Wave and Current Data

Waves

Wave data are collected from three different sets of instruments. The first is an array of fifteen pressure gauges, collectively referred to as gauge 3111 (gauge 111 being one of them). Directional information is computed from these gauges using a iterative maximum likelihood estimator. The second is a Baylor staff gauge (625) and a pressure gauge (641), both attached to the pier. The third is a Waverider buoy (630). Be aware that 630 was non-directional prior to November of 1996.

The results are based on each 34 minute record (of 4096 data points). The exception is the 8 Meter Array (3111) which condenses the first four records into one statistical value.

Wave height, Hmo, is an energy-based statistic equal to four times the standard deviation of the sea surface elevations. Wave height reported from the pressure gauge has been compensated for hydrodynamic attenuation using linear wave theory. Wave period is identified from the computation of a variance (energy) spectrum with 60 degrees of freedom calculated from a 34- min record. Peak wave period Tp is defined as the period associated with the maximum energy in the spectrum.

Differences in wave periods between wave gauges may be the result of wave breaking, wave reformation, the presence of multiple wave trains containing nearly equal energy, and statistical variations in spectral estimations.

Currents

Current data are collected from a Marsh-McBirney electromagnetic biaxial current meter.

Since the shoreline orientation is approximately N20W, long shore currents flow either toward 340 deg (i.e. northward) or toward 160 deg (i.e. southward). Similarly, cross-shore currents are either onshore (westward) or offshore (eastward). All current speeds are given in meters per second (m/sec). Resultant speeds and directions are determined by vector averaging the cross- shore and long shore data. Current directions indicate the direction that the current is moving towards.

Wave and current Data Files

Parameter Column

Gauge The instrument identification number.

Mean See below.

Hmo Significant wave height in meters. Computed from the 0th moment of the variance spectrum.

Tp Wave period in seconds.

Depth Total depth of water in meters. (pressure gauges only)

Tide Water variation from NGVD. (pressure gauges only)

DESCRIPTION OF MEAN COLUMN

Gage id                                 Units for "MEAN"

 630     Waverider 4 km offshore       N/A
 625     Baylor at pier end           N/A
 111     Pressure gauge in 8M depth.  Meters of water above gauge.
         900M offshore.
 641     Pressure gauge on 
         long shore bar                Meters of water above gauge.
3111     8m Array Resultant           Dir. degrees true north
3511     8m PUV Resultant             Dir. degrees true north
3411     Surf Zone PUV Resultant      Dir. degrees true north
3519     8m Current Resultant         Speed m/s
3419     Surf Zone Current Resultant. Speed m/s

Examples:

                    Mean    HmO    Tp       Depth   Tide
  921025 100  111   7.888   0.295  11.130   8.288   0.388
  921025 100  630   0.601   1.013  12.800  17.601   0.601


  Notice:  The waverider (gauge 630) has been replaced,as of Nov96, with 
  a new directional waverider(still gauge 630) which has a different format.  
  Formerly in "degrees magnetic north" the data files have been upgraded 
  to "degrees true north" on 08Sep98.


  Wave direction(8m Array and Waverider(Nov96-present))
                   Degrees  HmO    Tp
                   True N
  921025 100 3111  88.734   0.788  12.190   5.690   1.240
  961125 100  630   0.601   1.013  12.800  17.601   0.601

  Wave direction(PUV)
                   Degrees  HmO    Tp
                   True N
  921025 100 3511  88.734   0.788  12.190   5.690   1.240
  921025 100 3411  88.734   0.788  12.190   5.690   1.240


  Current Resultant
                    Sp m/s Degr    Tp
  921025 100 3519   0.230 340.537  12.190   5.690   1.240 
  921025 100 3419   0.230 340.537  12.190   5.690   1.240

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