User Guide 028

17 Appendix G: Inverse Distance Interpolation

The inverse-distance interpolation also referred to as Shepard interpola-tion is given by (Shepard 1968)

$\phi ({\overrightarrow {x}})=\sum _{i=1}^{N}w_{i}\phi _{i}$

(17-1)

where the interpolation weights are given by

$w_{i}={\frac {d_{i}^{-\rho _{s}}}{\sum _{j}^{\ }d_{j}^{-\rho _{s}}}}$

(17-2)

where

$\rho _{s}$ = real and positive power parameter [-]

d = distance between the known points ${\overrightarrow {x_{i}}}$ and the unknown interpolation points ${\overrightarrow {x}}$ equal to the Euclidean norm $d=||{\overrightarrow {x}}-{\overrightarrow {x}}_{i}||$ .

In this interpolation, the weight of each point decreases with distance from the interpolated point. One advantage of the inverse-distance interpolation is the interpolation weights are independent of the interpolation function, and therefore only need to be calculated once and can be saved for computational efficiency.

18 Appendix H: Providing Sea Buoy Data to CMS-Wave

Directional spectral data collected by NDBC or CDIP buoys can be pro-cessed as alternative source for wave input to CMS-Wave. Two examples are given below using CDIP 154 and NDBC 44025 standard spectral files for December 2009.

• NDBC buoy data – run ndbc-spectra.exe (FORTRAN) to read the NDBC standard directional wave file and generate the CMS-Wave input spectral *.eng.

1. Download the NDBC standard monthly directional wave spectral file from

http://www.nodc.noaa.gov/BUOY/buoy.html (e.g., 44025_200912) - see Figs 2.3.1 to 2.3.4 for accessing NDBC spectral data from the Web.

2. In the DOS window, run ndbc-spectra.exe

3. Responding to the on-screen input, type the NDBC spectral filename

4. Type the starting timestamp (default value is 0) for saving output files

5. Type ending timestamp (default is 99999999) for saving output files

6. Type the time interval (hr) for saving output data

7. Type 2 to save the CMS-Wave *.eng and *.txt files

8. Type the CMS-Wave input spectrum filename (*.eng)

9. Type the local shoreline orientation (the CMS-Wave grid y axis) in clockwise polar coordinates (deg, positive from North covering the sea, e.g., 180 deg for St Mary’s Entrance, FL/GA, or 360 deg - the wave grid orientation angle in *.sim)

10. Type the NDBC buoy location water depth (m) and then the CMS-Wave seaward boundary mean water depth (m), e.g. Buoy 44025 has a nominal depth of 36.3 m relative to Mean Sea Level

11. Type 1 to include wind or 0 to skip the wind input information

12. Type 1 or 2 or 3 for different choice of calculated frequency bins to complete the run – see Fig 2.3.5 for running ndbc-spectra.exe in DOS.

The output files include *.txt, *.eng, *.out (time series of wave parameters at the buoy), and *.dat (time series of shoreward wave parameters at the CMS-Wave offshore boundary).

Figure G-1. NODC buoy data access website.

Figure G-2. NODC buoy data access world map.

Figure G-3. NODC buoy data access regional map.

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• CDIP buoy data - run cdip-spectra.exe (also FORTRAN code) to read the CDIP standard directional wave file and generate the CMS-Wave input *.eng file. Download the CDIP wave file from http://cdip.ucsd.edu/?nav=historic&sub=data (e.g., sp154-200912) – see Figure G- 6 to Figure G- 8.

Run cdip-spectra.exe in the DOS window similar to ndbc-spectra.exe – see Figure G- 9. Because CDIP spectral file already contains the buoy location depth information, cdip-spectra.exe will not prompt for this depth input. For processing either NDBC or CDIP data, users shall check and manually fill any data gaps in *.eng and *.txt files (using the first available spectral data from the neighboring time interval).

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