A brief introduction to GNSS Reflections (GNSS-R)

GNSS-R, the use of Global Navigation Satellite Systems  (GNSS) reflected signals is a powerful and potentially disruptive technology for remote sensing: wide coverage, pas-
sive, precise, long-term, all-weather and multi-purpose.  GNSS emit very precise signals which will be available for decades as part of an emerging infrastructure resulting from
the enormous effort invested in GPS,GLONASS,Galileo and augmentation systems. Moreover, GNSS-R technologies will be mature for space applications by the time Galileo and GLONASS are fully deployed, thanks to ongoing ground, air and space research. In this short tutorial we review the basic concepts of GNSS-R, focusing on marine applications using GPS signal (the pioneering US Global Positioning System).