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42. Temporal averaging

Another approach in image filtering is presented here. This simple technique can be called temporal averaging. It has the advantage of reducing the speckle without looing spatial resolution: the contrary is the case of multilooking.

A subscene from Flevoland/The Netherlands has been used. The ERS SAR image to the left is the acquisition of 23 May 1993. To the right is a pixel by pixel averaged image of a data set consisting of 11 superimposed SAR scenes of that year (one each month with the exception of July).

As a result, fields become more homogeneous and their boundaries are better defined. Point-targets are enhanced, rendering the image much more focused.

Such simple techniques can be applied to improve spatial resolution, in the case high resolution optical data are not available or can not be afforded. It is required as input for the extraction of field boundaries in order to segment SAR images. The scope is to extract mean-values and other statistical parameters of each field of individual scenes for subsequent classification.

A more general application is its use in mapping, for the detection and interpretation of smaller objects.

(M.Mangolini, ESA/ESRIN, now at Aerospatiale Cannes)