Wave Systems Module
Perform a wave partitioning analysis to identify the wind sea and swell wave systems
Wave Systems is the primary data analysis module. Wave system information is extracted from the input directional wave spectra records. Specific details on the method are documented in the Primer on Wave Spectral Partitioning.
To process the data, click Wave System-> Process Data from the module drop down menu or click the Wave Systems Processing icon on the toolbar to open an interactive Wave Systems Parameter Table. This allows the user to customize an analysis session based on input data quality, resolution, etc. Tips for selecting parameter values can found in the Wave Systems Parameter Table Help Pages.
Once data are processed, the results are automatically displayed in a wave vector history map. This is actually a sophisticated data exploration tool with many user-selectable features. The initial display is at most one week of wave system and related information in two separate displays. The top panel displays wave component height, period and direction represented by vector length, origin, and azimuth, respectively. To return to this wave vector history map at any time click Wave System-> Wave Vector Display from the module drop down menu or click the Wave Vector Display icon on the toolbar.
If the Extract Windsea option was selected in the Wave Systems Parameter Table, identified wind seas are displayed as black arrows and evolving swell systems are displayed as colored arrows. Each color corresponds to a group of wave partitions evolving from a common origin on the ocean.
If the Wind Force option was selected in the Wave Systems Parameter Table, there are no black arrows and the various color groups represent distinct evolving wave systems (regardless of wind forcing). Wave components that are forced by the wind are displayed with a double line width. The Wind Force cut-off (see below) controls the identification of wind forced wave components. The default value is that any wave components that are at least 70% wind sea (wind force cut-off = 0.7) will be highlighted.
For non-directional wave data the vectors are replaced with frequency points. The lower panel displays a time series of summary wind or wave data as selected.
A number of interactive plot controls and pull-down menu commands are provided to allow the user to fully investigate the results. With the exception of the data export utility, Wave Systems plot commands only affect the display of data. No changes are made to the actual data file.
Wave Systems Interactive Plot Features
Locate Legend Entry – Click on any wave vector to locate the corresponding legend entry.
Partition Editor – Right-click on any wave vector and select Edit Partition to open the Partition Editor for that particular record. From there the user may reassign or combine partitioned wave systems.
Wave System Editor – Right-click on any wave vector and select Edit Wave System to open the Wave System Editor for that particular system. From there the user may reassign or combine partitioned wave systems.
Change Wave System Color - Click on the corresponding legend entry for the wave system to be changed. A color input window will appear, click on the preferred color and hit OK.
Legend Slider - If there are many wave systems, then a slider bar may appear to the right of the legend. Slide the bar up and down to view the different legend entries.
Scroll Bar – For some views, a scroll bar will appear the bottom of the window, allowing navigation forward and back through time. Right click the scroll bar to change the time axes.
Change Scale Height – Click on scale arrow in upper left corner of plot. This will open an input window for the user to enter a new significant wave height scale in meters. Once the new scale height is entered, click OK and the arrows in the Wave Vector History plot will be adjusted to the new settings. By default, the scale height is set to 2m.
Adjust Compass - The compass has several customizable features. These features can be accessed by right-clicking the compass. A menu will appear with options to move or resize. If the user selects to move the compass (by clicking move), the user should move the mouse to a preferred location, then click again. If the user selects to resize the compass, a dialog box will appear prompting the user for a percentage, used to increase or decrease the size of the compass.
Change Lower Plots - The data displayed in the bottom plots can be changed by right clicking the title of either lower plot and selecting from the pull-down menu. After clicking the preferred plot from the menu, the selected plot will be changed accordingly. By default, the lower plots will display Significant Wave Height.
Zoom – Click on the magnifying glass to toggle the zoom feature on. Zoom in by positioning the mouse cursor where you want the center of the plot to be and either press the mouse button or rotate the mouse scroll wheel away from you (upward). Zoom out by positioning the mouse cursor where you want the center of the plot to be and either simultaneously press Shift and the mouse button, or rotate the mouse scroll wheel toward you (downward). Each mouse click or scroll wheel click zooms in or out by a factor of 2. Clicking and dragging over an axes when zooming in is enabled draws a rubber band box. When you release the mouse button, the axes zoom in to the region enclosed by the rubberband box. Double-clicking over an axes returns the axes to its initial zoom setting. Click on the magnifying glass again to toggle the zoom feature off.
Options Menu Commands
Resample Data: Resample the data appearing in the plot. The user may resample data for All Systems, Wind Seas, Swells, or Wind Vectors. Enter the desired sampling factor in the display window. By default, the resample factor is two (i.e. every other arrow will be plotted).
Wind Forcing: Turn highlight of wind-forced vectors on and off. Highlighting is in the form of thicker line widths on those wave vectors that have a percentage of wind sea greater than or equal to the cut-off value. An option exists to change the wind force cut-off used for identification of wind forced seas. This selection is not available if Extract Windsea option was selected in Wave Systems Parameter Table.
Toggle Swell System -Add or remove a wave system from the plot.
Filter Swells - Filter the displayed wave systems by the number of members in each wave system. An input window will appear to prompt the user for the number of members a swell system must contain in order to be displayed in the plot. The default value for the filter is 5.
Isolate a Swell - Isolate a single swell system to appear on the plot.
Show All Swells -Display all the wave systems.
View – Change the plot view from between one and three panels.
Data Type - Switch between the display of Wave Systems and Swell Events. Swell Events are segments from evolving Wave Systems that are used to compute the storm source parameters displayed in Swell Map Module.
Change Color - Change the background color of the plot
Edit Lines - Edit the line thickness and style for the arrows in the Wave Vector History plot.
Axes Menu Commands
Time Axis: Allows the user to switch between pre-set lengths of time for the time axis. The options are Daily, Weekly, Monthly, and All Times. If the user is not in the All Times setting, then a slider bar will appear at the bottom of the plot for long records. Slide the bar forward and backward in time to adjust the viewable time axis range. Clicking on the arrows on either side of the slider will shift the time axis by a day, week, or month, depending on the current time axis setting. The default value (if record is long enough) is a Weekly view.
Y-Axis: Set Wave Vector Plot Y-Axis to Frequency or Wave Period
Reset: Modify plot axes limits. Enter the desired axes limits in the display window.
Wave System results can also be visualized in a variety of Data View plots. Select Data View from the Module pull-down menu to access.
The Wave Systems Parameter Table is used to set processing parameters for the Wave Systems Module. Adjustable wave system parameters allow the user to select a windsea identification method, set data processing thresholds, and activate a temporal trend analysis for smoothing the results. The spectral noise floor, sharpness of spectral peaks, and distinctiveness of the wind seas may all vary between observation sets and lead to differences in output. These differences can be minimized using the adjustable parameters in the Wave Systems Parameter Table.
The Wave Systems Parameter Table is divided into 3 main sections: 1. Settings Commands (Left column of buttons), 2. Wave System Parameters (center column of inputs), and 3. Interactive display (right figure window). The features in each of these sections are described below.
The commands appearing on the left side of the Wave Systems Parameters Table control the saving and use of selected parameters. The following Commands and options are available:
Named Settings – Select from a list of pre-existing parameter settings. Parameter values will automatically update. To see the results of these new parameters in the plot, click Update Plot.
Update – Update the displayed parameters to the current named parameter set.
Save New – Save the displayed parameters to a new named parameter set. User will be prompted to provide a name for the new parameter set.
Reset – displayed parameters to saved values
Delete – Delete the current named parameter set
Run – Process the data set using the current named parameter set
Cancel – Exit the Wave Systems Parameter Table without processing any data
There are 4 options for separating windsea and swell:
1. Wave Age 2D – This is the standard tool for extracting wind seas using a directional wave age criterion. This method classifies peaks as windsea or swells using the user-defined Windsea Multiplier. A wave system is considered windsea if it is forced by the local wind such that the mean phase speed of the waves is less than or equal to the wind speed component in the direction of the waves when multiplied by the Windsea Multiplier wsmult:
, then wave system is windsea.
The factor broadens the windsea search angle to allow for turning winds or coastal effects. All other wave systems are considered swell.
Typically, this approach works best on measured data, such as from a buoy or acoustic sonar. Model data tend to be to smooth across frequency bands for the software to find a distinct wind sea peak with this approach (for model data see Wind Force option below). A Windsea Multiplier value of 1.5 to 1.7 works well for measured data. The results are best checked by (1) inspection of the wave vector history plot (Wave System module) to evaluate how well the windseas follow the wind; and (2) inspection of the various windsea wave system plot options in Data View for comparing the input spectra with the selected windsea spectra.
2. Wave Age 1D – This technique is similar to the Wave Age 2D, except that wave direction is not considered in the calculation. A wave system is considered windsea if it is forced by the local wind such that the mean phase speed of the waves is less than or equal to the wind speed when multiplied by the Windsea Multiplier wsmult:
, then wave system is windsea.
All other wave systems are considered swell. This is the default approach for 1D (non-directional) data. A Windsea Multiplier value of 1.5 to 2.0 works best for most measured data.
3. Wind Force – In this approach was first developed by Hanson and Tolman for the windsea identification in the NOAA Wavewatch III numerical wave model (see WAVEWATCH III users guide). This method treats all wave partitions the same without an initial attempt to locate windsea components or partitions. Once the partitions are identified, the amount of wind forcing on each wave partition is computed. Wind Forcing (wf) is computed as a ratio:
wf = partition windsea energy/ partition total energy
where the windsea energy is computed from the portion of the partition that is forced by the component of the wind in the wave direction, using to compute the wind component as described above. Pure windseas have wf~1 (as in 100% windsea energy) and pure swell has wf~0 (as in 0 % windsea energy). In-between these values the seas are mixed.
When implementing this approach, the user is required to set a value for the Windforce Threshold (%). This threshold is then used to set each partition as windsea or swell depending on the Wind Force value:
Windsea: Wind Force x 100 ≥ Windforce Threshold
Swell: Wind Force x 100 < Windforce Threshold
This is the preferred windsea identification approach for wave modeling applications. However it can be used on measured data as well. Depending on how the user decides to define windseas, Windforce Threshold values from 30% to 70% are recommended. Note that NOAA NCEP uses Windforce Threshold = 33% for the routine identification of windseas in WAVEWATCH III.
4. Friction Velocity - This method isolates windsea partitions based on the method used by the European Center for Medium Range Weather Forecasting (ECMWF) during creation of their ERA-40 reanalysis. The spectral partitioning conducted by ECMWF is described in ECMWF, 2009 and a spectral partition (f,θ) is assumed to windsea if the following inequality is satisfied.
Here is the friction velocity (ustar), c is the phase speed derived from linear theory for a given peak wave frequency fp, θ is the wave direction, and ϕ is the wind direction. When this option is selected, the user has the option of using friction velocity estimated from the winds (Large and Pond, 1981) or from a data file. In this latter case, in the event friction velocities have not already been previously loaded into wave data file, the user is asked to browse for a friction velocity data file. This file is then opened and the provided friction velocities are interpolated in time to match the wave record time stamps. A new data field ‘ustar’ is added to the wavedat variable. Alternatively, friction velocity data can be loaded into the processed data file within the Data View Module through the Load command in the Options pull-down menu.
5. None – Use this option if no windsea identification is desired. All partitions are treated equally throughout. The Spectral Fit and Sea State Modules will not recognize any windseas in the data – all the wave systems will be treated as swell. Further note that several plots in the Data View Module Climatology and Sea State plot libraries will reflect the complete absence of any windseas in the data.
Max Components per Record
Sets the maximum number of wave partitions allowed per observation. The wave partitions are first sorted based on total energy. Wave components falling below the threshold number are recombined to their nearest neighbor in frequency-direction space. This ensures that energy is conserved in that the sum of the partition energy is equal to the original spectrum energy. Values from 1 to 8 are normal depending on the geographic location. For example, an inland sea may only see 1 or 2 components, whereas the open pacific can experience 5 or more components simultaneously.
Minimum Wave Height (m)
To reduce the “noise” resulting from small isolated peaks in the input directional wave spectra, wave systems falling below this significant wave height threshold are combined with a nearest neighbor. The user enters the desired minimum significant wave height (m) for output wave systems. Values from 0-1 m may be reasonable depending on the amount of wave energy in the data set. Model data typically has less random noise and may not need as high a threshold as observed data.
Selecting ‘yes’ reserves one of the wave components for wind sea, which may or may not be present in any given record. So the maximum number of swells with ‘yes’ selected would be
Max Swells per record = Max Components per record – 1
If ‘no’ is selected, the wave components can be any combination of wind sea and swell. For example, if a user sets
Max Wave Components =2, and
Windsea Placeholder = ‘yes’
The results will return one of the following scenarios for each wave record:
1. No partitions
2. 1 Windsea partition
3. 1 Swell partition
4. 1 Windsea and 1 Swell partitions
With the Windsea Placeholder set to ‘no’, a fifth option is available:
5. 2 Swell partitions
This controls the number of levels that the wave spectrum is divided into for partitioning.The higher the partition resolution, the better resolved the partition boundaries are but at the cost of increased computation time. There are three ways to input a Partition Resolution value: enter a number directly into the text box, use the slider, or check the ‘Use Default’ checkbox to compute a default partition resolution based on the number of frequency and direction bins. Acceptable values are in the range of 50 – 550.
Activate Trend Analysis
Trend Analysis Window (h)
A trend analysis of the output partition data can be performed to increase temporal consistency. The Trend Analysis Window sets the duration in hours of a sliding analysis window. To activate the trend analysis, select values that are at least twice the interval between records. For example, for a data set with records every 3 hours, select a trend analysis window of 7 hours to ensure at least 3 records are contained in the sliding window. Larger values will provide consistency over longer time periods. No trend analysis is performed with Trend Analysis Window = 0.
Note: The results of the trend analysis do not appear in the Wave System Parameter Table graphical display. To see results the data must be processed first and then viewed in Data View.
3. Interactive Display
The plot on the right side of the Wave Systems Parameter Table can be used to view the results of various parameter settings prior to processing data. The following user-controls are provided:
Plot Title – Right click on the plot title to select from several display options:
Change Plot Date and Time – Navigate through the data file records using the Previous and Next buttons or by clicking on the scroll-down arrow in the date-time box under the plot.
Update Plot – Update the plot to reflect the selected parameter settings.
ECMWF, 2009. ECWMF IFS Documentation Cy33r1 Part VII: ECMWF Wave Model, European Centre for Medium-Range Weather Forecasts
Shinﬁeld Park, Reading, RG2 9AX, England (http://www.ecmwf.int/research/ifsdocs/CY33r1/WAVES/IFSPart7.pdf)
Large, WG and Pond, S 1981. Open Ocean Momentum Flux Measurements in Moderate to Strong Winds, J. Phys. Ocean., Vol. 11, 324-336
The Wave Partition Editor allows the user to make manual adjustments to the partitions in a given record. The partitions are generated automatically from the Wave Systems module based on the parameters set in the Wave Systems Parameter Table.
Launching the Wave Partition Editor
Data must first be loaded (see Start Up) and processed using Wave Systems. The Wave Partition Editor can be launched by selecting the Partition Utilities; an extension of Data Utilities found in the Module pull-down menu. Because the Wave Partition Editor will make changes to the data in memory, a Save Data window appears and provides the opportunity to save user data before proceeding. If the Spectral Fit or Sea State modules have been run, a dialogue will appear warning the user that this data will be lost. These modules analyze the Wave Systems data and should be re-run after using the Wave Partition Editor. In addition, if the Wave Systems Editor has been run previously, a warning dialogue will appear warning the user that those changes may be discarded after Wave Partition Editor processing. The changes made by using the Convert to Wind Sea option within the Wave Systems Editor will remain intact. Separating or combining wave systems will be discarded.
Once launched, a Partition Contour plot for the first record in memory along with a record list selector and a text box with the available partitions will appear in the interactive Partition Utilities window. From this window, the user can select which partitions to combine or reassign in any record.
To reassign a partition is to change a swell to a wind sea or a wind sea to a swell. Simply select the desired partition from the text box and click Reassign button.
To combine a partition is to merge a partition with its nearest neighbor. To combine a partition, select the partition from the text box and press the Combine button.
To undo the last change (combine or reassign), press the Undo Last button. This will only undo the last change. Subsequent calls to this command will have no effect.
To undo all of the changes made while in the Wave Partition Editor, press the Undo All button. This will revert back to the original partitions.
There are three ways to select a new record. The Previous button brings up the record previous to the current record selected.
The Next button brings up the following record.
Record List Selector
Jump to any record by choosing from the list of records in the drop down menu. Records are sorted by date and time.
Once finished with the Wave Partition Editor, press the Update button to run the wave system tracking algorithm and return to DataView or Wave Systems. Beware that if the Spectral Fit or Sea State modules have been run, the data will be removed.
Press Cancel to discard all changes and return to DataView or Wave Systems.
OverviewThe Wave Systems Editor allows the user to make manual adjustments to the Wave Systems in a given record. The wave systems are generated automatically from the Wave Systems module based on the parameters set in the Wave Systems Parameter Table. The user can combine or separate wave systems as desired but the following restrictions apply:
1. The wind sea system cannot be combined or separated.
2. Wave Systems that overlap in time cannot be combined.
Launching the Wave Systems Editor
Data must first be loaded (see Start Up) and processed using Wave Systems. The Wave Systems Editor can be launched by selecting the Wave Systems Utilities; an extension of Data Utilities found in the Module pull-down menu. Because the Wave Systems Editor will make changes to the data in memory, a Save Data window appears and provides the opportunity to save user data before proceeding.
Once launched, a Wave Systems Significant Wave Height plot and a text box with all the available wave systems will appear in the interactive Wave Systems Utilities window. From this window, the user can select which Wave Systems to combine or separate. Each wave system is labeled and color coded for convenience.
To separate a wave system, select the desired wave system from the text box and click the Separate button. A new window will appear with a list of all the records containing this wave system. Select one of the records in the list to determine when to separate the wave system.
To combine a wave system, select any two wave systems from the text box and press the Combine button. Select more than one system by holding the Ctrl button while clicking. Only two wave systems can be combined at a time. Wave systems that overlap in time cannot be combined. If the gap between selected wave systems is greater than 6 hours, a warning will appear and ask the user if they would like to continue.
Convert to Wind Sea
The user also has the capability to select an existing swell system and convert it to wind sea. Select the desired wave system to convert and press the Convert button.
To undo the last change (combine or separate), press the Undo Last button. This will only undo the last change. Subsequent calls to this command will have no effect.
To undo all of the changes made while in the Wave Systems Editor, press the Undo All button. This will revert back to the original wave systems.
The Next button moves the cursor on the wave systems plot to the next record. This can help the user visualize how many systems are present in each record.
The Previous button moves the cursor to the previous record.
Record List Selector
Jump to any record by choosing from the list of records in the drop down menu. Records are sorted by date and time.
To zoom in on a wave system, right click inside the plot axes and select Zoom. Zoom in by positioning the mouse cursor to the desired plot center and either press the mouse button or rotate the mouse scroll wheel upward. Clicking and dragging within the plot axes draws a rubber band box. When you release the mouse button, the axes zoom in to the region enclosed by the rubber band box. To return the zoom back to the original settings, double click anywhere in the plot axes or right click within the plot and select Reset.
To pan the view of the plot, right click inside the plot axes and select Pan. To return to the original plot, double click anywhere in the plot axes or right click within the plot and select Reset.
Once finished with the Wave Systems Editor, press the Update button to update the wave systems and return to DataView or Wave Systems.
Press Cancel to discard all changes and return to DataView or Wave Systems.