Loading Data

Import data from wave sensors, models and internet archives

XWaves operates on non-directional or directional wave spectra in a variety of data formats.  Wind speed and direction data can also be read in for some data types.  Special formatters are included for reading data from selected commercial wave sensors, numerical wave models, and internet data archives.  Furthermore Generic MATLAB and text file formats allow the user to convert wave spectrum data from any source into a useable form.  Custom data formatters are available upon request.

 

Import Raw Data

From the File dropdown menu, mouse over Load Raw Data to see all of the available data types. Select the appropriate data type and a Verify Parameters window will appear with the default settings for that data type. Click on Modify to create your own settings in the Import Parameters Table.

 

Import Parameters Table

The Import Parameters Table is used to select and prepare raw data for loading.  The user can select the files to load, specify to use measured or estimated winds, apply data smoothing or sub-setting, etc.  The specific contents of the table vary depending on what data type are selected to load.  For example, loading Datawell Waverider *.SPT files requires the user to identify the latitude, longitude and water depth at the observation station, whereas this information is included in the Coastal Data Information Program (CDIP) raw data and not a required user input.  The selected settings are saved to a named parameter set, and can be retrieved at any time.

 

The various user inputs to the Import Parameters Table are described below. Not all of these will be available for each data type.

 

Parameter Set Name

This option allows the user to select a named set of import parameters.  If changes are made in the Import Parameters Table, the user is requested to provide a new name for the parameter set when the Select button is activated.

 

Station Location

Enter the Latitude (+N/-S) and Longitude (+E/-W) of the data in decimal degrees

 

Estimate Winds

This parameter is used to specify how the winds will be obtained for processing:

 

 Yes – Wind data will not be provided by the user, and the winds will be estimated from the input wave spectra.

 No – Wind data will be provided by the user.  Choose the wind file to be processed by using the Select button to the right.

 

If the user is providing wind data, they must reside in a MATLAB *.mat file containing the variable wind with the following 8 column-oriented data fields:

 

    Year (YYYY),  Month (MM),  Day (DD), Hour (hh),  Minute (mm), Second (mm), Wind_Direction (deg From),  Wind Speed (m/s)

 

The duration of this file must cover the time period of the wave data.  For each wave record, the wind file is searched for a matching wind record.  If no matching records exist at this time, the software will either interpolate the wind data (u and v components) to the time of the wave record or estimate the winds over large data gaps.  See Wind Data Processing below for additional details.

 

Observation Year

Enter the year that the observations were made.  This parameter is necessary for data types that do not include the year in the filename.

 

Magnetic Compass Correction (deg)

As many conventional wave sensors collect wave direction data using a magnetic compass, correction is necessary in order to rotate the wave directions relative to True North.  Most of the data formatters allow the user to input a Magnetic Compass Correction factor to facilitate this correction.  This parameter is the magnetic declination, sometimes called magnetic variation, which is the angle between magnetic north and true north. The Magnetic Compass Correction should be entered as positive east of true north and negative when west.  The input wave directions will be rotated by this angle to generate directions relative to True North.

 

The magnetic compass correction is a function of latitude and longitude and can be computed on a web page hosted by the National Geophysical Data Center:  http://www.ngdc.noaa.gov/geomag/declination.shtml.

 

 

Water Depth (m)

Enter the approximate water depth in meters at the data location.

 

Processing Method

For Datawell data select either On-Board or Off-Board data processing.  Spectra computed by the buoy software and then transmitted are considered On-Board.  Spectra computed by a base station from transmitted time series are considered Off-Board.  This designation is important as the Datawell software uses different spectral energy units for each.  All spectra will be stored in units of m2/Hz/deg.

 

First File to Process

Click Select to navigate to the first data file to process.

 

Last File to Process

Click Select to navigate to the last data file to process.  Click Process All to select all the files in the folder.

 

Select Records (OWI NetCDF only)

Click Select Records to select which records from the NetCDF file that are to be imported. A message box will ask the user to Import All Records, to View Records List in order to manually select records, or to Cancel in order to return to the Import Parameters Table.  Clicking View Records List brings up a selection box that lists all the records by date and number.  Multiple records can be selected using the left mouse click + Shift or Ctrl.  The selection box defaults to the last selected records.  After selecting records, the Import Parameters Table will update which records are selected.  Only one group contiguous records can be selected and imported at a time.

 

Angle Bins

Enter the desired number of angle bins in the output directional spectra.  Hit the Enter Key and the angular resolution for this number of bins will be computed.  Input spectra are linearly interpolated to the requested resolution.

The use of this feature can greatly reduce output file sizes and save on processing times for large data sets.  Measured data are often set at a directional resolution that is much greater than the instrument can actually resolve.  Try setting your angular resolution at 10 or 15 degrees, corresponding to 36 or 24 angle bins.

 

Smoothing Interval (h)

Enter the desired wave spectrum smoothing interval in hours.  Over this specified duration window, a running average of the input directional wave spectra will be performed.  This feature is helpful for noisy spectra, usually obtained from short time series, and will help reduce processing time.  Enter a Smoothing Interval of 0 for no smoothing.

 

Data SubSample Interval (h)

Select the desired interval in hours for record sub-sampling.  Records that fall in-between this interval will be removed.  For example, if a 3-h Data SubSamplet Interval is selected for data that is provided hourly, every third record will be saved.  Set the Data SubSample Interval to 0 to save every record.

 

Wind Data Processing

The Wave Systems routines require wind information to separate windsea from swell wave components.  If winds are not provided, the 10-m wind speed (U10) and direction (if 2D data) will be estimated based on the shape of the input wave spectra.  If wind data are provided by the user, the following two wind data processing options are available through a separate Wind Processing Options window that appears after the Import Parameters Table:

 

Estimate Winds in Data Gaps

Enter Yes to estimate winds in large gaps in the input wind data file.  The user will be prompted to specify the maximum gap duration (h) for interpolating winds. Wind information in data gaps larger that this will be estimated.

 

Wind Measurement Height

The processing routines are based on wind speeds at 10-m height (U10).  If winds are provided from a different measurement height, they will be adjusted to a neutral 10-m height following Large and Pond (1981), J. Phys. Oceanog., 11, 324-336.  Enter ‘0’ if the measurement height is unknown and no adjustments will be made.

 

 

Import Processed Data

Processed data files are files that have been previously saved from XWaves. These can be reloaded using the Open XWaves File command in the File dropdown menu. The selected file is automatically loaded into the Data View module.

When working with NetCDF data files, the user is presented with the following features and options:

 

  • File Menu: Open NetCDF file –Open and load records from a NetCDF data file.

 

  • File Menu: Save to NetCDF– Export data to a new NetCDF file.

 

  • File Menu: Subset to XWaves File – Export data from any active file (wavedat or NetCDF) to a new XWaves data file (wavedat format).

 

  • Settings Menu: NetCDF– View and adjust NetCDF data interface settings.  Toggle data processing wait bars on or off.

 

  • DataView Record Scrolling – Data View reads in only the information needed to create the existing plots.

 

 

  • Wave Systems Module – NetCDF interface provides selective record I/O to eliminate memory issues.

 

  • Spectral Fit Module – NetCDF interface provides selective record I/O to eliminate memory issues.

 

  • Evaluate Module – Select 2 NetCDF data files for a temporal correlation comparison.

 

Opening NetCDF Files

 

Click on Open NetCDF File from the File menu, navigate to the .nc file of interest, and the NetCDF Setting window will appear as seen above. This is where the user maps available attributes and variables found in the NetCDF file to what’s needed to run the software. Required fields are:

 

Frequencies  –  Array of Frequency Bins (Hz)

Sectors  –  Array of Angle Bins (deg)

2D Directional Spectrum  – Directional Wave Spectra (m2/(hz x deg)

 

XWaves Features Not Supported

The following XWaves features and Modules are not yet supported by NetCDF:

 

 

 

Note that the user has the option of exporting NetCDF data to an XWaves file (see File Menu commands above) and then having access to all XWaves capabilities for processing their data.