SonarWiz Datum Align Reference Rev 8.0, 12/22/2015 Chesapeake Technology, Inc. email: support@chesapeaketech.com Main Web site: http://www.chesapeaketech.com Support Web site: http://www.chestech-support.com 1605 W. El Camino Real, Suite 100 Mountain View, CA 94040 Tel: 650-967-2045 Fax: 650-450-9300
Table of Contents 1 Datum Align Feature... 2 1.1 Initial Release and Documented Adjustments in Datum Align Feature... 3 1.2 Why Do This?... 4 1.3 Sequence Effects - Datum Align, then Reflectors, Cores... 4 1.4 Dependencies - Coordinate System, Units, Numerical Values... 5 2 How to Use the SBP Datum Align Feature... 5 2.1 Importing and Bottom-tracking your SBP file... 5 2.2 Making or Importing a Grid File... 7 2.2.1 Making your own GRD File... 7 2.2.2 Importing a GRD file... 7 2.2.3 GRD import with unknown projection... 8 2.3 Operating the Datum Align Calculation... 12 2.3.1 Datum Align - Output Results... 16 2.4 Exporting the CSF file + corrections-csv to a datum-aligned SEG File... 20 2.5 Viewing your Exported SEG file... 24 2.5.1 Finding Your SEG File... 24 2.5.2 SEISEE View of Original SGY File... 25 2.5.3 SEISEE View of Datum-Aligned SGY File... 26 2.5.4 Importing your Datum-Aligned SGY File with SonarWiz5... 26 2.6 Reflector Export - with Datum Align Added... 30 3 Document Versions... 33 1 Datum Align Feature The datum align feature is described in the SonarWiz 5 User Guide section 5.19 like this: "SonarWiz SBP Datum Align (SBP DA) utility is a function for computing the datum separation between a reference surface such as a multi-beam bathymetry grid, and one or more sub-bottom profiler files in your SonarWiz project. Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 2
In order to successfully use the SBP DA utility you must first accurately bottom track your sub-bottom profiles. The SBP DA utility computes the vertical separation between the altitude of each ping in the SBP profiles, and the reference surface at that ping s X/Y location. The distance between these two surfaces is referred to as datum separation, and this information is stored in the CSF file. This datum separation value corrects for several different vertical offsets at once. These vertical offsets include the heave of the sensor due to wave motion, the depth of a towed sensor below the sea surface and any offset between the ship s GPS antenna and the sensor. " In the document sections below, we explain how to use the SBP DA tool to your advantage, in your own projects. It is a very complicated feature to use, involving several steps, so this supplement to the user guide description may help you. 1.1 Initial Release and Documented Adjustments in Datum Align Feature The feature was introduced in January, 2013, and enhanced several times since then. The item entries below come directly from the www.chestech-support.com site, VERSION HISTORY SonarWiz 5 area: 5.08.0001 5.07.0010 5.06.0039 5.06.0035 11/28/2014 7:07:00 PM 10/2/2014 5:00:07 PM 11/8/2013 4:53:45 PM 9/27/2013 3:37:37 PM 13. BUGFIX:SBP:MINOR:GM:0 -- The SBP Datum Align utility did not clear any values in the geoid height value, when computing the separation between the SBP profile and the reference datum (grid). When SBP datum align is applied, the internal value for geoid height is now zeroed out so that the aligned profiles will match up in the 3D editor and subsequent exports. 3. ENHANCEMENT:SBP:MINOR:GM:0 -- Added option to SBP reflector exports to add the SBP Datum Alignment offset to exported reflector files like CSV and XYZ text. 1. ENHANCEMENT:SBP:MINOR -- Make the SBP Datum Align tool work with grids that contain either negative or positive depth values. 5. ENHANCEMENT:SBP:MINOR -- Add checkbox to the CSF to SEGY export utility to generate SEG-Y files that adjust the output sensor depth to reflect the datum separation computed in the Datum Align SBP Utility. 6. ENHANCEMENT:SBP:MINOR -- Minor cleanup to the SBP Datum Align utility and dialog. 5.06.0001 1/23/2013 1. ENHANCEMENT:BATHY:MAJOR First release of beta Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 3
3:20:52 PM bathy enabled build. 2. ENHANCEMENT:SBP:MINOR First cut at datum alignment of SBP profiles to a bathymetry grid. 1.2 Why Do This? The datum separation value can be used to generate a corrected SEG-Y file that contains a more accurate bottom-track altitude value. So if you have a sub-bottom profile with a simple echo sounder, and a multi-beam or interferometric scan of the same area, with more accurate depth information, you can basically enhance the accuracy of your sub-bottom bottom-track with the bathy grid depth information. You take advantage of all this by exporting a corrected SEGY format file. The reason to do this, is a perfect multi-beam survey grid should take into account several factors that may not have been used to "correct" your sub-bottom survey data, such as: (1) tide effects in effect at the day and time of the survey; (2) sound-velocity profile effects; (3) roll, pitch, yaw, heading effects; (4) heave motion effects. A well-done multi-beam survey would take ALL those into account, and you get the benefit of all that, by adjusting your sub-bottom bottom-track to the reference grid from the multi-beam survey. 1.3 Sequence Effects - Datum Align, then Reflectors, Cores Since you are making an adjustment in the SEG file "elevation", with respect to a reference grid, any post-processing steps that depend upon the elevation, like reflectors and cores, should be re-done on the adjusted SEG. So take that into account and do not bother recording reflector or core annotation on your sub-bottom data, if you are going to be using datum align. Do the datum alignment adjustment first, then continue with sub-bottom post-processing. If you happened to have annotated reflectors BEFORE applying datum align, the adjusted heights can be applied in your reflectors in SonarWiz versions 5.07.0010 and later, per the 5.07.0010 enhancement described above in section 1.1. Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 4
1.4 Dependencies - Coordinate System, Units, Numerical Values Your project coordinate system and bathymetric grid should both be in the same coordinate system and units, and meters works best. We have not verified the whole process using US FEET, for example, but typically use this in meters-based units and coordinate systems. 2 How to Use the SBP Datum Align Feature If you are going to change the global SOUND VELOCITY value in a project, please do this before any other operations, after CREATE PROJECT. Do it before bottom-tracking, and before datum alignment, for example, because the sound velocity will affect the apparent depth of the bottom, and all subsequent depth measurements. Here's how use the feature, in overview: 1. Import your sub-bottom file and bottom-track it, creating a bottom-tracked CSF file. 2. Create or obtain a bathy grid file (e.g. GRD file) (e.g. feed in an XYZ file and create the GRD file, using SonarWiz 5) 3. Run the Datum Align tool to compare the bathy grid file to your bottom-tracked subbottom file, and create the corrections CSV file (exports to your CSF folder) 4. Export the CSF file as a SEGY file, and specify to adjust the SEGY file using datum alignment corrections. SonarWiz 5 will select the corrections CSV file by name, and apply the corrections. You will see this in LAGA (byte 105, msecs) and CPD-X (byte 181, microsecs) fields in the SEG file exported. View it in SEISEE to confirm. 5. Import and view your corrected SEGY file, using a special SENSOR DEPTH selection upon import (FGSI AUV), and display your SEG file with topographic correction enabled. 6. Continue post-processing on the adjusted SEG file that has been imported again, doing reflector annotation and cores, intersections, and image export. Sections 2.1 to 2.6 below give more detail of the summary steps outlined above. 2.1 Importing and Bottom-tracking your SBP file No special instructions here - we assume you are good at this already. Here's an example sub-bottom profile with a reflector added BEFORE datum alignment, using 5.08.0004 software: Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 5
Note that the bottom-track starts (left-side, first ping) at 87m depth, and the reflector starts at 113m depth. Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 6
2.2 Making or Importing a Grid File 2.2.1 Making your own GRD File You may use the SonarWiz 5 post-processing menu choice Grid and Contour to create a sample grid file for your survey, and it may then be used for your Datum Align operation. A Surfer 11 *.GRD grid file may be created in the Grid and Contour tool in the Tools section. See Section 6.6 on page 606 of the SonarWiz 5 User Guide for more information. 2.2.2 Importing a GRD file Alternatively, if you have a bathymetric XYZ file, and have access to the GoldenSoftware.com product Surfer10 or Surfer11, you can convert your bathy XYZ file to s *.GRD grid file, for input to this process in SonarWiz 5. SonarWiz5 converts an XYZ file to GRD format just fine though. Here's an example: Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 7
Remember that the grid should be in the same coordinate system, and units, as the SonarWiz project. For our reference GRD file in the example from section 2.1, we will use this bathymetric grid, previously stored in the MISC folder of the project: Note that having a PRJ file is sometimes the key to importing a GRD file back into SonarWiz. Here follows a specific example of a GRD import where the user had to CREATE a PRJ file to facilitate the import. 2.2.3 GRD import with unknown projection Sometimes you know that the GRD file represents the same area as the project data, but SonarWiz does not know it. Here's an example of GRD file import where you tell SonarWiz in more detail how to do it. It's an actual customer example: 1. I verified the grid was a valid surfer grid in Surfer (it was fine). 2. I copied the grid into my project Grids folder. This isn't necessary, but it is a better place than any else on my machine. 3. I Add/Imported the Grid... file and selected the grid. 4. When prompted for the projection, I set it to match the project (UTM Zone 19 N) and Saved the PRJ file to the same directory as the grid (this might be the key) Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 8
5. My Grids directory looks like this now: 6. The grid loaded without errors for me. 7. I centered the display on my grid and it was all red (color bar problems) 8. I opened the grid properties and found the z range of the grid: Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 9
Note that depths are negative, so rescale the color legend accordingly: Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 10
9. If you have a bathymetry post-processing license and have the Bathymetry Tab > shaded relief option, it's another nice touch to the grid. Make sure that the vertical exaggeration shade settings are non-zero. I noticed that the default on a new project sets the sliders all the way to the left, and that won't work. They need to be set in the middle for a start, otherwise vertical exaggeration is zero (bad) and the sun is on the horizon (bad) and won't cast any light on the topography. Oops. Set is something like this or use Views > Bathymetry Views > Shaded Relief Settings... to set the values more precisely. Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 11
10. Here is the GRD I got with those settings: Then you can proceed with the datum align operation, using your imported grid file. 2.3 Operating the Datum Align Calculation To open Datum Align SBP Profiles to BathymetryGrid, left-click on the Datum Align button within the Sub-bottom group: Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 12
Once opened the Datum Align dialog (Figure 441) asks for two things: (1) First input required is the Bathymetry Grid File (*.GRD) to be used as the Datum. This file must be in one of the supported SonarWiz grid file formats. NOTE: Either positive or negative grid polarity works fine. There is logic to handle the case where you have elevations (negative numbers) instead of depth (positive numbers). If both (MinElevation < 0 && MaxElevation < 1) then we invert the sign of the elevation data, before doing the datum alignment, so that positive numbers (depth) format are used in the calculations. In this example, we will browse to this reference grid: (2) The second choice to make is which CSF file will have the corrections applied. The user must select the sub-bottom file(s) that will have their bottom tracks snapped to the reference grid. Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 13
After the OK button is left-clicked each sub-bottom file bottom track is aligned (snapped) to the grid, and a CSV file is created in the CSF folder of your project. Let's look at what you get. In this example, we are going to datum align only file 14 of this set: Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 14
If SonarWiz is unsure of the coordinate system of the grid, it may ask for confirmation, like in this case - using a dialog like this: Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 15
We simply click OK to confirm that the reference grid is in the same UTM84-30N coordinate system as the project. 2.3.1 Datum Align - Output Results Here's an example CSV file created using the example from 2.1: Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 16
This is inside the CSF folder. In addition to the BTK (bottom-track results) and CSF files, we now have a datumalign.csv file we can open and view: Here we see the corrections which will be applied when we export the CSF file as a SEG file, or adjust a reflector (versions 5.07.0010 and later can do this): Note than neither your SEG file, nor your CSF file, have been adjusted according to the reference grid yet. All you have is an exported CSV file, which computed the difference between the reference grid and your previous bottom-track in that CSF file. The important columns to note in this CSV file are GridDepth (depth in meters from the+mbes survey as the same locations, which accounted for tides, sound velocity profile, roll, pitch, yaw, heave, etc), and the "Delta" column. Delta means change - and this is the amount of adjustment in meters that will be applied to your conmputed bottom-track depth, when you export a CSF-to-SEG file, or export reflectors (adjustment possible in versions 5.07.0010 and later). So we were only off by 3m. Here's a view of the bottom-track (CSF file) after datum align has been computed: Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 17
It's the same as before - no adjustment has been applied. Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 18
To verify this, look at your ALTITUDE column of the original CSF file, before and after running the DATUM ALIGN step. The CSF file ALTITUDE column can be viewed by doing TOOLS -> CSF -> Extract CSF to CSV file, like this: The exportd CSV goes to your CSF folder, and opens in EXCEL. The ALTITUDE column, after datum align, remains the same as before: The bottom-track depth shown at 87.76 m in the images is a combination of sensor depth (72m in this case) and "altitude", computed as a function of the time the ping took Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 19
to descend and return to your designated seafloor, according to the global sonud velocity setting in SonarWiz (adjustable in ADVANCED OPTIONS): 2.4 Exporting the CSF file + corrections-csv to a datum-aligned SEG File The next step is to re-create a SEG file using the original data from the CSF file for the imported SEG file, plus the corrections-csv. Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 20
Next, all you need to do in this export dialog is select your CSF file, and one special checkbox: Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 21
Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 22
The SEG file will be exported to the SBP folder of the project, and will have the same name as the CSF file. We have selected 16-bit fixed point export format, because that was the original SGY file format: Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 23
and asked to apply datum alignment, since it is available. You get a little progressdialog while it is happening: 2.5 Viewing your Exported SEG file 2.5.1 Finding Your SEG File The SEG file exports to the SBP folder of your project, here. The first SGY file listed was the original imported SGY file, and the second one was the result of our datumaligned CSF export: Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 24
The changes in the two files are apparent in SEISEE. 2.5.2 SEISEE View of Original SGY File The place to look in the TRACE HEADER is the LAGA (byte 105) and CDP-X (byte 181) fields. Here are the values in the original file: Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 25
2.5.3 SEISEE View of Datum-Aligned SGY File The LAGA and CDP-X trace header fields now holf the datum align infromation: 2.5.4 Importing your Datum-Aligned SGY File with SonarWiz5 To see the corrections in your imported SGY file, you need to: 1) Use a special selection during the file import, using FileTypeSpecificOptions, and 2) View your file with Topographic Correction enabled. Here's how to do it. 2.5.4.1 Import using Special Settings In the SGY file import "OPEN" Dialog, click on File Type Specific Options. For clarity in this example, we renamed the SGY file to Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 26
For file-type specific options, use these. Specifically, select this import option for READ SENSOR DEPTH FROM BYTES: Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 27
Using this setting, SonarWiz 5 looks for sensor depth in the LAGA (byte 105) and CDP- X (Byte 181) fields, in msec and microsecs, and can use this information to apply topographic correction. 2.5.4.2 View the SGY File in SonarWiz 5 with TOPO CORRECTION enabled Once you have imported your SEG file, view it in the DIGITIZER VIEW and apply topo correction: ON like this: Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 28
For comparison, the DIGITIZER VIEW of the ORIGINAL SGY file looked like this: Now, with topo correction applied, the datum-aligned SGY file looks like this: Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 29
It's clear that the effects are present, the bottom has been adjusted down approx 3m, so the correct-csv file data have been applied. 2.6 Reflector Export - with Datum Align Added Since 5.07.0010, the ability to export reflectors, digitized on the original SGY file, with the datum align correction added in, has been supported, like this. Open the Feature Manager and select EXPORT: Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 30
Then select the reflector to export, and export it with datum alignment added: Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 31
We are going to export a CSV file version of our reflector, saving it to the SHP file folder. You can open these in EXCEL and see the datum align effect: Exported UNADJUSTED: Exported with DATUM ALIGN ADJUSTMENT: Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 32
3 Document Versions Rev 8, 12/22/2015 - Semantic update - giving a complete and detailed example of overcoming GRD file import issues by saving the PRJ file to match the project, as well as a case of a negative-going GRD depth scale - section 2.2.3 Rev 7, Format change only - using new CTI graphics - corporate and product logos. Rev 6, 1/15/2015 - Ability to export corrected reflectors added in 5.07.0010. Rev 5, 9/10/2014 - Grid polarity usage clarified - either negative or positive grid work fine. Rev 7, 5/8/2015 support@chesapeaketech.com 650-967-2045 Page 33