Persistent negative vertical velocity in Signature 1000 data

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William Edge

• January 22, 2020 02:44

Has anyone observed a vertical velocity anomaly such as the one pictured? This effect is persistent for our entire deployment. It can be seen as a blue band along the bottom of the 3rd subplot. Any suggestions would be appreciated.

About the deployment:

Our Signature 1000 was deployed at 0.35 m above the sea bed in 250 m of water on the continental shelf of Western Australia. The instrument was set up to measure the bottom ~20 m of the water column with a bin size of 0.2 m. Internal waves regularly propagate past the site generating strong near bed currents.

Sea bed was predicted to be very flat mud, and a grab sample confirmed fine sediment with a mean diameter of ~25 um. It was suggested the instrument could have been deployed within a near bed 'fluid mud' layer.

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  Oddrun Christin Myklebust

  • February 26, 2020 05:52

  Thanks for addding a post reagarding this matter. We are looking at this and would appreciate any input others might have. The raw .ad2cp datafile is highly appreciated since this is the only way for us to study this in more detail. You can reach our support engineers and experts at support@nortekgroup.com

   

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  Lars Planert

  • February 17, 2020 14:35
  • Edited

  Hi William, the same issue here (Deployments: up-looking, cell sizes: 0.5 and 0.6m). Anomalies showed up in all 5 beams, typically within 4 cells distance from the transducers with some variation in height (height apparently depending on flow velocity).

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  Rachel Allen

  • November 24, 2020 13:49

  Hi William,

  I think we see something similar.  See the third subfig in the attached plot. I'm curious if you learn anything. 

  Rachel

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  Oddrun Christin Myklebust

  • November 26, 2020 23:08

  Hi Rachel,

  possible reason could be interference, but the only way for us to make sure is to study the raw data file. If possible it would be really helpful if you could send us the ad2cp file.

  Kind regards,

  Oddrun

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