Microsoft Word Report 11 02 Wave Power final ex appendix doc

How can the wave resource at a given location be determined? 
The ultimate activity in order to establish the wave resource at a given 
location is to deploy a wave-measuring buoy on the site and let it measure 
the waves. This is however a time consuming action since several years of 
data is required to get a data set of significant sample size. If the information 
is more urgent, and there is no time to wait for a measuring campaign to 
finish, the wave resource can be estimated by way of numerical modelling. 
Different ways to measure waves 
There are more ways than deploying buoys to measure waves. Acoustic 
instruments could be used or even satellites. The different methods are 
shortly described below. 
Wave buoys 
Wave buoys are the standard equipment for wave measurements, and they 
generally include an accelerometer and a GPS. The accuracy is fairly good; a 
typical buoy records wave heights and period with a few percents error 
margin and wave direction with a few degrees accuracy. The power supply is 
in most buoys today based on renewable energy, solar cells and back up 
batteries is the usual combination. The buoy registers samples of the wave 
elevation and directions and processes that information into directional 
spectrum, which is the ultimate wave data in order to describe a sea state. All 
other wave parameters can be derived from the directional spectrum. 
Directional spectra are composed of a wide range of frequencies and 
directions so these data sets become quite large. This spectral data is usually 
stored locally in the buoy and only statistical parameters, e.g. Hs, Hmax, Tp 
etc., are transmitted from the buoy. The detailed data can however be 
recovered, but that implies visiting the buoy on site.
Acoustic instruments 
Acoustical instruments are deployed on the ocean floor and are mainly used 
for current measurements. These devices can however also generate detailed 
wave data (directional spectrum) e.g. by letting a vertical sound ray measure 
the distance to the water surface. The accuracy of these wave measurements 
is in the same range as those performed with wave buoys.
Satellites 
Satellites are also used for measuring the waves. However, these 
measurements are not as detailed as those from buoys or acoustic 
instruments. What is actually measured is the scatter of a radar pulse that is 
sent down from the satellite. The form of the reflected pulse is used to 
determine the smoothness of the sea surface, which is proportional to the 

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significant wave height. Since satellites are devices in orbits are only 
snapshots of the wave condition registered and this information is mostly 
used to improve e.g. forecasted wave data.