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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
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.
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