## 1 Introduction  
The continuous development of satellite navigation technology and the increasing number of satellite constellations have brought new opportunities for Global Navigation Satellite System reflectometry (GNSS-R). As an emerging passive remote sensing technology, it was first proposed in 1988 as bistatic scatterometry [1]. After continuous development over time, GNSS-R technology was first proposed for ocean altimetry in 1993 [2], and its feasibility has been proven through many ground-based and airborne experiments [3,4]. GNSS-R can be divided into ground-based GNSS-R, airborne GNSS-R, and spaceborne GNSS-R based on the installation location of the GNSS receiver. Compared with ground-based GNSS-R and airborne GNSS-R, spaceborne GNSS-R technology has unique advantages such as a short revisit period, high spatiotemporal resolution, and low observation cost. In addition, spaceborne GNSS-R uses L-band GNSS signals that can penetrate clouds and heavy rain [5], making it capable of all-weather observation. The Disaster Monitoring Constellation (DMC), a low-Earth-orbit satellite constellation launched by the UK in 2003, first demonstrated the feasibility of spaceborne GNSS-R [6]. The successful launch of TechDemoSat-1 (TDS-1) in the UK in 2014 facilitated further research on spaceborne GNSS-R, such as sea surface height measurement [7], sea ice detection [8], ice sheet height measurement [9], and soil freezing and thawing [10]. However, the sparse data coverage and calibration issues of TDS-1 limited its data availability. The Cyclone Global Navigation Satellite System (CYGNSS) launched by the United States in 2016 was an important milestone in spaceborne GNSS-R. It is a satellite constellation consisting of eight low-Earth-orbit satellites, mainly responsible for monitoring tropical cyclones [11]. In addition, the successive launch of various spaceborne GNSS-R missions, such as Spain's 3 Cat-5 A/B (FSSCat) [12], the European Space Agency's PRETTY [13], China's BuFeng-1 (BF-1) A/B [14], Fengyun-3 series satellites [15], Tianmu-1 constellation [16], and the Jilin-1 wide range 01B satellite (J1-01B) [17], and Muon Space (Muon) in the United States [18], as well as the upcoming launch of HydroGNSS [19], demonstrate the enormous potential of spaceborne GNSS-R technology. The current spaceborne GNSS-R technology has been widely applied in various fields such as ocean [20] and land [16]. However, most studies are based on the generation of delay Doppler maps (DDMs) of direct and reflected signals as the main data products (referred to as level 1 or L1 data). The sampling rate of these power DDM products is usually 1 Hz (coherent integration time of 1 s), corresponding to a spatial sampling resolution of 6-8 km. However, in addition to standard data products, in order to explore other possible GNSS-R applications, optimize future spaceborne GNSS-R instruments, and develop new GNSS-R applications, some spaceborne GNSS-R missions also collect a large amount of raw intermediate-frequency (IF) signals, which are bit streams of raw signal samples recorded after analog-to-digital converters (ADCs) and prior to any onboard digital processing [21]. At present, the raw IF data of spaceborne GNSS-R has shown great potential in many geophysical applications and has provided important theoretical support for the design and optimization of spaceborne GNSS-R instruments. The detailed processing process can be found in references [21,22]. [PERSON] et al. have conducted extensive and in-depth research on the processing of spaceborne GNSS-R raw IF signals and their related applications. In 2017, [PERSON] et al. [23] achieved the first phase height measurement of sea ice using TDS-1 L0 raw samples, which showed a good consistency with the mean sea surface (MSS) model, with a root mean square difference (RMSD) of 4.7 cm.