Perspective-SS -- Sidescan Processing Guide -Software Version 7.6 By: Tony M.
Triton Imaging Inc. Engineering Office 2121 41st Avenue, Suite 211 Capitola, CA 95010 USA 831-722-7373 831-475-8446 sales@tritonimaginginc.com support@tritonimaginginc.com © 2014 TRITON This user guide is provided as a means to become familiar with TRITON’s software through an explanation of the options available for processing sidescan data. The user interface presented in this guide is subject to change to accommodate software upgrades and revisions.
Table of Contents 1.0 Introduction ................................................................................................. 1 2.0 Settings ...................................................................................................... 1 2.1 File Paths .............................................................................................................................................................................. 1 2.2 Number of Cores ...............................................
1.0 Introduction This document presents a sample workflow for processing sidescan data using Triton’s Perspective software. Also covered are some of the interpretation tools available in Perspective and a brief discussion of export options. Having Perspective open and following the steps outlined in this document from start to end will provide the user with a basic understanding of how the software works and the tools available with the MosaicOne sidescan processing module in Perspective. 2.
3.0 Import 3.1 File Import To get started, the raw sidescan data files need to be imported into Perspective using the Raw Data File option from the Import menu as shown in the capture to the right. Please note that currently Perspective only supports the XTF and SEGY file formats. To convert from other formats we have a several converters on our website at: http://www.tritonimaginginc.com/site/content/support/downloads.
If the projection used for the raw data files is not present in the standard lists, select the Custom button to either manually enter the projection values or download a custom projection string from: http://spatialreference.org/ A custom datum can also be created by manually entering the datum values. For more information on using the custom projection and datum options, open the Help file and look under Program Settings.
3.4 Import Processing Option In the Program Settings, there is an option to launch the processing wizards upon importing raw data. If this is selected, upon importing the raw data file(s), the dialog shown below will pop-up asking if you would like to process the data at this time.
As the waterfall scrolls, the position in the map view updates to show the current location of the waterfall display. The other option to open the waterfall window is right-clicking on the navigation line in the file tree as shown to the right. This will launch the waterfall at the beginning of the navigation line but will still place the position circle on the map display for tracking the waterfall position.
4.2 Bottom Tracking To the right is an example of the waterfall view showing sidescan data collected using a Klein 5000 sonar. The red line in the waterfall window shows that the selected file already has bottom tracking saved in the raw data file. If the file is not bottom tracked, or to either review or reset the bottom tracking, select the bottom tracking toolbar button shown here. Selecting this toolbar button will open the window to the right for setting or adjusting the bottom tracking.
3. If the file includes both amplitude and depth information, then the bottom track can be automatically extracted from the bathy nadir depth. Doing this may require the user to apply a Bottom Track Offset to move the entire bottom track line up or down by a specified value. 4. Auto Update XTF is the only place in Perspective that the user is able to overwrite their raw data!.
4.3 TVG Adjustments Many modern sidescan sonars already account for TVG during acquisition and no adjustments are required. However, when needed TVG corrections will greatly increase the sidescan mosaic image quality. Prior to adjusting the TVG, it is important to slant range correct the sidescan data in the waterfall view using the bottom track information. This is accomplished by selecting the Slant Range toolbar button shown below.
Below is the same example from the previous page but with the TVG manually adjusted: Comparing the image above with the one on the previous page shows the attenuation loss with increased range has been corrected for. As mentioned above it is possible to use an automated routine for adjusting the TVG which often has very good results. By default this will generate individual curves for each channel. Selecting the automatic TVG button will open the dialog shown right.
Below is the same example again but with the TVG automatically adjusted: It is interesting to note that the curve is similar to the one created manually but slightly lower, increasing the overall gain level. Also note that sometimes with the automatic TVG there is still a black stripe down the nadir. In these cases it is helpful to manually adjust the automatically generated TVG curve in order to produce the results as shown below.
5.0 Process 5.1 Sidescan Mosaic Wizard Once the navigation has been processed, the bottom track verified, and a TVG curve has been created and saved, the sidescan data is ready to be processed. The easiest method for launching the sidescan mosaic wizard is by selecting this toolbar button. It is also possible to right-click on the Sidescan node in the Imagery file tree layer and select Create. Sidescan processing options are divided into six stages 1. Choose/Create Mosaic File 2. Choose Mosaic Settings 3.
5.1.2 Choose Mosaic Settings Settings pertaining to assembling the sidescan mosaic are located on page 2 of the processing wizard. An overview of the options available is presented below. General Settings o Resolution: This is where the mosaic resolution is set (in meters). o Combine Overlapping Lines: Methods for selecting which cell value to use where lines overlap. o Single Channel Auto-Flip: Uses alternating channels (port, starboard) to create a mosaic with a consistent shadow direction.
5.1.3 Select/Order Input Lines This page allows the user to select which lines to include in the processing as shown below. Note that the line order can also be specified by right-clicking on a line and selecting Move Up, Move Down, or Move to Top. 5.1.4 Geometry Settings Towfish Configuration: There are two primary options for vessel geometry for sidescan processing. Traditionally, most sidescan sonars are towed behind the survey vessel with the layback amount stored on the raw data file.
5.1.5 Line and Channel Settings This page of the wizard is for settings that apply on the individual survey lines before they are assembled into a mosaic. Select Channel port and starboard channels can be selected or turned off. Clip Channel Ground Range o User Defined: These slider bars set the amount of clipping to perform in either percentage or in meters. The outer boundary can be set by clipping the maximum range or by setting the maximum distance to use from the nadir position.
o Include Adjacent Cells - uses the values in adjacent cells to calculate value of filled cell. o Non-Zero Shadow - fills sidescan shadows where there is no data with a zero amplitude for each grid cell in the shadow so imagery behind the mosaic does not show through. Channel Sampling Method Both the Downsampling and Combine Overlap options refer to the method by which overlapping data from within one line is handled. o Downsampling: refers to the across track element (sample to sample within a ping).
5.1.6 Corrections and Filters The last page of the sidescan processing wizard is for correcting position and gain loss in the mosaic. Process Navigation This section selects the correct navigation to use for creating the mosaic, with three options available: o Process Navigation - If processing is needed and has not been done, then the top option allows the user to set the navigation processing parameters.
Pitch Corrections This option uses the 'pitch' value in the motion data (if available) to apply along track position corrections. Options include: o From XTF: Reads the pitch value for each ping from the XTF file. There is an option here for setting an absolute angular offset o Static Offset: AIf the sidescan sonar was mounted at an angle or was known to be inclined in the water at a fairly steady angle, a static pitch value can be applied to the mosaic.
5.2 Re-merge Mosaic After the mosaic is created, it is possible to make a few changes and have those changes incorporated into the mosaic with the Re-Merge Mosaic option. This option is found by rightclicking on the mosaic file in the Imagery file tree. When running the Re-Merge Mosaic option, the user will not have any input and the same exact options used when the mosaic was created will be used again.
5.3 Other Processing Options Presented here are a few optional processing tools: 5.3.1 Navigation Processing The sidescan processing wizard only allows one pass at filtering the navigation. However, for really bad navigation, either due to faulty equipment or overhead obstructions, this may not be adequate to get good results from the sidescan data. To launch the Process Navigation module, right-click on the Sidescan Navigation file tree node. 5.3.
6.0 Enhance There are two primary options for enhancing the appearance of the sidescan mosaics in Perspective. These are adjustments to the Color Settings and to the Histogram. 6.1 Color Settings To open the Color Settings, rightclick on the mosaic file in the file tree as shown to the right. Selecting this will open the window below. Apart from changing the color bar as shown in the window below, increasing the Gamma can help bring out the details in the mosaic. 6.
Selecting the Histogram menu option will open the window below. The histogram and image on the left have the default histogram while the histogram and image on the right have had their histogram adjusted to bring out the details in the data. Please note that these color and histogram options are also available in the waterfall viewer and can have either the same settings or can be different from the mosaic color and histogram settings.
7.0 Interpret To assist with interpretation of the sidescan data Perspective has many added features and toolsets. This section briefly describes some of the options available. 7.1 dB-based Imagery To preserve the full dynamic range of the raw data file, Perspective keeps the data in dBs instead of downsampling to fit a bitmap palette. This keeps the maximum data range in the intact in the mosaic file.
The sidescan waterfall accesses the raw XTF data and therefore preserves the raw data quality. It can be launched by double-clicking on a sidescan navigation line, tracked while scrolling by the circle moving along the navigation line, and moved around that line or to another while scrolling by dragging it across the screen. 7.3 TargetOne Integrated into Perspective is our full targeting package.
8.0 Export There are two primary exports for sidescan mosaics from Perspective. The main export is to a GeoTiff, but it is also possible to export to a KML file. 8.1 GeoTiff The sidescan mosaic can be exported to a GeoTiff by right-clicking on the mosaic file in the file tree and selecting the GeoTiff export option. This will export a GeoTiff of the entire sidescan mosaic with no other information overlain on the image. The other GeoTiff export option is in the main File menu.
9.0 Workflow Step 1 - Launch Perspective: Start application and open project or start new project Step 2 - Check Settings: Verify maximum number of cores is selected and if desired preset projection and datum for data and background imports. Step 3 - Import Data: Import raw data files into Perspective Step 4 – Process Navigation: Process navigation from file tree and enable Show Beamlines to monitor results.
