# Co-located CTD for oxygen sensors

**URL:** <https://discourse.oceanobservatories.org/t/co-located-ctd-for-oxygen-sensors/639>\
**Category:** HelpDesk\
**Tags:** cgsn\
**Created:** [February 15, 2023, 7:52pm UTC](https://discourse.oceanobservatories.org/t/co-located-ctd-for-oxygen-sensors/639 "2023-02-15T19:52:12Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![fogaren](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.oceanobservatories.org/fogaren/32/55_2.png) [@fogaren](https://discourse.oceanobservatories.org/u/fogaren)\
**Post date:** [February 15, 2023, 7:52pm UTC](https://discourse.oceanobservatories.org/t/co-located-ctd-for-oxygen-sensors/639/1 "2023-02-15T19:52:13Z")

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Hi, I am looking for the list of co-located CTDs that are used to process data from oxygen sensors. Specifically, I am trying to figure out which CTD (METBKA or METBKB) was used to do the pressure and salinity compensations for the Aanderaa oxygen data collected on the surface buoy (1m ) of the a GI Apex SUMO.

Thank you,  
Kristen

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**Author:** ![areed](https://avatars.discourse-cdn.com/v4/letter/a/e5b9ba/32.png) [@areed](https://discourse.oceanobservatories.org/u/areed)\
**Post date:** [February 15, 2023, 10:37pm UTC](https://discourse.oceanobservatories.org/t/co-located-ctd-for-oxygen-sensors/639/2 "2023-02-15T22:37:47Z")

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Hi Kristen,

If you look in the attributes of the associated salinity variable (which should be “met\_salsurf”) you’ll see it has an “instrument” attribute which gives you the reference designator of the sensor it pulled data from. I’ve attached a screenshot of what I get when I downloaded a dataset from the oxygen sensor on the GI SUMO. It looks to be METBKA.

 ![image](https://canada1.discourse-cdn.com/flex036/uploads/ooidata/original/1X/c425e1691738cab34a2d7170ae5510a239122135.png)

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**Author:** ![fogaren](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.oceanobservatories.org/fogaren/32/55_2.png) [@fogaren](https://discourse.oceanobservatories.org/u/fogaren)\
**Post date:** [February 17, 2023, 3:32pm UTC](https://discourse.oceanobservatories.org/t/co-located-ctd-for-oxygen-sensors/639/3 "2023-02-17T15:32:59Z")

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Thanks, Andrew! Following up on that instrument attribute is there a reason why the source for the ‘pressure’ variable in the DOSTA files is the ‘flort’ and the result is a ‘NaN’; Why isn’t the CTD pressure used?

 ![image](https://canada1.discourse-cdn.com/flex036/uploads/ooidata/original/1X/2c273c6437e1bc08d3cb185277a2e88942591ddd.png)

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**Author:** ![areed](https://avatars.discourse-cdn.com/v4/letter/a/e5b9ba/32.png) [@areed](https://discourse.oceanobservatories.org/u/areed)\
**Post date:** [February 17, 2023, 5:55pm UTC](https://discourse.oceanobservatories.org/t/co-located-ctd-for-oxygen-sensors/639/4 "2023-02-17T17:55:02Z")

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For DOSTAs that are not colocated with a CTD, OOINet is searching for a pressure stream to associate with the dataset, and finding the FLORT pressure. That said, as I understand it, what its actually defaulting to for the value of P to plug into the correction is the nominal depth value for the DOSTA (not an issue for the buoy dosta). You see a similar thing with the DOSTAs located on the Flanking Moorings.

 ![image](https://canada1.discourse-cdn.com/flex036/uploads/ooidata/original/1X/589e437960670593e1083f4f5d3fb54b22476e5b.png)

For the DOSTAs colocated and/or plugged into a CTD (the NSIF and those on the mooring risers at 40, 80, and 130m on the surface mooring wire) all utilize the “int\_ctd\_pressure” for the pressure correction

 ![image](https://canada1.discourse-cdn.com/flex036/uploads/ooidata/original/1X/85c2cf1d2d647770fd09e5959139d819a4a73ebc.png)

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**Author:** ![areed](https://avatars.discourse-cdn.com/v4/letter/a/e5b9ba/32.png) [@areed](https://discourse.oceanobservatories.org/u/areed)\
**Post date:** [February 24, 2023, 9:44pm UTC](https://discourse.oceanobservatories.org/t/co-located-ctd-for-oxygen-sensors/639/5 "2023-02-24T21:44:17Z")

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@fogaren  
This prompted me to dig into this issue more and it looks like I gave you some bad info about the Flanking Moorings (the SUMO is still pulling the data from the METBK-CT sensor with doesn’t have a pressure sensor so its defaulting to deployed depth).

There IS a colocated CTD which is delivering the sea\_water\_practical\_salinity and sea\_water\_temperature parameters to the DOSTAs on the Flanking Moorings. I’m not sure why the pressure stream is not being delivered and instead its defaulting to its deployment depth.

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**Author:** ![fogaren](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.oceanobservatories.org/fogaren/32/55_2.png) [@fogaren](https://discourse.oceanobservatories.org/u/fogaren)\
**Post date:** [March 1, 2023, 6:13pm UTC](https://discourse.oceanobservatories.org/t/co-located-ctd-for-oxygen-sensors/639/6 "2023-03-01T18:13:17Z")

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@areed Thanks for digging into the issue more. Let me know what you find. Thanks!