Development And Application Of The L-band Radar Earth Echo Measurement System

Backscatter coefficient's measurement is an important part of the research on the echo characteristics of the earth, and the radar scatterometer designed for the needs of scattering coefficient's measurement of the earth is one of the key technology to support its development.This thesis introduces the design and realization of a L-band radar scatterometer system which is used to measure the scattering coefficient of the earth worked at near vertical incidence. This radar scatterometer uses a narrow-beam dual-antenna linear frequency modulation continuous wave (LFMCW) system. RF-front of this system uses a way of self-beat mixing, the echo signals received from the mixer will be gathered synchronously and saved to the computer by a digital acquisition module after the pretreatment and PGA amplification. After the power spectrum estimation for the collected signals, the measured objectives'scattering coefficient can be calculated out combined to the radar parameters and environmental parameters.FM non-linearity of FMCW radar is an important indicator of the system performance, it affects mainly on the system's range resolution and ranging accuracy. In this thesis, a digital-analog hybrid system constituted by the closed-loop linearity correction method has been used to correct the FM non-linearity for the radar scatterometer, and compared with the original 10%, the FM non-linearity of this system is better than 0.5% after correction, which is already fully meet the requirements of the system.Calibration is the core difference between scatterometer and normal detection radar, it directly affects the measurement accuracy of the scattering coefficient. This thesis describes the general method for scatterometer's calibration: internal calibration and external calibration, and consider to this system's feature, a specific calibration program has been developed to fit it. A standard metal ball with known RCS value has been used as the calibration body in the external calibration experiment which used a relative calibration method and acquired the calibration data. In the internal calibration, PGA gains and rang measurement also have been calibrited using radar delay line and the corner reflector at indoor and outdoor experiments.Finally, an experiment has been done to measure the scattering coefficient of the tillage fields using this scatterometer and acquire measurement data, and the analysis of measurement data has been done too.In conclusion, the two aspects of following works have been done in the thesis.First, the development of the radar scatterometer System, including:According to the requirements of measurement designed the whole system and specified its parameters.Designed and debuged the RF-front and IF module of the L-band LFMCW radar scatterometer.Corrected the FM non-linearity of this system to make the system to achieve the using standard.Second, the calibration and scattering coefficient's measurement method of this scatterometer, including:Research the calibration method. Through the indoor and outdoor calibration experiments, calibrited the PGA gains and rang measurement, and used metal ball to complete the system absolute calibration.Measured and analysised the scattering coefficient of the tillage fields. Got the scattering coefficient curves of this kind of terrain.