A millimeter wave radar-based river surface flow velocity measurement method

Abstract

The application discloses a kind of river surface flow velocity measurement methods based on millimeter wave radar, the method includes the following steps: millimeter wave radar transmits frequency-modulated continuous wave beam to irradiate water surface, radar detection module launch end emits radio frequency signal to detection area, radar detection module receives water surface echo signal, further by radar mixer, raw signal and echo signal are mixed into low-frequency signal, obtain the original signal data containing river surface flow velocity and water level height characteristics, utilize communication module to transmit original data to server in real time for subsequent processing.The application is non-contact water flow velocity measurement method and device, is not affected by water surface environment, can realize real-time detection, while ensuring the accuracy of velocity measurement.

Description

Technical Field

[0001] This invention belongs to the field of millimeter-wave radar measurement technology, and particularly relates to a method for measuring river surface velocity based on millimeter-wave radar. Background Technology

[0002] Currently, methods for measuring water flow velocity can be divided into two types: contact and non-contact. Contact methods include impeller-type and rotor-type current meters, and ultrasonic Doppler current meters, which contact the water surface. However, in some special environments, such as river sections with rapid rises and falls and abundant floating debris, it is not convenient to use contact methods for velocity detection. These methods suffer from low efficiency and poor accuracy, and the equipment in contact with water has a limited lifespan and high maintenance costs. With increasingly stringent requirements for the timeliness of water flow monitoring information, research into non-contact measurement methods has significant practical implications. Non-contact measurement methods do not interfere with the measurement target during the measurement process. Commonly used non-contact current meters and Doppler radar sensors utilize the laser Doppler velocimetry principle to detect water flow velocity. Because it is a laser measurement method, it is easily affected by adverse weather conditions; in rainy or foggy weather, the detection capability of the laser gradually decreases as visibility decreases. Continuous wave or non-pulse Doppler radar sensors can limit the receiver's dynamic range, and these sensors are incapable of ranging, leading to inaccuracies in the measured river surface velocity. This poses a significant challenge to the performance of water flow monitoring.

[0003] Radar detection of river surface velocity relies on the Doppler effect; by calculating the Doppler frequency shift, the relative velocity between the radar detection module and the water flow can be estimated. Unlike radar detection of vehicles or pedestrians, the complex surface motion of water results in various velocity broadening characteristics in the Doppler power spectrum of river surface detection. Furthermore, the degree of Doppler power spectrum broadening is affected by beamwidth, leading to different widths for different detection angles. Estimating radial velocity based on the Doppler power spectrum is a key research focus. Specifically, some studies define the peak value after smoothing the Doppler power spectrum as the Doppler center and use it to estimate radial velocity. However, this estimation method is unsuitable for gently flowing rivers. The energy reflected from a gentle river surface to the radar is limited, resulting in a Doppler power spectrum without a significant peak, leading to a large deviation in the estimated radial velocity. Secondly, some studies have set a power threshold and defined the average of the Doppler offset values ​​of the two edges that intersect with the threshold as the Doppler center. However, this method is not universal and it is difficult to determine a fixed power threshold so that the Doppler power spectrum obtained in any watershed is higher than the noise level, making it difficult to estimate the Doppler center.

[0004] Therefore, it is of great practical value to study a new non-contact measuring device that can operate in all weather conditions, regardless of weather, temperature, and air pressure, and has stable performance. At the same time, it is necessary to determine a universal surface velocity detection method to obtain accurate velocity measurement results. Summary of the Invention

[0005] Technical Problem: To address the problems existing in the background technology, this invention proposes a method for measuring river surface velocity based on millimeter-wave radar. As a non-contact method for measuring river surface velocity, it can measure river surface velocity under various weather and environmental conditions.

[0006] Technical Solution: To achieve the above objectives, the present invention provides a method for measuring river surface velocity based on millimeter-wave radar, comprising the following steps:

[0007] Step 1: Illuminate the water surface with a frequency-modulated continuous wave beam emitted by a millimeter-wave radar. At the same time, the radar detection module emits a radio frequency signal to the detection area. The radar detection module receives the echo signal from the river surface. The radar mixer further mixes the original emitted radio frequency signal and the echo signal into a low-frequency signal to obtain the original signal data containing surface flow velocity and water level characteristics. The signal data is then transmitted to the server module in real time through the communication module for subsequent processing.

[0008] Step 2: Perform Fast Fourier Transform (FFT) processing on the distance dimension of the low-frequency signal to obtain the one-dimensional Fourier Transform result, and use the constant false alarm rate (CFAR) algorithm to determine whether water surface reflection energy has been obtained.

[0009] Step 3: Extract the distance index value corresponding to the highest peak in the one-dimensional Fourier transform result obtained in Step 2, and then estimate the river surface velocity at that distance.

[0010] Step 4: Perform a sweep frequency period Fourier transform on the distance-dimensional Fourier transform result from Step 2 to obtain the range-Doppler estimation result. At this point, perform one-dimensional cell-averaged constant false alarm rate (CFAR) detection on the range-Doppler result in both the distance and velocity dimensions, or perform two-dimensional cell-averaged CFAR detection simultaneously. Extract the velocity dimension data corresponding to the distance index value obtained in Step 3 from the CFAR result. Positive and negative velocity values ​​can then be obtained, representing two possible radial velocities.

[0011] Step 5: When using the millimeter-wave radar to emit a frequency-modulated continuous wave beam to illuminate the water surface in Step 1, the placement of the millimeter-wave radar relative to the direction of water flow is selected from the positive and negative velocity values ​​obtained in Step 4.

[0012] The velocities estimated in steps six and five are radial velocities. By combining these with the angle between the radar surface normal and the horizontal plane measured by the gyroscope, the current surface flow velocity of the river can be estimated.

[0013] in,

[0014] The relationship between the surface velocity and radial velocity of the river is as follows:

[0015]

[0016] Among them, v radial β represents the radial velocity currently measured, β is the angle between the radar surface normal and the horizontal plane as measured by the gyroscope, and v is the surface velocity of the river.

[0017] The distance dimension refers to the dimension after performing a one-dimensional Fourier transform on the low-frequency signal, where the peak points of the spectrum in this dimension correspond to targets at different distances.

[0018] The constant false alarm rate (CFAR) algorithm is used to determine whether water surface reflection energy has been obtained. Specifically, two states may occur: State 1: Water surface reflection energy has been successfully obtained, and the one-dimensional Fourier transform result after processing by the CFAR algorithm has multiple peaks; State 2: Only radar interference signals exist, and the one-dimensional Fourier transform result after processing by the CFAR algorithm has a peak only in the first range cell. The cell-average CFAR algorithm is used to determine whether it is State 1. If it is State 1, the subsequent steps can continue. If it is State 2, the process returns to step one and re-detects until State 1 is obtained.

[0019] The estimated velocity value has two possibilities: Possibility 1: If the millimeter-wave radar beam illuminates the upstream of the river, the negative velocity value in step four should be selected as the current estimated radial velocity; Possibility 2: If the millimeter-wave radar beam illuminates the downstream of the river, the positive velocity value in step four should be selected as the current estimated radial velocity.

[0020] The radial velocity refers to the velocity component of the river surface velocity in the normal direction of the millimeter-wave radar surface, that is, the projection of the river surface velocity vector in the normal direction of the millimeter-wave radar surface.

[0021] The communication module is used to transmit radar detection data to the server for processing in real time.

[0022] The server module is used for data processing, including FFT processing, constant false alarm rate (CFAR) algorithm processing, and radial velocity selection.

[0023] The gyroscope is used to measure the tilt angle between the radar surface normal and the horizontal plane, and the river surface velocity is obtained from the estimated radial velocity.

[0024] Beneficial effects: Compared with the prior art, the advantages of the present invention are as follows:

[0025] 1) This invention uses millimeter-wave radar to transmit frequency-modulated continuous waves to monitor the water surface. Compared with continuous wave radar, which cannot measure distance, it can simultaneously estimate the distance between the water level and the radar placement platform, as well as the current river surface velocity.

[0026] 2) This invention utilizes millimeter-wave radar for non-contact water surface velocity detection. The device is small in size, can be combined with various platforms, and offers highly flexible measurement methods.

[0027] 3) Advantages of additional aspects of the invention will be set forth in the description which follows, and in some respects will be obvious from the description or may be learned by practice of the invention. Attached Figure Description

[0028] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0029] Figure 1 This is a schematic diagram showing the relative placement of the millimeter-wave radar to the water surface when measuring the surface velocity of a river.

[0030] Figure 2 This is a flowchart of the method for measuring river surface velocity using millimeter-wave radar according to the present invention;

[0031] Figure 3 This is a flowchart of the velocity estimation process in this invention;

[0032] Figure 4 This is a schematic diagram illustrating the positive and negative velocity correspondences of the present invention to river conditions;

[0033] Figure 5 This is a flowchart of the data processing involved in speed estimation according to the present invention;

[0034] Figure 6 This is a schematic diagram of the velocity value distribution corresponding to the distance index extracted in this invention;

[0035] Figure 7 This is a structural diagram of the device used in this invention for measuring the surface velocity of a river using millimeter-wave radar. Detailed Implementation

[0036] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. The described embodiments are only some embodiments of the present invention, and not all embodiments.

[0037] Reference Figure 1-7 A method and apparatus for measuring river surface velocity based on millimeter-wave radar, comprising the following steps:

[0038] Step 1: The millimeter-wave radar is tilted at an angle β, and the radar beam is irradiated onto the water surface. The radar detection module transmits radio frequency signals to the detection area, and the water surface reflects the signals. After the radar detection module receives the echo signals from the river surface, the radar mixer further mixes the original signal and the echo signal into a low-frequency signal to obtain the original signal data containing surface flow velocity and water level characteristics. The above data is then transmitted to the server in real time through the communication module for further processing.

[0039] Step 2: The data obtained in Step 1 has a dimension of N×D×C, where N is the number of ADC samples selected by the frequency-modulated continuous wave radar within one signal sweep cycle, D is the number of sweep signals transmitted by the frequency-modulated continuous wave radar, and C is the number of receiving channels of the frequency-modulated continuous wave radar. First, a one-dimensional FFT transformation is performed on the data in the ADC dimension, keeping the data dimension unchanged. Then, one-dimensional constant false alarm rate (CFAR) detection is performed to determine whether water surface reflection energy has been obtained. Specifically, after the cell-averaged CFAR, two states occur: State 1: Water surface reflection energy has been successfully obtained, and the one-dimensional FFT result has multiple peaks; State 2: Only radar self-interference signals exist, and the one-dimensional FFT result has a peak only in the first range cell. The cell-averaged CFAR algorithm is used to determine whether it is State 1. If it is State 1, the subsequent steps can continue. If it is State 2, return to Step 1 and remeasure until State 1 is satisfied.

[0040] The decision threshold for constant false alarm rate (CFAR) detection can be expressed as: k is a factor used to set the desired false alarm rate, M is the total number of reference units used, and P m This represents the power of the m-th distance unit;

[0041] Step 3: The one-dimensional FFT result obtained in Step 2 after processing by the constant false alarm rate algorithm has multiple peaks. Different peaks correspond to targets at different distances. Take out the distance index value n corresponding to the highest peak. This index value is the straight-line distance between the river surface and the radar in the direction of its surface normal. Then estimate the river surface velocity at this distance.

[0042] Step 4: Based on the one-dimensional FFT result from Step 2, perform another FFT transformation along the sweep period dimension to obtain the range-Doppler estimation result, which has dimensions of N×D×C. This matrix is ​​then called the range-velocity matrix. Perform non-coherent accumulation on multiple channels to obtain an N×D matrix. Next, perform two-dimensional cell-averaged constant false alarm rate (CFAR) detection, or perform one-dimensional cell-averaged CFAR detection separately along the range and velocity dimensions. Then, as... Figure 5As shown, the velocity dimension data corresponding to the index value obtained in step three is extracted from the distance-velocity matrix. That is, the data in the nth column is extracted from the matrix. This data represents the velocity distribution value of the current distance unit. The velocity unit in the middle has a velocity of 0, and the two sides represent positive and negative velocities, respectively. Specifically, starting from the leftmost and rightmost ends, the velocity corresponding to the first non-zero data is the velocity value that can be calculated for the current distance unit. At this time, positive and negative velocity values ​​can be obtained, which are two possible radial velocities.

[0043] Step 5: Combining the relationship between the orientation of the millimeter-wave radar illuminating the water surface and the direction of the river's surface flow, as discussed in Step 1, select the velocity value from Step 4. There are two possibilities, such as... Figure 6 As shown: Possible scenario 1: If the millimeter-wave radar beam illuminates the upstream of the river, the negative velocity value from step four should be selected as the currently estimated radial velocity; Possible scenario 2: If the millimeter-wave radar beam illuminates the downstream of the river, the positive velocity value from step four should be selected as the currently estimated radial velocity v. radial ;

[0044] Step 6: Obtain the radial velocity v estimated in Step 5. radial Then, at this point, the tilt angle between the radar surface normal and the horizontal plane, measured by the gyroscope, is... Figure 1 β in the equation can be used to estimate the current surface velocity of the river. The relationship between surface velocity and radial velocity is as follows:

[0045]

[0046] Among them, v radial β represents the radial velocity currently measured, β is the angle between the radar surface normal and the horizontal plane as measured by the gyroscope, and v is the surface velocity of the river.

[0047] Based on the above-mentioned water surface velocity measurement method, the present invention also discloses a river surface velocity measurement device based on millimeter-wave radar, including a radar detection module, a communication module, a server module and a gyroscope.

[0048] The millimeter-wave radar detection module can employ frequency-modulated continuous wave (FMCW) millimeter-wave radar to detect water surface data and receive the echo energy reflected from the water surface. The communication module transmits the detection data to the server in real time for processing. The server module is used for data processing, including FFT, constant false alarm rate (CFAR) algorithm processing, and radial velocity selection. The gyroscope is used to measure the tilt angle between the radar surface normal and the horizontal plane, and the river surface flow velocity is obtained from the estimated radial velocity.

[0049] Further explanation of the invention: When a radar beam illuminates a water surface, the water surface can reflect energy, and the water flow causes a Doppler frequency shift from the Bragg scattering waves. Therefore, we can measure these data and estimate the surface velocity of the water flow at the radar line of sight based on the characteristics of these data. The radar detection module used in this invention can detect the echo energy and Doppler frequency shift of the water surface. Its general working process is as follows: The transmitting end of the radar detection module transmits a radio frequency signal, and the echo signal reflected from the water surface is received by the receiving end of the radar detection module. The radar mixer mixes the original transmitted radio frequency signal with the received echo radio frequency signal to obtain a low-frequency signal. After performing a one-dimensional FFT, different frequencies correspond to the delay of targets at different distances. Combined with the propagation speed of electromagnetic waves, the distance between the radar and the water surface can be calculated. The movement of the water surface will generate a Doppler frequency shift, thereby calculating the radial velocity. Combined with the tilt angle between the radar surface normal and the horizontal plane measured by the gyroscope, the surface velocity of the water surface corresponding to the current distance index can be estimated.

Claims

1. A method for measuring river surface velocity based on millimeter-wave radar, characterized in that, The measurement method includes the following steps: Step 1: Illuminate the water surface with a frequency-modulated continuous wave beam emitted by a millimeter-wave radar. At the same time, the radar detection module emits a radio frequency signal to the detection area. The radar detection module receives the echo signal from the river surface. The radar mixer further mixes the original emitted radio frequency signal and the echo signal into a low-frequency signal to obtain the original signal data containing surface flow velocity and water level characteristics. The signal data is then transmitted to the server module in real time through the communication module for subsequent processing. Step 2: Perform Fast Fourier Transform (FFT) processing on the distance dimension of the low-frequency signal to obtain the one-dimensional Fourier Transform result, and use the constant false alarm rate (CFAR) algorithm to determine whether water surface reflection energy has been obtained. Step 3: Extract the distance index value corresponding to the highest peak in the one-dimensional Fourier transform result obtained in Step 2, and then estimate the river surface velocity at that distance. Step 4: Perform a sweep frequency period Fourier transform on the distance-dimensional Fourier transform result from Step 2 to obtain the range-Doppler estimation result. At this point, perform one-dimensional cell-averaged constant false alarm rate (CFAR) detection on the range-Doppler result in both the distance and velocity dimensions, or perform two-dimensional cell-averaged CFAR detection simultaneously. Extract the velocity dimension data corresponding to the distance index value obtained in Step 3 from the CFAR result. Positive and negative velocity values ​​can then be obtained, representing two possible radial velocities. Step 5: When using the millimeter-wave radar to emit a frequency-modulated continuous wave beam to illuminate the water surface in Step 1, the placement of the millimeter-wave radar relative to the direction of water flow is selected from the positive and negative velocity values ​​obtained in Step 4. The velocities estimated in steps six and five are radial velocities. By combining these with the angle between the radar surface normal and the horizontal plane measured by the gyroscope, the current surface flow velocity of the river can be estimated.

2. The method for measuring river surface velocity based on millimeter-wave radar according to claim 1, characterized in that, The relationship between the surface velocity and radial velocity of the river is as follows: in, V radial This represents the currently measured radial velocity. β The angle between the radar surface normal and the horizontal plane, as measured by the gyroscope. V The surface velocity of the river.

3. The method for measuring river surface velocity based on millimeter-wave radar according to claim 1, characterized in that, The distance dimension refers to the dimension after performing a one-dimensional Fourier transform on the low-frequency signal, where the peak points of the spectrum in this dimension correspond to targets at different distances.

4. The method for measuring river surface velocity based on millimeter-wave radar according to claim 1, characterized in that, The constant false alarm rate (CFAR) algorithm is used to determine whether water surface reflection energy has been obtained. Specifically, two states may occur: State 1: Water surface reflection energy has been successfully obtained, and the one-dimensional Fourier transform result after processing by the CFAR algorithm has multiple peaks; State 2: Only radar interference signals exist, and the one-dimensional Fourier transform result after processing by the CFAR algorithm has a peak only in the first range cell. The cell-average CFAR algorithm is used to determine whether it is State 1. If it is State 1, the subsequent steps can continue. If it is State 2, the process returns to step one and re-detects until State 1 is obtained.

5. The method for measuring river surface velocity based on millimeter-wave radar according to claim 1, characterized in that, The estimated velocity value has two possibilities: Possibility 1: If the millimeter-wave radar beam illuminates the upstream of the river, the negative velocity value in step four should be selected as the current estimated radial velocity; Possibility 2: If the millimeter-wave radar beam illuminates the downstream of the river, the positive velocity value in step four should be selected as the current estimated radial velocity.

6. The method for measuring river surface velocity based on millimeter-wave radar according to claim 5, characterized in that, The radial velocity refers to the velocity component of the river surface velocity in the normal direction of the millimeter-wave radar surface, that is, the projection of the river surface velocity vector in the normal direction of the millimeter-wave radar surface.

7. A river surface velocity measurement device based on millimeter-wave radar, based on the measurement method of claim 1, characterized in that, The communication module is used to transmit radar detection data to the server for processing in real time.

8. A river surface velocity measuring device based on millimeter-wave radar according to claim 7, characterized in that, The server module is used for data processing, including FFT processing, constant false alarm rate (CFAR) algorithm processing, and radial velocity selection.

9. A river surface velocity measuring device based on millimeter-wave radar according to claim 7, characterized in that, The gyroscope is used to measure the tilt angle between the radar surface normal and the horizontal plane, and the river surface velocity is obtained from the estimated radial velocity.

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