Research On Diameter Estimation And Biomass Of Rhizomes Of Phyllostachys Heterocycla Based On GPR Technique

There is growing concern about climate change problem,the effects of forests as the largest terrestrial ecosystem in carbon sequestration is increasingly prominent.Phyllostachys pubescens which is a typical forest type spreads around the southern China.Bamboo growth and development is based on its rhizomes system.To obtain correct rhizome parameters which has profound significance in researching the bamboo underground biomass.In this paper,the basic informations of rhizomes were investigated and analyzed by traditional method.Then we used Ground-penetrating radar(GPR),a nondestructive detection technology for coarse root detection and rhizomes diameter estimation.To do this,the simulation values and measured values of diameter are obtained by simulating two scenes with the GprMax software and field experiments,and then two methods about the echo hyperbola model were used to estimate the diameter.Finally,the biomass models of rhizomes were established by using the measured rhizomes data.The results were showed as follows:(1)To analyse the diameter structure of rhizome,they were not evenly distributed,which show that the horizontal diameter is larger than vertical diameter,and the diameter increases or decreases from one side to the other.A larger amplitude of change about diameter exist in young rhizomes,and deeper soil layer usually had coarser rhizomes.To analyse the age structure,the plot was dominated by the young rhizomes and healthy rhizomes possessed thicker roots than young rhizomes and elder rhizomes according to the ratio of the rhizome biomass to root..Rhizomes were clustered in-10?40cm soil layer.Indexes ratio of this layer were above 90%.The distribution of unit rhizome biomass was mostly at the same level in horizontal direction,with little difference.(2)For dealing with data about GprMax and measured diameter,the diameter estimation error of the hyperbola parameter optimization method with the L-M algorithm is smaller.The method based on ellipse fitting is only applicable for fitting shape of hyperbola and detecting large diameter target.Besides,this method has a awful result and useless for small diameter target.(3)the hyperbolic model can get stable results in the vertex coordinates of hyperbola estimation.The estimation accuracy of target diameter depends on setting a correct the lower limit value of the wave velocity.The estimation accuracy of the diameter can be greatly improved after choosing the proper velocity value.(4)Compared with ten bamboo rhizome models after used cross validation,we found that the exponential function model with D2L as the variable was the best model,and its R2 and RMSE values are 0.9352 and 21.43g respectively,and the concrete form of the model was BR = 65.17·e0.002496D2L.