The Effect Of Dust On Spectral Characteristics,water Content And Pigment Concentration Retrieval Of Urban Plants

With the development of economy and rapid urbanization,the residents paid attantion to the pollution of the dust in air which was one of air pollution problem.Plants can reduce the dust concentration in the air by covering bare land,adsorption,reducing wind speed,etc.The ability of plants to retain dust has the characteristics of the permanent under certain conditions.Although the plant has the ability to retain dust,but the dust will also have an impact on plants.This phenomenon attracted much attention of scholars at home and abroad,and became one of hot research topics in research field.The data in this paper mainly include the canopy and leaf spectrum of the target tree species(using ASD FieldSpec 3)in different urban functional areas,the corresponding data of detaining dust(using electronic analytical balance),water content(baking method)and pigment concentration data(chemical solvent method)of canopy and leaf scales during early April to the end of August at 2016.In this paper,firstly we analyzed the effect of dust or different amount of dust on plant reflectance and red edge position on the basis of the above data.Secondly we analyzed the change of leaf reflectance spectra at different water content levels and different pigment concentration levels based on spectral reflectance of leaves before and after cleaning the dust.Finally we analyzed the effect of detaining dust on the inversion of plant water content and the inversion of pigment concentration based on the above research.The results show that:(1)The visible light band has the highest sensitivity to the change of the different amount of dust on plant,and the higher sensitive band is in the1450-1750 nm,and the plant reflection spectrum in the 700-1350 nm band is most stably effected by the different amount of dust on plant which is reducing with the increase of the amount of dust.Detaining dust or different level dust do not cause the moving of vegetation “red edge” positon,but its position is related to plant species.The value of “main peak” and “secondary peak” would reduced with the dust weight increasing and the positon of “two peak” is also related to the plant species.These corresponding results can provide spectral support for the identification of plant species and the degree of dust pollutionin in different functional areas of the city.(2)The effect of detaining dust on the plant reflectance of different water content or different pigment concentration mainly include the two aspects that changethe value of spectrum reflection and change the interval between adjacent reflection spectrums.For different water content,the effect of water content on the plant reflectance is relatively stable and the interval between the reflections of each water level is larger than that of other bands in the 750-1350 nm band before and after dust,so this band can reflect the changes in water content of vegetation well.For different pigment content,the band of 350-700 nm and 750-1350 nm can reflect the changes in plant pigment concentration well.(3)For the leaf scale: detaining dust does not change the correlation nature between EWT and FWC with each index,but it can change the correlation coefficient between EWT and FWC with each index;detaining dust can reduce the correlation coefficient between EWT with each index and increasing the correlation coefficient between FWC with each index but no matter under dust circumstance or not,the value of former is higher the latter;so EWT can reflect the water content of plant leaves better.For the canopy scale,the correlation coefficient between the canopy EWT with each index is much lower than the correlation coefficient between the FWC witn each index,so FWC can reflect the water content of plant canopy better.(4)The correlation coefficient between EWT and FWC of different plants with various spectral indices is different and the degree of influence of detaining dust is also different.Each plant exist the index that has the highest correlation coefficient with water content(optimal index),and detaining dust can change the kind of optimal index.In addition,the optimal index is related to tree species—a spectral index does not have the universal ability to invert the leaf water content.So inversion of water content in different species at the same time will increase the difficulty of the study.(5)Detaining dust does not change the correlation nature between the various pigments with the spectrum band or spectrum index,but it can change the correlation coefficient between pigment with the spectrum band and spectrum index.Detaining dust can increasing the correlation coefficient between the chlorophyll a and carotenoids with band,but it can reduce the correlation coefficient between the chlorophyll b with band.No matter under dust circumstance or not,the correlation coefficient between chlorophyll a with each band is higher the correlation coefficient between chlorophyll b with each band and the correlation coefficient between chlorophyll with each band is higher the correlation coefficient between carotenoid with each band.Although the effect of detaining dust on the correlation coefficient between each pigment with each index is related to the selected index,on thewhole(average change)the discipline is same as the fomar.(6)Detaining dust can effect the inversion of leaf water content and pigment concentration.In terms of leaf water content inversion,the effect of dust retention on the accuracy of water content inversion is related to the amount of dust.But overall performance: Detaining dust not only reduce the coefficient of decision of invesion regression model,but increasing the value of RMSE and RE of estimation model and reduce the inversion accuracy.The effect of dust on the inversion of chlorophyll concentration showed two kinds of changes: one is to improve the inversion accuracy;the second is to reduce the inversion accuracy;this phenomenon is related to the selected spectral index.But the degree of increasing is much lower than the degree of reduction.The effect degree of dust retention on the above is related to the selected modeling index.