Remote Sensing Simulation Of Forest Canopy Rainfall Interception Based On Thinness

The revelation of the rainfall interception function of the forest canopy plays an important role in improving the soil loss area in southern China.The canopy porosity is an important indicator to quantitatively describe the spatial shape of the canopy.Based on remote sensing methods,the canopy porosity is studied to reveal the vertical spatial porosity of the canopy and the rainfall interception function of the canopy under different rainfall intensities.It provides a theoretical basis for effectively quantifying and expressing the rainfall interception function of the forest canopy,and for precise soil erosion control.The study took Camphor and Eucommia ulmoides in Fujian Agriculture and Forestry University as the research objects.The rainfall data in the forest was collected by setting up rainfall buckets,and the three-dimensional laser scanner（TLS）was used to obtain the data to reconstruct the three-dimensional structure of the forest canopy.The index factor of permeability was used to construct a comprehensive index of tree canopy permeability under different stratification modes,and to explore and reveal the rainfall interception function of tree canopy based on the permeability.The main conclusions of canopy rainfall interception are the followings:（1）A total of 33 effective rainfalls were collected in the study,and the total rainfall range was 4.14-261mm;according to the total rainfall（within 12h）≤4.9mm is light rain,5.0-14.9mm is moderate rain,15.0-29.9mm is heavy rain,≥30.0 mm is the rainstorm as the standard to divide the rainfall grade.The rainfall frequency is 3,17,9,4,and the rainfall frequency is 9.09%,51.52%,24.24%,15.15%.The interception rates of camphor and Eucommia were light rain for 57.86%,61.75%,moderate rain for 39.92%,41.71%,heavy rain for 33.82%,30.19%,rainstorm for 26.92%,32.74%.There is a significant linear relationship between rainfall and interception;both rainfall intensity and interception have a significant exponential correlation.The average retention rate of camphor was 31.24%,and the average retention rate of Eucommia ulmoides was 34.09%.（2）The canopy permeability directly determines the penetration rainfall in the forest and affects the interception function of the forest canopy.In order to describe the influence of leaf density,distribution and aggregation on interception of rainwater,LAD and porosity were selected as the parameters to describe the degree of leaf density,and six Shannon diversity（SHDI）and landscape shape index（LSI）were selected in the landscape pattern index.The factor was used as the descriptive parameter for the spatial distribution of leaves,and a total of 8 factors were used as the index for constructing the permeability.Among them,LAD is based on the voxel canopy analysis method,and is extracted by counting the contact frequency of point clouds with different voxel side lengths:the best model voxel side length of Eucommia LAD is 76mm,and the RMSE and TA are 0.7101 m2/m2and 80.30%,respectively;The voxel side length of the best model of the camphor LAD is 65mm,and the RMSE and TA are 1.216m2/m2and 67.44%,respectively.The porosity was extracted based on the canopy point cloud model.The best model voxel side length of the porosity of Camphora camphora and Eucommia ulmoides was 70mm,and the RMSE and TA were 0.0991 m2/m2and90.86%,respectively.The voxelized point cloud model with a side length of 70mm was used as the quantitative canopy model for each landscape pattern index.（3）Considering that the canopy shape difference and canopy height have an impact on the tree canopy permeability,two models of three equal divisions and five equal divisions were used to explore the effects of different equal division modes on the canopy vertical structure permeability,combined with the factor analysis method to realize the construction of comprehensive permeability index of tree canopy.The results show that the maximum values of the monolayer permeability under the three-equal distribution mode of camphor and Eucommia are:1.385,1.338,the minimum values are:1.147,1.089,the average values are:1.266,1.204,and the coefficients of variation are:0.040,0.050.The maximum values of single-layer porosity in the five-equal division mode are:1.163,1.324,the minimum values are:0.86,1.009,the average values are:0.999,1.028,and the coefficients of variation are:0.086,0.107.The permeability model of Cinnamomum camphora is as follows:FQI（Trisection）=0.2399×f_LAD+0.3249×f_LSI+0.1883×f_SH+0.2852×f_PAF+0.3781×f_CON+0.3711×f_SHDI+0.3621×f_AI+0.3504×f_KXDFQI（Quintile Distribution）=0.2466×f_LAD+0.3245×f_LSI+0.1826×f_SH+0.327×f_PAF+0.363×f_CON+0.3574×f_SHDI+0.3519×f_AI+0.3424×f_KXDThe permeability model of Eucommia ulmoides is as follows:FQI（Trisection）=0.3545×f_LAD+0.1808×f_LSI+0.2982×f_SH+0.3698×f_PAF+0.3434×f_CON+0.3549×f_SHDI+0.3549×f_AI+0.27×f_KXDFQI（Quintile Distribution）=0.2644×f_LAD+0.3313×f_LSI+0.1852×f_SH+0.3306×f_PAF+0.3621×f_CON+0.3509×f_SHDI+0.3529×f_AI+0.3403×f_KXD（4）The rainfall interception model was constructed according to the canopy layered porosity,the results showed that:when the total rainfall is≥15mm,the two layered models of Camphora are invalid for revealing the interception law,and when the total rainfall is≥30 mm,the two types of Eucommia ulmoides the stratified model is invalid for revealing the interception law.When the rainfall grades are light rain,moderate rain and heavy rain,the three-equal division model of the canopy reveals the best law of the permeability and interception rate of Eucommiaulmoides.Themodelsare:y（28）0.131x1+0.36x2-0.993x3+1.216,y（28）0.23x1（10）0.118x2-0.1.56x3（10）1.794,y=0.443x1+0.099x2-1.427x3+1.442,R2is 0.668,0.521,0.521respectively;when the rainfall intensity is light rain and heavy rain,the canopy reveals the best law of the permeability-retention rate of camphor under the three-equal division model and the fifth-equal division model,respectively.The models are:y=0.43x1+0.079x2-1.432x3+0.488,y=-0.128x1-0.824x2-1.734x3-1.262x4-0.617x5+5.312,R2is 0.512,0.664（where xi represents the permeability of the i-th layer,where x1 is the permeability of the lower layer of the canopy）.The overall accuracy of the five rainfall interception models is above 70%.The simulation results show that the above models can effectively reveal the rainfall interception function of Cinnamomum camphora and Eucommia ulmoides,and the third layer canopy permeability has a greater contribution rate to the rainfall interception function.The permeability increases and decreases.