THE RADIOMETRIC QUALITY OF AGRISAR DATA

The AgriSAR '86 data set for the Feltwell, U.K. 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. 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. 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.