this PDF is about synthetic aperture radar(The basic SAR theory is conceptually simple yet when one looks into the inner workings of the
SAR processor it appears quite complicated. The most difficult part of the problem is related to
the coupling between the azimuthal compression and the orbital parameters. In the old days
when the satellite orbits were not known very accurately, one would use techniques such as
clutterlock and autofocus to derive the orbital parameters from the data. This is no longer
necessary with the high accuracy orbits available today. A standard processing sequence follows
where the first two steps are done onboard the satellite while the remaining 4 steps are done by
the user with a digital SAR processor.)