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Autofocusing using multiscale local correlation

Ground imaging using a Synthetic Aperture Radar (SAR) requires the knowledge of the antenna trajectory with a relative accuracy of a fraction of the wavelength upon an integration time of a few seconds. This information is not always available from inertial navigation unit especially in the airborne framework and must be recovered from the radar signal itself using the techniques known as 'autofocus.' We describe in this paper an original method designed at ONERA for the registration of looks. We show how it applies to autofocusing. It improves the map-drift algorithm making it time variant thus allowing for the correction of low frequency trajectory errors, and not only velocity bias.