The use of ERS-1/2 Tandem interferometric coherence in the estimation of agricultural crop heights

In this study, the relationship between ERS-1/2 SAR Tandem interferometric coherence and the height of sugar beet, potato, and winter wheat is investigated using measurements of crop growth and coherence. The development of both coherence and crop height is observed to be approximately linear during the early growing season, and linear crop-specific relationships between Tandem coherence and the heights of the studied crops are derived. The coherence of all the studied crops decreases as the crop heights increase, a probable explanation for this is that as the crop grows, it screens the ground more effectively, and a greater part of the incident radar energy is backscattered from vegetation that decorrelates more rapidly than the more stable soil. The relatively dense canopies of the root crops sugar beet and potato screen the ground considerably more effectively than the cereal crop winter wheat. This study gives a strong indication that ERS-1/2 Tandem interferometric coherence is related to the height of agricultural crops, and that this relationship can be used to retrieve crop heights.