Interest in Global Navigation Satellite Systems reflectometry (GNSS-R) has grown substantially in the last few years, with the launch of several GNSS-R missions: the UK TechDemoSat (SSTL), the constellation CYGNSS (a NASA Earth Ventures mission), three Chinese GNSS-R missions (Bufeng 1A and 1B and FY3-E), ESA FSScat and multiple commercial GNSS-R CubeSats owned by Spire Global. ESA PRETTY GNSS-R CubeSat is under rapid development and is planned to be launched in 2022, while the European Agency has also approved a GNSS-R mission as its 2nd ESA Scout Mission, called HydroGNSS. Applying the interferometric reflectometry technique to the broader class of signals of opportunity (SoOps) enables measurements at almost any frequency penetrating the Earth’s atmosphere. This concept will be demonstrated by the ongoing NASA SNOOPI mission, expected to be launched in 2023.
Reflectometry is a relatively new technique in microwave remote sensing, using a bistatic radar configuration to observe the changes in signal properties of a forward-scattered digital signal. The re-utilization of SoOp, including GNSS-R, is now called GNSS+R to include non-GNSS opportunistic signals. GNSS+R has gained popularity recently, with new instruments and measurement techniques being developed to measure ocean winds and roughness, sea surface height, snow and ice properties, soil moisture, and vegetation indexes, from fixed towers, airborne, stratospheric and orbital platforms. By recycling communication satellite signals, reflectometry is not restricted to a protected spectral band, in contrast to radars or radiometers. Strong transmitted signals, and a forward scattered configuration, produce measurements with a high signal-to-noise ratio. Furthermore, the direct signal is available as a calibration source.
Because of the characteristics of the technique (cost-effective, passive, components off the shelf) and the wide range of products and applications it can produce (land parameters, ocean and cryosphere variables), it has the potential to contribute towards some of the United Nations’ Sustainable Development Goals (SDG). This session is focused on the recent advances made in GNSS-R remote sensing, to give detailed pictures about both the state of the art of modeling activities, of retrieval approaches, and of other applications for different SDGs.