Research On Tree-trunk Scattering At VHF/UHF And It's Modeling Algorithm

This paper presents our global approach to model tree-trunk scattering at VHF/UHF. In this approach,we consider plane wave scattering (in time domain) from the tree trunks above the soil. The time-domain scattering is computed via FDTD method,which is particularly well adapted to frequency-dependent soil. This method is processed prior to a Fast Fourier Transform (FFT),which is performed to come back to the frequency domain. Thus,we may have rich information for applicability to the FOPEN detection need.The accuracy and temporal nature of the Finite Difference Time Domain (FDTD) is well suited to the UWB studies. Yet,Some problems are put forward in modeling tree trunks-soil clutter with FDTD algorithm:First,the incident wave of tree-trunks is composed of the direct transmission and the soil scattering. And the interpolation operations of these complex incident-field values on the 3-D FDTD connecting boundary is impossible.Secondly,tree trunks sit on the soil,thus two mediums,air and the soil,surround them. And it's impossible to obtain a closed surface in the environment of uniform medium for the time-domain near-zone to far-zone transformation.However,in this paper,we propose an electromagnetic analysis of the tree trunks-soil clutter by FDTD method according to a 4-steps solution,as mentioned in section 5.And in section 6,we prove the liability of this analysis. Numerical results are presented in section 7. We compared our results with that of Duke University,and both are in good agreement.Finally,other researches we have done are mentioned.First,a new absorbing boundary condition (ABC),Standing-Traveling Wave Boundary Condition (STWBC) is presented for the truncation of FDTD grid. Secondly,two applications of GPML ABC in modeling pulse radar are shown:one is detecting pipeline underground,and the other is its application to highway technology.Thirdly,with back-projection algorithm,we have formed the image of tree-trunks.In summary,the application of FDTD in UWB FOPEN so far is impressive. Yet we recognize that there is much to do.