The use of Global Navigation Satellite System (GNSS) signals for mesoscale altimetry was first proposed in [1]. Since then, many experiments and a couple of space missions have been carried out to validate the concept in multiple fields including not only ocean scenarios, but also land and ice [2]. The ensemble of these techniques is referred to as GNSS Reflectometry (GNSS-R). The most complete observable of these techniques is the so-called Delay Doppler Map (DDM), which is the 2D cross-correlation between the reflected signal and a reference one at different Doppler frequencies. In the conventional method (cGNSS-R), the reference signal is a clean replica of the transmitted one, whereas in the interferometric technique (iGNSS-R), the reference signal is the direct onesignal itself.

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