Radiation Measurement User Facility

> **[act.retrievals.compute\_winds\_from\_ppi — ACT Documentation](https://arm-doe.github.io/ACT/API/generated/act.retrievals.compute_winds_from_ppi.html#act.retrievals.compute_winds_from_ppi)**