Polar Wave Spectra

 

This is a place holder for soon to follow instructions on the use of polar wave spectra plots for understanding the seaway and for setting up optimum routing corrections for waves, including how to generate the plots with our new, free 

 Polar Wave Spectrum Plotter app

get the spectra data at this custom link we made

NDBC Buoys with Spectra Data

Thanks to the staff at NDBC for providing notes on the computation (References).

________________________

INSTRUCTIONS

1) Enter the NDBC buoy no, such as 41010

2) That will generate the link to the spectra data on the right

3) Click the link below that line to open that page in a new tab.

4) cmd+A or ctrl+A to select the full set of data, the cmd+C or ctrl+C to copy it

5) Paste it into the space provided

6) Click plot pasted data, which would typically load 5 days, with data every 30 min. This may vary with buoy.

7) The slide bar steps through the data.

Here is a sample of what the data should look like 

Not: period (sec) = 1/frequency(Hz)

YYYY MM DD hh mm bands
freq bandwidth energy r1 r2 alpha1 alpha2
2026 06 27 22 50 46
0.033 0.005  0.000 999.00 999.00 999 999 = 30s period
0.038 0.005  0.000 999.00 999.00 999 999
0.043 0.005  0.000 999.00 999.00 999 999
0.048 0.005  0.000 999.00 999.00 999 999
0.053 0.005  0.000 999.00 999.00 999 999
0.058 0.005  0.000 999.00 999.00 999 999
0.063 0.005  0.000 999.00 999.00 999 999
0.068 0.005  0.000   0.27   0.53 120 112 = 14.7s period
0.073 0.005  0.043   0.43   0.49 116 116
0.078 0.005  0.100   0.59   0.18 104 100
0.083 0.005  0.100   0.38   0.21 116 176
0.088 0.005  0.143   0.35   0.27 112 156
0.093 0.005  0.315   0.63   0.35 108 108
0.100 0.010  0.529   0.85   0.68 108 108
0.110 0.010  0.958   0.87   0.67 124 124
0.120 0.010  1.430   0.88   0.61 120 124
0.130 0.010  1.301   0.91   0.76 128 128
0.140 0.010  0.758   0.84   0.55 124 124
0.150 0.010  1.115   0.91   0.73 112 112
0.160 0.010  0.601   0.85   0.63 128 132
0.170 0.010  0.601   0.86   0.57 128 128
0.180 0.010  0.586   0.88   0.66 128 124
0.190 0.010  0.529   0.82   0.46 132 132
0.200 0.010  0.300   0.69   0.08 144 168
0.210 0.010  0.300   0.80   0.42 136 140
0.220 0.010  0.157   0.75   0.38 128 136
0.230 0.010  0.129   0.68   0.19 152 148
0.240 0.010  0.200   0.72   0.23 136 156
0.250 0.010  0.086   0.61   0.46 124  96
0.260 0.010  0.100   0.67   0.05 140 128
0.270 0.010  0.043   0.73   0.33 128 136
0.280 0.010  0.057   0.72   0.30 132 120
0.290 0.010  0.043   0.61   0.10 156 172
0.300 0.010  0.057   0.76   0.41 156 160
0.310 0.010  0.014   0.55   0.21 132  84
0.320 0.010  0.043   0.69   0.25 160 184
0.330 0.010  0.014   0.66   0.42 160 180
0.340 0.010  0.029   0.55   0.14 144 188
0.350 0.010  0.014   0.66   0.30 148 124
0.365 0.020  0.014   0.41   0.21 164 196 = 2.7s period
0.385 0.020  0.000   0.48   0.46 208 220
0.405 0.020  0.000   0.57   0.47 144 136 
0.425 0.020  0.000 999.00 999.00 999 999
0.445 0.020  0.000 999.00 999.00 999 999
0.465 0.020  0.000 999.00 999.00 999 999
0.485 0.020  0.000 999.00 999.00 999 999

All 9s means no data for those specs. We only plot 4s to 25s.

Back soon with notes on what the plots show and how we can use them.

Periods of 3 to 8 sec are waves (global mean ~ 5s) ; periods over 10 sec are swells, with global mean of about 11s... but with large variations on ocean and season (~8 to 18s). 

Note that not all NDBC buoys have spectra data. Ones we know about are in the interactive link above.

___________________

References

NDBC Technical Document 03-01:
Nondirectional andDirectional WaveData AnalysisProcedures 

See also:  https://www.ndbc.noaa.gov/faq/measdes.shtml Section on Spectral Wave Data.

See also SOFAR Spotter Buoy Reference Manual