# What obs operator should I use to assimilate surface observation?

**URL:** <https://forums.jcsda.org/t/what-obs-operator-should-i-use-to-assimilate-surface-observation/386>\
**Category:** JEDI\
**Created:** [September 26, 2022, 9:38am UTC](https://forums.jcsda.org/t/what-obs-operator-should-i-use-to-assimilate-surface-observation/386 "2022-09-26T09:38:59Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![jw12](https://avatars.discourse-cdn.com/v4/letter/j/5fc32e/32.png) [@jw12](https://forums.jcsda.org/u/jw12)\
**Post date:** [September 26, 2022, 9:38am UTC](https://forums.jcsda.org/t/what-obs-operator-should-i-use-to-assimilate-surface-observation/386/1 "2022-09-26T09:38:59Z")

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Hi,

I am trying to assimilate surface observation using JEDI-MPAS 1.0.0.

I tried a few operators listed in this page ([ufo/src/ufo/operators at master · JCSDA/ufo · GitHub](https://github.com/JCSDA/ufo/tree/master/src/ufo/operators)), such as VertInterp, Identity, GSISfcModel. However, I either got wrong results or encountered errors with these operators. I wonder what obs operator should I use to assimilate surface observation.

Thanks!

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**Author:** ![gthompsnJCSDA](https://yyz1.discourse-cdn.com/flex031/user_avatar/forums.jcsda.org/gthompsnjcsda/32/159_2.png) [@gthompsnJCSDA](https://forums.jcsda.org/u/gthompsnJCSDA)\
**Post date:** [September 26, 2022, 6:01pm UTC](https://forums.jcsda.org/t/what-obs-operator-should-i-use-to-assimilate-surface-observation/386/2 "2022-09-26T18:01:55Z")

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All three of these operators have worked fine when using FV3-jedi. They should also work with MPAS, but you will have to describe the problem(s) in more detail. Simply provide the yaml file you are attempting and more complete diagnostic info and we can likely help you.

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**Author:** ![jw12](https://avatars.discourse-cdn.com/v4/letter/j/5fc32e/32.png) [@jw12](https://forums.jcsda.org/u/jw12)\
**Post date:** [September 29, 2022, 2:29am UTC](https://forums.jcsda.org/t/what-obs-operator-should-i-use-to-assimilate-surface-observation/386/3 "2022-09-29T02:29:26Z")

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Hi @gthompsnJCSDA ,

Thanks for your help. Actually I found out that I forgot to specify `vertical coordinate: height` for `VertInterp` so segmentation fault occurred. I will stick to `VertInterp` for now because it seems to produce the best result.

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**Author:** ![jjguerrette](https://yyz1.discourse-cdn.com/flex031/user_avatar/forums.jcsda.org/jjguerrette/32/146_2.png) [@jjguerrette](https://forums.jcsda.org/u/jjguerrette)\
**Post date:** [September 30, 2022, 7:44pm UTC](https://forums.jcsda.org/t/what-obs-operator-should-i-use-to-assimilate-surface-observation/386/4 "2022-09-30T19:44:55Z")

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One thing to note is that for surface _pressure_ observations, JEDI-MPAS developers use SfcPCorrected as shown in this YAML stub:

> <https://github.com/NCAR/MPAS-Workflow/blob/develop/config/jedi/ObsPlugs/variational/base/sfc.yaml#L14-L16>

It includes a station height correction to account for smoothing in the model height field.

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<div class="post-metadata">

**Author:** ![jw12](https://avatars.discourse-cdn.com/v4/letter/j/5fc32e/32.png) [@jw12](https://forums.jcsda.org/u/jw12)\
**Post date:** [October 19, 2022, 10:15am UTC](https://forums.jcsda.org/t/what-obs-operator-should-i-use-to-assimilate-surface-observation/386/5 "2022-10-19T10:15:42Z")

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Hi @jjguerrette ,

Thanks for your reminder. I wanted to use SfcPCorrected for surface pressure and VertInterp for other variables. However, SfcPCorrected requires linear obs operator, and I couldn’t find a way to apply linear obs operator to surface pressure only and not other variables. How can I write in the YAML to achieve that? Thanks.

This is the obs operator part of my YAML:

```auto
    obs operator:
      name: Composite
      components:
      - name: VertInterp
        vertical coordinate: height
        variables:
        - name: air_temperature
        - name: eastward_wind
        - name: northward_wind
      - name: SfcPCorrected
        da_psfc_scheme: UKMO
        variables:
        - name: surface_pressure
    linear obs operator:
      name: Identity

```

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**Author:** ![jjguerrette](https://yyz1.discourse-cdn.com/flex031/user_avatar/forums.jcsda.org/jjguerrette/32/146_2.png) [@jjguerrette](https://forums.jcsda.org/u/jjguerrette)\
**Post date:** [October 19, 2022, 2:35pm UTC](https://forums.jcsda.org/t/what-obs-operator-should-i-use-to-assimilate-surface-observation/386/6 "2022-10-19T14:35:06Z")

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Unfortunately I do not have any experience with the composite operator. My usual practice is to use the `SfcPCorrected` operator with a separate `obs space` than what is used for other profile type variables. Then there will only be `surface_pressure` as a `simulated variable`. Note that when reading the same observation file twice for two different `obs space` sections, only the `simulated variables` associated with each `obs space` are stored in memory. There will be duplication of `MetaData` entries, however.

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**Author:** ![jw12](https://avatars.discourse-cdn.com/v4/letter/j/5fc32e/32.png) [@jw12](https://forums.jcsda.org/u/jw12)\
**Post date:** [October 20, 2022, 1:20am UTC](https://forums.jcsda.org/t/what-obs-operator-should-i-use-to-assimilate-surface-observation/386/7 "2022-10-20T01:20:28Z")

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I see. I will definitely give it a try. Thanks!