Heave/Swell Removal Tool option from the Tools→Dynamic Grid Shifts menu in the Main Menu bar.
What it Does
This tool will compute a time based heave/swell series along selected lines and shift the grid to reduce the heave/swell artifacts.
General Description
This tool computes a smoothed ping/beam based vertical offset for the current dynamic grid, which is applied to all systems within the associated source files. This tool is designed to allow the user to choose the system and beams which best represent the affected grid area to use for the computation. A Line object can also be selected using the Area Exclusion Mask where swaths of beams can be removed from the shift or, only those beams inside the selection will be shifted. Once you save the results using the Save Shift button, Qimera will prompt you to reprocess the relevant files after you run the tool and every raw sonar file that is part of the Dynamic Grid you are shifting will have a vertical shift applied on a ping-by-ping basis. Qimera will then automatically update all Dynamic Grids containing the affected lines. A statistical summary of each file's continuous shifts can be reviewed in the Processing Settings Dialog and a review of the shift can be observed in the Time Series Editor under the label 'Heave/Swell Shift'.
For more information on navigating the data of the plot, see the section on Qimera Plot Grids.
Toolbar
Explore Mode
This is the primary exploration mode of the tool. As you move your cursor over the plot, the label in the lower left of the window will update to show the X/Y axis values, the current vertical offset associated with the time of the cursor position as well as the survey line at that location. The cursor in the Scene in the main app will also update with a red cursor for the synchronized location along the survey line's navigation track.
Zoom Mode
When in zoom mode, simply click and drag an area of the plot to zoom into. Click the Home button to return to the full extents of the data. At any time, you can Shift-Click to drag the plot to a new location, you can also re-position with a middle mouse click. This is especially useful when you are zoomed in.
Zoom Out Button
If you have zoomed into an area of the plot, this button will zoom out to the extents of the data.
Interpolation Edit Mode
If you Click-Draga selection of the time series, Qimera will flag the selected samples invalid and interpolate across the selection using the sample on either side of the selected area. During processing, time series data queries will then use these new interpolated values. This is a simple way to get rid of spikes in your data. You can always undo an edit using the Undo button. Once you are satisfied with your edits, you must press the Save button. Note that you can do further editing of the height shift in the Time-Series Editor.
Validate Edit Mode
This mode is an easy way to bring back data that you have marked as rejected or for interpolation. Simply Click-Draga selection over the previous edit and Qimera will restore the original data. You can always undo an edit using the Undo button. Once you are satisfied with your edits, you must press the Save button.
Undo Button
This will undo the last edit actions. It is a pseudo-infinite undo buffer in that you can make several edits in sequence and then undo those edits in the reverse sequence.
Redo Button
This will redo the last undo edit action.
Plot Point Size
Clicking this icon will change the point size drawn in the widget. If you click and hold the button, it will display a menu where you can select point sizes between Small and XX-Large. Simply clicking will cycle through all sizes.
Menu
Show Current Offset
If you have previously run this tool, this option allows you to control whether or not the previously computed offset is shown in the plot or not. If shown, it is drawn in blue.
Show Statistics
This option allows you to show summary statistics of the time-series of shifts on the graph. It will show the mean, min, max and +/- 1-sigma standard deviation. These are drawn as dashed lines in the graph along with numeric labels on the right-hand side of the plot.
Show Gridlines
This option controls the display of grid lines on the time-series graph.
Dynamic Grid to Shift
Use this combo box to select the Dynamic Grid you wish to shift. It will set the Dynamic Grid you had selected in the Project Layers Dock when you launched the tool.
System
Use this combo box to select the system and beams you would like to to use for the heave calculation for each ping. It is best to select beams that are not affected by variations in topography (ie a ship wreck would not be a good candidate). Mousing over the associated line edit beams box will display a tooltip identifying the available beams for the current system.
Area of Computation
Use this combo box to selected either Everywhere or Inside Selection to constrain where the algorithm runs the grid difference computation. Selecting the Inside Selection option will shift the source pings of all footprints that fall within the selected area. If a ping has footprints that fall inside and outside the selection area all of the footprints will be shifted for that ping.
Area Mask
Use this combo box to select a line object from the Project Layers Dock that can be used to mask areas used in the computation. The line can be used for both exclusion and inclusion. When used for inclusion only the beams inside the selected area will be shifted in the final output.
Pre Smoothing Window
Use this numeric entry field to specify the number of samples/pings which will be used to compute the initial vertical difference from the source data. The minimum is 3 samples which will result in a minimal removal of heave/swell from the source with minimal distortion of the source data.
Smooth Across Gaps
This option allows you to smooth across the small gaps that sometimes occur when logging stops and starts along a survey line. The time window parameter controls the decision on whether the next sample should be included in the current vertical heave computation.
Post Smoothing Window
Use this numeric entry field to specify the number of samples the be used in the post smoothing window. This will further refine the heave/swell removal and can be updated dynamically after the initial computation is done. Increasing the number of samples can reduce any remaining noise in the initial computation.
Export Button
Export to ASCII...
This option allows you to save the entire time-series of vertical shifts as an ASCII output for reporting or further analysis. This is useful in the tool since it exports the time-series for all of the survey lines together in a single export.
Export Plot as Image...
This option allows you to save a view of the time-series graph as an image for reporting purposes. This is useful in the tool since it plots the time-series for all of the survey lines together in a single graph.
Export Window as Image...
This option will export the entire contents of the dialog as an image. This is useful for an overview for reporting.
Export Scene as Image...
This option will export the main Qimera window scene work area as an image.
Export All...
This option will launch a dialog and allow you to specify the location and items you would like to export. The selectable list contains the content listed under 'Export Button'.
Auto Export Checkbox
Selecting this box will automatically save all of the listed exports under the Export Button to a unique timestamp folder in the current projects export directory.
Create Reference Grid
This checkbox will create a static reference grid from the data before the heave/swell shift is applied.
Cancel Button
This button will cancel the operation and exit the dialog.
Save Shift Button
Click this button to run the continuous shift computation.
