| Since 1950s, the detection of electromagnetic wave over the horizon which is based on the Bragg scattering theory has become one of the indispensable ways of inversing the ocean state in high-tech fields. The present stage extraction of wind, wave, flow of ocean dynamic parameters by ground wave radar theory mostly comes from the first and second order radar scattering cross section equation. Based on the first-order scattering cross section, the extraction of sea current has reached a high accuracy to meet the requirement of marine monitoring, however, due to the second-order scattering cross section, the extraction of wind and wave field are still being explored. The reason is revealed to be the lack of understanding the interaction mechanism between the electromagnetic waves and the ocean wave. Although, in a quantitative way, the relevant researchers and scientists have conduct the Bragg scattering mechanism examination on scaled experiments with X-band radar system, the experiment content is limited to the first and second-order scattering, ignoring non-Bragg scattering theory. In order to extract the information of the wind and wave field accurately, with a thorough understanding of the Bragg and non-Bragg scattering mechanism. This article aims to use the ultra-high frequency radar system as the hardware platform with proposing a definition of Bragg and non-Bragg scattering, conducts a in-depth study of Bragg and non-Bragg scattering on scaled experiment, and then, verifies the accuracy and stability of the radar system through the comparative experiment of current vectors. Specific work includes the following contents:1. Put forward to the design and implementation of the all-digital UHF radar system. UHF radar system operate at 340MHz, the bandwidth is 15MHz. The receiver consists of three main modules:signal source board,the analog front end and digital board. A novel model of "DSPLL+DDS" is applied to achieve RF signal, there is only one DDS chip in signal source board due to the elimination of local oscillator analog mixing module. Weak echo signal is prefiltered and amplified by the analog front end, which is then provided to the input of digital board. AD converter of digital board adopts the direct radio frequency band-pass sampling, the demodulation and down conversion are all completed in digital domain. Under the premise of accuracy, the radar system achieves a further downsizing.2. This radar system adopts the Frequency Modulated Interrupted Continuous Wave-form (FMICW) mechanism. For the different requirement, the author designs several waveform parameters from the perspective of maximum detection range to promote the energy utilization of echo signal, and verifies the effects of different waveform parameters on echo SNR by experiment.3. After the completion of the hardware platform, a series of tests and closed-loop experiments have been accomplished in the laboratory, the results reach the system design and field experiment requirements. Cooperating with the Xiantao hydrological station, Hubei province, the author carries contrast experiment of river velocity and flow. During the experiment, the receiving antenna system is divided into two pair to realize that one radar system operation obtains two-dimensional current vectors. The transmitting signal power is only 1W, the SNR of Doppler spectrum is about 50dB, which provides ideal raw date for further river velocity extraction, the radius of current filed is about 300m, echo velocity field is covering the entire channel. During the one-month comparative experiment, the agreement between the combined current vectors of radar system and the data provided by the hydrological station is good with a correlation coefficient of 0.98,the volume flow difference between of these two systems is less than 10% in long term observation, which demonstrates the feasibility of river monitoring by using UHF radar system, and in the meanwhile, indicates the correctness and stability in long-term work of the UHF radar system.4. In March and June,2014, cooperating with the Changjiang Water Resources Com-mission and the Dalian University of Technology, the author conducts high-order Bragg scattering experiments in Qianpin,Yichang research basement and the S-tate Key Laboratory of Coastal and Offshore Engineering respectively. This article ground-breakingly adopts UHF radar system in Bragg and non-Bragg wave scatter-ing research based on tank scaled experiment. The main research contents can be divided into two parts:first of all, by changing the wave parameter(wave depth, wavelength and wave height),the author presents a quantitative analysis of the re-lationship between the wavelength, the wave height and the echo amplitude, and then draw wavelength-wave height-echo amplitude three-dimensional map by s-tatistical experimental data. Moreover, the author continues the research with the first peak of Doppler spectrum of Bragg and non-Bragg scattering between electro-magnetic wave and water wave at different wavelength, after excluding the impact of the traditional phase velocity theory on the echo signal, the author raises the "1/(?)" method based on the amplitude modulation impact of the water particle to the electromagnetic wave, and qualitatively reveals the single wave manifestation of Bragg and non-Bragg scattering in Doppler spectrum, the repeatability of "1/(?)" phenomenon is verified by changing the wavelength of the waves. Meanwhile, from the perspective of the water particle movement, the author deduces the proof of the "1/(?)" theory and confirm the correctness of which by specific experiments.
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