7.7 Wave Heights

This wave-height data set contains three data variables (all variables expressed in meters): the maximum significant wave height, the 20-year mean wave height, and the standard deviation of the mean). This data set was originally obtained from published documents of the Coastal Engineering Research Center (CERC), U.S. Army Corps of Engineers, Wave Information Study (WIS). In the study CERC calculated wind speeds from station histories, National Weather Service surface charts, surface pressure data, ships-at-sea observations, and monthly air-sea temperature gradients, in a 3-phase process. Phase 1 hindcasted wind speeds/directions for each 120 nautical-mile-long segment while Phase 2 hindcasted wind speeds and deep ocean waves for a 30 nautical-mile spacing (Hubertz et al. 1992). In Phase 3, wind data were input into a transformation model that hindcasted near-shore wave heights for 10 nautical-mile-segments of the West Coast (Jensen 1989; Corson et al. 1987).

The 10 nautical-mile-segment data were originally received as point data which included longitude and latitude coordinates, maximum significant wave height, 20-year mean wave height, and the standard deviation of the mean wave height. To transfer this point data into the 0.25° longitude by 0.25° grid cells used in this NDP the following methodology was used:

  1. The longitude/latitude coordinates were read into ARC/INFOTM to produce a point coverage. This point coverage was then plotted over the 1:2,000,000 digitized U.S. West coastline and checked for reasonableness.
  2. 1.0° was added to and subtracted from the original longitude coordinates to produce a line segment coverage which defined each 10 nautical-mile line segment along the West Coast.
  3. The ARC/INFO BUFFER command was used on the 1:2,000,000 digitized line segment coverage, to form a polygon of the study area.
  4. The polygon coverage produced in step 3 was read into ARCEDIT, where it was joined with the line segment coverage produced in step 2. All errors and discrepancies were corrected, and a final polygon coverage defining each 10 nautical-mile segment along the U.S. West Coast was produced.
  5. The ARC/INFO IDENTITY command was then used to transfer the polygon data produced in number 4 above onto the 1:2,000,000 digitized line segments used in this NDP.
  6. Finally, the ARC/INFO IDENTITY command was used once more to transfer the 10 nautical-mile line segment data into the 0.25° longitude by 0.25° grid cells used in this NDP.

The WIS data variables (i.e., maximum significant wave height, 20-year mean wave height, and the standard deviation of the mean) were transferred during this overlay process and are included within this NDP. Figure 7 illustrates this transformation process.