| Oregon Inlet Main | Tide | Wave |

Oregon Inlet Wave Measurements

Two Sea-Bird tide gauges (Model SBE-26) were deployed at Oregon Inlet for measuring water elevation and waves inside and outside the inlet. These gauges were mounted in nominal depths of 3m and 9m, respectively. These gauges record pressure (D), temperature (T), and conductivity (C). Salinity and density are computed from conductivity and temperature, depths for tide estimates are determined from the pressure and density. Density (or depth) estimates for wave processing are set to nominal values in the analysis program (listed in the table below). Errors in wave statistics from using an assumed density are negligible.

The SeaBird wave processing program, WAVES26, was used for the analysis. This program genarated wave spectra and statistics that were computed from auto-spectra and from surface wave zero-crossing analysis.

The wave data are available through ftp as ASCII files (statistics and surface wave spectra) and plots (GIF and Postscript). The file names for the plots are in a year-month format. For example the December 2001 plot files are 200112_OIwave.gif, and 200112_OIwave.ps. The data files are available in the Sea-Bird (SB) format and in columnar formats (better for spreadsheets, Matlab, IDL, ...). The ASCII data files are listed by deployment number.

For example, the second (#2) deployment these files are:

* There are two stats files for deployment #3 since wave collections were at different times, OI_Wave_3S.txt and OI_Wave_3D.txt.


These gauges were serviced approximately every 2 months - the deployment dates are listed below.


Deployment #

Dates

Nominal Temperature (C)

Nominal Salinity (psu)

1

10 Jun - 30 Aug 2001

20

30

2

30 Aug - 18 Nov 2001

20

30

3

20 Nov 2001 - 29 Jan 2002

15

30

4

29 Jan - 2 Apr 2002

10

30

5

2 Apr - (still deployed)





The wave data are 1024-points at 2 Hz recorded at 6 hour intervals, resulting in 512s (~ 8.5 minutes) records. These records are shorter than desirable for wave measurements but were limited by the memory available and the tide collection interval (wave records must be less than the tide record and a power of 2 number of points). Hovever, these wave data may be useful to identify periods of high wave energy, which may also suggest a well mixed water column and reduce the error in the assuming constant density in the tide elevation measurements. The analysis used a 10-band frequency average which was a balance between averaging enough bands to improve spectral confidence while still retaining some freqency resolution to determine wave period. For example, the period resolution for 10s waves is ~1.5s, the periods for these bands are 7.8, 9.2, and 11.3 s. The frequency resolution is 0.01953 Hz. A high frequency cutoff is set when the pressure amplitude correction (linear wave theory) exceeds 10. This is approximatly 0.34 Hz for the deep gauge and 0.7 Hz for the shallow gauge.

The spectra were computed without correcting for atmospheric pressure variations. This will have a small effect on the offshore gauge that is about 8m deep, however, for the inlet gauge the atmospheric pressure correction could be substantial relative to a 2m depth. Furthermore, as mentioned in the tide analysis section there appears to be large depth variations at the inlet gauge. To see an example spectra click here.


If there questions concerning this data please email Kent Hathaway at the FRF.