Swell Map Module

Estimate the generation time and location of measured swell events

Swell Map Module

The Swell Map Module uses the principle of wave dispersion to estimate the time and location of the various swell events.  The results are displayed on an interactive world map.  The display shows great-circle swell propagation routes from the estimated sources to the observation location.  A variety of map projections and display features are available.

 

The Swell Map results are estimates.  Erroneous results, including swell sources over land, are possible.  As the Swell Map calculations are based on deep water linear wave theory, the estimated source locations will not be accurate for wave observations made in shallow water.  Furthermore the calculations assume a point source, so estimates of swell sources from moving storm systems can have a degree of error introduced.  Finally, the user is cautioned that numerical wave predictions do not behave as point sources and hence model data do not work well with Swell Map calculations.

 

Swell Map Features

Worldwide Coastline Database – Allows users to view their data over a high resolution NOAA NGDC GSHHS map database.

 

Multiple Projection, Customizable Maps – Users can choose between 17 different projection types, change land and ocean colors, add bathymetry data,  specify map dimensions, or freely zoom in and out using the toolbar.

 

Customizable Data Display – Users can select which Events to display, customize track line color, width, and style, all using the interactive sliding legend.

 

Swell Map Data Processing

Swell Map is activated from the Module pull-down menu.  Swell Map has 2 adjustable parameters that the user can modify.  These appear in the Swell Map Parameter Table which opens when Swell Map is launched from the Module pull-down menu.

 

Swell Map Parameter Table

These swell tracking parameters help identify specific swell events based on deep water linear wave theory.  The user can select values based on observation variability and duration of expected events.  The results of chosen settings can be inspected using the Swell Map module displays.  The two  parameters are described below.

 

Variance Threshold

This parameter controls the allowable data scatter (or variance) about the fitted line that is used to identify swell source events. The max mean square error is defined as

 

 

 

Values are set in the range of  -1,0,1,2,3, etc. Increase the value to raise the number of identified swell events.  Values of 1-4 are typical.  Fractional values are allowed.

 

Minimum Number of Records

This parameter sets the minimum number of records for a swell event to be considered valid.  For half-hourly wave data, start with a value of 5, corresponding to a 2.5 hour period.  Increasing the Minimum Number of Records will require the swell events to be active for longer time periods and decrease your output number of swell sources.

 

Swell Map Pull-Down Menu Commands

Options

 

Reprocess Data - Return to the Swell Map Parameter Table

Export to Google Earth® - Export Swell Map Event data to a KML file that can be read by Google Earth by using GOOGLE EARTH TOOLBOX functions (see details below).  The user is given the option to launch Google Earth after the KML file is saved.

Events - Submenu containing the following options for customizing Event displays. .  These options are also available on the legend.

Show All* - Set all Events in data to visible.  This option only appears in Events menu when the legend is off.

Hide All* - Set all Events in data to invisible.  This option only appears in Events menu when the legend is off.

Show/Hide Event Numbers - Toggle Event numbers on or off.

Event Information - Display available Event information in a pop-up dialog window. Multiple events can be selected at once and separate dialog windows will appear for each Event.

Zoom to Event - Automatically adjusts map to view selected Event.  Event will be set visible if currently invisible.

Zoom Visible Events - Automatically adjusts map to view all currently visible Events.

Show Only Events - Users can select which Events they would like to view.  All other Events will be set to invisible.

Edit - Submenu containing the following options for adjusting Event settings.  These options are also available for individual events on the legend.

Event Color - Adjust color of Event track line and marker.  Multiple Events can be selected.  User will be prompted to select a color for each selected Event.  Pressing Cancel will skip the color choice for that Event.

Marker Size - Adjust size of marker color. Multiple Events can be selected at once, selection method similar to above. 15 is default.

Line Style - Adjust line style of Event track lines.  Multiple Events can be selected at once, selection method similar to above. Solid line is default.

Line Width - Adjust line width of Event track lines.  Multiple Events can be selected at once, selection method similar to above. 1 is default.

Station - Submenu containing the following options for customizing the data Station

Zoom to Station - Automatically adjust map view to center on the data Station.

Station Information - Display available Station information in a pop-up dialog window.

Change Station Color - Adjust color of Station marker.  Default is black.

Change Station Size - Adjust size of Station marker. Default is 20.

Map Toolbar - Toggle the map toolbar on or off.

Map Legend - Toggle the map legend on or off.

 

Map

Projection - Submenu containing 17 different map projection types.  Projections described below.

Coastline Detail - Select detail level for map coastline.  Swell Map will automatically adjust detail level for the zoom level, up to level 3.  Level 4 and 5 are only suggested for use at close up views of the Earth. Process time is greatly increases at high detail levels.  Coastline Detail level can also be selected using the toolbar, see below.

Data - Submenu containing options for overlaying additional data onto the world map.  Currently setup for elevation data.

Hide Data - Set elevation data to invisible.

Colored Data - Set elevation data to display as colored contours.

Black Data - Set elevation data to display as black contours.

Color Filled Data - Set elevation data (ocean depths only, range not adjustable) to display in color filled contours.

Map Data Range - Adjust elevation data display range and resolution.  Smaller increments will increase map display process time.  Default is: Min: -100000, Increment: 2000, Max 100000

Land Color-  Adjust color of land masses on world map.

Ocean Color - Adjust color of bodies of water on world map.

Refresh – Round map dimensions to nearest degree and redraw current view of Swell Map keeping current settings.

Enter View - Map dimensions and coast detail level can be manually entered here.  The map will not automatically adjust for best window view or detail level when using Enter View.  If there are erroneous values the changes are discarded and the prompt will reappear.  Blank dimensions will be discarded and replaced with last values.

 

Swell Map Toolbar

 

 

Arrow - Normal cursor mode.  The legend can only be used in this mode.

Zoom Window - Zoom Window cursor mode.  Left click and hold to select an area of the map to view.

Zoom In - Zoom In cursor mode.  Left click on the map to center the map to that point and zoom in.

Zoom Out - Zoom Out cursor mode.  Left click on the map to center to map to that point and zoom out.

Pan View - Pan View cursor mode.  Left click on the map to center the map to that point.

Zoom Visible Events - Automatically adjusts map to view all currently visible Events.

View Reset - Returns map view to default view of the Earth with the data Station at the center.

Coastline Detail Level 1 – 5 Select detail level for map coastline.  Swell Map will automatically adjust detail level for the zoom level, up to level 3.  Level 4 and 5 are only suggested for use at close up views of the Earth. Process time is greatly increases at high detail levels.  Coastline Detail level can also be selected using the Coastline Detail submenu in the Map pull-down menu, see above.

Export to Google Earth® - Export Swell Map Event data to a KML file that can be read by Google Earth. This option can also be found in the Options pull-down menu, see above.

 

Swell Map Legend The Swell Map Legend displays Event numbers and colors and provides access to settings for each Event.

 

Swell Map Projection Types There are 17 different projection types available for use in Swell Map including Azimuthal, Cylindrical, Conic, and Global projections.  Miller Cylindrical is the default projection type.  More information on the different map projections is available at the M_Map website at: http://www2.ocgy.ubc.ca/~rich/private/mapug.html#p2.1

 

M_Map

 

Swell Map is built using M_Map, a mapping package for Matlab.

M_Map is available free and is provided “as is” without warranty of any kind.

Please visit the M_Map website at: http://www2.ocgy.ubc.ca/~rich/map.html

 

Global Self-consistent, Hierarchical, High-resolution Shoreline Database - GSHHS

The GSHHS database is available free online at the NOAA Nation Geophysical Data Center website:
http://www.ngdc.noaa.gov/mgg/shorelines/gshhs.html and is also included with the software.

 

GOOGLE EARTH TOOLBOX by Scott L. Davis and Jurriaan H. Spaaks is available free at the MATLAB Central File Exchange:

 http://www.mathworks.com/matlabcentral/fileexchange/loadFile.do?objectId=12954&objectType=FILE

 

 Some of its functions are provided here to work with Swell Map Module.

 

 See README.txt in folder: <path to software>\programs\SwellMap\GoodEarthToolbox

 

 GOOGLE EARTH is also available free at: http://earth.google.com/

 

 

Swell Map Module

Swell Map Legend The Swell Map Legend can display up to 27 Events at a time and provides access to settings for each Event.

 

 

Event Menu

These options are also available in the Events menu in the Options pull down menu or by right clicking on the top legend buttons as described above.

Event Information       Display available Event information in a pop-up dialog window.

Zoom to Event             Automatically adjusts map to view Event.  Event will be set visible if currently invisible.

Show Event Only         Set Event visible and all other Events will be set to invisible.

Edit Event                     Submenu containing the following options for adjusting settings for each Event.

 

     Event Color Adjust color of Event track line and marker.

     Marker Size Adjust size of Event marker color.

     Line Style Adjust line style of Event track line.  Solid line is default.

     Line Width Adjust line width of Event track line.  1 is default.

 

Swell Map