Forward Modeling And Calibration Technique Of Full Polarimetric GPR

Ground penetrating radar (GPR) is now a well-accepted geophysicaltechnique. The method uses radio waves to probe “the ground” which meansany low loss dielectric material. Use the way of rapid, continuous,non-detection and have fast acquisition speed and high resolution.Ground-penetrating radar is widely used in the field of engineering,environmental, hydrological, geological survey, archaeological,geological survey, mineral exploration, military exploration of theplanet detection. Like other detection method, ground penetrating radarhas some limitations. Such as the existence of weak penetrating powerseveral times spread to other serious clutter, uni-polar data acquisitionto provide a limited amount of information, the impact of the antennacoupling shortcomings.Traditional ground-penetrating radar transmitting and receiving arethe same linear polarized wave. In progress of the same offset distancemeasurement, the two antennas are placed side by side on the measured line.Transmitting antenna generate a linear polarized wave along antenna axisdirection. From the nature of the linear polarized wave, we can see, thereceiving antenna is most sensitive to the electric field parallel alongthe axis of antenna polarization. Since transmitting antenna andreceiving antenna have the same polarization direction, only in thereceiving antenna parallel along the axis of antenna electric fieldpolarization components can be received.Electromagnetic radiation to the target surface, the target causesthe polarization of electromagnetic wave to produce different degrees ofrotation. Traditional ground-penetrating radar antennas only transmitand receive the same polarization direction of the reflection wave. Itwill cause the lack of information of the target reflectance. On the basisof the traditional ground-penetrating radar antenna, keep transmittingantenna polarization is fixed leaving the receiving antenna rotated90°. We define H polarization which parallel with measurement lines, Vpolarization which perpendicular to measurement lines. So, there are fourkinds of polarization antennas. They are HH, HV, VH, VV, where HH and VVcalled co-polarization mode, HV and VH called cross-polarization mode.Based on the above principles, we developed full-polarimetric groundpenetrating radar system, it base on the vector characteristics of thereflected signal of the target. From studying the signal vector components,we can get better access to information of the geological bodies andgeometric. As encountered in our lives, an amount of information containedin the color photographs included in the amount of information is muchexcess of a black and white picture.In this paper, we use the finite difference time domain method to writethe3D-FDTD forward modeling program. Forward modeling some typicaltargets and obtained different location’s and different target rotationangle’s polarization responses. Found that such goal with theperspective of a single electromagnetic target like mental platepolarization response is not obvious, with multiple electromagneticperspective of the target like the trihedral reflector polarizationresponse strongly.Continue to discuss the polarization response of thefull-polarization measurements on the model of random surfaces andinclined strikes. Found that the surface roughness can affect theelectromagnetic co-polarization response and cross-polarizationresponse. For different inclination of the inclined strikes, the azimuthof polarization measurement of the polarization response is not the same.Through the cross-polarization response and the co-polarization responseinformation can approximate solve the direction of inclined strikes’angle.Full polarimetric GPR system will inevitably brought someinterference, such as the environment, the system itself during themeasurement. At this time, if not do some of the relative amplitude andphase calibration of full polarimetric GPR system, the measurementresults will not accurately reflect the response of the target. So, thepurpose of calibration is to determine the measurement of the polarizationscattering matrix in the four measurement channel gain and the estimatedgain of the cross-polarization distortion caused by transmit and receive antennas. Once these calibration coefficients are determined, the systemeffect can identify and remove.A calibration procedure for a polarimetric GPR system has beendescribed in this paper. This calibration algorithm provides a simplemethodology, both in taking calibration measurements and processingcalibration parameters. The procedure effectively separates thecrosstalk from the channel imbalance and radiometric calibration andremoves the crosstalk errors caused by higher-order terms. We used thestandard calibration targets consisting of a0°and a45°orienteddihedral corner reflectors. From the theoretical values and measured dataof the two calibration targets, the calibration parameters were derived.Measured scattering matrices of targets could then be calibrated usingthese calibration parameters. Comparison of the calibrated scatteringmatrix of a22.5°oriented dihedral corner reflector and its theoreticalscattering matrix has indicated satisfactory calibration accuracy,especially for the crosstalk. The experiments results have demonstratedthe feasibility of this proposed calibration technique.In short, the main contents of this paper is use the finite differencetime domain (FDTD) to forward modeling polarimetric ground penetratingradar system and give a new polarization calibration technique. Thepurposes of studying polarimetric ground penetrating radar system are toidentify the target body, direction judgments and attribute extractionapplications. Improve the ability of ground penetrating radar to identifyunderground targets.