Interpreting ERS SAR signatures of agricultural crops in Flevoland, 1993-1996

This paper discusses an analysis of ERS SAR imagery of agricultural crops in Flevoland, The Netherlands, over a four-fear period (1993 to 1996) to study the stability of multitemporal radar signatures from one year to the next. Direct comparisons of the multitemporal profiles of crop signatures are made to derive limits on their stability and to examine the differences between them from one year to the next. Sharp rises (of several dB) in temporal crop signatures are linked to variations in rainfall, freezing, and incident angle (due to imaging passes from different orbit tracks). Model simulations confirm the plausibility of these mechanisms and emphasize their importance for quantitative monitoring of agricultural crop development. The possibility of timing critical phases of the crop growth cycle is highlighted using field-to-field variations with particular regard to the emergence and closure of sugar beet. The interyear comparison also enables generalized comments to be made 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 crops from cereals. There is some evidence that other times of the year assist in distinguishing specific crops, but this evidence is not stable from one year to another