GNSS-R altimeter based on delay-Doppler Maps

The GNSS-R concept is a well-known spaceborne remote sensing technique that, by exploiting GNSS signals reflected from the earth, allows performing simultaneous observations of the Earth on several points over a very wide swath, very promising for applications such as mesoscale altimetry. However, for a single observation on earth, due to the intrinsic low power transmitted by the GNSS satellites, this technique provides reduced performance when compared to conventional spaceborne radars. In order to overcome this limitation, an innovative processing and retracking concept for GNSS-R altimeters based on the acquisition of the full delay-Doppler Map has been recently proposed by the authors. This differs with respect to the conventional GNSS-R processing technique, which exploits only the zero-Doppler power waveform of the DDM. The proposed processing adapts the SAR delay-Doppler concept of spaceborne radar altimeters for use in a GNSS-R system. This processing yields additional multi-look with respect to conventional GNSS-R concepts, and translates into an improvement of the altimetry performance estimated to be up to 35% for practical cases with low SNR. The present paper, after a brief introduction of the delay-Doppler altimetry processing, focuses on the performance analysis of this technique when applied to the for the reference case of the proposed GNSS-R GEROS-ISS experiment to be embarked on the International Space Station.