# Performance Analysis of Ground Target Detection Utilizing Beidou Satellite Reflected Signals
## 1 Introduction  
Global navigation satellite system (GNSS) reflectometry has been widely used in the remote sensing field because of its low cost, all-weather capability, and global coverage [1, 2]. Good results have also been achieved in sea ice detection [3, 4], ocean altimetry [5, 6], sea wind retrieval [7, 8], soil moisture monitoring [9, 10], oil slicks [11], and dry snow detection [12]. The P(Y) and C/A ReflectOmeter (PYCARO), which flew on-board a stratospheric balloon, has been exploited to measure the scatterers' height fluctuations using the peaks of reflected complex waveforms [13]. In addition, the difference in the coherent-to-incoherent scattering ratio over boreal forests and lakes has also been discussed. The signal scattering over ocean surface from GPS satellites have been discussed in [14]. In the case of smooth surface, the signal-to-noise (SNR) ratio and phase information will follow the Fresnel coefficients. In the case of rough surface, the signal scatteredsimilarly at vertical polarization and horizontal polarization. Based on it, the results of polarimetric ratio over the sea ice has good performance. At the same time, the scattering properties over land have also been evaluated using SNR information, the polarimetric ratio, and the widths of the waveforms' trailing and leading edges [15]. During the balloon experiments for university students (BEXUS), the presence of 17 stratospheric balloons, which are strong coherent components of the forward scattered signal, was proven [16]. Based on the multimodal behavior of received power, the coherent scattering component from a forest was analyzed. The variability of the coherent phase samples and polarimetric measurements was compared with in situ observations to make a realistic rough characterization of the ice cover [17]. The signals reflected from this were used to monitor the complete process of sea ice formation and melting of Greenland during a seven-month period in 2012. However, most of these studies used GPS and Galileo systems, whose satellites move at the medium Earth orbit (MEO). The BeiDou system can not only provide the signal of the MEO satellite, but also the signals of the inclined geosynchronous orbit (IGSO) and the geostationary Earth orbit (GEO) satellites, which can provide stable geometry and better coverage capability in the mid- and low-latitude regions [18; 19]. With the completion of the global network of the BeiDou system in recent years, more and more research has been done in the field of remote sensing using its reflected signals. The BeiDou reflectometry software receiver has been exploited in two coastal experiments on Dishui Lake and Dayangshan Port [20], whose resulting error was 0.11 m. Coastal Typhoon observations were completed by using the ocean reflected signals from BeiDou GEO satellites [21]. The relationship between reflected waveform parameters, such as coherent time, and the ocean wind speed were analyzed in [22]. After comparing the in situ wind measurements collected during two tropical cyclones, it was confirmed that the BeiDou reflected signals can retrieve wind speed effectively. Besides that, the feasibility of coastal ocean phase altimetry and sea state observation in the frequency domain with BeiDou GEO reflected signals was proven in [23]. Because of the stable elevation of the BeiDou GEO satellite, two experiments on coastal sea ice detection were performed in Bohai Bay in China from 30 January to 4 February 2016. The results showed that the concentration of sea ice is correlated with the polarization ratio of BeiDou GEO satellites [24]. The same application was also tested in [25]. The soil moisture retrieval method was proposed based on the reflected signals from BeiDou GEO satellites, using a support vector regression machine (SVRM)-assisted method. It was found that BeiDou satellites are appropriate for use in this field [26]. The literature [27] has also investigated the feasibility of soil moisture estimation based on BeiDou B1 band interference signals.