**Preface**

SmallSats are changing the paradigm in Earth remote sensing, taking advantage of innovative payloads. As such, the operation of constellations of these instruments has the potential to observe the Earth's dynamic processes with a higher spatiotemporal sampling than traditional techniques. In particular, the so-called Global Navigation Satellite Systems Reflectometry (GNSS-R) is a type of L-band passive multi-static radar (as many transmitters as navigation satellites are in view) that provides a wide swath of up to 1500 km. GNSS-R spatiotemporal sampling properties could provide new process insights on mesoscale studies, wind speed determination, soil moisture content determination, vegetation water content monitoring, etc.

This reprint is intended to prompt the development of a potential virtual network of satellites, providing inter-comparable data to the scientific community, based on the new GRSS Standard for GNSS-Reflectometry. New and novel GNSS-R scientific applications, methodologies, and retrieval algorithms are the focus of this reprint, including contributions from academia, international space agencies, and private industry.

We thank all contributing authors for their interest in this project. It is our great pleasure to share this reprint with you and the wider GNSS-R community. We encourage all members of the community to contemplate and envisage the future of this remote sensing technique, and to continue working together in a coordinated manner.

> **Hugo Carreno-Luengo and Chun-Liang Lin** *Editors*
