This paper discusses aspects of the medium scale spatial variation in the characterisation of wave climate. There have been relatively few investigations of simultaneous measurement of sea states at spatial separations of the order of 1 km. However the authors feel that this is an area that deserves more consideration and this paper will hopefully provoke a discussion of why such scale variations are important. Firstly, there is increasing interest in estimating the downstream effect of array scale wave developments. Many of the studies to date have used modified wave propagation models such as SWAN or Mike21 and the question of the physical basis for using such models must be considered. One possible solution is to undertake physical measurements of absorption at an operational wave farm to determine the downstream effects of removing energy from the climate. Such physical measurements might provide the means to tune the output from conventional numerical models. Secondly, the spatial variations across a wave energy site will also influence the determination of the short term performance of WEC devices and indeed the aggregated short term output from a small farm. This paper discusses some of these issues, with some illustrating data and examines the problems of implementing any measurement and analysis program.
