Multi-path reflection coefficient calculation method using signal-to-noise ratio amplitude of GNSS geodetic measurement type receiver

Abstract

The invention provides an earth surface multipath reflection coefficient calculation method based on the signal-to-noise ratio amplitude of a geodetic survey receiver of a global navigation satellite system (GNSS), which comprises the following steps: preprocessing the signal-to-noise ratio of the GNSS, and screening available waveforms; solving an envelope of a signal-to-noise ratio oscillation item by utilizing Hilbert change, and calculating an initial value of a multi-path reflection coefficient; deducing a multi-path reflection coefficient theoretical value; correcting system errors; random error correction; and an accurate multi-path reflection coefficient is obtained. According to the method for calculating the multi-path reflection coefficient by using the GNSS geodetic survey receiver, related parameters such as the snow density and the frozen soil ice content can be calculated subsequently through the dielectric constant according to the multi-path reflection coefficient, and the application potential of the GNSS receiver is expanded.

Description

Technical Field

[0001] The present invention relates to the field of remote sensing applications of navigation satellites, and particularly to a method for accurately calculating the multipath reflection coefficient through the signal-to-noise ratio amplitude of a GNSS geodetic receiver. This multipath reflection coefficient is the basis for accurately estimating subsequent surface dielectric constants and other related parameters such as snow density and ice content in frozen soil, and serves climate change assessment, water resource management, disaster monitoring, etc. Background Art

[0002] In the past fifteen years, Global Navigation Satellite System (GNSS) geodetic receivers have been widely used in the field of remote sensing. Utilizing the stable and free L-band microwave signals provided by GNSS satellites has become an effective means for detecting surface parameters. It is a supplement to the observation means between ground observations and satellite remote sensing. Typical stations can provide surface parameter products with a spatial resolution of 1000m 2 and a temporal resolution of hourly.

[0003] The surface parameters can be characterized by the phase and amplitude information of the signal-to-noise ratio in a GNSS geodetic receiver. Among them, the utilization of phase information has been relatively mature. Phase delays have been used for variables related to the height of the reflecting surface such as snow depth, water surface height, and surface elevation changes in permafrost regions. The amplitude information carries signal intensity information, and theoretically, the dielectric constant can be reflected through the multipath reflection coefficient (the ratio of the amplitude of the reflected signal to the amplitude of the direct signal). Current research has verified the sensitivity of the signal-to-noise ratio amplitude to surface parameters related to the dielectric constant such as vegetation water content and freeze-thaw state, and has used preliminary dielectric constant estimates for applications such as clearly discriminating the water-land boundary with obvious thresholds. However, accurately calculating small-range and dynamic dielectric constant-related parameters through a geodetic receiver remains a difficult point to be solved. The reason is that the systematic error introduced by the antenna gain and the random error introduced by the surrounding environment restrict the acquisition of accurate surface dielectric constants. Summary of the Invention

[0004] The content of the present invention is based on the signal-to-noise ratio amplitude information of a geodetic receiver, and provides a method for calculating the multipath reflection coefficient. The multipath reflection coefficient is closely related to the surface type, and this multipath reflection coefficient is the basis for estimating the dielectric constant and related parameters under the subsequent corresponding surface types.

[0005] To achieve the above-mentioned invention objectives, the present invention provides the following technical solutions:

[0006] A method for calculating the multipath reflection coefficient using the signal-to-noise ratio amplitude of a GNSS geodetic receiver, the method comprising the following steps:

[0007] Step 1: Preprocessing of the signal-to-noise ratio data of navigation satellites;

[0008] Step 2: Obtaining the initial value of the multipath reflection coefficient;

[0009] Step 3: Deriving the theoretical value of the multipath reflection coefficient;

[0010] Step 4: System error correction;

[0011] Step 5: Random error correction;

[0012] Step 6: Obtaining the accurate multipath reflection coefficient.

[0013] Furthermore, the "preprocessing of the signal-to-noise ratio data of navigation satellites" described in Step 1 is specifically implemented as follows:

[0014] (1) Receive the standard format RINEX (Receiver Independent Exchange Format) file from navigation satellites through a geodetic receiver;

[0015] Obtain the observed value information of navigation satellites from the above standard format file, including time, signal-to-noise ratio, satellite elevation angle, and azimuth angle information; the information received by the geodetic receiver is an interference composite signal formed by the direct signal of each navigation satellite and the reflected signal passing through the ground surface.

[0016] (2) For the signal-to-noise ratio of each navigation satellite, separate the trend term and the oscillation term; perform polynomial fitting on the signal-to-noise ratio of each navigation satellite to obtain the trend term, and obtain the oscillation term by subtracting the trend term;

[0017] (3) Perform frequency domain conversion (such as Lomb-Scarge transform) and spectral analysis on the oscillation term obtained for each navigation satellite to obtain the ratio of the main frequency to the noise (pknoise), which can reflect the quality of the signal, and the quality is positively correlated with this value. Screen out the trend term and the oscillation term with pknise greater than a specific threshold (such as pknoise > 3).

[0018] Furthermore, the "obtaining the initial value of the multipath reflection coefficient" described in Step 2 is specifically implemented as follows:

[0019] (1) Process the trend term and the oscillation term of the signal-to-noise ratio of the navigation satellites screened in Step 1, and obtain the envelope and phase of the normalized signal-to-noise ratio oscillation term;

[0020] (2) Calculate the initial value α0 of the multipath reflection coefficient using the envelope and phase of the normalized signal-to-noise ratio oscillation term.

[0021] Furthermore, the "deriving the theoretical value of the multipath reflection coefficient" described in Step 3 is specifically implemented as follows:

[0022] (1) Acquisition of the direct signal power P d and the reflected signal power P r ;

[0023] (2) Derivation and acquisition of the multipath reflection coefficient α t from theoretical simulation.

[0024] Furthermore, there is a systematic error in the initial value of the multipath reflection coefficient caused by antenna gain estimation. The "systematic error correction" described in Step 4 is specifically implemented as follows:

[0025] (1) Correction formula. The accurate multipath reflection coefficient formula is as follows:

[0026] α = α s + A0

[0027] where α is the corrected multipath reflection coefficient, α s is the multipath reflection coefficient after systematic error correction, and A0 is the correction for surface random error.

[0028] (2) Observation systematic error correction. The multipath reflection coefficient α s after systematic error correction is as follows:

[0029] α s = α0 + f elev (θ) + E

[0030] where f elev (θ) = a + b * θ + c * θ 2 + d * θ 3

[0031] f elev (θ) is the correction for satellite elevation angle systematic error, a, b, c, and d are corresponding parameters, and E is the antenna gain correction parameter.

[0032] (3) Calculate the corresponding parameters a, b, c, d, and E in the correction formula using a period of bare soil. The random error during the bare soil period is considered 0. The multipath reflection coefficient α t from theoretical simulation during the bare soil period is used as the corrected value, and an equation is established with the multipath reflection coefficient inverted during the bare soil period to solve for a, b, c, d, and E.

[0033] Furthermore, there is a random error in the initial value of the multipath reflection coefficient caused by the surrounding environment. The "random error correction" described in Step 5 is specifically implemented as follows:

[0034] (1) Surface random error correction. The correction rule for the random error A0 of the multipath reflection coefficient is as follows:

[0035] A0 = f(x)

[0036] The calculation of the random error f(x) needs to consider the actual surface conditions.

[0037] Furthermore, the "multipath reflection coefficient correction" described in Step 6 is specifically implemented as follows:

[0038] (1) Calculate the accurate multipath reflection coefficient using the correction formula solved in Steps 5 and 6. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a flowchart of the method for calculating the multipath reflection coefficient using the signal-to-noise ratio amplitude of a GNSS geodetic receiver according to the present invention.

[0040] Figure 2 is the envelope obtained from the signal-to-noise ratio waveform based on the Hilbert transform according to the present invention.

[0041] Figure 3 is the comparison between the multipath reflection coefficient calculated according to the present invention and the theoretical multipath reflection coefficient. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0042] The method for calculating the multipath reflection coefficient using the signal-to-noise ratio amplitude of a GNSS geodetic receiver provided by the present invention will be further described in detail below. The specific steps are as follows:

[0043] Step 1: Preprocessing of the signal-to-noise ratio data of navigation satellites

[0044] (1) Receive the standard format RINEX (Receiver Independent Exchange Format) file from navigation satellites through a geodetic receiver;

[0045] Obtain the observation value information of navigation satellites from the above standard format file, including time, signal-to-noise ratio, satellite elevation angle, and azimuth angle information; the information received by the geodetic receiver is an interference composite signal formed by the direct signal of each navigation satellite and the reflected signal passing through the surface.

[0046] (2) For the signal-to-noise ratio of each navigation satellite, separate the trend term and the oscillation term; perform polynomial fitting on the signal-to-noise ratio of each navigation satellite to obtain the trend term, and separate the trend term by taking the difference to obtain the oscillation term;

[0047] The signal-to-noise ratio SNR formula received by the geodetic receiver is shown in Equation (1), the trend term SNR trend is shown in Equation (2), and the oscillation term SNR detrend is shown in Equation (3).

[0048]

[0049]

[0050] Wherein, A i is the amplitude of the interference signal, P n is the noise power, A d is the amplitude of the direct signal, A r is the amplitude of the reflected signal, is the interference signal phase.

[0051] In an embodiment of the present invention, the elevation angle range is selected as 15 - 30 degrees.

[0052] (3) Perform Lomb - Scarge spectral analysis on the oscillation terms obtained for each navigation satellite to obtain the ratio (pknoise) of its main frequency to the noise. This value can reflect the quality of the signal, and the quality is positively correlated with this value. Screen out the trend terms and oscillation terms with pknise > 3.

[0053] Step two: Obtain the initial value of the multipath reflection coefficient

[0054] (1) According to the rules of step one, screen out the corresponding trend terms and oscillation terms, and obtain the envelope and phase of the normalized signal - to - noise ratio oscillation term. Divide the trend term by the oscillation term, which is called the normalized signal - to - noise ratio oscillation term The initial value of the multipath reflection coefficient α0 = A r / A d , and use formulas (2) and (3) to calculate the ratio to obtain formula (4).

[0055]

[0056] Perform Hilbert transform on the normalized signal - to - noise ratio oscillation term, and its envelope can be expressed and phase

[0057]

[0058] (2) Substitute the phase of formula 7 into the normalized signal - to - noise ratio oscillation term (formula 4), and combine it with the envelope calculated by formula 6 to calculate the initial value of the multipath reflection coefficient α0.

[0059]

[0060] Step three: Deduce the theoretical value of the multipath reflection coefficient;

[0061] (1) Obtaining the direct signal power P d and the reflected signal power P r :

[0062]

[0063] In the formula, is the intensity of the direct signal, is the antenna gain of the direct signal, X is the reflection coefficient considering the antenna gain, as shown in formula (10). The power influence caused by roughness is represented by S, W d and W r are the Woodward function values. If the energy attenuation of the reflected signal caused by the roughness of the ground surface is ignored. W d and W r are approximately equal.

[0064] (2) The multipath reflection coefficient α of the theoretical simulation t Obtained through derivation and expressed as follows:

[0065]

[0066] The reflection coefficient X considering the antenna gain can be expressed as:

[0067]

[0068] In the formula, R RL and R RR are the left - hand circular polarization reflection coefficient and the right - hand circular polarization reflection coefficient respectively. and are the left - hand circular polarization antenna gain and the right - hand circular polarization antenna gain of the reflected signal respectively. The multipath reflection coefficient α t is related to the antenna gain and the Fresnel reflection coefficient. The antenna gain data is known, and the Fresnel reflection coefficient formula is as follows,

[0069]

[0070] In the formula, R H and R v are the horizontal polarization reflection coefficient and the vertical polarization reflection coefficient respectively, ε is the dielectric constant of the underlying surface, and θ is the satellite elevation angle.

[0071] Step Four: System error correction

[0072] (1) Correction formula. The accurate multipath reflection coefficient formula is as follows:

[0073] α = α s +A0 (13)

[0074] α is the corrected multipath reflection coefficient, α s is the multipath reflection coefficient after system error correction, and A0 is the correction for the surface random error.

[0075] (2) Observation system error correction. The multipath reflection coefficient α after system error correction s is as follows:

[0076] α s = α0 + f elev (θ) + E (14)f elev f(θ) = a + b*θ + c*θ2 + d*θ 3 (15)

[0077] f elev f(θ) is the correction for the satellite elevation angle systematic error, a, b, c, d are the corresponding parameters, and E is the antenna gain correction parameter.

[0078] (3) Use a period of bare soil to calculate the corresponding parameters a, b, c, d, E in the correction formula. The random error during the bare soil period is regarded as 0. The multipath reflection coefficient α in the theoretical simulation during the bare soil period t is used as the corrected value to establish an equation with the multipath reflection coefficient retrieved during the bare soil period, and solve for a, b, c, d, E.

[0079] During the bare soil period, the soil dielectric constant ε soil is calculated as follows

[0080] ε soil = ε′ soil + ε″ soil * i (16)

[0081]

[0082] In the formula, the values of S and C are the percentage contents of sand grains and clay grains in the soil, and m v is the soil volumetric water content.

[0083] In a specific embodiment, the bare soil period is defined as DOY 270 - 300.

[0084] Step Five: Random error correction

[0085] (1) The random error A0 correction rule for the multipath reflection coefficient is as follows:

[0086] A0 = f(x) (19)

[0087] The calculation of the random error f(x) needs to consider the actual surface conditions.

[0088] In a specific embodiment, when solving the reflection coefficient of the vegetated soil, the random error A0 = m*ndvi + n;

[0089] The NDVI is the historical average of the daily normalized difference vegetation index, and m and n are the corresponding parameters of the correction formula. After calculating the systematic error in step four, the corresponding parameters m and n in the correction formula are calculated using a 30-day surface period with vegetation cover. The theoretical simulation multipath reflection coefficient corresponding to the vegetated soil is used as the corrected value, and an equation is established with the multipath reflection coefficient calculated during this period to solve for m and n.

[0090] Step Six: Obtain the accurate multipath reflection coefficient

[0091] (1) Calculate the accurate multipath reflection coefficient using the solved correction formula.

[0092] In a specific embodiment, the multipath reflection coefficient for any day with vegetation cover is solved. The random error A0 is calculated based on the normalized difference vegetation index and formula (19); the multipath reflection coefficient α after systematic error correction is calculated based on formulas (14 - 15). s Finally, the accurate multipath reflection coefficient is calculated based on formula (13).

[0093] The embodiments described above are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations, variations, modifications, and substitutions made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for calculating multipath reflection coefficient using the signal-to-noise ratio amplitude of a GNSS geodetic receiver, characterized in that: The method comprises the following steps: Step 1: Navigation satellite signal-to-noise ratio data preprocessing; Step 2: Obtain the initial value of multipath reflection coefficient observation; Step 3: Derive the theoretical value of multipath reflection coefficient; Step 4: System error correction; Step 5: Random error correction; Step 6: Get the accurate multipath reflection coefficient.

2. The method for calculating the multipath reflection coefficient using the signal-to-noise ratio amplitude of a GNSS geodetic receiver according to claim 1, characterized in that The specific implementation steps of "navigation satellite signal-to-noise ratio data preprocessing" described in step 1 are as follows: (1) Receive RINEX (Receiver Independent Exchange Format) files from navigation satellites via geodetic receivers; Obtain the observation value information of the navigation satellite from the above standard format file, including time, signal-to-noise ratio, satellite altitude angle, and azimuth angle information; The information received by the geodetic receiver is an interference composite signal formed by the direct signal of each navigation satellite and the reflected signal passing through the surface. (2) For the signal-to-noise ratio of each navigation satellite, separate the trend term and the oscillation term; The trend term is obtained by polynomial fitting of the signal-to-noise ratio of each navigation satellite, and the oscillation term is obtained by performing difference separation on the trend term; (3) The oscillation term obtained from each navigation satellite is transformed into the frequency domain (such as Lomb-Scarge transform) and analyzed in the spectrum to obtain the ratio of its main frequency to noise (pknoise). This value can reflect the quality of the signal, and the quality is positively correlated with this value. The trend terms and oscillation terms with pknise greater than a specific threshold (such as pknoise>3) are screened out.

3. The method for calculating the multipath reflection coefficient using the signal-to-noise ratio amplitude of a GNSS geodetic receiver according to claim 1, characterized in that The specific implementation steps of "obtaining the initial value of the multipath reflection coefficient" described in step 2 are as follows: (1) Processing the navigation satellite signal-to-noise ratio trend term and oscillation term selected in step 1, and obtaining the envelope and phase of the normalized signal-to-noise ratio oscillation term; (2) The initial value of the multipath reflection coefficient αo is calculated using the envelope and phase of the normalized signal-to-noise ratio oscillation term.

4. The method for calculating the multipath reflection coefficient using the signal-to-noise ratio amplitude of a GNSS geodetic receiver according to claim 1, characterized in that The specific implementation steps of "deriving the theoretical value of multipath reflection coefficient" described in step 3 are as follows: (1) Direct signal power P d and the reflected signal power P r Acquisition of (2) Multipath reflection coefficient α of theoretical simulation t Derived acquisition.

5. The method for calculating the multipath reflection coefficient using the signal-to-noise ratio amplitude of a GNSS geodetic receiver according to claim 1, characterized in that The specific implementation steps of "system error correction" described in step 3 are as follows: (1) Correction formula. The accurate multipath reflection coefficient formula is as follows: α＝α s +A0 α is the corrected multipath reflection coefficient, α s is the multipath reflection coefficient after systematic error correction, and A0 is the surface random error correction. (2) Observation system error correction. The multipath reflection coefficient α after system error correction s as follows: a s =α0+f elev (i)+E f elev (θ)=a+b*θ+c*θ 2 +d*θ 2 f elev (θ) is the satellite elevation angle system error correction, a, b, c, d are the corresponding parameters, and E is the antenna gain correction parameter. (3) Use a bare soil period to calculate the corresponding parameters in the correction formula, ab, c, d, E, and the random error in the bare soil period is considered to be 0. Multipath reflection coefficient ɑ of the bare soil period theoretical simulation t As the corrected value, an equation is established with the multipath reflection coefficient inverted in the bare soil period to solve a, b, c, d, and E.

6. The method for calculating multipath reflection coefficient using the signal-to-noise ratio amplitude of a GNSS geodetic receiver according to claim 1, characterized in that The specific implementation steps of "surface random error correction" mentioned in step 3 are as follows: (1) Surface random error correction. The correction rule for the random error A0 of the multipath reflection coefficient is as follows: A0=f(x) The calculation of random error f(x) needs to be considered in combination with the actual surface conditions.

7. The method for calculating multipath reflection coefficient using the signal-to-noise ratio amplitude of a GNSS geodetic receiver according to claim 1, characterized in that The specific implementation steps of "obtaining accurate multipath reflection coefficient" described in step 4 are as follows: (1) Use the correction formula to calculate the accurate multipath reflection coefficients for other time periods.

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