CODAS+UHDAS Documentation

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Serial messages to record

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On a per-cruise basis:

This Page

Initial setup

These things only need to be set up once: In VmDAS, under Options: Edit Data Options

Assuming you have:

  • gyro going into the deck unit as a synchro feed
  • a pcode or other reliable GPS position device (simple, not complicated: this device only does positions)
  • some other gps-aided heading device, such as POSMV, ADU3, or Seapath

Communications:

Set up com ports for ADCP, gps, and otherheading

  • the GPS port gets written to the N1R files. It should have GGA and

    optionally VTG messages, but nothing else

  • the otherheading port gets written to the N2R files. It should also have

    a GGA message (if one is available), the attitude (heading and tilts) message, and any quality messages that are relavant. (For instance, a Seapath should have PSXN,20 for attitude, and PSXN,22 for quality.

NOTES

  1. until a VmDAS bug is fixed, if you have a POSMV, you should output

    BOTH PRDID and PASHR messages. Then someone can use PRDID if they want, but the quality information is still there for later. (PRDID has no quality indicator)

  2. Keep the number of extra messages to a minimum. VmDAS can choke if it has too many serial messages. (The LOG files get really big and can stop data acquisition)

ADCP Setup:

Recommend using a text file for data acquisition rather than the gui options at the top of the tab. The two main advantages of using a text file for data acquisition are:

  1. You can set the EA command to tell the instrument the orientation of the transducer relative to the axis of the ship. The data are still gathered in beam coordinates, but the “ambiguity lanes” are adjusted so there is less chance of beam velocities “wrapping”. (This is most likely to occur on a very fast ship, or under severe pitching conditions).
  2. You have more control over the actual pinging.

Make sure the appropriate files exist so they can be chosen later (see below). When setting up these files, make sure to edit the transducer depth and transducer alignment angle for your installation.

Recording

(the cruise name will change for each cruise, but go ahead and set the rest) (let VmDAS pick the “number”)

Max size 2-5Mb (you choose, but don’t go over 5Mb or they’re too large to load easily)

You choose whether there is a dual output directory (but don’t write to a networked disk – it tends to cause problems)

You choose primary and secondary path

Transform

  • “Heading Source”
    • choose ADCP compass/gyro (better for reliability)
    • choose some other message for the otherheading device, if you REALLY know that device works
  • “tilt source” choose one if you have it

  • DISABLE heading correction (VmDAS will use the correct value from the text file)

    Evidently if you enable heading correction here, VmDAS sends EA0 to the instrument and then uses the value specified in the gui.

    There will be only one EA command in use, but it can be in one of two places.

    • If you are using a text file, there is an EA command which you should set to match your instrument. In that case, the gui “enable heading correction” should be false: VmDAS will use the value from the text file. It’s not a bad idea to have the same value in the gui (in case someone wants to use the gui instead of the text file, it provides a record of the value, even if you don’t use it).
    • If you are using the gui, then put the appropriate EA value here.
  • DISABLE tilt correction (this is our recommendation, but we make no comment on this, having not studied the results. This is your choice)

None of these things should change between cruises.


These might change on a specific cruise, but probably not:

  • Transform (heading source) Someone might request gyro to be the primary

    heading source or someone might want the otherheading (POSMV etc) to be the primary heading.

    Unless there is a compelling need for highly accurate real-time velocities (i.e. withing 2-3cm/s), UH ADCP recommends gyro as the primary heading (that is much more reliable and will give currents good to 10cm/s). Data can be post-processed to incorporate the better heading source if it was reliable during the cruise, and it’s much easier to do that in post-processing than to fix bad data if the POSMV or Seapath or Ashtech had problems. But it’s your (or the chief sci) choice.

Averaging

  • Probably 30-60 seconds for STA (short time averages)
  • The standard for ADCPs is 5 minutes or 300 seconds (for LTA)
  • ENABLE reference layer, bins 3-10 is fine.

You probably won’t need these tabs: Data Screening,
User Exits, Simulated Inputs

Processing software for turning VmDAS data into edited and calibrated velocities suitable for use in scientific calculations and public release to the National Ocean Data Center ADCP archive is available at http://currents.soest.hawaii.edu/docs/adcp_doc/index.html

University of Hawaii uhdas@hawaii.edu