  The Global Navigation Satellite System (GNSS) has been a very powerful and
important contributor to all scientific questions related to precise
positioning on Earth's surface, particularly as a mature technique in geodesy
and geosciences. With the development of GNSS as a satellite microwave (L-band)
technique, more and wider applications and new potentials are explored and
utilized. The versatile and available GNSS signals can image the Earth's
surface environments as a new, highly precise, continuous, all-weather and
near-real-time remote sensing tool. The refracted signals from GNSS Radio
Occultation satellites together with ground GNSS observations can provide the
high-resolution tropospheric water vapor, temperature and pressure, tropopause
parameters and ionospheric total electron content (TEC) and electron density
profile as well. The GNSS reflected signals from the ocean and land surface
could determine the ocean height, wind speed and wind direction of ocean
surface, soil moisture, ice and snow thickness. In this paper, GNSS remote
sensing applications in the atmosphere, oceans, land and hydrology are
presented as well as new objectives and results discussed.
