The main problems existing in GPR technology include:
1) The detection depth is shallow, and the contradiction between detection depth and resolution cannot be overcome. Increasing detection depth means sacrificing detection resolution;
2) Multiple spread and other clutter jamming are serious, and there has been no good elimination method, which exists in radars at home and abroad;
3) The influence of medium unevenness is great and can not be eliminated, resulting in difficulty in obtaining necessary velocity data;
4) The data collection method of single sending and single receiving can provide limited information for post-processing and interpretation.
The above problems are fatal defects for GPR. Although many geophysicists, electromagnetic experts and geophysical workers have done a lot of research and improvement on radar antenna design, signal processing and underground target imaging, these works are only partial modifications to the existing GPR system. In order to develop GPR technology, we must update our ideas and solve the problems from the fundamental principle.
In view of this situation, experts proposed to develop a new GPR system - phased array GPR detection system in 1999.
The basic research idea is to replace the current monopole radar antenna with the phased array radar antenna by using the relatively mature military phased array radar technology. Its purpose is to gather the electromagnetic wave into a narrow beam to transmit underground (or detection object) through the phased array technology, and receive the radar echo signal reflected by the target by using the multi-channel acquisition technology, The advanced data processing is carried out, and finally the three-dimensional image of the internal structure of the detection object is given.
Development prospect of ground penetrating radar technology
It is worth noting that at present, similar products have appeared in the market, such as RIS antenna array series of a company, but these products simply combine multiple monopole antennas into array antennas, which is essentially different from the idea of phased array ground penetrating radar.
Because the phased array radar converges the electromagnetic wave into a narrow beam by controlling the phase delay of each channel, the energy is concentrated and the wave front diffusion is small. Therefore, the detection depth of the phased array radar is much larger under the condition of the same frequency and transmission power; On the contrary, under the same detection depth, phased array radar can improve the transmission power, so its resolution is much higher than the existing radar. In addition, since the spherical wave transmission is changed to beam transmission, the influence of medium heterogeneity is much smaller.
Secondly, the phased array radar works in a continuous scanning mode and can scan in multiple directions. Therefore, the amount of information is much larger than that of the existing ground penetrating radar. For some special detection work, such as the quality detection of embankment cut-off wall, its role is unmatched by the existing ground penetrating radar (monopole antenna radar can not detect the joints, forks and other defects of embankment cut-off wall at all).
Because phased array radar is a multi-channel received signal, multi-channel superposition can be carried out, just like the multiple coverage technology of reflection seismic exploration. Therefore, multiple interference can be greatly eliminated, which is difficult for existing radars. The antenna of high frequency (600mhz-1ghz) phased array ground penetrating radar can be made smaller, and its advantages are unmatched by the existing ground penetrating radar in shallow detection.
At present, the system prototype has been completed. The carrier free pulse working system with center frequency of 900MHz is adopted, and the transmitting and receiving antennas are separated. 16 (4 Ã 4) Transmit channel forming, beam aggregation and scanning 16 (4) Ã 4) The channel receives the echo, and the optional scanning angles are - 36 Â°, - 24 Â°, - 12 Â°, 0 Â°, 12 Â°, 24 Â° and 36 Â°.
The software part of the system has rich data processing functions. The main conventional processing includes filtering, gain adjustment, static and dynamic correction, deconvolution, complex signal analysis, time-frequency analysis, etc., and multi-channel data processing, such as velocity analysis, superposition technology, coherence analysis technology, array signal processing, etc. And weak signal extraction, target automatic recognition and inversion interpretation under various clutter interference. A large number of field experiments on concrete detection in Yichang Three Gorges dam are carried out. The experimental results show that the spotlight scanning function of phased array radar has been realized, the penetration depth is greater than 1.5m and the resolution is higher than that of ordinary radar.