WO2016145723A1

WO2016145723A1 - River flow speed measuring method and system based on gnss-r technology

Info

Publication number: WO2016145723A1
Application number: PCT/CN2015/077832
Authority: WO
Inventors: 白伟华; 孙越强; 杜起飞; 王先毅; 孟祥广; 柳聪亮; 王冬伟; 吴迪; 李伟; 蔡跃荣; 吴春俊; 赵丹阳
Original assignee: 中国科学院空间科学与应用研究中心
Priority date: 2015-03-19
Filing date: 2015-04-29
Publication date: 2016-09-22
Also published as: CN104865581A; CN104865581B

Abstract

A river flow velocity measuring method base on the GNSS-R technology at least comprises the following steps: down-conversion and sampling are performed on the received direct signals and reflection signals; the received direct signals are processed and the tracking frequency, the pseudo-range and the carrier wave phase observation value of the direct signals are obtained; data screening is performed on the received GNSS satellite reflection signals, eligible GNSS satellite reflection signals are selected, then the tracking frequency of the direct signals is used as a local reference frequency, each selected GNSS satellite reflection signal is processed by using an open-loop tracking method, and the residual phase of each GNSS satellite reflection signal is obtained; and the river flow velocity is inversely solved by using the residual phases output values of each eligible GNSS satellite reflection signal and in combination with the pseudo-range and the carrier wave phase observation value. A river flow velocity measuring system based on the GNSS-R technology is also provided.

Description

Method and system for measuring river flow rate based on GNSS-R technology

Technical field

The invention relates to the field of remote sensing technology, in particular to a method and a system for measuring river flow rate based on GNSS-R technology.

Background technique

The Global Navigation Satellite Positioning System (GNSS) is a collection of all global navigation satellite systems and their enhanced systems, including the established US GPS, the Russian GLONASS, the European Union's GALILEO, and China's Beidou navigation system. As one of the most influential and most practical space technology achievements, GNSS not only provides powerful tools for navigation and mapping, but also for applications in ocean measurement. Some scholars have found that GNSS Reflected signals can be received and utilized, thus opening up a new field of research - GNSS-R technology, and emerging GNSS-R ocean remote sensing based on this technology.

GNSS-R (Global Navigation Satellite Systems Reflections) remote sensing technology, GNSS reflection signal remote sensing technology, is a new type of remote sensing technology that has emerged since the 1990s. The technology uses the navigation satellite L-band signal as the transmission source, and receives the GNSS signals reflected by different targets such as ocean and land through the receiver on the shore-based, airborne and on-board receiving platforms, and finally realizes the extraction of geophysical parameters. The detection method based on GNSS-R remote sensing technology belongs to passive remote sensing method, and its working mode is to transmit and receive dual (multi) base radar mode, which has the following outstanding advantages:

a. Concealed

The detection system is not required to actively transmit the detection signal, and the heterogeneous observation mode is adopted, and the globally shared navigation constellation is used as the transmission source.

b. Rich signal source

GNSS-R remote sensing technology has a large number of signal sources. China's Beidou system, GPS, Galileo and GLONASS can all be used as signal sources for GNSS-R remote sensing technology.

c. The system has low equipment complexity and is easy to use.

With the continuous improvement of GNSS signal receivers, the degree of automation is getting higher and higher; the receiver is getting smaller and smaller, and the weight is getting lighter, which greatly reduces the work tension and labor intensity of the survey workers.

d. All-weather operation

GNSS-R remote sensing can be performed at any time within 24 hours a day, and is not affected by bad weather conditions such as cloudy nights, fog, wind and rain.

Based on the above advantages of GNSS-R, a large number of experimental and theoretical studies have been carried out at home and abroad:

In 1998 and 2000, NASA Langli Research Center carried out airborne experiments using GNSS-R for wind farm remote sensing, which proved that the GNSS-R signal normalized correlation power can be used to invert the sea surface wind field. The Zeeland-Bridge I, II, and III tests conducted by M. Martin-Neria and others in 1997, 2001, and 2003 respectively proved that the relative delay between the GNSS-R reflected signal and the direct signal can be used to invert the sea surface. height. At present, the wind speed accuracy of the GNSS-R wind measurement technology can reach ±2.0m/s, the wind direction is ±20°, and the sea surface height accuracy can reach 5cm. In addition to being successfully applied to sea surface wind field and high-level remote sensing detection, GNSS-R remote sensing technology has also been applied in remote sensing technology such as soil moisture, eddy current, tidal level and sea ice, and has obtained a lot of research results. In addition, the ultimate goal of conducting GNSS-R research is to implement on-board applications. In October 2003, the British National Space Center launched a 680-kilometer polar-pole UK-DMC disaster detection satellite. The on-board GNSS-R receiver equipment successfully received GPS signals from the ocean, snow and ice, and land reflections. The feasibility of the on-board GNSS-R ocean wind field detection is preliminarily verified. More strikingly, NASA (National Aeronautics and Space Administration) and European Space Agency ESA (European Space Agency) are planning to implement the new GNSS-R satellite in-orbit observation program CYGNSS (Cyclone Global Navigation Satellite System) And PARIS IoD (Passive Reflectometry and interferometry System in-Orbit Demonstrator).

It is worth noting that although GNSS-R technology is currently conducting extensive research in the oceans, lakes, land and snow regions, research on rivers, especially for river flow rates, is still blank.

Summary of the invention

It is an object of the present invention to invent an apparatus and method for accurately detecting river flow rates based on GNSS-R technology.

In order to achieve the above object, the present invention provides a method for measuring a river flow rate based on GNSS-R technology, comprising at least the following steps:

Step 1): performing down-conversion and sampling on the received direct signal and the reflected signal;

Step 2): processing the received direct signal to obtain a tracking frequency, a pseudorange, and a carrier phase observation value of the direct signal;

Step 3) Perform data screening on the GNSS satellite reflected signals that can be received, select the GNSS satellite reflected signals that meet the conditions, and then use the tracking frequency of the direct signals obtained in step 2) as the local reference frequency, using the open loop tracking method. Processing the selected GNSS satellite reflected signals to obtain the residual phase of the reflected signals of the respective GNSS satellites;

Step 4) Inverting the river flow velocity by using the residual phase output values of the reflected signals of the respective eligible GNSS satellites obtained in step 3) in combination with the pseudorange and carrier phase observations obtained in step 2).

In the above technical solution, in step 3), the GNSS satellite reflected signal to be selected needs to satisfy the following three conditions:

a. The specular reflection point falls on the target observation river;

b. The specular reflection point is within the coverage area of the reflective antenna;

c. The effective tracking time is between 100s and 1000s.

In the above technical solution, in step 3), processing the reflected signal of any GNSS satellite includes: generating a local replica in-phase signal and a quadrature signal by using a tracking frequency of the direct signal as a reference frequency, and the in-phase signal and After the quadrature signals are coherently integrated with the reflected signals, the four-phase phase detector is used to output the residual phase in [-π, π].

In the above technical solution, the step 4) further includes:

Step 401), performing the following step 402) - step 404) on the residual phase obtained by processing the reflected signals of the respective GNSS satellites selected in step 3), until all the GNSS satellite reflection signals have been After the processing, step 405);

Step 402), performing Fourier transform on the time domain residual phase data of the GNSS satellite reflected signal selected in step 3), obtaining a spectrum map, analyzing the low frequency component region in the spectrum map, and obtaining the maximum value thereof to obtain the maximum Low frequency component frequency;

Step 403), using the pseudorange and carrier phase observation of the direct signal obtained in step 2) for accurate positioning, obtaining the precise position of the platform load; calculating the GNSS position by using the precise ephemeris of the GNSS satellite; and calculating the platform load according to the previous calculation Calculating the elevation angle of the GNSS satellite in the center-of-center coordinate system of the receiver carrier by the geometric relationship between the precise position and the GNSS position;

Step 404), according to the maximum low frequency component frequency obtained in step 402) and the geometric elevation angle obtained in step 403), the average flow velocity of the target river during the time period is inverted, and the flow velocity observation value is obtained; the calculation formula is as follows:

V _flow =f _flow ·c/(cos(el)·f _GNSS )

Where V _flow is the river flow rate, c is the speed of light, el is the elevation angle of the GNSS satellite, and f _GNSS is the carrier frequency of the GNSS signal;

Step 405): averaging or obtaining a plurality of previously obtained flow velocity observation values to obtain a final observation.

The invention also provides a river flow rate measuring system based on GNSS-R technology, which comprises: direct signal antenna, reflected signal antenna, multi-channel intermediate frequency sampler, direct signal processing subsystem, reflected signal processing subsystem, flow rate product Data processing subsystem;

The direct signal collected by the direct signal antenna and the reflected signal collected by the reflected signal antenna are down-converted and sampled by a multi-channel intermediate frequency sampler, and then the direct signal is transmitted to the direct signal processing subsystem, and the reflected signal is transmitted to the reflection. Signal processing subsystem;

The direct signal processing subsystem processes the received direct signal by using a closed-loop tracking method to obtain a tracking frequency, a pseudorange and a carrier phase observation value of the direct signal; wherein the tracking frequency is used as a reference for the open-loop tracking of the reflected signal Frequency, pseudorange and carrier phase are prepared for post processing to obtain the exact position and speed of the receiver carrier;

The reflected signal processing subsystem performs data screening on the GNSS satellite reflected signals that can be received, selects the GNSS satellite reflected signals that meet the conditions, and then uses the tracking frequency of the direct signals output by the direct signal processing subsystem as the local reference frequency. , using an open loop tracking method to process the reflected signals of each visible GNSS satellite;

The flow rate product data processing subsystem inverts the river flow rate using the residual phase output value output by the reflected signal processing subsystem.

The advantages of the invention are:

1. The method and system of the present invention only need to receive single-frequency GNSS signals, and is applicable to all current GNSS signals, including signals of navigation systems such as GPS, Beidou and Galileo, and has the advantages of wide application range;

2. The method and system of the invention are suitable for remote sensing observation of all-weather river flow rates on shore and airborne, and the algorithm is simple and rapid, and can realize high-precision measurement of river surface velocity in a short time.

DRAWINGS

Figure 1 is a schematic diagram of the principle of inversion of river flow by residual phase spectrum analysis;

Figure 2 is a specific implementation step of the method of the present invention;

3 is a flow chart of inverting river flow rate from the residual phase of a reflected signal in the method of the present invention;

4 is a general block diagram of a GNSS-R technology detecting river flow rate device of the present invention;

Figure 5 is a schematic diagram of the flight path of the Zhengzhou airborne GNSS-R river remote sensing test on May 30, 2014;

Figure 6 is a GPS satellite azimuth and elevation starry sky map;

7 is a schematic diagram showing changes in residual phase with time after open-loop tracking of a reflected signal; wherein FIG. 7(a) is a reflected signal power I ² +Q ² , and FIG. 7( b ) is a residual phase change with time;

Fig. 8 is a diagram showing the result of phase spectrum analysis of the residual signal of the reflected signal.

detailed description

The invention will now be further described with reference to the drawings.

Figure 1 is a schematic diagram of an application scenario for measuring river flow rate. It can be seen from the figure that the signal transmitted by the GNSS satellite is received by a receiver in a receiver carrier (such as the aircraft in Figure 1) operating above the river. To implement the method of the present invention, the receiver needs to acquire two types of signals: a direct signal, a reflected signal. The direct signal refers to a signal of a visible GNSS satellite that can be directly received; the reflected signal refers to a signal that is received after the GNSS signal is reflected by a reflective surface (land surface or water surface). These two types of signals are received by two antennas respectively and will receive The antenna of the direct signal is called a direct antenna, and the antenna that receives the reflected signal is called a reflective antenna. The direct antenna is vertically erected toward the zenith, and the reflective antenna is vertically erected downward. In the embodiment shown in FIG. 1, the direct antenna is implemented by a right-handed circularly polarized antenna, and the reflective antenna is implemented by a left-handed circularly polarized antenna.

Using the collected direct and reflected signals, the river flow rate can be calculated. The principle is explained below.

1. The direct signal received by the direct antenna can be expressed as:

u _d (t)=C _d (t)·D _d (t)·A _d (t)·cos(2·π·f _d (t)−φ _d0 ) (1)

Where t is time, the amplitude and frequency of the received direct signal at time t are denoted as A _d (t) and f _d (t), the navigation message is D _d (t), and C _d (t) is the direct signal The code is divided into multiple modulation codes, and φ _d0 is the phase of the direct signal at the initial time. The frequency f _d (t) of the direct signal at time t can be further expressed as;

f _d (t)=f ₀ +f _T (t)+f _R (t)+f _a (t) (2)

Where f ₀ represents the frequency at which the GNSS signal itself is transmitted, f _T (t) represents the Doppler frequency of the GNSS satellite due to motion, and f _R (t) represents the Doppler frequency due to the motion of the receiver carrier, f _a (t) represents the Doppler frequency that is added during the propagation of the signal in the ionosphere and the atmosphere.

As shown in Fig. 1, in order to facilitate subsequent analysis, the Doppler frequency f _R (t) caused by the motion of the receiver carrier is decomposed into a horizontal Doppler frequency f _RH caused by the receiver moving velocity V _H parallel to the reflecting surface. The vertical Doppler frequency f _RV caused by the vertical velocity V _V of the reflecting surface, the frequency of the direct signal represented by the equation (2) at time t can be further rewritten as:

f _d (t)=f ₀ +f _T (t)+f _RH (t)+f _RV (t)+f _a (t) (3)

2. The reflected signal received by the reflective antenna can be expressed as:

u _r (t)=C _r (t)·D _r (t)·A _r (t)·cos(2·π·f _r (t)−φ _r0 ) (4)

Where t is time, the amplitude and frequency of the received reflected signal are A _r (t) and f _r (t), the navigation message is D _r (t), and C _r (t) is the C/A modulation of the direct signal. The code, φ _r0 is the phase of the reflected signal at the initial moment. The frequency of the reflected signal at time t can be further expressed as:

f _r (t)=f ₀ +f _T (t)+f _RH (t)-f _RV (t)+f _flow (t)+f _a (t) (5)

Where f _flow (t) represents the Doppler frequency due to the river reflection panel velocity (ie the flow rate of the river to be measured), due to the specular reflection principle (see Figure 1), the reflection caused by the receiver carrier motion perpendicular to the reflector surface The Doppler frequency of the signal is opposite to the Doppler frequency of the direct signal (see equation (3) and equation (5), the opposite of the operator before f _RV (t) in the two equations). In the case of shore-based or airborne conditions, the direct and reflected signal path delays are small due to the low platform height, so the direct and reflected signals can be considered to have the same Doppler frequency f _a (t) due to the atmosphere and the ionosphere.

3. Based on the obtained direct signal and reflected signal, the open loop tracking method is adopted in the present invention, and the direct signal closed-loop tracking frequency f _d (t) is used as the model reference frequency to generate a local replica in-phase signal υ ⁱ ( t)=cos(2·π·f _d (t)) and the quadrature signal υ ^q (t)=cos(2·π·f _d (t)), respectively, the in-phase signal and the quadrature signal are respectively The reflected signal u _r (t) is correlated and the resulting coherent integration result in T(1ms) is:

Wherein, the subscript n represents time t _{n ≤} t < t _n + T, sinc (x) = sin (x) / x. Δf _n is the average frequency difference between the received reflection and the direct signal in the time t _{n ≤} t < t _n + T:

Δf _n =f _r (t _n )-f _d (t _n )=-2·f _RV (t _n )+f _flow (t _n ) (8)

Δφ _n is the initial phase difference at which the phase of the reflected signal and the local phase are received at time t _n .

with

The noise of the I and Q channels when tracking the receiver.

The output residual phase of the GNSS-R receiver can be obtained from the previously obtained coherent integration results I and Q signals.

Among them, arctan 2 represents the four-image phase detector, φ _C is the phase 180° flipping caused by the modulation code (the C/A frequency modulated by the GPS L1 signal position is 1.023MHz, and the frequency of the Beidou B1I signal modulation is 2.046MHz), φ _D is the phase 180° flipping caused by the navigation message modulation (50Hz for the L1 signal message of the GPS and 500Hz for the B1I signal of the Beidou), all of which belong to the high frequency component and have a fixed frequency, so It does not affect the detection of river flow rates. The Doppler frequency f _RV (t) caused by the vertical movement of the receiver platform carrier is 0 in the static application of the shore, which can be neglected; in airborne applications, the aircraft is required to have a fixed altitude and a smooth flight, f _RV (t) is mainly The aircraft is caused by vertical jitter, and the high frequency component is still dominant in frequency. Moreover, the aircraft speed can be obtained by using the GNSS direct signal high-frequency sampling data (sampling rate=1/T) to obtain precise aircraft post-processing speed information. , especially the velocity information in the vertical direction, thereby removing the influence of f _RV (t).

Assume that the flow rate of the target watershed illuminated by the reflected antenna is the same for a period of time, and the residual phase output is

The fast Fourier FFT transform is performed during this period of time, and the maximum value f _flow is obtained in the low frequency component of the spectrum. As shown in Fig. 1, the flow velocity of the river can be inverted:

V _flow =f _flow ·c/(cos(el)·f _GNSS ) (10)

Where V _flow is the river flow rate, c is the speed of light, el is the elevation angle of the GNSS satellite, and f _GNSS is the carrier frequency of the GNSS signal.

The above is a description of how to calculate the flow rate of the river. The specific implementation steps of the method of the present invention will be described in detail below with reference to FIG.

In this step, the sampling rate of the sampling operation needs to conform to the Nyquist theorem. In one embodiment, the sampling rate is 16.368 MHz;

Step 2): processing the received direct signal to obtain a tracking frequency, a pseudorange and a carrier phase observation value of the direct signal; wherein the tracking frequency is used as a reference frequency for the open-loop tracking of the reflected signal, and the pseudorange and the carrier phase are Post-processing to prepare the receiver carrier for precise position and speed;

The direct signal processing can be implemented by the closed loop tracking method in the prior art;

In this step, the GNSS satellite reflected signal to be selected needs to satisfy the following three conditions:

a. The specular reflection point falls on the target observation river;

c. The effective tracking time is within a certain range of values; in one embodiment, the effective tracking time is 500 s (corresponding to a frequency domain minimum frequency resolution of 0.002 Hz), and in other embodiments, the specific tracking event is taken specifically. The value can be modified according to the actual situation, but the recommended time range is between 100s and 1000s. The specific processing process for the reflected signal of any GNSS satellite includes: generating a local replica in-phase signal and a quadrature signal by using the tracking frequency of the direct signal as a reference frequency, and cohering the in-phase signal and the orthogonal signal with the reflected signal respectively After integration, using a four-image phase detector to output the residual phase in [-π, π], in one embodiment, the output phase of the residual phase of the four-image phase detector output is 1 kHz;

Step 4): inverting the river flow rate by using the residual phase output value obtained in step 3);

Referring to FIG. 3, the step further includes:

Step 4-1), reflecting the signals of each GNSS satellite selected in step 3) (at least one GNSS) The residual phase obtained by the satellite reflected signal is respectively subjected to the following steps 4-2) - step 4-4), until all the GNSS satellite reflected signals have been processed, and then steps 4-5);

Step 4-2), performing Fourier transform (FFT) on the phase domain residual phase data selected in step 3), obtaining a spectrogram, analyzing the low frequency component (positive and negative 10 Hz) region in the spectrogram, and obtaining the region thereof. The maximum value gives the maximum low frequency component frequency.

Step 4-3), using the pseudorange and carrier phase observation of the direct signal obtained in step 2) for accurate positioning, obtaining the precise position of the platform load; calculating the GNSS position by using the precise ephemeris of the GNSS satellite; The geometric relationship between the precise position of the platform load and the GNSS position calculates the elevation angle of the GNSS satellite in the center of the receiver carrier.

Step 4-4), according to the maximum low frequency component frequency obtained in step 4-2) and the geometric elevation angle obtained in step 4-3), the average flow velocity of the target river during the time period is inverted, and the flow velocity observation value is obtained.

Step 4-5), averaging or obtaining the median observation values obtained before, and obtaining the final observation. Obviously, if the GNSS satellite reflection signal selected in step 3) has only one segment, the flow velocity observation obtained in step 4-4) is also the final observation.

The above is a description of the method of the present invention. The present invention also provides a system corresponding to the method. Referring to FIG. 4, the system includes: a direct signal antenna, a reflected signal antenna, a multi-channel intermediate frequency sampler, a direct signal processing subsystem, and a reflection. a signal processing subsystem, a flow rate product data processing subsystem; wherein

The reflected signal processing subsystem performs data screening on the GNSS satellite reflected signals that can be received, selects the GNSS satellite reflected signals that meet the conditions, and then uses the tracking frequency of the direct signals output by the direct signal processing subsystem as the local reference frequency. The open-loop tracking method is used to process the reflected signals of each visible GNSS satellite; wherein the specific processing process of the reflected signal of any visible GNSS satellite includes: generating a local replica in-phase signal by using the tracking frequency of the direct signal as a reference frequency And orthogonal signal, the in-phase signal and the quadrature signal are respectively coherently integrated with the reflected signal, and the residual phase in [-π, π] is outputted by the four-image phase detector, and the output rate is 1 kHz;

Experimental verification

Experimental overview

On May 30, 2014, the National Space Science Center of the Chinese Academy of Sciences, the Institute of Remote Sensing of the Chinese Academy of Sciences, the Tsinghua University, the Meteorological Bureau and other large units conducted airborne GNSS-R river remote sensing experiments in Shangjie District, Zhengzhou City, Henan Province, China. The GNSS-R payload used in the experiment was developed independently by the space center and consisted of three antennas and a receiver. The flight path of the aircraft is shown in Figure 5. The trajectory 1 represents the flight path of the aircraft. The area 2 represents the target observation area of the aircraft flying over the Yellow River. The airborne GNSS-R observations are carried out from the southwest-northeast and northeast-southwest respectively. The flight time is 1 hour and 10 minutes and lasts for about 20 minutes over the target area of the Yellow River. In order to obtain the precise position of the aircraft, two reference stations are assumed at points B and C respectively, and the differential positioning calculation is carried out in combination with the GPS positioning and receiving data on the aircraft. The buoys were set up in the area A to detect the surface water level and the river flow rate of the Yellow River, and used as comparative verification data.

Experimental result

The GPS satellite star map in the GNSS-R airborne test is shown in Figure 6. The black straight line in Figure 6 represents the direction of the Yellow River. The different line segments represent the azimuth and elevation of each GPS satellite during the time of the aircraft flying over the target Yellow River. It can be seen from the geometric relationship that the closer the GPS satellite trajectory and the Yellow River strikes to its specular reflection point, the more likely it is to fall in the Yellow River region. Therefore, in the GNSS-R river surface height detection, three satellite data of PRN18, PRN 21 and PRN 24 are selected for processing. . According to the theoretical analysis of GNSS-R detecting river flow rate, the GPS elevation angle is about the more sensitive to the flow velocity inversion, but it is affected by the antenna beam. The elevation angle is too low. The reflected signal falls below the antenna illumination range, and the received reflection signal power is small. The intermediate height of the PRN24 star was selected for processing analysis.

The segment of the residual phase of the PRN24 star reflection signal obtained in the time domain using the open-loop tracking algorithm is shown in Fig. 7. The frequency spectrum obtained by frequency analysis of the phase is shown in Fig. 8, wherein Fig. 7(a) is the reflected signal power I ² +Q ² , Fig. 7(b) is the value of the residual phase with time. It can be seen from the figure that the residual phase has some obvious trend (between 12 and 17 seconds), and some regions have a blurred trend (9-12 seconds). Between), so you need to obtain useful information through the frequency analysis of the phase change. The spectrum analysis diagram of the residual phase of the reflected signal is obtained by FFT. As shown in FIG. 8, the frequency distribution in the range of ±100 Hz is output, wherein a high-energy low-frequency component is visible near the low frequency, and the frequency is -0.3898 Hz. The inversion river flow rate obtained by formula (9) is -0.1471m/s. The negative sign indicates that the river flow velocity direction is directed by the aircraft to the GNSS satellite. Combined with the starry sky map, it can be seen that the flow velocity direction flows from the southwest to the northeast. The average flow velocity of the multiple buoys is 0.1265m/s, and the section of the Yellow River flows from the southwest to the northeast.

Conclusion: The GNSS-R open-loop residual phase spectrum analysis method is used to process the airborne GNSS-R experimental data of Henan Shangjie. The river flow velocity obtained by the inversion is compared with the measured data of the in-position buoy. The error is 0.0206m/s, and the flow direction is The measurement results are consistent with the actual ones. This experiment verifies that the GNSS-R open-loop residual phase spectrum analysis method is used to detect the positive velocity of the river. Authenticity and feasibility.

Finally, it should be noted that the above embodiments are merely illustrative of the technical solutions of the present invention and not limiting. While the invention has been described in detail herein with reference to the embodiments of the embodiments of the invention Within the scope of the claims.

Claims

A method for measuring river flow rate based on GNSS-R technology includes at least the following steps:

Step 1): performing down-conversion and sampling on the received direct signal and the reflected signal;

Step 2): processing the received direct signal to obtain a tracking frequency, a pseudorange, and a carrier phase observation value of the direct signal;

Step 3) Perform data screening on the GNSS satellite reflected signals that can be received, select the GNSS satellite reflected signals that meet the conditions, and then use the tracking frequency of the direct signals obtained in step 2) as the local reference frequency, using the open loop tracking method. Processing the selected GNSS satellite reflected signals to obtain the residual phase of the reflected signals of the respective GNSS satellites;

Step 4) Inverting the river flow velocity by using the residual phase output values of the reflected signals of the respective eligible GNSS satellites obtained in step 3) in combination with the pseudorange and carrier phase observations obtained in step 2).
The method for measuring river flow rate based on GNSS-R technology according to claim 1, wherein in step 3), the GNSS satellite reflection signal to be selected needs to satisfy the following three conditions:

a. The specular reflection point falls on the target observation river;

b. The specular reflection point is within the coverage area of the reflective antenna;

c. The effective tracking time is between 100s and 1000s.
The method for measuring river flow rate based on GNSS-R technology according to claim 1, wherein in step 3), processing the reflected signal of any GNSS satellite comprises: generating a reference frequency of the direct signal as a reference frequency The in-phase signal and the quadrature signal are locally copied, and the in-phase signal and the quadrature signal are respectively coherently integrated with the reflected signal, and then the residual phase in [-π, π] is output using the four-image phase detector.
The GNSS-R-based river flow rate measuring method according to claim 1, wherein the step 4) further comprises:

Step 401), performing the following step 402) - step 404) on the residual phase obtained by processing the reflected signals of the respective GNSS satellites selected in step 3), until all the GNSS satellite reflection signals have been After the processing, step 405);

Step 402), performing Fourier transform on the time domain residual phase data of the GNSS satellite reflected signal selected in step 3), obtaining a spectrum map, analyzing the low frequency component region in the spectrum map, and obtaining the maximum value thereof to obtain the maximum Low frequency component frequency;

Step 403), using the pseudorange and carrier phase observation of the direct signal obtained in step 2) for accurate positioning, obtaining the precise position of the platform load; calculating the GNSS position by using the precise ephemeris of the GNSS satellite; and calculating the platform load according to the previous calculation Calculating the elevation angle of the GNSS satellite in the center-of-center coordinate system of the receiver carrier by the geometric relationship between the precise position and the GNSS position;

Step 404), according to the maximum low frequency component frequency obtained in step 402) and the geometric elevation angle obtained in step 403), the average flow velocity of the target river during the time period is inverted, and the flow velocity observation value is obtained; the calculation formula is as follows:

V flow =f flow ·c/(cos(el)·f GNSS )

Where V flow is the river flow rate, c is the speed of light, el is the elevation angle of the GNSS satellite, and f GNSS is the carrier frequency of the GNSS signal;

Step 405): averaging or obtaining a plurality of previously obtained flow velocity observation values to obtain a final observation.
A river flow rate measurement system based on GNSS-R technology, characterized in that the system comprises: direct signal antenna, reflected signal antenna, multi-channel intermediate frequency sampler, direct signal processing subsystem, reflected signal processing subsystem, flow rate product data Processing subsystem; wherein

The direct signal collected by the direct signal antenna and the reflected signal collected by the reflected signal antenna are down-converted and sampled by a multi-channel intermediate frequency sampler, and then the direct signal is transmitted to the direct signal processing subsystem, and the reflected signal is transmitted to the reflection. Signal processing subsystem;

The direct signal processing subsystem processes the received direct signal by using a closed-loop tracking method to obtain a tracking frequency, a pseudorange and a carrier phase observation value of the direct signal; wherein the tracking frequency is used as a reference for the open-loop tracking of the reflected signal Frequency, pseudorange and carrier phase are prepared for post processing to obtain the exact position and speed of the receiver carrier;

The reflected signal processing subsystem performs data screening on the GNSS satellite reflected signals that can be received, selects the GNSS satellite reflected signals that meet the conditions, and then uses the tracking frequency of the direct signals output by the direct signal processing subsystem as the local reference frequency. , using an open loop tracking method to process the reflected signals of each visible GNSS satellite;

The flow rate product data processing subsystem inverts the river flow rate using the residual phase output value output by the reflected signal processing subsystem.