ABSTRACT
BRCS Bistatic radar cross section CHAMP Challenging minisatellite payload COSMIC Constellation observing system for meteorology,
ionosphere, and climate CYGNSS Cyclone Global Navigation Satellite System DMC Disaster monitoring constellation ESA European Space Agency GEROS-ISS GNSS re©ectometry, radio occultation and scat-
terometry onboard the International Space Station GGOS Global geodetic observing system GNSS Global Navigation Satellite System GNSS-R GNSS re©ectometry GNSS-RO GNSS radio occultation GPS Global positioning system GRACE-A Gravity recovery and climate experiment IAG International Association of Geodesy IERS International Earth Rotation and Reference
Systems Service IGS International GNSS Service ILRS International Laser Ranging Service IMU Inertial measurement unit ITRF International Terrestrial Reference Frame IVS International VLBI Service for Geodesy and
Astrometry LEO Low earth orbit LHCP Le¬-hand circularly polarized
LNA Low-noise ampli¦er NASA National Aeronautics and Space Administration PARIS Passive Re©ectometry and Interferometry System PDF Probability density function PNT Positioning, navigation, and timing PRN Pseudo random noise RHCP Right-hand circularly polarized SAR Synthetic aperture radar SSP Specular scattering point SSH Sea surface height STD Standard deviation SWH Signi¦cant wave height SWP Signi¦cant wave period TPL Total path length UNSW University of New South Wales
Investigating the use of re©ected Global Navigation Satellite System (GNSS) signals for remotely sensing the earth’s surface was initiated about two decades ago (Martín-Neira 1993). Remote sensing based on processing and analyzing re©ected GNSS signals is commonly termed GNSS re©ectometry (GNSS-R). When using the GNSS-R technique to build a remote sensing system, only the receiver needs to be designed and manufactured. Ÿe receiver platform (static or mobile; land-based, aircra¬, or satellite) needs to be selected based on the speci¦c application. In the case of an aircra¬ or satellite platform, the direct signal is
Acronyms and De¦nitions ................................................................................................................ 493 24.1 Introduction ............................................................................................................................ 493 24.2 Satellite Missions Related to GNSS Remote Sensing ......................................................... 494 24.3 Ocean Observation ................................................................................................................. 495
24.4 Land Applications ................................................................................................................... 503 Soil Moisture • Forest Change Detection
24.5 Challenging Issues and Future Directions ......................................................................... 505 24.6 Conclusions.............................................................................................................................. 506 References ............................................................................................................................................ 506
received via a zenith-looking right-hand circularly polarized (RHCP) antenna, while the re©ected signal is received through a nadir-looking le¬-hand circularly polarized (LHCP) antenna. Ÿe reason for such an antenna selection is that the GNSS signals are designed as RHCP; however, when re©ected over a ground surface, they are changed to be LHCP. In the case of a land-based platform, either two antennas are used to receive the direct and re©ected signals separately or a single antenna is used to capture both the two signals.
