Welcome to visit Scientia Silvae Sinicae,Today is

Scientia Silvae Sinicae ›› 2021, Vol. 57 ›› Issue (4): 90-106.doi: 10.11707/j.1001-7488.20210410

Previous Articles     Next Articles

Inversion of Forest Leaf Area Index Based on PROSAIL Model and Multi-Angle Remote Sensing Data

Ying Pan1,2,Mingming Ding3,Jie Lin1,*,Qiao Dai1,Geng Guo1,Linlin Cui1   

  1. 1. Co-Innovation Center for Sustainable Forestry in Southern China, Nanjing Forestry University Nanjing 210037
    2. East China Branch of Yangtze River Channel Engineering Bureau Co., Ltd Nanjing 210011
    3. Nanjing Water Conservancy Bureau Nanjing 210036
  • Received:2019-06-18 Online:2021-04-25 Published:2021-05-21
  • Contact: Jie Lin

Abstract:

Objective: The aim of this study was to improve the inversion accuracy of vegetation LAI (leaf area index) on the regional scale based on multi-angle PROBA/CHRIS remote sensing data and field measured data, and provide a new method and model for regional soil erosion remote sensing quantitative monitoring. Method: In this study, Mount Zijin and Mount Mufu in Nanjing were selected as the study areas. Through the methods of field experiments, remote sensing image, radiation transfer model and mathematical models, this study established the LAI inversion model of random forest model based on PROSPECT+SAIL (scattering by arbitrarily inclined leaves) model—PROSAIL model and multi-angle PROBA/CHRIS (project for on-board autonomy/compact high resolution imaging spectrometer) remote sensing data. The sensitivity analysis and applicability evaluation of PROSAIL model were carried out, and the optimal LAI inversion model was also determined. The accuracies were verified and evaluated by the ground measured LAI values. Result: The sensitivity of input parameters of the PROSAIL model was LAI>Cab (chlorophyll a and b content)>Cm (leaf dry matter content)>SL (hotspot parameters)>N (blade internal structure parameters)>Cw (equivalent water thickness). The accuracy of the canopy reflectance simulated by the PROSAIL model was 0°> 36°>-36°>55°>-55°. In the single angle LAI inversion models, the accuracy of forward observation angle 55° was the highest, and the R2 (coefficient of determination), RMSE(root mean square error) and MAPE(mean absolute percentage error) were 0.915 7, 0.235 7 and 0.042 6, respectively. Compared with the traditional vertical observation, the R2 of the 55° model increased by 0.75%, and the RMSE and MAPE decreased by 3.76% and 5.12%, respectively. Compared with the nonlinear regression model, the R2 of the 55° model increased by 0.7%, and the RMSE and MAPE decreased by 15.40% and 11.98%, respectively. The accuracy of single angle inversion models was 55°>36°>0°>-55°>-36°. In the LAI inversion models based on the multi-angle data, the three angles combination of 0°, 36° and 55° had the highest accuracy with the R2, RMSE and MAPE of 0.918 4, 0.231 9 and 0.041 5, respectively. Compared with single angle 55°, the R2 of the three angles combination model increased by 0.29%, and the RMSE and MAPE decreased by 1.61% and 2.58%, respectively. Compared with the traditional vertical observation, the R2 of the three angles combination model increased by 1.05%, and the RMSE and MAPE decreased by 5.31% and 7.57%, respectively. Compared with the nonlinear regression model, the R2 of the three angle combination model increased by 0.79%, and the RMSE and MAPE increased by 6.72% and 9.19%, respectively. The LAI in the western region of Mount Zijin was between 0.44 and 6.70, and the average LAI of forest was 3.04. The spatial distribution pattern of LAI in the western woodland of Mount Zijin showed "high in the north and south and low in the middle" as a whole. Conclusion: The optimal LAI inversion model was the random forest LAI inversion model based on three angles combination (0°, 36°, 55°). On the one hand, increasing the observation angle can provide more information about vegetation crown structure, and the inversion accuracy of LAI will increase with the increase of observation angle. However, on the other hand, too many observation angles will lead to more uncertainty in pixel space resampling, leaf shadow, soil shadow and so on, and the accuracy of LAI inversion will decrease. No matter single angle and multi-angle data, the accuracy of random forest LAI inversion model was higher than that of nonlinear regression model, which indicated that the random forest model can obviously improve the inversion accuracy of LAI and was suitable for the inversion of LAI on the regional scale. Multi-angle remote sensing data can reflect the three-dimensional structure information of vegetation and the characteristics of multi-dimensional spatial structure of ground objects, and significantly improve the low accuracy of LAI inversion by traditional vertical observation, thus effectively improve the inversion accuracy of vegetation LAI.

Key words: leaf area index(LAI), multi-angle PROBA/CHRIS remote sensing data, PROSAIL model, random forest(RF) model

CLC Number: