This is usually a result of two things:
- If you are relatively close to the shore, then you will probably see some reflection in the data (no easily seen by simply watching the waves but most often present).
- The approach that we are using to estimate wave directions is very good at estimate waves from two different directions at the same frequency. In fact sometimes it is too good. By being too good I mean that the reflected wave energy sometimes is estimated to be greater than the incident wave energy and thus the wave direction is reported as the reflected wave direction. This affect is a result of an imperfect method of resolving wave direction (and unlikely to have greater reflected energy than incident), but at the same time it provides you with a heads up that "hey we have some serious reflection here."
When investigating this there are two things that should be the starting point: (1) Get a map and see where the AWAC is relative to the shoreline. (2) Look at the full directional spectrum in relation to frequency and direction and try to see if there is more than one peak in the direction. Once you have done this, try and see if the angles of incident and reflected waves make sense with the angle to the shoreline.
Aside: The full directional spectrum is found in the *.WDS file and the format of this file is found in the *.WHR file.
For further reading, N4000-716 is recommended, covering how to resolve transformed wave directions near coastal structures.