With an array of three radars the elevations of the sea surface is measured at three positions. Knowing the slopes and the phase relations, the directional spectrum can be accurately calculated. Radac is the only company that brings this technology to the market.
The directional system consists of three downward-pointing radars. Depending on the set-up, all are perpendicularly pointed downwards or one/two are tilted. We recommend the one-point array (3) for most applications. All three radars are mounted in the one-point frame. One radar points downwards, and the other two are tilted under an angle of 15 degrees. See visualisation below.
Wavelengths are optimally monitored with 3 to 30 times the array size. For example, if the wave radar system is mounted at a 18.6 m height, the footprints of the radars are five meters apart. So the optimal measurements are between 15m and 150m wave length (3-10 sec period).
Other, less used options are the three-point array (1) with three downward pointing radars and the line array (2) with one radar is tilted. See image below.