A 10 m spatial resolution Land Form Profile Digital Terrain
Model (DTM) acquired from the Ordnance Survey [31] showed that
terrain slopes varied from 2 to 15%. However, with the exception of
a few fields in the 2011 crop survey, none of the fields in 2009 and
2013 crop survey exceeded the critical threshold of 7% slope. Only
slopes of 7% or higher would be significant enough to impact on the
crops' spectral signatures [32].