Chesapeake Times
Technical Review, Issue 14
July 2023
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Letter from the General Manager – Harold Orlinsky
Last week, with the Titan submarine incident, our niche for ocean survey work got a large audience. We all know the effort it takes to find something underwater, challenged by the vastness of the ocean and how unforgiving it can be. Yet this past week, the rest of the world got an education on the difficulties the ocean presents to us as hydrographers. And I am guessing some folks just couldn’t understand why it was so difficult to find the small submarine. We were given only 96 hours to search a large and deep area of the ocean. For a few days, international teams worked together in the search effort to find the submarine. Here at Chesapeake, we provided software, and I’m sure many others were asked for equipment or support. Our small industry was given an almost impossible task, and the world was watching. In the end, we learned of the tragic loss of lives. But that didn’t stop us from trying. Knowing we are part of this small niche of professionals should make us all proud. Thank you for all who helped, on board the ships or back home in the office.
I always wondered why in a baseball game the 7th inning stretch was not done earlier in the game. I would have thought 4½ innings - the halfway mark - should be the break. Football players get a break halfway through and come back ready to go for another half. With six months down and six to go, we’re at the halfway mark for the year. Time to see how we did so far and plans for the second half. Last weekend the Chesapeake team had their break. They stretched; they got up, and now they are back at work.
We did a lot in the first half of the year, with three releases and 142 updates, and will continue with our updates throughout the rest of 2023. We have a planned release later this summer, one set for October, and then a major update set to go in December, to be presented it at our Winter workshop. It is significant enough that we will be calling it SonarWiz 8.0. As Sinatra had used to sing, “The best is yet to come.”
Over the next 5 months, we will be working on this major release, with new important new features and updates throughout the program. As we continue to collect larger data sets, we set out to improve AWS and Azure Cloud performance, and increase the overall speed of all operations, including drawing and mosaicking. We will be introducing a new CSF file format with this change. We also are taking on two areas that have been somewhat of an Achilles heel for our clients, namely Auto Target Recognition (ATR) and Sub bottom multiple suppression. In addition to these major new features, we will introduce a single file import option for multiple sensor data types which will save time and be more convenient and easier to use. So, stay tuned for updates and previews of this major new release. We are excited that these long planned major features and enhancements are nearly here and eager to share them.
For now, sit back, relax and enjoy the summer.
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New Features and Technical Notes
The Side Scan Sonar 10% Rule................................ Christopher Favreau, CTO
The CsfCalc Tool ...................................................... Jonathan Fleetwood, Engineer
Sidescan Gain: Updates to th.................................... David Finlayson, Chief Scientist
Contacts: An Update ................................................. Harold Orlinsky, General Manager
Battling SEGY Once Again! ...................................... Patrick Zynda, Support Manager
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The Side Scan Sonar 10% Rule |
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Recently the question came up, “What is the best height to tow my Side Scan Sonar off of the bottom?” The general answer is the altitude should be 10% to 20% of the slant range. While this is a good rule of thumb, or general rule to follow, where does it come from? |
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- First, let us go over the reasons for adjusting the height of the towfish:
- Limiting the amount of water column in the Side Scan Sonar image. This minimizes slant range distortion.
- Placing the center of the beam in the center of the range. This ensures the transducer sensitivity is optimized for the largest area so you get the best image.
- Minimizing side lobes and first surface return. We do not want artifacts in the image.
- Ensuring an optimal shadow length for effective height measurements and identification of underwater objects.
- The down angle, or depression angle (angle from horizontal), and transducer beam pattern varies from manufacturer to manufacturer
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For a couple years now, SonarWiz has been shipping with a little command-line utility called CsfCalc.exe. It hasn’t gotten a lot of attention, but it can be pretty handy for some purposes. We’ve mainly used it as a repair tool for files having some bad data in them; this allows for us to provide a script or instructions to repair files without a customer having to upload a large project. It can also be used to extract columns of computed (per-record) data from CSF files, for further inspection/manipulation within a spreadsheet, or perhaps as part of an automated ETL pipeline.
CsfCalc’s operation is fairly simple: for each CSF file specified by its command-line arguments, open the file and read each row; for each row, calculate a value, and then output that value to a specified location.
Invoking the CsfCalc utility with no arguments, as in the following example, shows a brief usage message listing the parameters:
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Sidescan Gain: Updates to the Empirical Gain Normalization |
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Empirical Gain Normalization (EGN)
The EGN algorithm is a black-box statistical approach to normalizing the backscatter intensity of mapping sonars. It is black-box, because the algorithm works with the observed amplitude values exclusively and makes limited assumptions about internal mechanics of the sonar system. It is statistical, because the correction tables are built empirically. This allows the algorithm to adapt to a wide range of sonar designs and configurations.
EGN has been available in SonarWiz since 2007. Originally, EGN was used for sidescan only, when SonarWiz added the bathymetry module, CTI wrote a new EGN library to support bathymetric sonars. In SonarWiz 7, the engineers combined the sidescan and the bathymetry code bases into a single EGN library.
Today, CTI is working on a new version of EGN that we hope will produce even better results. The new EGN user interface will allow updating EGN tables after they have been created and allow users to move EGN tables between projects. More on these ideas below.
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In the latest release of SonarWiz, we added a new way of real time target marking. Called the “Waypoint Contact”, it is a single check box to enable this function. The hardest part was to decide where to place this user command option, without adding more dialog boxes and buttons to SonarWiz. (For now), we added the option in the Motion Sensor set up, as the serial I/O structure was already in place.
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Battling SEGY Once Again! |
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Over the past few years, we have spent considerable development time on addressing the needs of our sub bottom processor geos. We have made great improvements to the available tools and workflow. We have time and time again had to battle with how to make sure that all of the processing steps done inside of the program can be translated out to .SEGY format. Despite being 50 years old, this file format somewhat unfortunately remains the industry standard for seismic.
In this month's battle we had a customer reach out to our support team with an issue. Their SEGY files had been corrected vertically inside of SonarWiz against a multibeam surface, but when exported into SEGY and then reimported downstream, the profile no longer aligned.
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