CN114167412A - River width extraction method using river flow meter - Google Patents

Abstract

The invention provides a river width extraction method by using a river flow meter, which comprises the steps of acquiring sampled original echo data detected by the river flow meter opposite to a river bank; performing FFT on the original echo data twice to obtain a range-Doppler spectrum; separating a zero-frequency part from the range-Doppler spectrum to obtain a zero-Doppler spectrum, and superposing all the zero-Doppler spectra in a file; determining a distance element where a demarcation point is located according to the amplitude difference between the river echo and the ground echo, and using the distance element as the distance between a river flow meter and the opposite bank; and measuring the distance between the river flow meter and the river bank close to one side of the river meter, and calculating to obtain the width of the river. The invention provides a new river width extraction method, which realizes high-efficiency, quick, real-time and high-precision river width extraction by using a river flow meter.

Description

River width extraction method using river flow meter

Technical Field

The invention relates to a river width extraction method, in particular to a river width extraction method by using river flow meters.

Background

Rivers are an important way of hydrologic cycle on the earth, provide the most important water resource for human civilization, and have obvious influence on the development of the human society and the geographic environment. The surface width (river width) of a river is one of three basic hydraulic factors of the river, is usually used as a basic parameter for calculating the river flow in a hydrodynamic model, and is an important basis for monitoring flood disasters. The accuracy of the river width data plays an important role in the accuracy of the calculation result of the section flow.

At present, due to the limitation of extreme weather conditions such as lightning and rainstorm and rugged dangerous terrain, detailed contact-type river width distribution measurement at various positions of a river cannot be realized under many conditions. The current main river width measuring and calculating methods are divided into a remote sensing image processing method and a statistical fitting method. The remote sensing image processing method has the advantages that the real-time performance is not achieved, the spatial resolution is not high enough, the influence of cloud layers, shadows and the like is easily caused, and the obtained water surface width has a certain error with a real value. Statistical fitting methods require a large amount of measured data and calculation of corresponding topographical elements, and the certainty factor is not high.

Disclosure of Invention

Based on the current situation, a river width extraction method using a river flow meter is needed to solve the problem of low river width measurement accuracy of the traditional method at present and realize efficient and high-accuracy extraction of dynamic river width in time. The river flow meter is a microwave Doppler radar for river detection, and is a non-contact hydrological test high-tech means.

The invention provides a river width extraction method by using a river flow meter, which comprises the following steps:

1) placing a river meter on the ground of a river bank on one side, detecting the water surface of the river and the ground of the river opposite to the bank through an antenna, obtaining the distance from the antenna to the ground of the river opposite to the bank as the position of a demarcation point, and obtaining the original echo data which is detected by the river meter opposite to the bank and is subjected to sampling;

2) performing first Fast Fourier Transform (FFT) on the original echo data in the step 1) to realize distance transformation, and obtaining echo data X (R, L) on each distance element, wherein R is 1 … R, L which is 1 … L, L represents the number of data frames in one file, and R is the number of distance elements; performing second FFT on the data in each distance metadata coherent accumulation time to obtain a distance Doppler spectrum S (R, f), wherein R is 1 … R, R is the distance metadata, and f is the Doppler frequency;

3) separating a zero-frequency part by using the distance Doppler spectrum in the step 2) to obtain a zero Doppler spectrum, and superposing all the zero Doppler spectra in one file;

4) determining a distance element where a demarcation point is located according to the amplitude difference between the river echo and the ground echo, and using the distance element as the distance between a river flow meter and the opposite bank;

5) and (4) measuring the distance between the river flow meter and the river bank close to one side of the river flow meter, and calculating the width of the river by combining the distance in the step 4).

Further, in the step 1, the river flow meter adopts Linear Frequency Modulation (LFM) pulses, river echo signals received by the receiving antenna are mixed with local oscillation signals, and then the mixed signals are passed through a low-pass filter to obtain difference frequency signals and sampled to obtain original echo data.

Further, the specific implementation manner of acquiring the original echo data in the step 1 is as follows;

let the center frequency of radar signal be f_cIf the initial phase is 0, the sweep period is T, and the sweep bandwidth is B, then the sweep slope is α ═ B/T, so that the radar transmission waveform signal can be written as:

S_t(t)＝cos(2πf_ct+παt²)0≤t≤T

where T represents the time within the sweep period T if the target is at distance R₀And moving towards the radar at a speed v, setting N sweep frequency pulses continuously transmitted in a field of data, and for the nth pulse, wherein N is more than or equal to 1 and less than or equal to N, the received target echo is delayed as follows:

wherein t is₀＝2R₀C, c represents the speed of light, and the target echo signal can be represented as:

s_r(t)＝A_nS_t(t-t_d)

wherein A is echo signal distance attenuation;

receiving signal passing and local oscillator signalObtaining difference frequency signal after mixing and low pass filter, wherein the local oscillator signal is the transmitting signal S_t(t) and converting t_dThe substitution is simplified to obtain:

for difference frequency signal S_rAnd (t) sampling to obtain original echo data.

Further, in step 2), the river section is divided into distance elements according to the distance resolution Δ R, and the distance resolution expression is as follows:

where the distance resolution represents the distance between two divided distance elements, c is the speed of light, and τ refers to the pulse width.

Further, in step 2), the frequency is divided according to the doppler frequency resolution α f, and the expression of the doppler frequency resolution is:

wherein the Doppler frequency resolution represents the distance between two divided Doppler frequencies, N represents the number of coherently accumulated sweeps, T_sRepresenting the doppler sample period.

Further, in step 2), since the value of the range-doppler spectrum S (r, f) is a complex number, the amplitude is expressed by the echo power, and the echo power calculation formula is as follows:

in the formula, P_rFor echo power, I, Q represents the real and imaginary parts of S (r, f), respectively.

Further, in step 4), a river echo and a ground echo are obtained based on the echo power calculation formula in step 2), the amplitude difference between the river echo and the ground echo is caused by the difference of radar scattering cross sections in a radar equation, and the radar equation expression is as follows:

wherein, P_tFor radar transmission power, P_r' is the received echo power at the radar receiving place, sigma is the scattering cross section area of the target to characterize its scattering characteristics, G is the antenna gain, lambda is the wavelength, L_rLoss coefficients introduced by loss of each part of the radar are obtained; the scattering cross-sectional area of the ground is much larger than that of the water surface, so that the amplitude of the ground echo is higher than that of the water surface echo even at a distance.

Further, in the step 4), considering the influence of the dynamic water surface of the river bank, the echo intensity changes slightly along with the time, and the abscissa of the point with the maximum amplitude after the zero Doppler spectrum is superposed is selected as the distance between the demarcation point and the river meter.

Further, in step 5), the calculation expression of the river width is as follows:

W＝L₂-L₁

wherein W represents the river width, L₂Representing the distance between the river meter obtained in the step 4) and the opposite bank, L₁Representing the manually measured distance of the river current meter to the near shore.

Compared with the prior art, the invention has the following advantages and beneficial effects:

1. the invention uses a river meter, and provides a new method for acquiring river width;

2. compared with other remote sensing detection methods, the river flow meter is used as a detection tool, is not influenced by external environments such as rain, fog and the like, and can be monitored in all weather;

3. the extraction method is simple and quick, and meets the real-time working requirement of the fluviograph;

4. the river distance resolution used by the invention is 5m, thus realizing high-precision river width extraction and providing reliable information for subsequent flow calculation.

Drawings

FIG. 1 is an overall flow chart of the present invention.

Fig. 2 is a schematic diagram of river gauging.

Figure 3 is a range-doppler spectrum obtained after processing.

Figure 4 is a zero doppler spectrum after superposition.

Detailed Description

The technical solution of the present invention will be clearly and completely described below with reference to the embodiments and the accompanying drawings.

Referring to fig. 1, the river width extracting method using the river flow meter according to the embodiment of the present invention based on the amplitude difference between the river echo and the ground echo includes the following steps:

step 1): referring to fig. 2, a schematic diagram of river meter detection is shown, the river meter is placed on the ground of the left bank of the river, the water surface of the river and the ground of the opposite bank of the river are detected through an antenna, and the position of the obtained dividing point is the distance from the antenna to the ground of the opposite bank of the river. Acquiring sampled original echo data of a river meter, which is opposite to a river bank for detection;

the river flow meter system adopts Linear Frequency Modulation (LFM) pulse, river echo signals received by a receiving antenna are mixed with local oscillation signals, then the mixture is processed by a low-pass filter to obtain difference frequency signals, and the difference frequency signals are sampled to obtain original echo data.

Let the center frequency of radar signal be f_cIf the initial phase is 0, the sweep period is T, and the sweep bandwidth is B, then the sweep slope is α ═ B/T, so that the radar transmission waveform signal can be written as:

S_t(t)＝cos(2πf_ct+παt²)0≤t≤T

if the target is at distance R₀And moving towards the radar at a speed v, setting N sweep frequency pulses continuously transmitted in a field of data, and for the nth pulse (N is more than or equal to 1 and less than or equal to N), delaying the received target echo as follows:

wherein t is₀＝2R₀And c, c represents the speed of light. The target echo signal may be represented as:

s_r(t)＝A_nS_t(t-t_d)

wherein A is_nDistance attenuation is performed on the echo signals.

The received signal is subjected to frequency mixing with a local oscillator signal (i.e. a transmit signal S)_t(t)), low-pass filtering to obtain difference frequency signal, and converting t_dThe substitution is simplified to obtain:

for difference frequency signal S_rAnd (t) sampling to obtain original echo data.

In the demodulation process, output frequency spectrums are separated and superposed through IQ channels. Within a single sweep period, the target echo signal may be represented in complex form:

where j is the sign of the imaginary part, frequency f_nAnd phase

In particular to

From the above equation, it can be seen that the frequency of the echo signal is composed of two parts, the first term

Frequency deviation caused by the target speed, namely Doppler frequency shift, and the speed information of the target can be extracted by demodulating N frequency modulation echoes with the same distance element; second item

Is the frequency deviation caused by the delay of the target distance

Namely, the frequency offset caused by the distance delay is far larger than the frequency offset caused by the speed, and the distance information of the target can be extracted after the single linear frequency modulation echo is demodulated.

Step 2): performing first Fast Fourier Transform (FFT) on the original echo data in step 1), implementing distance transform, and obtaining echo data X (R, L) on each distance element, where R is 1 … R, L which is 1 … L, L represents the number of data frames in one file, and R is the number of distance elements; performing second FFT on the data in each distance metadata coherent accumulation time to obtain a distance Doppler spectrum S (R, f), wherein R is 1 … R, R is the distance metadata, and f is the Doppler frequency;

dividing the river section into distance elements according to the distance resolution Delta R, wherein the expression of the distance resolution is as follows:

where the distance resolution represents the distance between two divided distance elements, c is the speed of light, and τ refers to the pulse width.

Dividing the frequency according to the Doppler frequency resolution delta f, wherein the Doppler frequency resolution expression is as follows:

wherein the Doppler frequency resolution represents the distance between two divided Doppler frequencies, N represents the number of coherently accumulated sweeps, T_sIndicating a dopplerThe period of the decimating.

The range-doppler spectrum S (r, f) is complex, so the amplitude is expressed in terms of echo power, which is calculated as follows:

in the formula, P_rFor echo power, I, Q represents the real and imaginary parts of S (r, f), respectively.

Fig. 3 is a range doppler spectrum in the direction of the river bank obtained after processing the measured data of the fluviograph, and it can be seen from the diagram that a strong echo exists in the vicinity of 1000m from the fluviograph.

Step 3): based on the distance Doppler spectrum in the step 2), separating a zero-frequency part to obtain a zero Doppler spectrum, and superposing all the zero Doppler spectra in one file;

the purpose of adding all the zero doppler in one file is to reduce the influence of noise and the echo of a moving target with a radial velocity of 0 at a certain time. Figure 4 is a superposition of the zero doppler spectra of all recordings in a file.

Step 4): obtaining river echo and ground echo based on the echo power calculation formula in the step 2), and determining a distance element where a demarcation point is located according to the amplitude difference of the river echo and the ground echo to be used as the distance between a river flow meter and a landing;

the amplitude difference between the river echo and the ground echo is caused by different radar scattering cross sections in a radar equation, and the radar equation expression is as follows:

wherein, P_tFor radar transmission power, P_rFor the receiving echo power of the radar receiving position, sigma is the scattering cross section area of the target and is used for representing the scattering characteristics of the target. G is antenna gain, λ is wavelength, L_rIs the loss coefficient introduced by the loss of each part of the radar. From this, the echo signal distance attenuation A_nProportional to the scattering cutoff of the targetThe area, the amplitude of the echo on the ground is higher than that on the water surface even at a distance because the scattering cross-sectional area on the ground is much larger than that on the water surface.

Considering the influence of the dynamic water surface of the river bank, the echo intensity changes slightly along with the time, and the abscissa of the point with the maximum amplitude after the zero Doppler spectrum is superposed is selected as the distance between the demarcation point and the river meter. As can be seen from fig. 3, the point of maximum amplitude appears at a distance of 985m from the river current meter.

Step 5): and (4) measuring the distance between the river flow meter and the river bank close to one side of the river flow meter, and calculating the width of the river by combining the distance in the step 4).

The computational expression for river width is as follows:

W＝L₂-L₁

wherein W represents the river width, L₂Representing the distance between the river meter obtained in the step 4) and the opposite bank, L₁Representing the manually measured distance of the river current meter to the near shore.

The foregoing illustrates and describes the principles, general features, and advantages of the present invention. The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.

Claims (9)

1. A method for extracting river width by using river flow meters is characterized by comprising the following steps:

1) placing a river meter on the ground of a river bank on one side, detecting the water surface of the river and the ground of the river opposite to the bank through an antenna, obtaining the distance from the antenna to the ground of the river opposite to the bank as the position of a demarcation point, and obtaining the original echo data which is detected by the river meter opposite to the bank and is subjected to sampling;

2) performing first Fast Fourier Transform (FFT) on the original echo data in the step 1) to realize distance transformation, and obtaining echo data X (R, L) on each distance element, wherein R is 1 … R, L which is 1 … L, L represents the number of data frames in one file, and R is the number of distance elements; performing second FFT on the data in each distance metadata coherent accumulation time to obtain a distance Doppler spectrum S (R, f), wherein R is 1 … R, R is the distance metadata, and f is the Doppler frequency;

3) separating a zero-frequency part by using the distance Doppler spectrum in the step 2) to obtain a zero Doppler spectrum, and superposing all the zero Doppler spectra in one file;

4) determining a distance element where a demarcation point is located according to the amplitude difference between the river echo and the ground echo, and using the distance element as the distance between a river flow meter and the opposite bank;

5) and (4) measuring the distance between the river flow meter and the river bank close to one side of the river flow meter, and calculating the width of the river by combining the distance in the step 4).

2. The method for extracting river width by using river flow meter according to claim 1, wherein: in the step 1, the river flow meter adopts Linear Frequency Modulation (LFM) pulses, river echo signals received by a receiving antenna are mixed with local oscillation signals, and then the mixture is processed by a low-pass filter to obtain difference frequency signals and is sampled to obtain original echo data.

3. The method for extracting river width by using river flow meter according to claim 1, wherein: the specific implementation manner of acquiring the original echo data in the step 1 is as follows;

let the center frequency of radar signal be f_cIf the initial phase is 0, the sweep period is T, and the sweep bandwidth is B, then the sweep slope is α ═ B/T, so that the radar transmission waveform signal can be written as:

S_t(t)＝cos(2πf_ct+παt²)0≤t≤T

where T represents the time within the sweep period T if the target is at distance R₀And moving towards the radar at a speed v, setting N sweep frequency pulses continuously transmitted in a field of data, and for the nth pulse, wherein N is more than or equal to 1 and less than or equal to N, the received target echo is delayed as follows:

wherein t is₀＝2R₀C, c represents the speed of light, and the target echo signal can be represented as:

s_r(t)＝A_nS_t(t-t_d)

wherein A is echo signal distance attenuation;

the received signal is mixed with local oscillator signal, which is transmitted signal S, and low-pass filter to obtain difference frequency signal_t(t) and converting t_dThe substitution is simplified to obtain:

for difference frequency signal S_rAnd (t) sampling to obtain original echo data.

4. The method for extracting river width by using river flow meter according to claim 1, wherein: in the step 2), dividing the river section into distance elements according to the distance resolution Δ R, wherein the distance resolution expression is as follows:

where the distance resolution represents the distance between two divided distance elements, c is the speed of light, and τ refers to the pulse width.

5. The method for extracting river width by using river flow meter according to claim 1, wherein: in step 2), dividing the frequency according to the Doppler frequency resolution delta f, wherein the Doppler frequency resolution expression is as follows:

wherein the Doppler frequency resolution represents the distance between two divided Doppler frequencies, N represents the number of coherently accumulated sweeps, T_sRepresenting the doppler sample period.

6. The method for extracting river width by using river flow meter according to claim 1, wherein: in step 2), the range-doppler spectrum S (r, f) has a complex value, so the amplitude is expressed by the echo power, and the echo power calculation formula is as follows:

in the formula, P_rFor echo power, I, Q represents the real and imaginary parts of S (r, f), respectively.

7. The method for extracting river width by using river flow meter according to claim 6, wherein the method comprises the following steps: in the step 4), a river echo and a ground echo are obtained based on the echo power calculation formula in the step 2), the amplitude difference between the river echo and the ground echo is caused by different radar scattering cross sections in a radar equation, and the radar equation expression is as follows:

wherein, P_tFor radar transmission power, P_r' is the received echo power at the radar receiving place, sigma is the scattering cross section area of the target to characterize its scattering characteristics, G is the antenna gain, lambda is the wavelength, L_rLoss coefficients introduced by loss of each part of the radar are obtained; the scattering cross-sectional area of the ground is much larger than that of the water surface, so that the amplitude of the ground echo is higher than that of the water surface echo even at a distance.

8. The method for extracting river width by using river flow meter according to claim 1, wherein: in the step 4), considering the influence of the dynamic water surface of the river bank, the echo intensity slightly changes along with the time, and the abscissa of the point with the maximum amplitude after the zero Doppler spectrum is superposed is selected as the distance between the demarcation point and the river meter.

9. The method for extracting river width by using river flow meter according to claim 1, wherein: in step 5), the calculation expression of the river width is as follows:

W＝L₂-L₁

wherein W represents the river width, L₂Representing the distance between the river meter obtained in the step 4) and the opposite bank, L₁Representing the manually measured distance of the river current meter to the near shore.

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