## 3 Results
### Influence of RH on the Revise and RRMSE of V\({}_{\text{I}}\) Relative to V\({}_{\text{M}}\)  
The distribution of RMSE with RH for the three visibility meters (see Figure 8a) showed that the RMSE of FD increased rapidly with RH, representing the largest increase rate among the three instruments, and the most significant increase occurred when 55% \(\leq\) RH! 95%. The variations in RMSE with RH for the two sets of LT were relatively moderate. The RMSE of LT\({}_{\text{23}}\) increased slightly overall, and the increase rate was much lower than that of FD; the RMSE of LT\({}_{\text{05}}\) decreased slightly in general, with the most remarkable decline being at RH \(\geq\) 95%. For the two sets of LT, the variation trends of their RMSE were essentially the same when RH! 75%, that is, the RMSE increased with RH at low humidity and then decreased when RH reached a certain level. The variation trends diverged when RH \(\geq\) 75%. From this point, the RMSE of LT\({}_{\text{23}}\) increased continuously with increasing RH; the RMSE of LT\({}_{\text{05}}\) rapidly decreased with increasing RH, only exhibiting a slight increase when 85% \(\leq\) RH! 95%. This may have been because LT\({}_{\text{23}}\) was closer to the sea, with a distance of less than 1000 m from the seashore; thus, it was frequently affected by sea fog. When RH \(<\) 65%, the RMSE of FD was significantly smaller than that of the two sets of LT; when RH \(\geq\) 75%, the RMSE of FD was apparently larger than that of LT\({}_{05}\) and comparable to that of LT\({}_{23}\). RRMSE increased with RH for all three sets of visibility meters (see Figure 8b), and the increase was particularly prominent when RH \(\geq\) 85%. The increase rate was the largest for FD, followed by LT\({}_{23}\). When RH \(<\) 75%, the RRMSE of LT was higher than that of FD; when RH \(\geq\) 85%, the RRMSE of FD was higher than that of LT\({}_{05}\) and comparable to that of LT\({}_{23}\). The above analysis shows that the influence of RH on LT\({}_{05}\) is relatively small, while FD is significantly affected by RH. As RH increased, the increase in \(\Delta\)V and \(\Delta\)V\({}_{\rm Mdi}\) for FD was more remarkable than that for LT. At low humidity, the RMSE and RRMSE of FD were smaller than those of LT. However, when RH \(\geq\) 85%, these two values for FD were significantly larger than those for LT\({}_{05}\) and comparable to those for LT\({}_{23}\). 5.2 Influence of RH on the Distributions of the Deviation and Relative Deviation of V\({}_{1}\) from V\({}_{\rm M}\)  
The \(\Delta\)V values of LT were predominantly distributed in [\(-\)2000 m, \(-\)500 m) under each RH level, but as RH increased, the proportion of \(\Delta\)V in this interval gradually decreased, and the proportion of \(\Delta\)V in [\(-\)500 m, 500 m] gradually increased (see Figure 9a,b). At low humidity (RH \(<\) 45%), the \(\Delta\)V of FD was evenly distributed over [\(-\)2000 m, 2000 m] (see Figure 9c). With increasing RH, the proportions of the data in [500 m, 2000 m] and [\(-\)500 m, 500 m] declined rapidly, and the proportion of \(\Delta\)V lower than \(-\)2000 m continuously increased until it reached dominance when RH \(\geq\) 85%. Therefore, with increasing RH, the proportion of small deviations in the FD results decreased rapidly, and that of large deviations increased rapidly. As shown by the distribution of the difference in the \(\Delta\)V of LT\({}_{05}\) and FD under different RH levels (see Figure 9d), when RH \(<\) 65%, the proportion of small \(\Delta\)V for FD was higher than that for LT\({}_{05}\), and the proportion of large \(\Delta\)V for LT\({}_{05}\) was higher than that for FD; as RH increased, the pattern changed, with an increase in the proportion of small \(\Delta\)V for LT\({}_{05}\) and an increase in the proportion of large \(\Delta\)V for FD; by RH \(\geq\) 85%, the proportion of small \(\Delta\)V for LT\({}_{05}\) was higher than that for FD, and the proportion of large \(\Delta\)V for FD was higher than that for LT\({}_{05}\).