Forward Looking Reflections on GNSS-R

It has now been about 30 years since concepts for utilization of reflected GPS signals for remote sensing of Earth surfaces was first introduced. Today there are scientific and commercial satellites operating in low Earth orbit (LEO) collecting data that is used for monitoring ocean surface winds; observing variations in soil moisture; detecting inundation of land surfaces; capturing variations in water surface heights and more. This article provides an overview of this unexpected application of GNSS and provides some perspective on the current state of the art.