Their work carries out useful exploration on high-precision distance measurement of millimeter-wave radar and inspires us to develop millimeter-wave radar for railway track settlement measurement. The current FMCW radar ranging requires high hardware requirements, and real-time performance is still limited. studied the effect of different frequencies on the ranging accuracy of the FMCW radar using the Cramér-Rao lower bound (CRLB). Literature proposed a continuous-wave (CW) radar based on a millimeter-wave six-port interferometer to measure the distances and Doppler frequencies with high accuracy. proposed a high-precision distance estimation algorithm for FMCW radar based on chirp-z-transform (CZT). By utilizing a 24 GHz bandwidth, frequency and phase can be combined to estimate the ultra-high-resolution range of radar reflection angle targets. For short distance ranging, combined with a tunable FIR filter, FMCW radar can correctly detect distance and small displacement in a multitarget environment. FMCW radar sensors use multiple frequencies to obtain distance information of one or more targets. With the track recognition, the distance measurement is another critical task for track settlement detection. The experimental results show that the accuracy of track classification and identification is at least 95%, and the accuracy of track settlement measurement exceeds 0.5 mm, which completely meets the accuracy requirements of the railway system. An experimental platform has been constructed to verify the effectiveness of the proposed method. Then, the adaptive chirp-z-transform (ACZT) algorithm is used to estimate the distance between the radar and the track surface, which realizes automatic real-time track settlement detection. Firstly, by constructing the RCS statistical feature data set of multiple objects in the track settlement measurement environment, a directed acyclic graph-support vector machine (DAG-SVM) based method is designed to solve the problem of track recognition in multi-object scenes. To address the issue, an ultra-high resolution track settlement detection method is proposed by using millimeter wave radar based on frequency modulated continuous wave (FMCW). The existing track settlement measurement approach requires sophisticated or expensive equipments, and the real-time performance is limited. This report presents example results from more than 200 mi (320 km) of surveys to demonstrate the capabilities and applicability of GPR to assess railway track substructure (ballast, subballast, and subgrade) conditions and to produce quantitative indices of railway track substructure condition for use in track substructure maintenance management efforts.The track settlement has a great influence on the safe operation of high-speed trains. The multiple sets of antennas provide transverse and longitudinal measurements of the track substructure. The railway GPR equipment is mounted on a hi-rail vehicle and includes multiple sets of 1-GHz air-launched horn antennas suspended above the track that permit fast survey travel speeds and high resolution measurements to a depth of 1 to 2 m. Included are brief discussions of some basic GPR principles, as well as data processing and modeling techniques that are applicable to railroad surveys. This report presents the results of the first three phases of a multiphase project to adapt Ground Penetrating Radar (GPR) to railroads for use in developing useful indices of substructure condition and performance.
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