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CDIP Spectral File Description
Each spectral file is composed of two parts, a header and the spectrum.
  • header - the first 10 lines of the file, which contain information about the station and data sample
  • wave spectrum - wave spectral information, generally split into 64 or 128 bands.

Sample header

File Name: sp07601199801091641     Analyzed(UTC): 1998 09/23 0103 hrs
Station Name: DIABLO CANYON BUOY
Location: 35 12.50 N 120 51.60 W   Sensor Type: Spherical Drctnl Buoy 
Water Depth(m):    23 MLLW    Sensor Depth(m): N/A      Sensor Elev(m):   23.0
Shore Normal(deg): N/A        Source File: df07600199801091708
Sample Length(s):  1600       Sample Rate(Hz): 1.282
Hs(m):  1.27 Tp(s): 15.38 Dp(deg): 246 Ta(s):  5.56

freq    Band      energy   Dmean     a1       b1       a2       b2    Check
  Hz    width     m*m/Hz    deg                                       factor

Header field descriptions

  • File Name - sp03601199812122400
    • length=19 characters, arranged as follows: file type (2 char); station (3); data set (2); year (4); month (2); day (2); hour (2); minute (2)
    • The date/time is the UTC time at the start of the first observation in the file
  • Analyzed - The UTC time the spectral file was produced.
  • Station Name - The geographical or other commonly used name for a station.
  • Location - The latitude and longitude of the station specified in degrees and decimal minutes.
  • Sensor Type - The type of instrument used to measure the waves, or the type of model used to generate predictions. A list of types follows.
    • pressure sensor
    • spherical non-drctnl buoy
    • spherical drctnl buoy
  • Water Depth - Water Depth, the measured water depth at the station location. If measured (or corrected) with respect to a datum such as MLLW, the datum is placed after the depth as in the example above.
  • MLLW - Mean Lower Low Water, a tidal datum. The average of the lower low water heights of each tidal day observed over the National Tidal Datum Epoch, a specific 19-year Metonic cycle. Only the lower low water of each pair of low waters, or the only low water of a tidal day is included in the mean. For more information visit NOAA's Oceanographic Products and Services Division.
  • Sensor Depth - Mean value, in meters, of the time series of samples used to produce the spectral wave energy. For a pressure sensor, this is the mean depth measured above the sensor during the sample.
  • Sensor Elev - The height of the primary wave sensor above the bottom in meters. For a floating (buoy), or surface piercing (wave staff) gage, this would be the same as the nominal depth.
  • Shore Normal - The direction of a vector normal to, and pointing away from, the shoreline in degrees clockwise from true North. Should only be provided/utilized when depth contours at the gauge, and between gauge and shore, are straight and parallel.
  • Source File - The file name of the time series, (or other input file type) used to produce the spectrum.
  • Sample Length - The length, in seconds, of the sample time series used to measure the waves.
  • Sample Rate - The sampling rate, in hertz, of the sample time series used to measure the waves.
  • Hs (Hm0) - Significant wave height in meters; derived from the zeroth moment of the reported energy spectrum. Hm0 = 4(m0)^.5
  • Tp* - Peak period, in seconds; inverse of the frequency with the highest energy density in the reported spectrum.
  • Dp* - Mean direction from which energy is coming at the peak period, in degrees clockwise from true North.
  • Ta - Average period, in seconds; Ta = m0/m1, where m0 and m1 are the zero'th and first moments of the reported energy spectrum.
* Note that spectral data from directional buoys obtained from CDIP before November 17, 2005 may have Tp and Dp values that differ from those now reported. This is a result of change in our processing; for more details, please refer to the change report.

Sample Spectrum

 freq   Band      energy   Dmean     a1       b1       a2       b2    Check
  Hz    width     m*m/Hz    deg                                       factor
0.0250  0.0050     0.0099   134   -0.2566   0.2701   0.3423   0.2882   2.52
0.0300  0.0050     0.0142   302    0.1914  -0.3030  -0.3758   0.0745   2.52
0.0350  0.0050     0.0240   344    0.4080  -0.1134  -0.0923   0.0571   2.52
0.0400  0.0050     0.0361   274    0.0474  -0.6519   0.6261   0.1205   2.52
0.0450  0.0050     0.0530   294    0.2616  -0.5920   0.1455   0.1924   2.52
0.0500  0.0050     0.3142   276    0.0812  -0.8333   0.3706   0.1351   1.37
0.0550  0.0050     2.2869   277    0.1154  -0.9439   0.6812   0.4330   1.33
0.0600  0.0050     6.4701   294    0.3858  -0.8730   0.7749   0.4563   1.17
0.0650  0.0050    10.7209   290    0.3292  -0.9231   0.8237   0.4645   1.19

Spectrum field descriptions

For each frequency the following estimates are reported:
  • freq - the midpoint of each band, in hertz (Hz).
  • Band width - width (in hertz) of the band over which the energy is calculated.
  • energy - wave energy density, in m*m/Hz
  • Dmean - mean wave direction within each band, in degrees clockwise from true north.
  • a1,b1,a2,b2 - coefficients of the directional Fourier series.
  • Check factor - approximately 1 for waves in deep water.
(A dot "." for any value indicates insufficient energy to calculate the parameter.)
FORTRAN format description for spectral files.

CDIP's major funding contributors are the US Army Corps of Engineers and the California Department of Boating and Waterways.
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