## 4 Simulation Experiment
### Experimental Results
#### 4.2.2 INS + LEO2 + Unbiased Altimeter and No Altimeter Scenario Experiment under Adjacent Tracks  
According to the parameter settings in Tables 1-3, in adjacent orbits, the experimental results of the INS + LEO2 switching + unbiased altimeter algorithm and the INS + LEO2 switching algorithm in adjacent orbits are shown in Figure 6. Similarly, as a comparison, we also included the standard INS + LEO2 switching navigation and positioning algorithm, and the standard INS + LEO2 switching + altimeter navigation and positioning algorithm as a reference.  
From Figure 6 we can see that, in addition to effectively suppressing the divergence of INS, the INS + LEO2 + unbiased altimeter algorithm in adjacent orbits can also suppress the error divergence problem of the INS + LEO2 switching algorithm under a longer switching time, especially when the switching time is 90 s. The final trajectory error statistical results of the two algorithms at 60 and 90 s are shown in Figure 7.  
From Figure 7 we can obtain that, with the aid of the altimeter, when the switching time is 60 s, comparing with the INS + LEO2 switching algorithm, the INS + LEO2 switching + unbiased altimeter navigation and positioning algorithm in longitude, latitude and altitude's errors improve by 50.50%, 37.55%, and 99.70%, respectively, and the corresponding standard deviation performance values improve by 59.93%, 54.77% and 94.25%, respectively. It can be seen that due to the addition of the altimeter, the new algorithm has the most obvious improvement in height error, this result is consistent with the analysis result in Section 2.1.2, and we will not analyze it in detail here.  
#### 4.2.2 INS + LEO2 + Unbiased Altimeter and No Altimeter Scenario Experiment under Adjacent Tracks  
According to the parameter settings in Tables 1-3, in adjacent orbits, the experimental results of the INS + LEO2 switching + unbiased altimeter algorithm and the INS + LEO2 switching algorithm in adjacent orbits are shown in Figure 6. Similarly, as a comparison, we also included the standard INS + LEO2 switching navigation and positioning algorithm, and the standard INS + LEO2 switching + altimeter navigation and positioning algorithm as a reference.  
From Figure 6 we can see that, in addition to effectively suppressing the divergence of INS, the INS + LEO2 + unbiased altimeter algorithm in adjacent orbits can also suppress the error divergence problem of the INS + LEO2 switching algorithm under a longer switching time, especially when the switching time is 90 s. The final trajectory error statistical results of the two algorithms at 60 and 90 s are shown in Figure 7.  
From Figure 7 we can obtain that, with the aid of the altimeter, when the switching time is 60 s, comparing with the INS + LEO2 switching algorithm, the INS + LEO2 switching + unbiased altimeter navigation and positioning algorithm in longitude, latitude and altitude's errors improve by 50.50%, 37.55%, and 99.70%, respectively, and the corresponding standard deviation performance values improve by 59.93%, 54.77% and 94.25%, respectively. It can be seen that due to the addition of the altimeter, the new algorithm has the most obvious improvement in height error, this result is consistent with the analysis result in Section 2.1.2, and we will not analyze it in detail here.