Retrieval Of Saline Soil Salinity Under Vegetation Cover Based On Remote Sensing

Soil salinization is the main cause of soil desertification and soil degradation.In the process of salinization,soil will lose water and solidify,dissolving a lot of soluble salts,causing strong toxic effect on plants and inhibiting the normal growth of plants.Soil salinization has become a major factor restricting the development of agriculture and animal husbandry,which has caused serious harm to economic development.Satellite remote sensing technology can monitor soil salinization in a large scale and provide support for the rational transformation and the development of salinized land.At present,the monitoring of soil salinization using remote sensing is mostly aimed at the soil with bare or sparse vegetation cover,while for the saline soil under vegetation cover,the existence of vegetation layer isolates the direct monitoring of optical remote sensing on the saline soil and increases the difficulty of inversion.However,the degradation of soil mostly occurs in farming,grazing areas and coastal areas,where a large number of alkaline-tolerant plants grow.At present,the remote sensing monitoring of saline soil under vegetation cover is insufficient.The research is carried out under the support of the National Natural Science Foundation of China " Research on real-time measurement of moisture and salinity of saline-alkali soil under different surface forms using near-surface multi-source remote sensing method(No.41671350)" project.Combined with the dielectric constant model and water cloud model,the remote sensing inversion of salt content in salinized soil under vegetation cover is realized.The main contents and conclusions are as follows:(1)Based on the modified Dobson salinized soil dielectric constant model,the relationship between dielectric constant and soil volumetric water content,salt content,temperature and soil texture was analyzed respectively.The results show that the real part of dielectric constant is mainly affected by soil volume water content,while the imaginary part of dielectric constant is affected by water content and salt content.The effects of temperature and soil texture on dielectric constant is much less than that of water content and salt content.(2)The model of backscattering coefficient of saline soil has been established and the sensitivity analysis has been carried out.It is found that the surface roughness had the greatest influence on the radar backscattering coefficient,followed by the soil water content and salt content.On this basis,a lookup table algorithm for surface roughness has been established by using the least square fitting equation.Based on the field sampling data,the simulation accuracy of the microwave backscattering coefficient model was verified in the bare saline soil area,the correlation coefficient R=0.78,and the root mean square error RMSE=2.51 d B.(3)Based on the backscattering coefficient model and the water cloud model,the inversion model of salt content in saline soil under vegetation cover has been established.The model was used to invert the salt content of 182 vegetation cover field sampling points,and the accuracy of the model was R=0.72,RMSE=0.74 g/kg.(4)The vegetation was divided into monocotyledons and dicotyledons according to plant classification,and the soil salt content models of different vegetation cover were established by fitting the water cloud model coefficients respectively.The model was used to invert the salt content of saline soil from areas of 124 monocotyledons and57 dicotyledons respectively,and the accuracy of the inversion was R=0.75 and RMSE=0.64g/kg and R=0.75 and RMSE=0.74g/kg.Compared with no classification,R increased by 4.16%.The research work in this paper provides a new approach and method for remote sensing monitoring of saline-alkali soil characteristics,and solves the problem of the influence of vegetation cover on optical monitoring of saline-alkali soil.This has laid a foundation for the National Natural Science Foundation of China(NSFC)project "Research on real-time measurement of moisture and salinity of saline-alkali soil under different surface forms using near-surface multi-source remote sensing method".