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Research On The Model Of Coastal Saline Soil Water And Salt Content In Yellow River Delta Based On GPR

Posted on:2020-05-17Degree:MasterType:Thesis
Country:ChinaCandidate:X W ZhaoFull Text:PDF
GTID:2370330572487590Subject:Land Resource Management
Abstract/Summary:PDF Full Text Request
The coastal saline soil in the Yellow River delta is the important reserve land resource in China and it is also one of the research bases of“bohai granary”science and technology project.Because of the high salt content of soil in this area,it is difficult to develop agricultural production and utilization.The regulation of salt content become the key to the effective utilization of coastal saline soil.But,the process of water and salt transport in coastal saline soil is complex and spatial and temporal variability is strong.So,the quantitative monitoring of soil water and salt content become the premise for the study of dynamic movement of soil water and salt,which have the vital practical significance.This research used GPR?ground penetrating radar?with the central frequency of250 MHz with FO?fixed offset?and CMP?common middle point?testing methods,designed simulation and field experiments,acquired groundwave and reflective wave si gnals.Meanwhile,get the soil moisture and electrical conductivity by field sampling.Th en,by contrast with the measured data and electromagnetic signals,through the inversi on analysis and BP neural network analysis to build the soil water and salt content model of GPR in coastal saline soil under different water and salt change conditions.The results indicate that:?1?Response characteristics of the GPR signals under different changes of soil wa ter and salt contentAccording to the different vegetation type or growing on the underground soil co nfigurations and characteristics of moisture migration and field experiments in binzho u and dongying two experimental locations typical plot,along the long side direction per site FO method measurement,CMP method of measurement in the center of ea ch plot,on the Line view software for image processing and data extraction.It is fou nd that GPR can effectively distinguish plots with different degrees of salinization,a nd the judgment accuracy is relatively high,in which the horizontal displacement err or is less than 0.5m.The response information of the underground soil layer within 1m can be obtained by using the electromagnetic wave amplitude changes and spectral images obtained by the detection.However,as the detection depth increases,due to t he rapid attenuation of the electromagnetic wave,the obtained information becomes more fuzzy,and it cannot be identified after reaching a certain depth.In coastal salin e soil area,the change of water and salt has a significant effect on electromagnetic wave signal.When the salt content is close to each other,with the increase of soil m oisture content,the electromagnetic wave signal will gradually attenuate,the propagati on speed in the soil will decrease,and the inverted soil dielectric constant will incre ase,and the error will increase.When the moisture content is similar,with the increa se of soil salt content,the amplitude energy value of electromagnetic wave decreases and the number of high-frequency wave peaks decreases.?2?The inversion and construction of soil water model in coastal saline soilBy comparison with commonly used empirical models of?-?and?-?patterns,select suitable soil moisture inversion models and determine the inversion accuracy.T hen,the correlation analysis was carried out between the inverted volumetric moisture content with GPR ground wave signal and measured mass moisture content.In the e mpirical models of?-?and?-?,the correlation coefficient of Zhu Anning model for silty clay fluvo-aquic soil achieved 0.7079and 7.677.The inverted soil moisture co ntent of 0-30cm with GPR reflection wave signal is more precious that of 30-60cm with average standard deviation of 0.045 m3·m-3 and 60-90cm with average standard deviation of 0.056m3·m-3.The inversion of topsoil moisture content by GPR reflected wave signal is better than that of ground wave signal especially for the plots with high salt content.Based on the propagation velocity of electromagnetic wave in layere d soil as the independent variable and the measured soil moisture content as the dep endent variable,the soil moisture content inversion models were constructed.Among them,the accuracy of logarithm model,quadratic model and linear model were high with adjusted R2 of about 0.7.?3?The construction inversion and inversion of soil salinity model in coastal sali ne soilWith the increase of soil salinity,the amplitude and propagation velocity of GPR electromagnetic wave decreased significantly.Taking the bare land in the test area as an example,in the 0-30cm soil layer,the average amplitude was 1.217mV 1.028mV 0.578mV under different treatment with water and salt.The soil amplitudes of 30-60cm and 60-90cm in the control plot were 0.198mV and 0.069mV,which have a obvious decrease in depth.Because of the relationship between amplitude and soil salinity is not single linear,the research choose BP neural network to make nonlinear analysis.Using the average amplitude ratio between different soil layers and the propagation velocity of electromagnetic wave as the input layer,the measured soil conductivity as the output layer to build the neural network.Through the network 27 groups of data were trained,and 6 groups of data were tested and predicted.Finally,we get the simulated salinity model Z=6.962-0.4748X-14.79Y+0.1627X2+0.842XY+8.262Y2?Z as the salt,X as the dielectric constant of soil,Y as the amplitude ratio?.The relative error of the model is between-14.17%and7.35%,the accuracy of the model is 86.54%,which shows that the model has better applicability.In the field experiment,GPR data of the Yellow River salty soil in different periods were collected,Then,the data of salinity model was further trained,simulated and outputted to obtain the salinity model of different flow paths.By comparison,it was found that the model of sweet ditch flow path formed in the earliest period had better adaptability to modification.
Keywords/Search Tags:Coastal saline soil, Soil moisture content, Soil salinity, Ground penetrating radar, Quantitative inversion
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