%0 Report
%F 6325
%T Detection of changes in the backscatter from agricultural plants using agriSAR 86 data
%D 1987
%9 RPQ
%A Quegan, S.,
%A Yanasse, Corina da Costa Freitas,
%C São José dos Campos
%K AgriSAR, dataset.
%X The AgriSAR 86 dataset, incorporating meteorological, crop, ground-truth, corner reflector and image data for the Feltweell, UK, test-site is assessed for its ability to provide information on the spatial and temporal variation of backscatter from growing crops. The image data is shown to contain several sources of radiometric distortion which affect any attempt at image calibration. Of these, the simplest to correct is that caused by range interpolation in the amplitude data. All interpolated pixels should be discarded from the amplitude data supplied by CNES. Measurements made without first performing this correction are related to the correct values by an expression involving both additive and multiplicative terms. Correction from slant range to ground range is comparatively straightforward. Effects due to variations in antenna pattern, in the range and azimuth direction, require assumptions about the angular variation of the backscatter of crops and statistical homogeneity of ground cover before they can be removed. The properties of system noise appear complicated and are not yet properly characterized, but interfere with corrections for the antenna pattern. Correlation properties of the data appear to vary little between images, and hence the standard errors associated with sample statistics are comparable between images. Offsets in the two channels of the complex data also interfere adversely with antenna pattern corrections. The size of these offsets cannot be estimated reliably from the AgriSAR amplitude data, and complex data should be supplied as a standard product. No sound basis for inter-image comparison has been found. As a result, only qualitative conclusions about the multi-temporal behaviour of the backscatter from crops are possible. Cereals and sugar beet appear to display different backscatter signatures with incidence angle. The statistical separability of wheat and sugar beet varies with time and incidence angle; the separability of wheat and barley varies with time but not incidence angle. Backscatter from cereals appears to display greater spatial variability than from sugar beet. Individual fields show great apparent variation in their multi-temporal behaviour, much of which can be attributed to the sample statistics, but appears to be real at least for winter wheat.