Use Of Electrical Resistivity Tomography And Ground Penetrating Radar To Map The Tree Roots

Root as an important organ of tree,support and transmit nutrients for tree's healthy growth aboveground,which greatly improve tree's productivity and have significant effect on maintaining the normal operation of ecosystem.Traditional research methods for tree roots are mainly base on excavation,which always get stuck in tedious steps,time-consuming and destroying the adjacent environment.In order to study the tree roots more efficiently and effectively,the nondestructive geophysical methodology is introduced into this area.According to the morphological characteristics of root of trees in the different life periods,the tree roots model I simulate Infancy,Adolescence,Adult,Old and Dying,respectively.The theoretical synthetic resistivity data for tree roots model I at different life periods,based on dipole-dipole array,and generated by the adaptive unstructured resistivity 2.5D finite element method.Then using the Newton-Gauss inversion method to obtain the resistivity imaging results of tree root zone.Compared with tree roots inversion morphology at different period,it can be found that the Electrical Resistivity Tomography(ERT)can track and monitor the development of tree roots,especially in the external contour shape and the relative position of the root zone.At the same time,the root biomass increasing and decreasing play a decisive role on tree's productivity,and the dynamic changes of resistivity tomography results provide a new way for qualitative interpretation of root biomass variation at different periods.The construction of the tree roots model ? mainly conducted by the profile matrix which stored electromagnetic parameters of tree roots,Ground Penetrating Radar(GPR)set the normalized first derivative Blackman-Harris window function as the source pulse.Two-travel time,the electromagnetic pulses arriving at root zone and then reflected back to the receive antenna,which can be calculated by two-dimensional Finite-Difference Time-Domain.Finally synthesized the common-offset reflection data that extracted from the output multi-offset data cube as radagrams which contain the information about buried tree roots.The results turned out that when the source transmitted low frequency electromagnetic pulse,the distribution information related subsurface buried tree roots can be observed accurately from radagrams,in addition to the intermediate section is shielded by tree roots barrier,the dipping boundary between clay layer and bedrock layer is clear enough to be noticed.With the increase of radar frequency,the electromagnetic pulse meet severe attenuation accompanied by the detection depth increase,thus the texture in radagram gradually blurred.ERT and GPR both achieved good results on trees roots detection,but the two geophysical methods have their own characteristics.ERT can reconstruct the main structure of tree roots,GPR has the potential to know more details about tree roots,combined the advantages of ERT and GPR will obtain better detection results in further research.