Exploration of Multi-Mission Spaceborne GNSS-R Raw IF Data Sets: Processing, Data Products and Potential Applications  
[PERSON]  
1 Institute of Space Sciences (ICE, CSIC), 08193 Cerdanyola del Valles, Barcelona, Spain, [EMAIL_ADDRESS] (E.C. ); [EMAIL_ADDRESS] (S.R. ); [EMAIL_ADDRESS] (S.O. ); [EMAIL_ADDRESS] (A.R. )12 Institute d'Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain2  
[PERSON]  
1 Institute of Space Sciences (ICE, CSIC), 08193 Cerdanyola del Valles, Barcelona, Spain, [EMAIL_ADDRESS] (E.C. ); [EMAIL_ADDRESS] (S.R. ); [EMAIL_ADDRESS] (S.O. ); [EMAIL_ADDRESS] (A.R. )12 Institute d'Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain2  
[PERSON]  
1 Institute of Space Sciences (ICE, CSIC), 08193 Cerdanyola del Valles, Barcelona, Spain, [EMAIL_ADDRESS] (E.C. ); [EMAIL_ADDRESS] (S.R. ); [EMAIL_ADDRESS] (S.O. ); [EMAIL_ADDRESS] (A.R. )12 Institute d'Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain2  
[PERSON]  
1 Institute of Space Sciences (ICE, CSIC), 08193 Cerdanyola del Valles, Barcelona, Spain, [EMAIL_ADDRESS] (E.C. ); [EMAIL_ADDRESS] (S.R. ); [EMAIL_ADDRESS] (S.O. ); [EMAIL_ADDRESS] (A.R. )12 Institute d'Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain2  
[PERSON]  
1 Institute of Space Sciences (ICE, CSIC), 08193 Cerdanyola del Valles, Barcelona, Spain, [EMAIL_ADDRESS] (E.C. ); [EMAIL_ADDRESS] (S.R. ); [EMAIL_ADDRESS] (S.O. ); [EMAIL_ADDRESS] (A.R. )12 Institute d'Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain2  
Footnote 1: email: 12 Institute of Space Sciences (ICE, CSIC), 08193 Cerdanyola del Valles, Barcelona, Spain, [EMAIL_ADDRESS] (E.C. ); [EMAIL_ADDRESS] (S.O. ); [EMAIL_ADDRESS] (A.R. )12 Institute d'Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain2
reported in the GPS/MET mission radio occultation (RO) observations in 2001 [11] and later from the Spaceborne Imaging Radar-C (SIR-C) measurements in 2002 [12], the most relevant and pioneering experience regarding GNSS-R from space came in 2003 from the UK Disaster Monitoring Constellation satellite (UK-DMC) [13]. Since then, different GNSS-R spaceborne missions have been launched, including the UK TechDemoSat-1 (TDS-1) [14], NASA's Cyclone GNSS (CYGNSS) 8-satellites constellation [15], ESA's FSSCat [16], Chinese BuFeng-1 (BF-1) A/B satellites [17], Spire Global's Lemur-2 GNSS-RO/R large constellation [18; 19], Surrey Satellite Technology Ltd's (SSTL) DoT-1 mission [20] and China Meteorological Administration's (CMA) FY-3E mission [21]. The landscape of GNSS-R space missions (as described in Section 2) shows that the potential of the GNSS-R technique has been well recognized among the scientific community after its early space demonstrations. Currently there is a good number of LEO satellites in orbit carrying dedicated GNSS-R payloads, from which different geophysical data products have been derived over ocean, land and polar ice. Most of these missions generate the delay-Doppler map (DDM) of the reflected signal as the main data product. Normally, the sampling rate of these power DDM product is 1 Hz (with 1 s coherent integration time), which corresponds to a spatial sampling resolution of 6-8 km. Meanwhile, new GNSS-R spaceborne missions and advanced instruments have been proposed or under study by different space agencies or even commercial sectors. These new missions trend to address different geophysical applications over different types of natural surface by fully exploiting the capability of the GNSS-R concept. In particular, the G-TERN mission [22] was proposed for high spatio-temporal resolution sea ice and ice sheet sensing, and the HydroGNSS mission aims to explore the potential for GNSS-R to sense hydrologically related Essential Climate Variables (ECVs) [23]. Meanwhile, with continuous evolution of GNSS constellations, there are more visible GNSS satellites in orbit and more available GNSS signals at different frequency bands.