## 4 Results
### Effect of Scanning Angle on Foliage Profile Estimation
Figure 7: The _RMSEs_ of the foliage profiles (**a**) and the _Diff_s of the total _LAI_s (**b**) at scanning angles from 0\({}^{\circ}\) to 30\({}^{\circ}\) at 5\({}^{\circ}\) intervals (the flying altitude and pulse density are 2000 m and one pulse/m\({}^{2}\), respectively). To explore whether the optimal scanning angle is dependent on the pulse density, we estimated the forest foliage profiles from the LiDAR data at all scanning angles at pulse densities of 0.25 pulse/m\({}^{2}\), one pulse/m\({}^{2}\), and four pulses/m\({}^{2}\). The _RMSE_s and _Diff_s were all calculated, and the results are shown in Figure 7, Figure 9, and Figure 10. Figures 9 and 10 show that the _RMSE_s and _Diff_s all first decreased and then increased, and the minimum values were reached at a scanning angle of 20\({}^{\circ}\), which was the same as the results in Figure 7. Therefore, when the pulse density increased from 0.25 pulse/m\({}^{2}\) to four pulses/m\({}^{2}\), the optimal scanning angle for foliage profile retrieval at plot level remained at 20\({}^{\circ}\), which demonstrated that the optimal scanning angle was independent of the pulse density at plot level when the pulse density increased from 0.25 pulse/m\({}^{2}\) to four pulses/m\({}^{2}\). To determine if combining multiple scanning angles can improve the accuracy of foliage profile estimations, we estimated the foliage profile from the LiDAR data at all single scanning angles and combinations of scanning angles. The _RMSE_s and _Diff_s were calculated to assess the estimation accuracies. Figure 11 shows that when using a single scanning angle, the _RMSE_ at the scanning angle of 20\({}^{\circ}\) was smallest, and it was 0.17. When using a combination of scanning angles to estimate the foliage profile, the _RMSE_s of the 15\({}^{\circ}\) and 20\({}^{\circ}\), 15\({}^{\circ}\) and 25\({}^{\circ}\), and 15\({}^{\circ}\) and 30\({}^{\circ}\) combinations were all smaller than 0.17. When the scanning angles of 15\({}^{\circ}\) and 20\({}^{\circ}\) were combined, the _RMSE_ was the smallest, at 0.16. Figure 12 demonstrates that when using a single scanning angle, the _Diff_ at the scanning angle of 20\({}^{\circ}\) was 0.072, which was the smallest. When using a combination of scanning angles to estimate the foliage profile, the _Diff_ of the 15\({}^{\circ}\) and 25\({}^{\circ}\) and 15\({}^{\circ}\) and 30\({}^{\circ}\) combinations were smaller than 0.072. Figure 8: The _RMSE_s of the foliage profiles (**a**) and the _Diff_s of the total _LAI_ (**b**) at scanning angles from 0\({}^{\circ}\) to 30\({}^{\circ}\) at 5\({}^{\circ}\) intervals (the flying altitude and pulse density are 4000 m and one pulse/m\({}^{2}\), respectively). Figure 9: The _RMSE_s of the foliage profiles (**a**) and the _Diff_s of the total _LAI_ (**b**) at scanning angles from 0\({}^{\circ}\) to 30\({}^{\circ}\) at 5\({}^{\circ}\) intervals (the flying altitude and pulse density are 2000 m and 0.25 pulse/m\({}^{2}\), respectively). estimation, and the results are shown in Figure 13. Figure 13a shows the estimated foliage profiles at all flying altitudes, and Figure 13b-e show the histograms of the foliage profiles estimated at each flying altitude. Figure 8 indicates that there was little difference between the foliage profiles derived from the LiDAR data at different flying altitudes. There was no obvious regularity, and the foliage profiles derived from different flying altitudes were all similar. The _RMSEs_ of the foliage profiles and the _Diff_s of the total _LAI_s at all flying altitudes were calculated to quantitatively analyse the foliage profile retrieval results, and the results are shown in Figure 14. Figure 14a shows that the _RMSEs_ at all flying altitudes were similar, and they were all very small and between 0.16 and 0.19.