The Key Technologies Of Linear Frequency Modulated Continuous Wave (LFMCW) Ground Penetrating Radar

Linear Frequency Modulated Continuous Wave（LFMCW） Ground Penetrating Radarhas advantages of high range resolution, low transmit power, high receiver sensitivity, simplestructure and minimal blind spot distance. So, LFMCW ground penetrating radar has becomea research hotspot. The theory of linear frequency modulated continuous wave air radar isvrelatively mature, and some air radars based on LFMCW have been used to detect militarytargets. Because of big difference between stratum media and air media, varies shapes and thedifferent electrical conductivity of layered medium and isolated medium, the theory ofelectromagnetic wave propagation in the air is more complicate than that in the stratum media.Therefore, in the development of a LFMCW ground penetrating radar, the theory of LFMCWair radar can’t be copied. This paper began with the propagation characteristics of linearfrequency modulation continuous wave in the stratum medium. Firstly, the relations amongthe transmiting power, the detecting distance and the detecting accuracy were studied.Secondly, the principle prototype of LFMCW ground penetrating radar was designed afteranalyzing the transmitted waveform and the echo signal. Thirdly, the high resolution processmethod and imaging technology of LFMCW ground penetrating radar were launched adetailed studied. Finally, the test proved that LFMCW ground penetrating radar has thoseadvantageous and the method and the technology are effective. The innovative achievementsare follows:1. In according to the formulation of stratified impedance and reflecting coefficient,introduces the formula among different dielectric constant, electromagnetic harmonic phaseabsorption and magnitude absorption derivate. Electromagnetic wave propagation parametersof the typical geological bodies under shallow surface were calculated.2. Beginning with the transfer equation of ground-penetrating radar signal this paperdeducted the relationship formulation between stepping frequency increment and themaximum unambiguous range. Taking the triangular wave form of linear frequencymodulation as the transmission wave, this paper formulated the expression of the beat signal.This formulation and the distance information formed a signal processing system of LFMWground penetrating radar. 3. Broadband synthetic time-domain algorithm, frequency domain algorithms, syntheticdistance algorithms were derived from the signal transfer process of the stepping frequencymodulated continuous wave. These algorithms are verified and compared in the three-layermodel and the five-layer model. The following conclusions can be made: As far as syntheticeffect is concerned, the synthetic distance envelope algorithm is worst because of energyleakage. But time-domain synthesis and frequency-domain synthesis is relatively good. As faras the effect of wave velocity is concerned, the three algorithms are all sensitive to velocity.the synthetic distance envelope algorithm is particularly serious, and it needs extracalculations. As far as amount of computation is concerned, the time-domain algorithms needlargest amount of the computation. Furthermore, the relationship between the dielectricconstant and the ability to distinguish were studied by changing dielectric constant ofthree-layer model.4. Taking the width, the close-range field and the far edge, the vertical distance of thesurvey line of wave velocity into account, the relationship between the range migration, thedistance migration and distance resolution and lateral resolution were studied. Side lookingrange migration correction algorithm and oblique lateral view distance dynamic correctionmethod were put forward. Then in according to requirements of total resolution, the delaytime of the synthetic distance envelope algorithm were discussed in four cases. Finally, asynthetic imaging algorithm based on stolt migration was put forward.5. A DDS device was employed to produce transmission waveform, and the amount ofcomputation was analyzed according to imaging algorithms. Then the sign processing systemwas designed by employing FPGA and DSP technology. Finally, a developed principleprototype was used to test.