## 2 Current Status of Spaceborne GNSS-R Microsatellites
Figure 1: Development history of spaceborne GNSS-R satellite missions [[https://web.archive.org/web/20070609192647](https://web.archive.org/web/20070609192647)]([https://web.archive.org/web/20070609192647](https://web.archive.org/web/20070609192647)), [[http://merbys.co.uk/about/introduction](http://merbys.co.uk/about/introduction)]([http://merbys.co.uk/about/introduction](http://merbys.co.uk/about/introduction)), [[https://podaac.jpl.nasa.gov/CYGNSS](https://podaac.jpl.nasa.gov/CYGNSS)]([https://podaac.jpl.nasa.gov/CYGNSS](https://podaac.jpl.nasa.gov/CYGNSS)), [[https://nanosatlab.upc.edu/en/missions-and-projects/3](https://nanosatlab.upc.edu/en/missions-and-projects/3) cat-2]([https://nanosatlab.upc.edu/en/missions-and-projects/3](https://nanosatlab.upc.edu/en/missions-and-projects/3) cat-2), [[https://snap.jpl.nasa.gov/mission/description/](https://snap.jpl.nasa.gov/mission/description/)]([https://snap.jpl.nasa.gov/mission/description/](https://snap.jpl.nasa.gov/mission/description/)), [[https://earth.esa.int/eogateway/documents/20142/37627/Spire-Product-Guide.pdf](https://earth.esa.int/eogateway/documents/20142/37627/Spire-Product-Guide.pdf)]([https://earth.esa.int/eogateway/documents/20142/37627/Spire-Product-Guide.pdf](https://earth.esa.int/eogateway/documents/20142/37627/Spire-Product-Guide.pdf)), [[https://satellite.nsmc.org.cn/FY3E/html/index.html](https://satellite.nsmc.org.cn/FY3E/html/index.html)]([https://satellite.nsmc.org.cn/FY3E/html/index.html](https://satellite.nsmc.org.cn/FY3E/html/index.html)), [[https://nanosatlab.upc.edu/en/missions-and-projects/fsscat](https://nanosatlab.upc.edu/en/missions-and-projects/fsscat)]([https://nanosatlab.upc.edu/en/missions-and-projects/fsscat](https://nanosatlab.upc.edu/en/missions-and-projects/fsscat)); [[https://space.skyrocket.de/doc_sdat/fsscat.htm](https://space.skyrocket.de/doc_sdat/fsscat.htm)]([https://space.skyrocket.de/doc_sdat/fsscat.htm](https://space.skyrocket.de/doc_sdat/fsscat.htm)), [[https://nanosatlab.upc.edu/en/missions-and-projects/3](https://nanosatlab.upc.edu/en/missions-and-projects/3) cat-4]([https://nanosatlab.upc.edu/en/missions-and-projects/3](https://nanosatlab.upc.edu/en/missions-and-projects/3) cat-4), [[https://www.esa.int/ESA_Multimedia/Images/2021/09/PRETTY_CubeSat](https://www.esa.int/ESA_Multimedia/Images/2021/09/PRETTY_CubeSat)]([https://www.esa.int/ESA_Multimedia/Images/2021/09/PRETTY_CubeSat](https://www.esa.int/ESA_Multimedia/Images/2021/09/PRETTY_CubeSat)), [[https://www.esa.int/ESA_Multimedia/Images/2021/03/HydroGNSS](https://www.esa.int/ESA_Multimedia/Images/2021/03/HydroGNSS)]([https://www.esa.int/ESA_Multimedia/Images/2021/03/HydroGNSS](https://www.esa.int/ESA_Multimedia/Images/2021/03/HydroGNSS)), [[http://www.uux.cn/viewnews94839.html](http://www.uux.cn/viewnews94839.html)]([http://www.uux.cn/viewnews94839.html](http://www.uux.cn/viewnews94839.html)), [[https://sat.huiiwiki.com/wiki/%E5%A4%A9%E7%98%AE%E5%BD%AB%E6%98%F](https://sat.huiiwiki.com/wiki/%E5%A4%A9%E7%98%AE%E5%BD%AB%E6%98%F)]([https://sat.huiiwiki.com/wiki/%E5%A4%A9%E7%98%AE%E5%BD%AB%E6%98%F](https://sat.huiiwiki.com/wiki/%E5%A4%A9%E7%98%AE%E5%BD%AB%E6%98%F)), [[https://space.skyrocket.de/doc_sdat/musat-1_muon.htm](https://space.skyrocket.de/doc_sdat/musat-1_muon.htm)]([https://space.skyrocket.de/doc_sdat/musat-1_muon.htm](https://space.skyrocket.de/doc_sdat/musat-1_muon.htm)) (the rectangle in the figure represents the completed satellite mission, and the arrow represents the satellite mission still in orbit). BuFeng-1 A/B: The BF-1 A/B satellite orbits at an altitude of 579 km, with an orbital inclination of 45\({}^{\circ}\)[14]. It occasionally collects raw IF data from the GPS L1 and BDS B1I bands [21], which has been applied in carrier-phase sea surface height measurement [46]. Spire: Spire's GNSS RO satellite is equipped with instruments and antenna configurations capable of receiving reflected signals from GNSS satellites. Specifically, they are able to receive reflected signals from GNSS satellites, which are transmitted in a \"grazing angle\" (GA) manner.