Comment by transpute

"SARLink: Satellite Backscatter Connectivity using Synthetic Aperture Radar" (2024), https://arxiv.org/abs/2402.09682

  SARLink is a passive satellite backscatter communication system that uses existing spaceborne synthetic aperture radar (SAR) imaging satellites to provide connectivity in remote regions .. As the first technique for passively sending information bits from the ground to a SAR satellite — and with some SAR systems offering open-access data — this system could enable anyone to send information without expensive licenses or subscriptions. 

  Thus, it provides an accessible way of sending messages in areas without connectivity or in censored environments where active radio transmissions cannot be used. Furthermore, SARLink requires no modification of the satellite infrastructure.. We demonstrate our system using the European Space Agency (ESA) satellite Sentinel-1A, as the data is freely available and the system regularly images all the land on Earth .. a 5.5 ft by 5.5 ft modulating corner reflector could send 60 bits every satellite pass, enough to support low bandwidth sensor data and messages.