Study On The Spectral Characteristics Of Typical Vegetation In The Yangtze River Estuary Nanhui Tidal Flat

Vegetation,an indispensable organic matter source in wetland ecosystem,is an important component of wetland ecosystems.The spectral properties of vegetation vary with their structure,biochemical composition and other characteristics.Therefore,various vegetation species have their special spectral curves.As an important method of vegetation remote sensing,spectral remote sensing can extract vegetation biological and physical information well.Nanhui tidal flat is one of the most important wetland in the Yangtze River estuary.The research on the spectral characteristics of the typical vegetation has great significance to the reasonable development and utilization of the resources of the Nanhui tidal flat and the environmental protection of the Yangtze River estuary.In the dissertation,we used the Field Spec,AccuPAR,TZS-I and SPAD 502 to acquire the vegetation data of Photosynthetically Active Radiation,spectral,chlorophyll and soil moisture.The extinction coefficient,spectral characteristic parameters and spectral indices of four species of Scirpus mariqueter,Phragmites australis,Spartina anglica and Solidago decurrens Lour were analyzed and studied.Finally,“Vegetation spectral characteristics extraction system" was designed based on MATLAB.In the course of the research,we had obtained the following results:(1)The extinction coefficient of vegetation,a parameter to describe the relationship between the canopy structure characteristics of vegetation and the utilization of solar energy,is an important parameter reflecting the optical properties of vegetation.Firstly,we choose the erectophile,as the model in the four kinds of vegetation,to obtain the simulation model of the extinction coefficient values.Finally,the simulated value s and measured values were compared and analyzed.In summer,the average relative error is 3.53%.For the relative error,the maximum was in Scirpus mariqueter as the minimum was in Solidago decurrens Lour.In autumn,the average relative error is 4.43%;the maximum of the relative error was also in Scirpus mariqueter.From the numerical analysis in autumn and summer,the values of Scirpus mariqueter,Phragmites australis,Spartina anglica and Solidago decurrens Lour were generally higher in autumn than in summer.The phenomenon was related to the increase of the solar zenith angle in autumn and the increase of the leaf area of these four plants.Compared with the Phragmites australis,Spartina anglica and Solidago decurrens Lour,the extinction coefficient of Scirpus mariqueter was smaller,which is related to the triangular shaped leaves and small leaf area.From the quantitative analysis of the error of the extinction coefficient between the measured value and the simulated value,it can be found that the fitting degree of the Scarps marquetry and Phragmites australis was better in the autumn,and the best fitted zenith angles of the two kinds of vegetation were distributed in 41 °-43 ° and 46 °-48 °.The fitting angle and error value in summer were better than those in autumn between the Spartina anglica and Solidago decurrens Lour.For Spartina anglica,the zenith angle with the fitting degree was concentrated at 20 °-25 ° and 35 °-38 °,and the Solidago decurrens Lour was at 10 °-12 ° and 26 °-28 °.(2)The spectral characteristic parameters and spectral indices of vegetation were closely related to vegetation growth,and were also affected by external factors such as soil moisture.In summer and autumn,the spectral characteristics of four plants in 435-1025 nm band and the relationship between PSDI(Plant Stress Detection Index)and soil moisture were analyzed.In the reflectivity,in summer,the maximum reflectance of the Scirpus mariqueter was close to 0.66;the reflectivity position of the Red Valley band of the Spartina anglica was between 0.2-0.7;the range of the Phragmites australis was from 0.6 to 0.2.The reflectivity of the Solidago decurrens Lour decreased slightly with time.The reflectance of vegetation in autumn had a rising trend after the red edge position,the reflectivity values begin to stabilize after 800 nm band,with the value range of 0.2-0.5.In the spectral characteristic parameters,in summer,the maximum correlation,between feature center and area and between half maximum width and characteristic area,were in the Spartina anglica;the maximum correlation between feature center and half maximum width was the Phragmites australis.In autumn,the maximum correlation,between feature center and area and between feature center and half maximum width,were in the Scirpus mariqueter.In the spectral index,it can be found that the diurnal variation of SIPI(Structureindependent pigment index)in summer and autumn was not obvious.Compared with autumn,the diurnal variation was 1.01-1.10 in summer.The diurnal variation of SIPI tended to oscillate in autumn,which range of variation is 0.985-1.020.The daily variation of PSSR(Pigment-specific simple ratio)in summer was not obvious,the value fluctuated between 4.0-13.6,which value in autumn is lower than that in summer,between 2.5-8.5.The PSND(Pigment specific normalized difference)fluctuated between 0.63-0.87 in summer and fluctuated between 0.44-0.80 in autumn,the PSND of autumn was lower than that of the summer.The Ratio showed oscillatory trend in summer and autumn,the diurnal variation of Ratio in summer was higher than that in autumn which were 4.8-12.0 and 4.0-8.8 respectively.Combined with soil moisture data,in summer,it was found that the maximum value of the Spartina anglica PSDI was 0.8597;the minimum value of the Scirpus mariqueter PSDI was 0.4804.The correlation between PSDI and soil moisture were 0.6139,0.9582,-0.1615 and 0.9058 in the Scirpus mariqueter,Phragmites australis,Spartina anglica and Solidago decurrens Lour.In autumn,the maximum PSDI was-0.5025 in the Phragmites australis,the minimum PSDI was 0.1395 in the Spartina anglica.The correlation between PSDI and soil moisture were 0.4277,0.9227,0.5008 and 0.8640 in the Scirpus mariqueter,Spartina anglica,Phragmites australis and Solidago decurrens Lour.(3)“Vegetation spectral characteristics extraction system” was developed using the visual interface design and operation of MATLAB GUI.It realized the input of measured data,the display of analog values,the calculation and display of spectral index,the 3D display and rotation of spectral reflectance,and the output of basic data products.