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Oregon Inlet Tides

Two Sea-Bird tide gauges (Model SBE-26) were deployed at Oregon Inlet for measuring water elevations 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 were computed from the conductivity and temperature, depth was determined from the pressure and density. Pressure (depth) have been corrected for atmospheric pressure variations based on a barometer at the FRF, approximately 32 miles (52 km) from the inlet.

Note: Before using this data see the important information on the data quality and processing below.

These data are available through ftp as monthly ASCII columnar files, GIF and Postscript plots. The file names for the plots are in a year-month format. For example the December 2001 plot files are 200112_OItide.gif, and 200112_OItide.ps. The ASCII data files are listed by deployment number, and for December, the third deployment, this file name is OI_Tide_3.txt.

These gauges also make wave measurements at 6 hour intervals. Wave spectra were computed from 8 minute records sampled at 2 Hz. For these data go here.

These gauges are serviced approximately every 2 months. CTD casts were taken during each deployment and the data are available in ASCII format and Postscript plots.

Additional tide data are available from a NOAA tide gauge that has been in operation dating back to 1978. NOAA site.

Deployment #

Dates

1

10 Jun - 30 Aug 2001

2

30 Aug - 18 Nov 2001

3

20 Nov 2001 - 29 Jan 2002

4

29 Jan - 2 Apr 2002

5

2 Apr -



The ASCII files have column header ID's that identify the data type - year, month, day are obvious, the other ID's for the inlet (S - shallow) and outside (D - deep) gauges are:

Column ID

Description

time

Eastern Standard Time

time_t

Epoch time - number of seconds since 1 Jan 1970 @ 0000 UTC

tideS

Inlet tide elevation, m (NGVD)

tideD

Outside tide elevation,m (NGVD)

tideDif

Tide difference, m (Inlet - Outside )

tempS

Inlet gauge water temperature (C)

tempD

Outside gauge water temperature (C)

salS

Inlet gauge salinity (psu)

salD

Outside gauge salinity (psu)

denS

Inside gauge density (kg/m3 )

denD

Outside gauge density (kg/m3 )


Click here for map of gauge locations and depth.

Important: Users of this data need to understand how these data were processed and the potential errors in these measurements. There are three primary sources of error for the tide estimates: pressure sensor accuracy, survey depths at deployment, and density estimates.

Elevation errors

Error (cm)

Pressure Sensor

+/- 0.3

Survey gauge depths

+/- 2

Density

~3 (deep gauge)

~1cm (shallow gauge)



The errors associated with density estimates are believed to be about 3 cm based on collocated CTD measurements made during gauge deployments and based on daily CTD measurements made at the FRF. Since the tide gauge only measures conductivity and temperature, hence density, near the bottom it was assumed this density was constant throughout the water column. Since these gauges are located at an inlet these are times with significant stratification due to salinity or temperature. The stratification is less pronounced during high wave events where the water tends to get mixed. Thermal stratification is also reduced during the winter months. It is believed that this error is generally less than 2 cm for the offshore tide gauge in ~8m depth, and probably only a few millimeters for the inlet gauge in ~2m depth.

The inlet gauge is believed to have gone through periods of burial as is evident from extended sequences of low conductivity. For example, the December 2001 plot shows unusually low salinity during 11-14 and 17-28 Dec. During these burial events a density was calculated from an assumed salinity of 25 psu and the measured temperature. Again since this gauge is shallow the error associated with the salinity approximation would be ~1cm. The ASCII data files have the approximated density for these periods but the salinity values were left as the original low value to help indicate when this gauge was possibly buried.

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