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Technical Note: FMGT - R2Sonics Backscatter Processing

Summary

The following information is a technical article about how to deal with R2Sonic Backscatter Processing in particulars with FMGT and related software.

QPS Workflow

QINSy

  • You need to use the multibeam driver presets to store the packets necessary for processing in FMGT.  This is well indicated in the driver setup. Note that QINSy is agnostic to the frequencies specifications and these are only visible during acquisition in the Sonic controller.
  • QINSy can do bathymetric processing during acquisition (while "online"), and it will make qpd files.  The raw sonar data is stored in the .db files.  If the online processing is sufficiently accurate in positioning, etc, and the bathymetric data is reasonably clean and free of outliers, then these files can be directly imported into FMGT for backscatter processing.  If not, the user can visit Qimera to do any of these processing steps.
  • QINSy can log TruePix, but FMGT cannot process TruePix to the same level that it can for snippets.  If you must process TruePix, you would need to export XTF files from QINSy with the TruePix as the sidescan data system.  See note about TruePix processing below.

Qimera

  • You can open your QINSy .db/.qpd data in Qimera to do further bathymetric processing (e.g. apply a tide, or an SBET, or apply different SVP), or simply to do some quick data editing to remove bathymetric outliers.
  • Once your work is done, you can export the db/qpd data into a GSF for use in FMGT.  The GSFs from Qimera will contain all the sonar ping metadata, the snippets imagery data and the edited bathymetric solutions.  These files can be used immediately in FMGT.

FMGT

  • If you are coming in directly from QINSy, you need to add Source Pairs under the file menu.  You will then choose the .db files and the .qpd files via a multi-stage import wizard.  This will create a set of GSF files inside the FMGT project directory and they will be added to the project.  At this point, the FMGT project can be completely decoupled from the original QINSy project since no other files are needed from the QINSy project.
  • If you are coming in from Qimera, you add the GSFs that were created by Qimera as a regular file under the file menu.  FMGT will not re-create the GSFs.  The GSFs will stay in the directory in which they are found, so the FMGT project must remain on the same computer as the Qimera project.  If you must decouple the projects, you can encapsulate the project and it will copy the GSF files from the Qimera project into the FMGT project (under the File menu).
  • In both cases, you can proceed with default settings.  Typically, the only setting you may need to change is to update the absorption coefficient in the event that the operator did not provide a reasonable value in R2Sonic's Sonic Controller while online.
Hypack Workflow
Always test the workflow as soon as possible in the field to ensure that you are correctly recording snippets!!  It is very easy to misconfigure the R2Sonic sonar and Hypack to leave you without any logged snippet data.

Acquisition

  • You need to have the Hypack driver configured to store raw binary datagrams, these are stored in the .R2S file that usually sits alongside the .HSX file in the Hypack project.
  • You cannot record both Snippets and TruePix in Hypack at the same time.  If both the sonar and Hypack are configured to deal with snippets and TruePix, Hypack will only record the Truepix data.  This has been confirmed by R2Sonic.  Their advice:
    • Configure R2Sonic's "Sonic Controller" to output snippets packets only and not TruePix.
    • Configure Hypack's hardware configuration for the R2Sonic to record snippets only.
  • You should have the Hypack project configured to be in the same time system as the sonar.  Hypack lets you choose a local time zone, but the raw binary packets from the R2Sonic are time tagged from the GPS ZDA.  We are currently working on a solution to allow users to recover from this.
  • Hypack can log TruePix, but FMGT cannot process TruePix to the same level that it can for snippets.  If you must process TruePix, you would need to export an XTF from Hypack with the TruePix as the sidescan data system.  See note about TruePix processing below.

Bathymetric processing

There are a number of ways that you can process the multibeam range/angles into bathymetry solutions.

  • In Qimera: You can process the Hypack HSX files in Qimera.  The results can be exported as GSF but these cannot be used directly in FMGT since the HSX file does not contain the ping metadata or the snippet data.  The Qimera GSF files must be paired with the Hypack .R2S files in FMGT in order to proceed. Note: when bringing HSX data into Qimera, the user must enter the coordinate system used while acquiring in Hypack because this information is not written to the HSX file
  • In Hypack MBMAX: You can do bathymetric processing in Hypack software (MBMAX 64) to create HS2X files.  These results cannot be used in FMGT directly.  You must first convert these to a GSF file by exporting your MBMAX results as a GSF.  Recent tests from some data from one client had GSF files without beam angles.  It's unclear if this is a normal configuration or if the user must choose to include the beam angles in the GSF.
  • In Caris HIPS: You can do bathymetric processing in Caris HIPS to create Caris results which can then be exported as GSF files.  These files do not contain ping metadata or snippet information and they must be paired with the .R2S files recorded by Hypack.

FMGT

  • None of the GSF files produced in the bathymetry processing solutions listed above populate the R2Sonic record in the GSF ping header.  As such, they cannot be used "out of the box" for backscatter processing in FMGT.  They must be paired with the binary snippet records recorded by Hypack (.R2S files), this pairing is done in FMGT.
  • When adding source pair files in the FMGT import wizard, the user must specify their GSF files and their R2S files.  The wizard converts the .R2S files to .R2SC in order to remove some Hypack specific headers and to return the binary contents closer to what comes straight from the sonar.  (Note: this is the same reasoning behind converting a Hypack .7K file into a Reson standard .S7K file).
  • The new GSF files that are created merge the bathymetric solutions computed in MBMAX with the raw ping metadata and snippet records in the .R2S file.  These new GSF files are stored in the FMGT project directory.
  • Once the GSF files are created, the FMGT project can be decoupled from the raw Hypack project.
  • Regular processing can proceed now with the same general advice as in the QPS workflow section above.
Raw Binary Workflow

Some users may be recording the raw data stream from an R2Sonic system.  This data stream should contain the bathymetry data and the snippet data.  If these files are recorded into a file as they arrive from the network UDP data stream from the sonar, they can be processed using QPS software as follows.

Acquisition

  • R2Sonic sonars broadcast the different data streams to different UDP ports.  Any custom acquisition solutions will need to combine these into a single data file for use in QPS software.  The raw data stream should have the file extension .R2SC to be correctly recognized by QPS software.
  • The R2Sonic data stream from the sonar does not include position, motion, SVP or vessel configuration.  These must be recorded from other sensors.

Bathymetric Processing

  • In Qimera, you can import the .R2SC file.  It will create an empty vessel file for you that you will then need to input all of the sensor offsets.
  • You would need to import the position and motion data, e.g. SBET or POSMV .000 files.  ASCII navigation can also be used.  You will create custom sensors for these when you import them and you should set the offsets at the import stage.
  • You would need to import an SVP profile, if one is not provided then the surface sound speed value used by the sonar for beamforming is used for the ray tracing.
  • You may need tide as well for a good bathymetric product, but this is not necessary at all for backscatter processing.
  • From this point forward, it's the typical Qimera workflow to process and clean data.
  • Once complete, you can export the data as a GSF file.  This GSF file will hold the bathymetric results, the sonar ping metadata and also the snippets records.  These files can be used directly in FMGT.

FMGT

  • You can import the GSFs from above directly and use them right away.  Note that the GSF files will reside in the Qimera project and the FMGT project cannot be decouple from this.  If it needs to be decoupled, the project can be encapsulated after the data is imported.


Appendix

TruePix

TruePix provides a sidescan-like data set that provides more or less the same image quality as snippets, but takes less disk space than snippets.  It also provides a time-series of angles at the same sampling interval as the intensity time-series.  Effectively, it provides a data stream that is equivalent to an interferometric sidescan's output.  This also means that the angular data needs significant filtering in order to be used for georeferencing of samples.

If you must process TruePix, you would import an XTF from QINSy (see notes in QINSy section above).  You would need to set a "Custom Override" in the processing parameters to force the sensor type and you may need to adjust the Head dB bias to get the data into a reasonable signal range (-70 dB to +10 dB).  Mosaics made from this would suffer from:

  • Flat seafloor assumption georeferencing limitations common to all sidescan systems
  • Potential signal level artifacts associated with variations in sonar settings by the operator (e.g. power, pulse and gain changes)

Notes from R2Sonic about configuring Hypack with R2Sonic systems

  • Hypack has check boxes in sonar setup in Hypack hardware setup, one for TruePix, one for snippets.  The fact that there are two checkboxes and not two radio buttons implies that it can do both, however R2Sonic's experience in Hypack 2016 and 2017 that it only records TruePix when both are checked.
  • If you enable both in Sonic Controller to output but snippets and TruePix, Hypack will only record TruePix.
  • R2Sonic's recommended configuration: only enable snippets in Hypack and only enable snippets output in Sonic Controller.
  • In Hypack, change the time zone of the PC to UTC.  Otherwise, you can get local time in HSX but the R2S files are in UTC as per the ZDA time-sync coming into the sonar.

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