## 3 Example Analysis
### Using the Model to Retrieve Tidal Level  
According to the model established in Section 2.1, when the frequency value of the triple-frequency combined-phase observation value of the satellite in the sea-surface reflection area is determined, the effective inversion height \(h\) can be obtained from Formula (15), and then the sea-surface height \(h_{r}\) can be obtained from antenna height h and \(h_{r}=H-h\).  
Based on the above basic theory and the tide level inversion model, the tide level of the sc02 station on 16 August and 31 August 2020 in the Friday Harbor port is inversed in this paper. In order to facilitate simultaneous interpreting with the traditional GNSS-MR tidal-level inversion method [15], a comparison is made. At the same time, GNSS-MR technology is used to retrieve the tide level of the Friday Harbor port. The results are shown in Figure 6. In the figure, the solid line is the measured tide level change curve of the tide-gauge station, the brown scattered point is the tide level value retrieved by the GNSS-MR technology, and the green scattered point is the tide level value retrieved by the algorithm in this paper. The tidal dispersion retrieved by this algorithm changes periodically with the change of the tidal level height, which shows that this method can monitor the tidal level and the GNSS-MR technology.  
By subtracting the measured tidal level from the inversion value, the inverse tidal level deviation scatter map can be obtained in Figure 7, where the horizontal axis represents the time in hours, while the vertical axis represents the inversion deviation value in meters. The brown scatter points represent the tide level inversion deviation results of the GNSS-MR technology  
Figure 8: The histogram of the statistical distribution of the tidal deviation of **(a)** triple-frequency combined inversion of the tide level method and **(b)** the GNSS-MR inversion.  
Figure 7: The inversion of the tide level by the triple-frequency combined tidal tide-inversion method and GNSS-MR, respectively. Bias represents the difference between the inversion tide point value and the measured tide point value of the tide detector; the abscissa T indicates the time of the tide level inversion.  
Figure 9: The relationship between the height of the GNSS-MR tide level inversion method/triple-frequency combined method and the tide level height of the tide gauge station.  
In this paper, root mean square RMSE and correlation coefficient \(r\) are used as the evaluation criteria for the accuracy of the tide level inversion, and the accuracy of the triple-frequency combined-phase observation tide level inversion method and the GNSS-MR tide level inversion method are evaluated, respectively. The results are shown in Table 1. The RMSE value of the inversion tide level of the triple-frequency combined-phase tide level inversion method is 16.2 cm, and the correlation coefficient with the measured tide level is 0.977. The RMSE value of the GNSS-MR tide level inversion is 15.7 cm, and the correlation coefficient with the measured tide level is 0.981. It can be seen that the inversion accuracy and the correlation coefficient of the triple-frequency combined-phase tide level inversion method are approximately the same as those of the GNSS-MR tide level inversion method, which further proves the effectiveness of the triple-frequency combined-phase inversion tide level method.