Chesapeake Times
Technical Review, Issue 2
July 2020
Letter from the General Manager

Although we have all been impacted by the Coronavirus these last few months, we also found ways to work through it – whether it was Zoom meeting, virtual training or sitting on opposite sides of a conference table for social distancing, we found a way to keep our clients going. Some of us learned a few new tricks along the way like using video chats and sharing files via cell phones. At Chesapeake, we will continue to work through these difficult times, supporting our clients wherever they go.

During this quarter, we released our 7.6 version and have had two incremental updates since. It is always a challenge to get the software out, add all the features, and fix all the bugs. We use the incremental updates to add in those features that we did not have time to do the previous time. Our release notes show the changes in each update. We also put on three webinars in June and had a few hundred folks attend. If you were not able to see them, you can watch from our home page or webinars page.

The team has been busy adding new features, working through the list sent in by our clients. We also continue to support our manufacturers as they introduce new systems and data formats. We recently added support for SEGY version 2 and made updates to the S7K packet. It certainly keeps us busy, and although we are not travelling to conferences, we’ll get the news out about these updates through webinars and press releases.

One new feature I am excited about is the work we are doing in the Cloud, allowing our software to run on the AWS platform. We are testing this now and it will be part of the SonarWiz 7.7 release. I like the idea that you can buy time on a fast computer – and for around $2 or $3 per day get something that might cost $5,000 or more to own. The licensing part works the same, allowing folks to enable their DFL on the software in the cloud and then deactivate and move to another computer once done.

This edition of the Chesapeake Times has some articles on new features and processing techniques. We hope you enjoy it. As always, if you have any questions or comments, please let the team know.

- Harold Orlinsky, General Manager
SonarWiz 7.6 New Features and Technical Notes

Seafloor Multiple Reflections.................................... David Finlayson Chief Scientist
Sub bottom feature enhancements.............. Jonathan Fleetwood, Senior Developer
SonarWiz Implements SEGY R2 for SBP.............. Stephen D'Andrea, Business Mgr
QPS and SonarWiz Streamline SSS Workflow ............ Harold Orlinsky, General Mgr
Improved Single Beam Log File Imports ............ Christopher Favreau, Program Mgr
Co-founder Corner .............................................. John and Eileen Gann, co-founders
Seafloor Multiple Reflections in Sub-bottom Profiles

The interpretation of marine seismic profiles is complicated by the fact that operators must separate useful information about subsurface geometry from a wealth of background interference and noise typical of marine surveying. One of these problems is the presence of multiple reflections or reverberations . These slowly decaying wave trains usually arise in the water layer, which tends to trap the sound wave bouncing back and forth between the seabed and the sea surface. The most prominent of these multiples and usually the first to arrive are harmonics associated with the seafloor reflection.

Take for example the ideal situation shown in Figure 1 where we can see the marine trace collected from a seismic source and receiver near the surface. The resulting primary reflections off of the seabed and a single reflecting interface beneath the seabed are drawn. In this case, there are no complicating reverberations to confuse the interpretation.
Figure 1: (left) Cartoon of the primary reflections off of the seabed and a reflecting interface, (right) Example seismic trace resulting from the situation on the left
However, if the seismic source bounces off of the sea surface and back down to the seabed a second time, we would get the situation shown in Figure 2. In this new case, the seismic trace shows both the primary water bottom reflection (in black) and the 2nd order harmonic of the bottom reflection (in red). The harmonic occurs because the sound bounces down to the seafloor twice (hence, 2nd-order) before being recorded at the receiver. Depending on the strength of the source and the seafloor reflection coefficient, many harmonics are possible. In any case, once harmonic reflections appear in the record it becomes difficult to sort out which reflections are primary and which are multiples of reflectors we have already observed.
Figure 2: (left) Cartoon of the primary reflections off of the seabed and a reflecting interface along with a second bottom reflection (in red), (right) Example seismic trace resulting from the situation on the left showing the second-order harmonic of the water bottom reflection.
Figure 3 shows a seismic profile with strong 2nd-order multiples. At the beginning of the trace (far left side), the trace starts showing primary reflections at around 380 ms (blue line). The second order bottom multiple occurs at 2x the primary so we look for the 2nd order multiple of the seafloor at around 760 ms (red line). Below this point, the whole profile begins to repeat itself.
Figure 3: (left) uninterpreted seismic trace. (right) interpreted seismic trace. The primary bottom reflection is shown in blue and the 2nd-order harmonic (multiple) of the bottom trace is shown in red. Note that the 2nd order harmonic is always twice the 2-way travel time of the primary it will change with the water depth.
The exact position of the seafloor multiple depends on the depth of the source and the altitude of the receiver above the seabed. In order to assist interpreters in identifying these important multiples, plans are for SonarWiz 7.07 to include an interactive multiple identification tool. When the tool is active, SonarWiz will identify the location of the bottom reflection and predict the position of all of its harmonic multiples, marking the multiples on the sub bottom display at the appropriate depth. This tool should help to prevent interpretation mistakes.

There are many types of reverberation present in marine seismic traces other than seafloor reflector harmonics. But, because it is usually the first to arrive, the first harmonic of the seabed reflector is an important marker in the seismic trace. Once this first multiple has arrived, interpretation below this point in the profile should proceed with caution because other reverberation artifacts are likely to be present in addition to primary features.

-David Finlayson, Chief Scientist
Enhancements of Sub Bottom Profiler Modules

Among the changes scheduled for the upcoming 7.7 release of SonarWiz are a number of improvements in the SBP modules. Several exciting features are in the development and testing pipelines to aid in the importing, processing and interpreting workflows - things like automated import from a monitored folder, assisted reflector tracking, multiple detection, and improvements to alignment to bathymetric surfaces.

In this article, though, I'd like to talk about a couple of simpler improvements in the SBP modules, particularly in the processing window. These improvements have been in the works, and conditionally available or some time now, but haven't been defaults or as easily accessible or easily used as they could be.

The first improvement is in the enabled range. An oft-repeated support request has been to allow for better control of visible across-track range water column or repeating multiples that just serve to detract from the important data. Getting just the data of interest into and held in view, though, could be tricky, so we're implementing some controls easily available through the window that will allow for clipping the near and far range in an intuitive, flexible manner, without image rebuilding.

A function similar to this has been available for some time in limited form in the batch image export process through the "Regions" button on that window. That button will bring up a dialog at export time to allow for choosing a region of data to export, with some choices available for controlling along- and across-track range display. That concept, applied with some interactive control, allows for finding and focusing on the right subset of the data quickly and easily.

In addition to control over displayed range, relative scaling in the along- and across-track dimensions can be a bit tricky to get right, with the current setting in the SBP portion of the advanced settings menu, and requiring an image rebuild to be made active. This too will be more easily controllable in 7.7, available interactively and not requiring a costly image rebuild.

Overall, these are pretty simple changes compared to the more advanced stuff mentioned at the beginning. That said, they're nice quality of life improvements, pair nicely with recent improvements in time and sound velocity handling in SonarWiz, and enable some even more substantial improvements in the future with the performance and interactivity of the SBP interpretation window.

-Jonathan Fleetwood,Senior Developer
Chesapeake Adds SEG-Y R2 Support and Tools to SonarWiz

Chesapeake Technology Inc (CTI) is proud to announce support for SEG-Y R2, a new and improved file format standard. Chesapeake worked with EdgeTech, a leading provider of sub-bottom profilers on this project, using their Discover software for the creation of the SEG-Y R2 data files.

Available in SonarWiz version 7.6.4 and later, SEG-Y R2 is the SEG technical standard committee’s updated data exchange format for sub bottom data. This new format enhances files with additional trace headers, additional field support and extended number of samples and millisecond resolution time tags.
SonarWiz file import for data processing can handle the new format and fields associated with the updated version. The Playback function and a data extraction tool for the SEG-Y extension data were also updated. This new format enhances the file with additional trace headers, additional field support and extended number of samples and millisecond resolution time tags.
 
Over the next few months, SonarWiz will be building new tools and features in the Sub Bottom Module. These will include some automation of reflector tracing, auto import and processing, as well as enhancements to the overall processing workflow. These will be included in the SonarWiz 7.7 release scheduled for October 2020.

-Stephen D'Andrea, Business Manager
Chesapeake and QPS - Streamlined Approach to Data Processing

Late last year, Chesapeake and QPS worked together on providing a simplified workflow to process sidescan data that had been collected in the Qinsy software. Raw Database (.db) files recorded in Qinsy can now be imported directly into SonarWiz, without the need for any conversion to XTF.

The Qinsy Database file is a proprietary format and, in the past, required users to have the sonar files converted to XTF before processing. This approach reduces the data processing time and can remove potential errors that might occur during the conversion to XTF. Using the raw Database files ensures that the full fidelity is in place for the sidescan mosaic.
For the file import into SonarWiz, both the raw Database and corrected QPD files are required as each contains specific information for the sidescan and ancillary information. Tools for samples per channel, data compression and frequency selection – all those in SonarWiz for importing sidescan, can be used during this import process.

Using the latest release of SonarWiz, I examine the time from import to final product creation. Granted, processing time will vary based upon computer speed and memory, and I have a mid range laptop for the work. Using a data set collected by The National Oceans and Applications Research Center (NORAC), a survey of 25 lines (6nm of survey data, covering 0.8 square miles) was processed. Also added to the project was an XYZ data set for the DTM.

  • Data import: 50 seconds
  • Batch Bottom Track: 20 seconds
  • 50-cm GeoTiff creation: 25 seconds
  • 2-meter grid creation: 15 seconds
  • 3D view import and display: 15 seconds

Total time to create a sidescan mosaic overlaid on a bathy DTM was just over 2 minutes. See mosaic and Google Earth images below:
Sidescan draped over Bathy and output in Google Earth
-Harold Orlinsky, General Manager
Improved Import of Single Beam Log Files

NMEA 0183 sentences are text strings that conform to the NMEA 0183 format specification. These are most commonly used in sending data over digital serial protocol links. These sentences are human readable and can be recognized easily because they start with a “$” character and end with a “*” character. The sentences can be received by a computer and logged to a text file using anything from a simple terminal program to CTI's Single Beam server.

Here is a sample set of sentences:

$GPRMC,161856.640,A,1759.40954,S,12212.67976,E,2.000,14.7,100720,0.0,E,A*2E
$GPDPT,17.8,0.0*69
$GPZDA,161856.64,10,07,2020,0,0*6F

The sample was generated by CTI's NMEAWiz software. It is capable of simulating a variety of NMEA 0183 data.

Supported NMEA 0183 Sentences
Data Type
Sentence Name
Depth
DBT, DPT, DBS
Position
GGA, GLL, RMC
Time
GGA, RMC, ZDA
Date
RMC, ZDA
Heading
HDT, HDG, RMC (Course Made Good), VTG (Course Made Good)

SonarWiz requires at least time, date, position, and depth for the successful import and processing of Single Beam sonar data. The user should configure their devices such as GPS and Depth Sounder to output a combination of these strings in order to provide the required data. We recommend using the RMC string since it covers 3 out of the 4 requirements (position, time, and date). In addition to the RMC string a DBT or DPT string should be provided. We recommend these be sent at a rate of 1 Hz or faster.

Previous versions of SonarWiz required the presence of heading information. This is no longer a requirement as of SonarWiz V7.06.04. If heading information (in the form of a HDT, HDG, RMC, or VTG string) is not present in a log file, simply leave the “Adjust soundings for Roll and Pitch” checkbox unchecked in the Single Beam Import Window as shown below. In addition to NMEA formatted log files, this setting applies to the other Single Beam import data types as well.
Sometimes a user works with equipment that is not configured correctly or is incapable of providing all of the information necessary. This commonly takes the form of missing date information. This can happen when a GPS is configured only for sending GGA sentences. In order to process this data the user would have to provide a manual date by manually inserting a ZDA sentence at the beginning of a data log file. This can be tedious when working with a survey with more than a few data log files. In order to assist the user, CTI has added detection of the missing date information during import. Upon detecting missing date information SonarWiz will now ask the user for the date information (pictured below).
The user can choose to use the date information for each additional file freeing them from the need to repeatedly enter the same date.

In summary, successful processing of NMEA Single Beam sonar data depends on having time, date, position, and depth data present in the data log files. SonarWiz has been improved to allow for missing date and heading information so that the user can easily process their surveys.

- Christopher Favreau, Program Mgr
Founders Corner

Harold has been throwing a few little projects my way lately. I think he’s worried about me. Maybe I was making a few too many COVID face masks, but it’s fun to write a little bit of code now and then. I pitched in on the SEGY R2 update and some of the digitized feature property updates. 

Other than that, things are good... 
Our band has started playing music in the driveway on weekends - "socially distanced" of course - and Eileen and I are discovering lots of new hiking trails in our area. Stay healthy everyone and keep moving.

- John Gann, Co-Founder
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