What are Reach Subsea Hydrographic Tools?

Reach Subsea has a large library of procedures and tools for how we acquire, process and quality control the data we collect for our client. As part of our commitment to Australian Industry Capability, Reach Subsea make some of these tools available to academia, government organisations and industry. We find the tools provide consistency in processing, are always available 24/7 and all you need to run them is a web browser. You are free to use these tools, all we ask is you acknowledge the use of these tools in your reports and publication you make. We also ask that you provide feedback on the tools so we can improve them for the benefit of all users.

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Total Propagated Error Computations

Total Propagated Uncertainty (TPU) of a sounding is a measure of the accuracy to be expected for such a sounding, when all relevant error / uncertainty sources are taken into account. Instead of “TPU”, the term “error budget” is also used. TPU is the parent term for Total Horizontal Uncertainty (THU) and Total Vertical Uncertainty (TVU).

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GNSS Buoy Processing

GNSS Buoy Processing Web App allows you to compute a hydroid separation using a GNSS .pos file and a nearby tide files in a standardised manner.

GNSS Tide Buoy...

  • GNSS Buoy data is a GNSS receiver which has been install on or inside a buoy in the ocean. It logs RAW GNSS observabled to RINEX files. These can be processed by many GNSS processing algorithms such as NRCAN, RTKLib, EMLID Studio.
  • This web app permits the easy processing of GNSS buoy data for the purposes of computing a connection to the ellipsoid.
  • The inputs into this app are a .pos file which is computed by GNSS PPP or RTK processing software from tools such as NRCan, Emlid, Trimble, RTKLib. This .pos file will contin a list of time/position/height. This app uses the time, height and position components.
  • GNSS heights represent the height of sea surface for the duration of the deployment, which means the GNSS data should be offset to the buoy waterlin. the logging duration should normally be at least 75 hours. The heights will contain the wave motion AND the tide height. We have found that with the correct signal processing algorithm we can accurately extract the tidal height from buoy data even in very poor weather conditions such as 4m swells.
  • The user drags/drops a .pos file into the app. The app decodes the file and creates a time series plot. It then computes a best fit polynomial which attempts to identify the actual tide curve signal from the height data.
  • The user can control the smoothing via 2 controls, the duration of the filter in seconds, and the polynomial weighting. If you are in open ocean then a longer filter duration such as 60 seconds is required to observe the oceaninc tidal signal.
  • The outputs from this app are a CSV file which can be used in the connection to the ellipsoid.
  • The app will display a raw and smoothed height curve so you can easily see the computed tide curve. once you are happy with the tide curve, export it to a CSV file.

    Bottom Mounted Tide Gauges...

  • A secondary aim for this app is for the user to ALSO upload a bottom mounted tide gauge .TID file, which is the regular CARIS .TID file format. If you upload a TID file the app will read the tid file into a time series plot. It can then AUTOMATICALLY compute the filter settings to match the BMTG tide curve. It does this by computing a linear regression and minimise the regression standard error. This will provide a very tight fit for your GNSS and BMTG data.
  • Notes: Care should be taken to ensure the BMTG is installed close to the GNSS buoy. if it is not close then the regression best fit will not be appropriate..

    • Copyright Reach Subsea, 2022
    paul.kennedy@reachsubsea.com