CN100386645C - Method and Radar System for Detecting Surface Velocity of Rivers and Lakes by Radar Waves - Google Patents

Abstract

The present invention relates to a method of detecting surface flow speeds of rivers and lakes by using radar electric waves and the radar system thereof. The present invention detects the radial speed of the river surface flow by using the Doppler frequency shift of the water flow to the Bragg scatterance of the radar electromagnetic waves. The work frequency of a UHF-SVR system is 300-350MHz, a receiver adopts one-time frequency mixing, the intermediate frequency is 21.4MHz, the sampling rate of a data acquisition system is 160KHz, the power of a transmitter is 1-5W, and an aerial system adopts a ternary yagi aerial. The UHF-SVR system has the characteristics of simple structure convenient installation, low requirement to sites, human resource saving and low cost. The UHF-SVR system has the advantages of high detecting precision and high range resolution, the corresponding frequency resolution can reach 10<-3 >Hz, and the speed resolution can reach 10<-1 >CM/S. The present invention also has the advantage of ultra high precision which other surface flow detecting technologies for rivers and lakes can not have.

Description

Method and Radar System for Detecting Surface Velocity of Rivers and Lakes by Radar Waves

technical field

The invention relates to a method for detecting the surface flow velocity of rivers and lakes with radar waves and the radar using the method. The radar system can be widely used in the water flow test of rivers and lakes to detect the radial velocity of the surface flow of rivers and lakes. detection of moving objects on the surface.

Background technique

At present, the surface flow detection technology of rivers and lakes has made great progress, and many new automatic detection technologies have been produced. In addition to the conventional buoy method for water surface velocity testing, the image method, photoelectric sensor method, and acoustic Doppler velocity testing have all become new testing methods. However, there are certain defects in the above several methods. For example, the conventional buoy method not only requires more manpower, but also can only detect a single buoy successively; the image method detection is affected by the working index of the camera itself, and is related to the selection of reference control points (Introduction to the method of image method water surface velocity measurement, "Hydrology "2003.1 2). Ordinary photoelectric sensing test methods need to use a lot of hardware when the flow field is complex and multi-point flow velocity needs to be tested, the test reliability is reduced, and the cost is increased. .

Wuhan University began to develop the high-frequency ground wave radar OSMAR system for marine environment monitoring in 1997, and it was accepted by the Ministry of Science and Technology in 2000. Because only river wave trains whose wavelength is half of the working wavelength of the radar will produce the strongest backscattering of radar waves, the operating frequency of the OSMAR system is 6-12MHz in the high frequency range, and the high frequency electromagnetic waves are used to propagate beyond the horizon on the ocean surface. characteristics, to detect and analyze sea state targets (High Frequency Ground Wave Radar Research Special, "Journal of Wuhan University" 2001.5).

Contents of the invention

The purpose of the present invention is to provide a method for detecting the surface flow velocity of rivers and lakes with radar waves and its radar. It is different from the existing method for detecting the surface flow velocity of rivers and lakes. It has simple structure, easy installation, small site requirements, and saves human resources. The characteristics of low cost and high distance resolution, according to the characteristics of many lakes in our country, have certain promotion and application value.

The technical scheme of the present invention is: the method for detecting the surface velocity of rivers and lakes with radar electric wave, it is characterized in that: utilize water current to the Doppler Doppler frequency shift of radar electric wave Bragg scattering to detect the radial velocity of river water surface flow, radar electric wave FM signal The working frequency band used is 300-350MHz of ultra-high frequency band UHF; the transmission signal of the radar wave is sent to the transmission antenna through the transmission channel, and the antenna faces the river target to be measured, and the interaction between the transmission signal and the river surface flow produces backscattering; the receiving antenna receives After this signal is mixed with the local oscillator signal through the receiving channel, the intermediate frequency after mixing is 21.4MHz; coherent demodulation, the intermediate frequency signal after coherent demodulation is processed by the data acquisition and processing system, and the data after sampling processing is transmitted The radial velocity of the surface flow of the river water can be obtained through subsequent signal processing by the microcomputer system.

The above-mentioned method is characterized in that: the radar adopts a primary mixing structure, and the sampling rate of the intermediate frequency is 160KHz.

The above-mentioned method is characterized in that: the signal generator is realized by a dedicated DDS chip instead of by a common frequency mixing method.

The above-mentioned method is characterized in that: the data acquisition system of the radar is realized by ADC+FPGA+USB.

The above-mentioned method is characterized in that: the synchronous controller of the radar is realized by FPGA.

Rivers and lakes surface flow detection radar system UHF-SVR, which includes transceiver antenna system, transmitting channel, receiving channel, clock source, phase-locked loop frequency multiplication, frequency synthesis, synchronous controller, data acquisition and processing and microcomputer system, is characterized in that: The transmitting antenna, transmitting channel, frequency synthesis, clock source and phase-locked loop frequency multiplication are electrically connected in sequence, and the receiving antenna, receiving channel, data acquisition and processing and microcomputer system are electrically connected in sequence; the synchronization controller is respectively connected to the transmitting channel, frequency synthesis, phase-locked Ring frequency multiplication, receiving channel, data acquisition and processing electrical connection, the working frequency band used by radar wave frequency modulation signal is 300-350MHz of ultra-high frequency band UHF, and the frequency sweep bandwidth is 5-30MHz.

The above-mentioned radar system is characterized in that: the radar adopts a primary mixing structure, and the sampling rate of the intermediate frequency is 160KHz.

The above-mentioned radar system is characterized in that: the signal generator in the clock source and frequency synthesis adopts a dedicated DDS chip, the clock source adopts ADF4360-7 or AD4106 to generate a 1G system clock, and the frequency synthesis adopts AD9858 to generate a chirp signal.

The above-mentioned radar system is characterized in that: the synchronous controller of the radar is realized by FPGA.

UHF-SVR is a river target detection radar system developed on the basis of OSMAR system. Because the wavelength of fresh water is about 0.5m, the operating frequency of the UHF SVR system is about 300-350MHz, and it works in the UHF frequency band.

The transmission signal of the UHF-SVR system adopts the linear frequency modulation system, and the frequency sweep bandwidth is determined according to the requirements of the detection targets of rivers and lakes. The frequency sweep bandwidth is generally 5-30MHz, so the corresponding distance resolution is determined to be (5-30m).

The transmission power of the UHF-SVR system is about 1-5w. On this basis, the detection target of the SVR system can be greater than 1km.

The UHF-SVR system can be widely used in surface flow detection of rivers and lakes, and can also be used in the detection of moving targets on the surface of rivers and lakes, and can be used as a software verification platform for OSMAR systems, which has a wide range of application values.

The UHF-SVR system has the characteristics of simple structure, low cost, and less manpower demand. According to the characteristics of many lakes in our country, it has certain promotion and application value.

In the UHF surface flow radar system of the present invention, the operating frequency of the system is 300-350MHz, the receiver adopts primary mixing, the intermediate frequency is 21.4MHz, the sampling rate of the data acquisition system is 160KHz, the power of the transmitter is 1～5w, and the antenna system is Three element Yagi antenna.

The advantages of the present invention are: the present invention uses the Doppler frequency shift of the Bragg scattering of the electromagnetic wave by the water flow to measure the speed of the water flow target. It has the characteristics of simple structure, convenient installation, small site requirements, saving human resources and low cost. The UHF-SVR system has high test accuracy and high distance resolution, the corresponding frequency resolution can reach 10 ^-3 Hz, and the velocity resolution can reach 10 ^-1 cm/s. It has ultra-high precision that other river and lake surface flow detection technologies cannot have.

Description of drawings

Fig. 1 is a system block diagram of a UHF-SVR embodiment of the present invention.

Fig. 2 is a block diagram of the clock source and frequency synthesis of the UHF-SVR embodiment of the present invention.

Fig. 3 is a block diagram of the receiving channel of the UHF-SVR embodiment of the present invention.

Fig. 4 is a synchronous control signal diagram of the UHF-SVR embodiment of the present invention.

Fig. 5 is a block diagram of data acquisition of the UHF-SVR embodiment of the present invention.

Fig. 6 is the test result 1 of the UHF-SVR embodiment of the present invention.

Fig. 7 is the test result 2 of the UHF-SVR embodiment of the present invention.

Detailed ways

The overall block diagram of the UHF-SVR system is shown in Figure 1.

The transmission signal of UHF-SVR is generated by frequency synthesis. This signal is sent to the transmission antenna through the transmission channel. The transmission power is 1~5w. After receiving the signal, the receiving antenna passes through the receiving channel and mixes with the local oscillator signal. The local oscillator signal is also generated by frequency synthesis, and the intermediate frequency after mixing is 21.4MHz. We call this deramping, coherent demodulation. The intermediate frequency signal after coherent demodulation is processed by the data acquisition and processing system, the sampling rate is 160KHz, and the sampled and processed data is transmitted to the microcomputer system through USB for subsequent signal processing.

Because the frequency utilization rate of frequency synthesis is up to 40%, so to generate FM signals up to 300MHz or more, a system clock of about 1GHz is necessary. Therefore, our radar system also needs to generate a 1GHz clock source through the PLL phase-locked circuit.

Because our UHF-SVR is a coherent system, in order to ensure the normal operation of the radar system, the synchronization control part provides stable and reliable synchronization signals for each part of the radar system. There must be a strict timing relationship between all signals to ensure the normal operation of the radar. The synchronous controller is realized by FPGA. The synchronous controller realized by FPGA has the characteristic of real-time programming.

Specifically, the present invention is to design a novel river and lake surface flow radar detection system UHF-SVR, which utilizes the Doppler frequency shift of Bragg scattering of radar electromagnetic waves by water flow to measure speed. Both the transmitting signal and the local oscillator signal of this radar system are generated by a frequency synthesizer, and the system clock of the frequency synthesizer is generated by a phase-locked loop circuit to generate a 1GHz system clock. The intermediate frequency signal after coherent mixing is 21.4MHz, and the intermediate frequency signal after demodulation is sampled by the sampling signal of 160KHz, and the sampled data is directly transmitted to the PC through the data acquisition system for subsequent signal processing. In order to ensure the normal operation of the radar system, a synchronous controller is designed by FPGA to coordinate the work of various parts of the radar system.

As Fig. 2, be the clock source of UHF-SVR of the present invention and frequency synthesis block diagram: in our UHF-SVR radar system, we adopt the special-purpose (Directly Digital Synthesize) DDS chip AD9858 of ADI Company to produce chirp signal. In the design of AD9858, there must be a clock source up to 1GHz. In order to generate a 1G system clock, we use ADI's ADF4360-7 or AD4106 to generate it, which can meet our requirements for the clock system. All system parameters can be set through control registers. All modules ensure system synchronization through a unified clock source. In actual work, we use ADF4106 frequency synthesizer to realize the clock source of our UHF-SVR system. It includes a low-noise digital frequency discriminator, high-accuracy charge pump, programmable reference frequency divider, programmable counter and double-ended prescaler. We can achieve a fixed frequency output through a phase-locked loop composed of an external loop filter and an additional VCO. In our system design, the temperature-compensated oscillator should be selected as the reference frequency source of the PLL, and a 50Ω terminal is not required. The charge pump output of the ADF4106 serves as the drive for the external loop filter. In the design of the loop filter, the natural angular frequency of the loop is 45 degrees. The output of the loop filter is used as the driving voltage of the VCO, and the output of the VCO is fed back to the RF signal input terminal of the phase-locked loop, and is output as the clock source of the system at the same time. The impedance of the RF input port of the ADF4106 is 50Ω. What should be considered in the design is that between the RF output end and the reference input end of the frequency synthesizer, a T-type network needs to be added for impedance matching. In our UHF-SVR system, according to the wavelength of the river water, the operating frequency of the system is also adjusted to UHF accordingly. Our transmission signal is a chirp signal with a bandwidth of 5-30MHz.

As shown in Fig. 3, it is a block diagram of the receiving channel of the UHF-SVR of the present invention: according to the general principle of the microwave receiver, high selectivity is provided on the low noise index. In the UHF radar receiver, the main goal is to reduce the noise inside the machine, and the sensitivity and good frequency selection characteristics of the radar receiver should be taken into account. Therefore, in our receiver design, the first thing to consider is the form of the receiver. Since the transmission frequency and the local oscillator frequency are very high, it is not easy to generate, so in order to reduce the difficulty of our design, we choose a mixing and intermediate frequency sampling scheme. The actual intermediate frequency signal is 21.4MHz. In a microwave receiver, a low-noise amplifier needs to be added before the frequency mixing, because the noise figure of the mixer is generally relatively large, and the front-end filter is generally a passive filter, which has a certain loss. If there is no such LNA, then The noise figure of the whole system will be large. The introduction of an LNA with a certain gain before frequency conversion can reduce the influence of the noise of the mixer and the baseband amplifier behind on the whole machine, which is beneficial to improve the sensitivity. However, the gain of the LNA should not be too high, because the mixer is a nonlinear device, and the signal entering it is too large, which will produce a lot of nonlinear distortion. Therefore, the gain of the LNA generally does not exceed 15dB. Band-pass filters are used to select the operating frequency band and can be placed before or after the LNA. Putting it at the back is beneficial to reduce the system noise system, and putting it at the front can pre-select the signal entering the LNA, filtering out many out-of-band signals, and reducing various intermodulation distortion interference caused by the nonlinearity of the LNA.

Figure 4 is a diagram of the synchronous control signal of the UHF-SVR of the present invention: all clock signals required by the system are shown in the figure, and a strict time relationship must be guaranteed between them, only in this way can the radar work normally. In actual design, we adopt Spartan3 series FPGA chip of Xilinx Company. Because Spartan3 contains a clock management unit, it is convenient to perform clock synchronization, phase shifting, frequency division, and dejittering. But due to the limitations of DCM's system clock and frequency division multiple, we can't completely use DCM to realize our synchronous controller. In the design, we use a DCM module to shape and synchronize the clock of the FPGA. On this basis, we design the clock. In order to ensure the phase consistency of all clock signals, register output is implemented at all signal output terminals, and all registers are driven by system reset signals.

As shown in Fig. 5, it is the data acquisition block diagram of UHF-SVR of the present invention: what UHF-SVR system adopts is FMCW system, utilizes the frequency and phase information of echo signal to extract river parameter, when echo signal and receiver local oscillator signal mix The high frequency and high frequency signals are generated by the data acquisition and processing system. The data acquisition and processing system collects this signal and performs two Fourier transforms to obtain the frequency and phase information of the echo signal on each distance element. In the UHF-SVR system design, our data acquisition system is implemented with ADC+FPGA+USB. The data after high-frequency sampling is stored in the FIFO implemented by FPGA, and then transmitted to the microcomputer system through USB for subsequent processing. In the experiment, we can use two ways to realize the transmission, one is to directly transmit the collected waveform data to the PC, and complete two FFT operations in the PC; the other is to complete the first FFT in the FPGA, through The USB transmits the data after the first FFT to the PC, and the PC completes the second FFT. There are pros and cons to both approaches. For the first method, we can get the most original data, simplify the internal design of FPGA, and have more practical significance for subsequent interference removal. However, the data volume of directly transmitting the wave file is relatively large, and the transmission speed must be guaranteed during the transmission process. For the second method, the amount of data after the first FFT is smaller than that of the original waveform file, which can be easily transmitted. However, the internal design of the FPGA is increased, and the resource overhead of the FPGA is increased. In practice, because our sampling rate is 160KHz, each sweep cycle is 0.1s, the number of data bits is 8 bits, and the corresponding data volume is 160KByte/s. Real-time transmission of the original waveform can be satisfied with USB.

Therefore, we adopted the first data transmission scheme.

Figure 6 and Figure 7 are the test results 1 and 2 of the UHF-SVR of the present invention: In the test, we simulated a river echo signal with a fixed distance element by delaying the transmitted signal. After this signal is mixed with the local oscillator signal, a fixed frequency offset will occur on the basis of the 21.4MHz intermediate frequency. The Doppler spectrum we need can be obtained by two FFTs of this signal. Since we are simulating the echo signal by delaying the transmitted signal, the speed of this simulated target is 0. Because the first FFT is to perform FFT transformation on a single frequency sweep period, and the second FFT is to perform the second FFT transformation on the first FFT results of multiple frequency sweep periods, so the signal corresponding to the target speed is 0, each The first FFT results of each frequency sweep cycle should be completely consistent, and the corresponding second FFT signals of multiple frequency sweep cycles should have a spectral peak at zero frequency. As shown in the figure, it is the result of the first single-cycle FFT and the second multi-cycle FFT.

According to our design, the distance resolution of the UHF-SVR system we designed is 5-30m, and the flow velocity resolution is 0.5cm/s. It has ultra-high precision that cannot be compared with other testing methods.

As shown in Table 1, it is the emission and antenna indicators of the UHF-SVR of the present invention: Compared with the high-power transmitter of the sea-penetrating radar, our UHF-SVR system does not need a large transmission power, and the transmission power only needs about 1-5W. Here we can use field effect tubes to realize our power amplifier module, which constitutes our transmission channel. Combined with the actual situation of our signal generator, and according to our actual needs, our power amplifier and antenna indicators are shown in Table 1.

Table 1

Claims (9)

1. use the method for detecting surface flow speed of river lake using radar electric wave, it is characterized in that: utilize current that the radial velocity that flow on the river surface is surveyed in the Doppler Doppler frequency displacement of radar wave Prague Bragg scattering, the used working frequency range of radar wave FM signal is the 300-350MHz of hyper band UHF; Transmitting of radar wave delivered to emitting antenna through transmission channel, and antenna surface is to river to be measured target, and signal to be transmitted and surface, river stream interact and produces back scattering; Receiving antenna receives behind this signal through receiving cable and local oscillation signal generation mixing, and the intermediate frequency after the mixing is 21.4MHz; Coherent demodulation, the intermediate-freuqncy signal after the coherent demodulation is carried out data processing through data acquisition and disposal system, and the data after the sampling processing are sent to microsystem and carry out follow-up signal Processing, can obtain the radial velocity of river surface stream.

2. the method for claim 1 is characterized in that: radar adopts a mixing structure, and the if sampling rate is 160KHz.

3. the method for claim 1 is characterized in that: signal generator is realized by the DDS chip of special use.

4. as claim 1 or 2 or 3 described methods, it is characterized in that: the data acquisition system (DAS) of radar is realized by ADC+FPGA+USB.

5. as claim 1 or 2 or 3 described methods, it is characterized in that: the isochronous controller of radar is realized by FPGA.

6. acquisition radar system is flowed on the rivers and lakes surface, it comprises dual-mode antenna system, transmission channel, receiving cable, clock source, frequency multiplication of phase locked loop, frequency synthesis, isochronous controller, data acquisition process and microsystem, it is characterized in that: emitting antenna, transmission channel, frequency synthesis, clock source and frequency multiplication of phase locked loop are electrically connected successively, and receiving antenna, receiving cable, data acquisition process and microsystem are electrically connected successively; Isochronous controller is electrically connected with transmission channel, frequency synthesis, frequency multiplication of phase locked loop, receiving cable, data acquisition process respectively, and the used working frequency range of radar wave FM signal is the 300-350MHz of hyper band UHF, and the frequency sweep bandwidth is 5-30MHz.

7. radar system as claimed in claim 6 is characterized in that: radar adopts a mixing structure, and the if sampling rate is 160KHz.

8. radar system as claimed in claim 6, it is characterized in that: signal generator adopts special-purpose DDS chip in clock source and the frequency synthesis, the clock source adopts ADF4360-7 or AD4106 to produce the system clock of 1G, and frequency synthesis adopts AD9858 to produce linear FM signal.

9. as claim 6 or 7 or 8 described radar systems, it is characterized in that: the isochronous controller of radar is realized by FPGA.

Images