Triaxys Wave Buoy Measurements
P.A. Work, School of Civil and Environmental
The numbers can be found here. The first link is for cumulative files, with one line per record, organized by year. Directional spectra for each instance of time is in a unique file. Formats described below.
The primary goal of the project described here is to provide real-time, nearshore, directional wave data to any and all interested users. There are a number of ways to collect this type of data, but after considering costs, logistics, etc., it was concluded that a wave buoy with built-in telemetry would be the most appropriate choice. A Triaxys wave buoy was purchased from Axys Environmental Systems (www.axystechnologies.com).
Figure 1. Triaxys buoy, deployed on July 29, 2004.
The buoy contains several accelerometers and angle sensors that are used to compute wave characteristics, including directional and non-directional spectra, and several estimates of wave height and period. Both time domain and spectral analysis techniques are employed. The buoy also contains a GPS receiver to determine its position, solar panels for recharging internal batteries, a navigation light, and an Iridium satellite telephone system for telemetry. It is configured to sample at 4Hz, for 20 minutes, compute wave characteristics by both time domain and spectral techniques, and report once per hour. Data are ultimately delivered via a standard phone line to the GT-Savannah campus.
The buoy was deployed on July 29, 2004 from the Skidaway Institute of Oceanography research vessel R/V Savannah.
Data Formats
These are the basic wave statistics likely to be of interest
to the greatest number of users. One line in the file is provided for each record received.
The buoy does both time domain and spectral analysis to determine wave
characteristics, and as a result, there are quite a few parameters provided.
The significant wave height, Hs, and Hmo
wave height are the most commonly used values by laypeople and for engineering.
They are typically about the same value. Hs represents
the average of the highest 1/3 of the waves, and typically matches up with most
visual estimates of wave height. Some of the parameters are self-explanatory;
I'll explain all of them briefly below.
Note: to compute meters to feet, multiply value in meters by 3.28. Values in red are computed via time-domain analysis; remainder come from spectral analysis.
|
Column |
Contents |
Units, explanation |
|
1 |
Buoy ID |
|
|
2 |
File type |
Wave |
|
3 |
Buoy time |
yyyymmddhhmm, GMT |
|
4 |
Buoy ID |
|
|
5 |
Lat, Long (occasionally shows as 'NoReport') |
ddmm.mmmm North, ddmm.mmmm West, from GPS |
|
6 |
# Zero-crossings |
used to compute wave period in time domain |
|
7 |
Avg. Wave Height, Hmean |
meters |
|
8 |
Mean spectral period, Tz |
seconds; Tz=sqrt(m0/m2) |
|
9 |
Maximum wave height, Hmax |
meters; max in record |
|
10 |
Significant wave height, Hs |
meters |
|
11 |
Significant period, Ts |
seconds |
|
12 |
H10 |
Average height of largest 10% of waves, meters |
|
13 |
T10 |
Average period of longest 10% of waves, seconds |
|
14 |
Mean wave period |
seconds |
|
15 |
Peak period, Tp |
seconds, period of peak of energy spectrum |
|
16 |
Tp5 |
seconds; peak period computed by READ method |
|
17 |
Hmo wave height |
meters; Hmo=4.0*sqrt(m0) |
|
18 |
Mean magnetic direction |
Degrees; direction from which waves are coming, w.r.t. magnetic north |
|
19 |
Mean spread |
degrees; a measure of how many wave directions are present at a given time |
|
20 |
Mean true direction |
degrees; direction from which waves are coming, w.r.t. true north |
|
21 |
Wave energy period, Te (not reported after 4/05) |
Te=M(-1)/M(0) |
|
22 |
Wave steepness |
Wave height over wavelength |
File format follows. These files describe buoy programming and status but do not include wave data. One line is provided per record received.
|
Column |
Contents |
Units |
|
1 |
Buoy ID |
|
|
2 |
File type |
|
|
3 |
Date, time |
yyyymmddhhmm, buoy time (GMT) |
|
4 |
Buoy ID |
|
|
5 |
Lat, long (occasionally shows as 'NoReport') |
ddmm.mmmm North, ddmm.mmmm West |
|
6 |
Surface water temp |
degrees C (degrees F = 9/5 * degrees C + 32) |
|
7 |
|
Volts |
|
8 |
Sampling rate |
Hz |
|
9 |
Samples per channel |
|
|
10 |
Acquisition interval |
minutes |
|
11 |
Transmission interval |
minutes |
|
12 |
Max. allowed transmission attempts |
|
|
13 |
Triaxys S/N |
|
|
14 |
Gpuc EPROM version |
|
|
15 |
PC104 EPROM version |
|
|
16 |
Boot times |
|
|
17 |
Status code |
0 or 1 |
|
18 |
Solar current |
amps |
|
19 |
Magnetic variation |
degrees; from GPS |
|
20 |
Acquisition duration |
minutes |
|
21 |
Mode |
|
Buoy Non-Directional
Spectrum Data
One record (line) is provided per burst of data. Energy is defined in units of m^2/Hz for each frequency bin in the spectrum.
Buoy Directional Spectrum Files
Similar to the non-directional files described above, except that these files describe energy vs. direction and frequency, and each record (point in time) is saved to a unique file. File format is defined within each file.
Buoy maintenance log
can be found here.
Page created August 28, 2004 PAW
Last modified September 27, 2006 PAW