A method for installing a shore-based current measuring radar

Abstract

The present invention provides a method for installing a shore-based current measuring radar, wherein the shore-based current measuring radar comprises a transmitting antenna and a receiving antenna array. The method comprises: S1. determining a distance L between the transmitting antenna and the receiving antenna array. A ; S2. Determine the distance Ly between the transmitting antenna and the receiving antenna array and the river bank; S3. Determine the center height H of the transmitting antenna and the receiving antenna array. Through the installation method of the above-mentioned current measurement radar provided by the present invention, the position of the transmitting antenna / receiving antenna can be reasonably set, reducing the interference of the radar transmitting antenna on the signal received by the receiving antenna, while overcoming the influence of the terrain environment and improving the measurement accuracy.

Description

Technical Field

[0001] The invention relates to the technical field of hydrological flow measurement, and in particular to an installation method of a shore-based flow measurement radar arranged on a river bank. Background Art

[0002] Using radar to utilize electromagnetic wave signals to measure river flow (flow velocity) is a non-contact measurement method with application prospects. It can not only ensure the life safety of on-site monitoring technicians, but also enable normal measurement during flood periods.

[0003] Application CN202111389548.6 discloses a radar for precise measurement of river surface flow fields based on computational intelligence. However, the radar system needs to modulate and encode the transmitted signal and perform complex calculations on the received echo signal.

[0004] However, current measuring radar usually adopts the working mode of continuous wave transmission. When the continuous wave radar transmitter and receiver work at the same time, the radar's transmitting antenna will interfere with the signal received by the receiving antenna, which leads to poor quality of received signal and increased measurement error. In addition, when measuring rivers, current measuring radar is often affected by the terrain environment. The distance between the radar antenna and the river bank and the height of the antenna will affect the accuracy of current measurement. Therefore, how to arrange current measuring radar to reduce these influences and improve the accuracy of measurement is an urgent problem to be studied. Summary of the invention

[0005] In view of the difficulty in installing the existing current measuring radar antenna, the present invention provides an installation method of a shore-based current measuring radar, which can reduce the interference of the radar's transmitting antenna on the signal received by the receiving antenna and improve the measurement accuracy.

[0006] The present invention provides an installation method of a shore-based current measuring radar, wherein the shore-based current measuring radar comprises a transmitting antenna and a receiving antenna array, and the method comprises:

[0007] S1. Determine the distance L between the transmitting antenna and the receiving antenna array A ;

[0008] S2. Determine the distance Ly between the transmitting antenna and the receiving antenna array and the river bank;

[0009] S3. Determine the center height H of the transmitting antenna and the receiving antenna array.

[0010] Furthermore, the distance L between the transmitting antenna and the receiving antenna array is A According to the transmit-receive isolation I tr Sure,

[0011]

[0012] Where: P r is the received power, P t is the transmission power, G t is the transmitting antenna gain, G r is the receiving antenna gain; L tr is the transmission loss in free space.

[0013] Furthermore, in the step S1, the distance between the transmitting antenna and the receiving antenna array is determined according to the positional relationship between the transmitting antenna and the receiving antenna array.

[0014] Furthermore, when the transmitting antenna is installed at the downstream position of the receiving antenna,

[0015]

[0016] When the transmitting antenna is installed upstream of the receiving antenna,

[0017]

[0018] Furthermore, in step S2, the installation position of the flow measurement radar is determined by the horizontal beam width of the transmitting antenna and the receiving antenna array and the distance from the river boundary, and should satisfy the following relationship:

[0019] The connecting line between the receiving antenna array and the transmitting antenna is kept parallel to the river flow direction;

[0020] The antenna normals of the receiving antenna array and the transmitting antenna are directed toward the upstream of the river at an angle of γ;

[0021] The height of the antenna centers of the receiving antenna array and the transmitting antenna, and the distance between the antenna and the river edge depend on the site.

[0022] Furthermore, the overlapping intersection point of the receiving antenna array and the transmitting antenna beam should be located near the river boundary and satisfy

[0023] Ly=(Lx-L A )×tgβ,

[0024]

[0025] Where Lx is the distance between the transmitting antenna and the intersection point in the x direction, Ly is the distance between the transmitting / receiving antenna and the intersection point in the y direction, α is the angle between the edge of the transmitting beam and the x direction, and β is the angle between the edge of the receiving beam and the x direction.

[0026] Furthermore, when the transmitting antenna is installed at the downstream position of the receiving antenna,

[0027] α=90°-γ-θ1 / 2;

[0028] β=90°-γ-θ2 / 2;

[0029] When the transmitting antenna is installed upstream of the receiving antenna,

[0030] α=90°+γ-θ1 / 2;

[0031] β=90°+γ-θ2 / 2.

[0032] Where θ1 is the transmit beamwidth and θ2 is the receive beamwidth.

[0033] Further, in step S3, the center height H of the transmitting antenna and the receiving antenna array is calculated by the following formula:

[0034]

[0035] in, It is the vertical beam width of the receiving antenna. During installation, the center of the vertical beam of the receiving antenna must be pointed parallel to the water surface.

[0036] Furthermore, when there are obstacles that cannot be avoided, the antenna center height and distance are set according to the proportional relationship between the antenna center height and the distance from the river surface.

[0037] The specific calculation method is:

[0038]

[0039] Among them, x is the distance between the obstacle and the river surface, h is the height of the obstacle, X is the distance between the center of the antenna and the river surface, and H is the center height of the antenna. The values ​​of X and H should meet the restricted conditions.

[0040] By means of the installation method of the flow measurement radar provided by the present invention, the interference of the radar transmitting antenna on the signal received by the receiving antenna is reduced by reasonably setting the positions of the transmitting antenna / receiving antenna, while overcoming the influence of the terrain environment and improving the measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below.

[0042] Figure 1 A system block diagram of the shore-based current measurement radar proposed by the present invention;

[0043] Figure 2 This is a schematic diagram of horizontal surface detection of current measuring radar;

[0044] Figure 3This is a schematic diagram of the installation layout of the current measurement radar's transmitting and receiving antenna spacing (the receiving antenna is upstream);

[0045] Figure 4 This is a schematic diagram of the installation layout of the current measurement radar's transmitting and receiving antenna spacing (the transmitting antenna is upstream);

[0046] Figure 5 This is a schematic diagram of the installation layout of the flow measurement radar from the river bank (the receiving antenna is upstream);

[0047] Figure 6 This is a schematic diagram of the installation layout of the flow measurement radar from the river bank (the receiving antenna is downstream);

[0048] Figure 7 This is a schematic diagram of the center elevation of the current radar antenna and its installation distance from the river bank;

[0049] Figure 8 This is a schematic diagram of the installation of the flow measurement radar to avoid obstacles. DETAILED DESCRIPTION

[0050] In order to make the technical problems, technical solutions and advantages to be solved by the present invention more clear, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0051] The system block diagram of the current measuring radar proposed by the present invention is shown in the attached figure. Figure 1 The current measurement radar system includes a transmitting antenna, a receiving antenna array, a radar host and a power supply system.

[0052] The transmitting antenna is composed of a combination of four-unit dipole unit antennas, using vertical polarization;

[0053] The receiving antenna array is composed of 8 two-unit dipole combination antennas.

[0054] The radar host is composed of a frequency synthesizer, a transmitting power amplifier module, a receiving acquisition module, a switch, an industrial computer and a power supply system.

[0055] The performance of the antenna is one of the important components that affect the detection performance of the radar. An antenna with good performance can simplify the radar equipment, such as reducing the transmission power and reducing the power loss of the equipment. In an optional implementation, the shore-based current detection mine adopts a method of separating the transmitting antenna and the receiving antenna. The transmitting antenna is used to transmit the radar signal, and the receiving antenna is used to receive the radar echo signal.

[0056] The transmitting antenna and receiving antenna are respectively installed on two antenna towers. The center height of the antenna is preferably 10m above the water surface. At the same time, the height difference between the flood season and the dry season should be considered. The distance between the transmitting antenna and the receiving antenna should be determined by the isolation between the receiving and transmitting. In principle, the farther the distance between the two antennas, the better the isolation. In practice, the transmission power loss, energy consumption and installation and maintenance costs should also be considered.

[0057] The receiving antenna uses a dipole unit antenna. Two units are combined into one receiving antenna. Eight receiving antennas form an antenna array with vertical polarization.

[0058] Next, the working principle of flow measurement radar is introduced.

[0059] The transmitting antenna and receiving antenna (array) of the current measuring radar are located on the bank of the river. The radar radiates electromagnetic waves to the river surface through the transmitting antenna, and the receiving antenna receives the electromagnetic waves reflected by the river surface. Figure 2 As shown. When the radar signal is scattered on the river surface, the carrier frequency of the water surface reflection wave received by the radar will shift. In order to obtain the Doppler frequency shift, the antenna normal is offset by a certain angle γ toward the upstream direction of the river, that is, γ is the angle between the normal direction of the antenna and the river section (here γ = 20°~25° is temporarily taken). In practical applications, a part of the electromagnetic wave emitted by the radar is reflected back by the surface waves, and the generated Doppler frequency shift information is received by the radar receiver. By calculating the frequency difference between the reflected signal and the transmitted signal, the surface flow velocity can be calculated.

[0060] When the radar transmitter and receiver are at the same location, the Doppler frequency f D The following relations are met:

[0061]

[0062] In formula 1: v—water surface velocity;

[0063] f0—transmitting frequency;

[0064] f D - Doppler frequency shift (frequency difference);

[0065] c—the speed at which electromagnetic waves propagate in the air;

[0066] Considering that the radar uses two antennas for transmission and reception and the problem of interference of the transmitted signal on the receiver, the two antennas should be separated by a certain distance. Therefore, this distance difference should be considered in the calculation of Doppler frequency shift.

[0067] The main difference between flow radar and other radars lies in the different target properties. Water flow targets are distributed in the ground space of rivers, lakes and seas, and the different impurities in the water cause the reflection / penetration characteristics of electromagnetic waves on the water surface to change. The radar transmits electromagnetic waves to the water surface at a certain depression angle and receives radar wave signals returned from the water surface. According to the reflection characteristics of electromagnetic waves and the Doppler velocity measurement characteristics, the frequency change of the echo signal is proportional to the water surface velocity. The sensor obtains the water surface velocity by detecting the frequency change, which can be calculated by the following formula:

[0068]

[0069] In formula 2: θ is the angle between the transmitted wave and the direction of the water flow, which is the synthesis of the depression angle and the azimuth angle.

[0070] Setting the distance between the receiving and transmitting antennas

[0071] This current measurement radar adopts the working mode of continuous wave transmission. The continuous wave radar transmitter and receiver work at the same time. Interference suppression is the difficulty of continuous wave radar operation. Therefore, it is necessary to consider the impact of radar transmission on the receiving system (interference). The installation of the transmitting and receiving antennas needs to be separated by a certain distance. The distance is determined by the requirements of the transmission and reception isolation. According to the electromagnetic wave transmission equation, when the receiving antenna and the incoming wave antenna (transmitting antenna) are polarized and impedance matched, the receiving power is:

[0072]

[0073] Where: P r is the received power, λ is the electromagnetic wavelength, R is the transmission distance, P t is the transmit power, G t is the transmitting antenna gain, G r is the receiving antenna gain.

[0074] The definition of radio wave transmission loss is used to measure the attenuation of electromagnetic waves during transmission. Free space transmission loss is defined as: between two ideal point sources in free space, the gain G t =1, the input power P of the transmitting antenna t With gain G r =1 receiving antenna output power P r The ratio of

[0075]

[0076] The free space transmission loss expressed in decibels is

[0077] L tr (dB)=32.45+20lgf+20lgR Formula 5

[0078] Formula 5 can be rewritten as

[0079]

[0080] Similarly, define P r / P t is the receiving isolation and is denoted as I tr , then

[0081]

[0082] Receive isolation is expressed in decibels (dB)

[0083] I tr (dB) = G t +G r -32.45-20lgf-20lgR Formula 8

[0084] Where: G t , G r Expressed in dB, the unit of frequency f is MHz, and the unit of distance R is km. Isolation I tr is a negative value. The working frequency of this current radar is f = 430MHz. The transmitting and receiving antennas are placed parallel to the river. Considering that the normal direction of the antenna is 20° away from the main river channel, there will be a certain position difference between the transmitting antenna and the receiving antenna. Replace the distance R with the distance L between the transmitting and receiving antennas. A , then Formula 8 can be rewritten as:

[0085] I tr (dB) = G t +G r -85.12-20lgL A Formula 9

[0086] Consider two situations:

[0087] 1. The transmitting antenna is installed downstream of the receiving antenna.

[0088] At this time, the edge of the transmitting antenna beam will affect the edge of the receiving antenna beam, such as Figure 3 , the transmitting antenna beam edge angle is about 70°, and its gain G t =-2.22dB; the receiving antenna beam edge angle is about 110°, and its gain G r =-9.2dB~-11.5dB.

[0089] Assume that the required isolation degree is I tr To require a fixed value, we have:

[0090] I tr (dB)=-I Gr -20lgL A Formula 10

[0091] Or rewritten as

[0092]

[0093] 2. The transmitting antenna is installed upstream of the receiving antenna.

[0094] When the transmitting antenna is installed upstream of the receiving antenna, the gain G at the edge of the transmitting antenna beam (110°) is t =-7.37dB; Gain G at the edge of the receiving antenna beam (70°) r =-6.92dB~-3.2dB, such as Figure 4 .

[0095] Substituting into formula 9, we have:

[0096] I tr (dB)=I Gr -20lgL A Formula 12

[0097] Or rewritten as

[0098]

[0099] Relationship between the center height of the antenna array and the distance from the river bank

[0100] The installation position of the antenna and equipment is determined by the horizontal beam width of the transmitting antenna and the receiving antenna and the distance from the river boundary, and should meet the following relationship:

[0101] 1. The transmitting and receiving antennas should be parallel to the river flow (mainstream);

[0102] 2. The normal direction of the antenna is offset by an angle γ toward the upstream of the river, that is, the angle γ between the normal direction of the antenna and the river section (here γ is temporarily taken as 20°~25°);

[0103] 3. The height of the antenna center and its distance from the river edge depend on the site.

[0104] Because the transmitting and receiving antennas cannot be installed on the same bracket, the transmitting antenna can be installed downstream or upstream of the receiving antenna according to actual conditions. The distance between the transmitting and receiving antennas should be ≥20m.

[0105] 1. The transmitting antenna is installed downstream of the receiving antenna.

[0106] The advantage of installing the transmitting antenna downstream of the receiving antenna is that it is suitable for narrow rivers and small sites. The disadvantage is that the isolation between transmitting and receiving is poor. The two antennas and the host are installed on one side of the river bank. The overlapping intersection of the receiving and transmitting antenna beams should be located near the river boundary, such as Figure 5. With the transmitting antenna as the origin O and the receiving antenna as point A, the vertical and horizontal coordinates of the beam intersection point are x, y, and the shaded area is the overlapping area of ​​the transmitting and receiving electromagnetic beams. Assuming that the edge of the beam is a straight line, the distance between the transmitting and receiving antennas is OA = L A , then:

[0107] Where Lx is the distance from the transmitting antenna to the intersection point in the x direction, Ly is the distance from the transmitting / receiving antenna to the intersection point in the y direction. α is the angle between the edge of the transmitting beam and the x direction, θ1 is the transmitting beam width, β is the angle between the edge of the receiving beam and the x direction, θ2 is the receiving beam width, and the above equation can be solved to get

[0108]

[0109]

[0110] Ly=Lx×tgα=(Lx-L A )×tgβ Formula 16

[0111] The transmit beam width θ1 is 70°, then:

[0112] α=90°-20°-θ1 / 2=35°;

[0113] The receiving beam θ2 takes a value of 45°:

[0114] β=90°-20°-θ2 / 2=47.5°;

[0115] From formula 14 and formula 16, we can get Lx = 2.79L A , Ly = 1.954L A The significance of obtaining Ly is to determine the distance between the antenna (radar) installation location and the river bank, and Ly should usually be nearby.

[0116] 2. The transmitting antenna is installed upstream of the receiving antenna.

[0117] The installation method of installing the transmitting antenna upstream of the receiving antenna has better transmission and reception isolation than the installation method of installing the transmitting antenna downstream of the receiving antenna. Similarly, the two antennas and the host are installed on the side of the river bank, and the intersection point of the receiving and transmitting antenna beams should be located near the river boundary, such as Figure 6 .

[0118] At this time, formulas 14 to 16 are also applicable, except that the values ​​of α and β are different. The transmit beam width θ1 is 70°, then:

[0119] α=90°+20v-θ1 / 2=75v;

[0120] The receiving beam value is 45°:

[0121] β=90°+20°-θ2 / 2=87.5°

[0122] From formula 14 and formula 16, we can get Lx = 1.195L A , Ly = 4.459L A .

[0123] ㈢Relationship between antenna center height and river boundary

[0124] The antenna center height is determined by the vertical beam width of the receiving antenna and the distance from the river boundary. Therefore, after obtaining Ly, we must also consider whether the actual site meets the antenna center height requirements. See formula 16.

[0125]

[0126] in: It is the vertical beam width of the receiving antenna. When installing, the vertical beam center of the receiving antenna should be parallel to the water surface. Then H = 0.2217Ly. Antenna center height The antenna center height should be ≤ 0.2217Ly.

[0127] Figure 7 This is a schematic diagram of the antenna center and the distance to the river boundary. Assuming Ly = 40m, the antenna center height H = 8.9m, usually 9m to 10m (erection height ≥ H).

[0128] ㈣Other requirements

[0129] ⑴ The antenna (radar) installation should take into account the impact of flood season / dry season, which is especially important for gentle rivers;

[0130] (2) There should be no obstacles higher than the beam angle within the antenna beam angle; if there are obstacles that cannot be avoided, the antenna center height and distance should be set according to the proportional relationship between the antenna center height and the distance to the river surface, such as Figure 8 .

[0131] Calculation method:

[0132]

[0133] Where: x is the distance between the obstacle and the river surface, h is the height of the obstacle, X is the distance between the center of the antenna and the river surface, and H is the center height of the antenna. The values ​​of X and H should meet the restricted conditions.

[0134] ⑶ The transmitting antenna and receiving antenna towers should be equipped with lightning protection facilities.

[0135] By means of the installation method of the flow measurement radar provided by the present invention, the interference of the radar transmitting antenna on the signal received by the receiving antenna is reduced by reasonably setting the positions of the transmitting antenna / receiving antenna, while overcoming the influence of the terrain environment and improving the measurement accuracy.

[0136] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for installing a shore-based current measuring radar, wherein the shore-based current measuring radar comprises a transmitting antenna and a receiving antenna array, and the method comprises: S1. Determine the distance L between the transmitting antenna and the receiving antenna array A ; S2. Determine the distance Ly between the transmitting antenna and the receiving antenna array and the river bank; S3. Determine the center height H of the transmitting antenna and the receiving antenna array; The distance L between the transmitting antenna and the receiving antenna array A According to the transmit-receive isolation I tr Sure, Where: P r is the received power, P t is the transmission power, G t is the transmitting antenna gain, G r is the receiving antenna gain; L tr is the transmission loss in free space; When the transmitting antenna is installed downstream of the receiving antenna, ； When the transmitting antenna is installed upstream of the receiving antenna, ； The overlapping intersection point of the receiving antenna array and the transmitting antenna beam should be located near the river boundary and meet the following conditions: ， ， Where Lx is the distance between the transmitting antenna and the intersection point in the x direction, Ly is the distance between the transmitting / receiving antenna and the intersection point in the y direction, α is the angle between the edge of the transmitting beam and the x direction, and β is the angle between the edge of the receiving beam and the x direction; In step S3, the center height H of the transmitting antenna and the receiving antenna array is calculated by the following formula: ， Wherein, φ is the vertical beam width of the receiving antenna. During installation, the center of the vertical beam of the receiving antenna is required to be pointed parallel to the water surface.

2. The method for installing the shore-based current measuring radar according to claim 1, characterized in that: In the step S1, the distance between the transmitting antenna and the receiving antenna array is determined according to the positional relationship between the transmitting antenna and the receiving antenna array.

3. The method for installing the shore-based current measuring radar according to claim 1, characterized in that: In step S2, the installation position of the flow measurement radar is determined by the horizontal beam width of the transmitting antenna and the receiving antenna array and the distance from the river boundary, and should satisfy the relationship: The connecting line between the receiving antenna array and the transmitting antenna is kept parallel to the river flow direction; and, The antenna normals of the receiving antenna array and the transmitting antenna are directed 20° upstream of the river; and, The height of the antenna center of the receiving antenna array and the transmitting antenna, and the distance between the antenna and the river edge depend on the site.

4. The method for installing a shore-based current measuring radar according to claim 1, characterized in that: When the transmitting antenna is installed downstream of the receiving antenna, ； ； When the transmitting antenna is installed upstream of the receiving antenna, ； ； Where θ1 is the transmit beamwidth and θ2 is the receive beamwidth.

5. The method for installing the shore-based current measuring radar according to claim 4, characterized in that: When there are obstacles that cannot be avoided, the antenna center height and distance are set according to the proportional relationship between the antenna center height and the distance from the river surface.

6. The method for installing a shore-based current measuring radar according to claim 5, characterized in that: The specific calculation method is: ， Where x is the distance between the obstacle and the river surface, h is the height of the obstacle, X is the distance between the center of the antenna and the river surface, and H is the center height of the antenna.

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