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1

Abruptly autofocusing property of circular Pearcey vortex beams with different initial launch angles in harmonic potentials

Liu Xianglian, Zhang Di, Zhao Lijiao, Li Pu, Zhang Jianguo, Liu Yi

Optica Applicata

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2022

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Vol. 52, nr 3

417--428

EN

We have studied and explored the influence of different launch angles on the circular Pearcey beams (CPBs) without vortex or with vortex for the first time. Although launch angles can manipulate the focal length and the contrast of peak intensity of the CPBs, the shape and propagation trajectory of the CPBs maintain invariant. When the vortex is considered, the focal pattern and the contrast of peak intensity of the circular Pearcey vortex beams (CPVBs) can be changed by adjusting the magnitude of topological charges and the position of vortex. In addition, we have deliberated the propagation of the CPVBs under the action of double opposite optical vortices.

2

Integrated ground penetrating radar and DGPS method for the continuous and long-distance GPR survey in the rugged terrain

Zhang Di, Gong HuiLi, Li JiaCun, Wu ZhongHai, Liu ShaoTang

Acta Geophysica

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2022

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Vol. 70, no 2

537--546

EN

The integrated ground penetrating radar (GPR) and global positioning system (GPS) survey has been extensively used to investigate the subsurface materials or buried-objects with the geographical information. However, when the GPR was pulled quickly, there was inadequate that the GPS signal receiver cannot real-time update its geographical coordinates by the serial com-port or USB port on the laptop. In this study, the integration of GPR and differential GPS (DGPS) was realized to acquire GPR image with the geographical information, especially for a continuous and long-distance GPR survey in the rugged terrain. When the operator with GPR system is moving on the ground surface, the pulse signals of the survey wheel were applied to trigger the GPR control unit and the GPS signal receiver at the same time. Meanwhile, the GPR data and the geographical coordinates were obtained by the GPR system and the GPS signal receiver, respectively. In addition, the time synchronization algorithm was proposed to combine each trace of the GPR image with the geographical coordinates of the GPS signal receiver. To evaluate the feasibility and efficiency of the integrated GPR and DGPS method, the 250 MHz and 500 MHz GPR profiles were performed in the four survey sites along the Litang fault. The difference between the pulse events on GPS and the GPR traces number, whether 250 MHz and 500 MHz GPR antenna, it indicates that the differences slightly increase when the distance increases on the graphs. The study results demonstrate that the integrated GPR and DGPS method has the capable of obtaining the GPR data with high-precision geographical information for a continuous and long-distance measurement in the rugged terrain. What’s more, the methodology that we introduce also offers the chance for comprehensive application of GPR data with other spatial data, such as the high-resolution remote sensing image, unmanned aerial vehicle, airborne LiDAR and so on.

3

Multi-frequencies GPR measurements for delineating the shallow subsurface features of the Yushu strike slip fault

Zhang Di, Li Jiacun, Liu Shaotang, Wang Guo

Acta Geophysica

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2019

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Vol. 67, no. 2

501--515

EN

In order to assess Ground penetrating radar (GPR) for imaging the shallow subsurface geometry and characteristics of the fault in Yushu area, details GPR measurements with 25 MHz, 100 MHz and 250 MHz frequencies antenna were firstly conducted in four sites along the Yushu fault after geomorphologic and geological investigation. The 25 MHz profiles delineated an excellent general view of deformation zones at a much wider area and greater depth. While the 100 MHz and 250 MHz data provided more detailed analysis of the shallow subsurface deformation about the geologic structure and the fault, including the stratigraphic structures, the dip angle and direction of the fault plane. The remarkable variation in the pattern and relative amplitude of electromagnetic waveform on the two-dimensional GPR profiles are all obvious and it is considered as the main fault zone with a nearly vertical fault with the dip angle of 70°–85°. High frequency GPR profiles show a good consistency with the trench sections at three sites. The geometry of the main fault zone can be depicted and deduced up to ~ 12 m deep or even deeper on the 25 MHz GPR profile in Yushu area and it is considered to be the result of the movement of active faults. What’s more, the geophysical features on GPR profile associated to the strike-slip fault are further summarized in different geological and geomorphological environment in Yushu area, the study also provides further evidence that GPR is valuable for fault investigation and palaeoseismic study in the Qinghai-Tibet Plateau area.