Starlink-Based Passive Radar for Earth's Surface Imaging: First Experimental Results

New satellite constellations for broadband Internet service emerge as promising illuminators of opportunity for the of passive radar (PR) applications. Their wideband signals, high power flux at ground level, and theoretical global availability anticipate ameliorated performance compared to preexisting satellite-based PRs. On the other hand, the constellation deployment in low Earth orbits generates favorable movements for the radar imaging of the Earth's surface. In this article, the Starlink constellation is considered for the formation of passive SAR images. The Starlink datalink concerning the data transmission from the satellite to the user's terminal is selected as the illumination signal. The users' downlink signal characteristics are studied using experimental data from a dedicated measurement campaign, confirming its suitability for radar applications. Then, the time-variant radar geometry and the passive SAR processing scheme are described. A back projection radar image formation approach is selected to tackle the complexity of the bistatic geometry. The system validation is performed in a second measurement campaign concerning dual-channel measurements using the Starlink-based PR demonstrator developed at the Warsaw University of Technology. The first Starlink-based passive SAR images are obtained under direct satellite illumination of the PR deployment area and under adjacent-cell illumination conditions. The experimental results confirm the feasibility of exploiting Starlink transmissions for the formation of passive SAR images of urban areas.