Complex sentence: Near the end of the breakwater in the fenced compound there is a tall steel frame mast housing air speed measurement devices gathering data on wind speeds at various heights for a planned offshore windfarm proposed by Northern Offshore Wind Limited.
Split into simpler sentences: Near the end of the breakwater, in the fenced compound, there is a tall steel framed mast, housing air speed measurement devices. These devices gather data on wind speeds at various heights for a planned offshore windfarm, which has been proposed by Northern Offshore Wind Limited.