Abstract
Leaf area index (LAI) is one of the key biophysical parameters in crop structure. The accurate quantitative estimation of crop LAI is essential to verify crop growth and health. The PROSAIL radiative transfer model (RTM) is one of the most established methods for estimating crop LAI. In this study, a look-up table (LUT) based on the PROSAIL RTM was first used to estimate winter wheat LAI from GF-1 data, which accounted for some available prior knowledge relating to the distribution of winter wheat characteristics. Next, the effects of 15 LAI-LUT strategies with reflectance bands and 10 LAI-LUT strategies with vegetation indexes on the accuracy of the winter wheat LAI retrieval with different phenological stages were evaluated against in situ LAI measurements. The results showed that the LUT strategies of LAI-GNDVI were optimal and had the highest accuracy with a root mean squared error (RMSE) value of 0.34, and a coefficient of determination (R2) of 0.61 during the elongation stages, and the LUT strategies of LAI-Green were optimal with a RMSE of 0.74, and R2 of 0.20 during the grain-filling stages. The results demonstrated that the PROSAIL RTM had great potential in winter wheat LAI inversion with GF-1 satellite data and the performance could be improved by selecting the appropriate LUT inversion strategies in different growth periods.
Highlights
Leaf area index (LAI), which is the most important biophysical parameter, represents the total one-half of green leaves area per unit ground surface area (m2 /m2 ), and is a dimensionless number [1]
As we knew that the look-up table (LUT)-B strategy with the highest R2 and the lowest root mean squared error (RMSE) would be the best choice in theory, practically, the optimal results may be difficult to achieve in most cases
The winter wheat LAI derived from GF-1 WFV images was estimated using the LUT strategies based on the method of PROSAIL radiative transfer model (RTM)
Summary
Leaf area index (LAI), which is the most important biophysical parameter, represents the total one-half of green leaves area per unit ground surface area (m2 /m2 ), and is a dimensionless number [1]. It is an indicator of vegetation ecological processes, the canopy interception of light, respiration, photosynthesis, net primary production, transpiration, soil respiration, and energy exchange between the plant canopies and atmosphere [2,3]. These methods have obvious shortcomings in terms of Sensors 2018, 18, 1120; doi:10.3390/s18041120 www.mdpi.com/journal/sensors
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