基于4-Scale模型的人工林郁闭度遥感估测

【目的】为了寻找受区域影响较小、精度较高且鲁棒性较好的郁闭度遥感估算模型，采用4-Scale几何光学模型估算人工林树冠孔隙率及郁闭度。【方法】选择内蒙古旺业甸林场和广西高峰林场为实验区，首先对4-Scale模型进行参数敏感性分析，模拟林分在不同敏感性参数下的树冠孔隙率P_vg＿c(树冠为刚体时的冠间孔隙率)和P_vg(考虑树冠内部孔隙的孔隙率),建立P_vg＿c、P_vg与敏感性参数的一一对应关系数据库。其次，根据数据库建立P_vg＿c和P_vg与敏感性参数的统计关系模型。然后根据获得的敏感性参数估算P_vg＿c和P_vg,进而估算林分郁闭度。最后，分别采用样线法与鱼眼相机测定法测量的郁闭度检验基于P_vg＿c和P_vg估算的林分郁闭度。【结果】基于P_vg＿c和P_vg估算的人工林郁闭度精度分别为88.17%和92.8%。P_vg＿c

Remote sensing estimation of plantation canopy closure based on 4-Scale model

【Objective】 Canopy closure is important for forest management planning. To find methods and models for estimating canopy closure that are less affected by the region, with higher accuracy and better robustness, the study adopted a 4-Scale geometric-optical model to estimate the canopy closure of plantations. 【Method】 Wangyedian Forest Farm in Inner Mongolia and Gaofeng Forest Farm in Guangxi Autonomons Region were selected as the study areas. First, a parameter sensitivity analysis of the 4-Scale model was performed, and the canopy gap fraction P_{vg_c} (the gap fraction when the canopy was a rigid body) and P_vg (the gap fraction of the gaps in a crown were considered) under different sensitivity parameters were simulated. Then, a one-to-one correspondence database of P_{vg_c}, P_vg and the sensitivity parameters was established. Second, statistical relationship models between P_{vg_c} and P_vg and the sensitivity parameters were established based on the database. Then, P_{vg_c} and P_vg were estimated based on the sensitivity parameters, and the stand canopy closure was estimated. Finally, the canopy closure measured by the transects and the fish eye camera measurement method were used to test the canopy closure based on P_{vg_c} and P_vg respectively. 【Result】 The accuracy of plantation canopy closure estimated by P_{vg_c} and P_vg was 88.17% and 92.8%, respectively. P_{vg_c} had a higher correlation with the number of trees and crown radius. The R² and RMSE values of the model are 0.814 and 0.043, respectively. The correlation between P_vg and LAI was high, and the R² and RMSE of the model were 0.795 and 0.040, respectively. 【Conclusion】 Both P_{vg_c} and P_vg can be used to estimate canopy closure in plantations. Although P_vg has higher accuracy in estimating canopy closure, the estimated canopy closure is not the canopy closure defined in forestry. Canopy closure is defined as the ratio of the vertical projection area of the canopy when it is a rigid body. Therefore, the use of P_{vg_c} to estimate the canopy closure of plantations was more accurate. To obtain the number of trees and radius of the crown, P_{vg_c} was used to estimate the canopy closure of the plantation.