Correlated Images

All of the routines in InfoPACK assume that the pixel values in an image are statistically uncorrelated. If this requirement is not satisfied, (you are using ERS-1 PRI data, for example) the performance of the routines can be affected.

Two major sources of correlations are:

• Oversampling the signal during the image formation process (making the pixel size less than the spatial resolution).

• Transforming the image so that the pixel lattice is aligned with latitude and longitude lines of the Earth. This process, known as geo-coding, can also alter the statistical properties of the image. We recommend geo-coding after processing the image.

To overcome the problems caused by oversampling, the image should be resampled before being processed. Section 6.5 gives a detailed discussion of the effect of correlation, and how to remove it from both intensity/amplitude and complex single look imagery, both when the degree of oversampling is known and when it is not known a priori but must be estimated from the data.