| Vegetation canopy is one of the most important physical and chemical processes in the ecosystem,and the theory of vegetation canopy radiative transfer model lays a theoretical foundation for the remote sensing community.Leaf area index(LAI)is an important index to characterize the land surface canopy.As an important characteristic parameter of the radiative transfer model,it is very important for the simulation and inversion accuracy of the model.There are two kinds of methods of ground LAI measurement,which are direct measurement and indirect measurement,which are suitable for LAI estimation in small area.The simulation for crops in the whole growth period of crop growth based on LAI model,time continuity,the "force" or "assimilation" to the study of remote sensing and crop growth model coupling increased gradually,but the focus model in some macro information into the crop remote sensing data inversion,estimate the correction or the relevant parameters,and then applied to the crop growth model of space expansion,mostly for the purpose of monitoring crop growth and yield,and the related research on analysis and evaluation of remote sensing model simulation results in a specific period and error sources rarely appeared.Based on the input parameters of the PROSAIL model is based on the sensitivity analysis of the CERESMaize Maize model calibration,get the optimal combination of the parameters of crop genetic and simulated pumping LAI change of heading stage.Then combined with the spectrophotometer physicochemical parameters specific to the growth period of corn(chlorophyll and carotenoids)experiment,established the input parameters of PROSAIL model simulation database,multi angle spectral data of the corn canopy specific growth period,the multi angle spectral information at different time points of four-dimensional observation platform observation of tower crane angle of spectral information and different panicle number under the model simulation results were compared to evaluate the model,determine the sources of error.The main methods and conclusions are as follows:(1)Coupling CERES-Maize model PROSAIL radiative transfer model was used to simulate the change of canopy reflectance of Maize during flowering stage.The results showed that canopy reflectance decreased with time.Based on the experimental results of multi angle canopy reflectance data,the results show that the canopy reflectance values of the same observation azimuth and zenith angle at five time points are consistent with the simulated values of the model.However,the measured value is higher than the simulated value,especially in the visible light(green,Red),but the difference is not obvious in the near infrared band.(2)Through parameter sensitivity analysis showed that Cab changes in reflectivity on the green band effect,reflectivity of brown pigment on near the red band about 700 nm value has a great influence on the quality of dry matter,reflectance in near infrared and shortwave near infrared band and infrared band influences,canopy reflectance after the main minority region 900 nm influence of equivalent water thickness change value,the change of leaf structure and hot coefficient has an impact on the total reflectance,LAI in the visible band reflectance greater impact,the change of Car has little effect on the reflectivity,mainly concentrated in the near 450 nm.(3)Observation data and field test data from remote sensing experiment station at Hebei HuaiLai in 2013 years,the genetic parameters of the CERES-Maize model on the growth characteristics of varieties were calibrated using the observed data at the same time,2014,2015 to the model simulation,LAI simulation of two years are more accurate,and can be used for long time sequence simulation of maize.Combined with the observation data of meteorological stations in 2016 station to simulate the whole growth of maize LAI distribution range of 0.01~5.48,tasseling stage LAI in 4.75,a high degree of agreement with the measured data,the model of maize tasseling and LAI simulation results is good.On the ground observation data of 2016 corn tasseling stage were calculated and analysis shows that the equivalent water thickness,dry weight,leaf angle,leaf chlorophyll content,carotenoid content of all parameter values were unchanged.(4)The effect of the number of tassel on canopy reflectance was studied by using the method of manual cutting.The results showed that the canopy reflectance was highest and the canopy reflectance was the lowest.By comparing the observed values of the five spike gradients and the simulated values of the five time points,the main reason for the error was found. |
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