## 3 Results
### The Normal Projection Reflection Reference Surface Correction Method
#### 3.1.1 The Angle of Incidence and Emergence
Figure 4: The angles of incidence and emergence corresponding to the specular reflection points: (**a**) the angles of incidence by TDS-1, (**b**) the angles of emergence by TDS-1, (**c**) the angles of incidence by the S-C Wu method, (**d**) the angles of emergence by the S-C Wu method, (**e**) the angles of incidence by the Gravity Field Reflection Reference Surface Correction Method (GFRRSCM), and (**f**) the angles of emergence by the GFRRSCM from 21:00 31 March to 3:00 1 April 2018 (UTC). Figure 5: The difference between the angles of emergence and incidence from 21:00 31 March to 3:00 1 April 2018 (UTC), (**a**) TDS-1, (**b**) the S-C Wu method, (**c**) the GFRSCM. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & & \multicolumn{2}{c}{**TDS-1**} & \multicolumn{2}{c}{**S-C Wu Method**} & \multicolumn{2}{c}{**GFRSCM**} \\ \hline
**Angle** & **incidence** & **emergence** & **difference** & **incidence** & **emergence** & **difference** & **incidence** & **emergence** & **difference** \\
**Mean** (*) & \(2.822\times\) & \(2.469\times\) & \(-3.515\times\) & \(2.653\times\) & \(2.653\times\) & \(-5.932\times\) & \(2.653\times\) & \(2.653\times\) & \(2.653\times\) & \(-5.932\times\) \\
**Standard** & \(10^{1}\) & \(10^{1}\) & \(10^{1}\) & \(10^{1}\) & \(10^{1}\) & \(10^{1}\) & \(10^{7}\) & \(10^{1}\) & \(10^{1}\) & \(10^{7}\) \\
**Standard** & \(5618\times\) & \(4.005\times\) & \(1.834\times\) & \(4.781557\) & \(4.781557\) & \(3.978\times\) & \(4.781557\) & \(4.781573\) & \(3.978\times\) \\
**Deviation** (*) & \(10^{2}\) & \(10^{2}\) & \(10^{2}\) & \(\times 10^{2}\) & \(\times 10^{2}\) & \(10^{4}\) & \(\times\)\(10^{2}\) & \(\times\)\(10^{2}\) & \(10^{4}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The angles of incidence and emergence with the difference between them (the angle of emergence – the angle of incidence). The angle of incidence and emergence determined by the GFRRSCM and the S-C Wu method are equal in the effective numbers, and the standard deviation of the angle of incidence is slightly larger than that of the angle of emergence for both the two methods, indicating that the reflection geometric relationships determined by the two methods are very close. Compared with these two methods, the angle of incidence by TDS-1 is about 1.7\({}^{\circ}\) larger, the standard deviation is about 0.8\({}^{\circ}\) larger, while the angle of emergence is about 1.8\({}^{\circ}\) smaller, and the standard deviation is about 0.8\({}^{\circ}\) smaller. The angle of incidence and its variation by TDS-1 are larger, the angle of emergence and its variation are smaller than the other methods, which is consistent with the 6 h data results shown in Figures 4 and 5. According to the standard deviations of the angles by all the three methods, the angles of incidence vary more than the angles of emergence by varying degrees, presumably due to the difference in satellite orbit height (GPS 20,200 km, TDS-1 635 km). The distance from the GPS satellites to the specular reflection point is much longer than that from the TDS-1 satellite to the specular reflection point, so that the specular reflection point positioning error is amplified in the incidence direction compared to the reflective direction. The GFRRSCM and the S-C Wu method both have much more stable angles of incidence and emergence along the tracks than TDS-1, these two methods apparently control the amplification effect of the specular reflection point positioning error with increasing distance better than TDS-1.