The inter-year stability of ERS agricultural crop signatures (Flevoland 1993-1996)

ERS SAR imagery of agricultural crops in Flevoland over a four year period (1993-96) are studied to determine the stability of multi-temporal radar signatures. The cause of sharp rises (of several dB) in multi-temporal signatures of some crop types can often be linked to rainfall and freezing. In addition to this, there also seems to be a link between the imaging geometry and the increases in intensity. Multi-temporal signatures composed of images from different orbit tracks can look different to those derived from a single track. Model simulations of rainfall and incidence angle change confirm the plausibility of these mechanisms and emphasise their importance in quantitative parameter retrieval. The inter-year comparison also allows them to make generalised comments regarding the performance and stability of crop classification algorithms from one year to another. Only summer months are consistently identified as helping to distinguish broad-leaved (sugar beet and potato) crops from cereals (wheat and barley). There evidence that other times of the year assist in distinguishing specific crops but this evidence is not stable from one year to another