A dual-antenna sea surface height monitoring method based on GNSS-IR

Abstract

The present invention provides a dual-antenna sea level monitoring method based on GNSS-IR, and belongs to the technical field of GNSS-IR sea level monitoring. The invention includes: assembling a dual-antenna GNSS-IR monitoring device; extracting direct and interference signal observation values ​​respectively; performing direct and reflected signal separation on the signal-to-noise ratio data at low elevation angles and high elevation angles respectively; calculating the characteristic values ​​of the reflection surface height in the low elevation angle and high elevation angle reflection components respectively; performing error elimination on the inverted reflection surface height, and calculating the inversion accuracy compared with the tide gauge station data. The method of the present invention makes up for the limitation of the traditional GNSS-IR sea level monitoring method on the elevation angle, and expands the original method that can only use low elevation angle data to the method that can use high and low elevation angle data for inversion, and greatly improves the sampling rate of sea level inversion by segmenting the observation data according to the elevation angle, and has the characteristics of high observation time resolution and low cost.

Description

Technical Field

[0001] The present invention relates to the technical field of sea level monitoring, and in particular to a dual-antenna sea level monitoring method based on GNSS-IR. Background Art

[0002] Accurate monitoring of sea surface height changes plays a key role in the inversion of long-term climate evolution and the unification and maintenance of global elevation benchmarks in modern geodetic measurement. At the same time, sea surface height monitoring is of great significance in many fields such as marine science research, climate research, marine resource development, marine activities and coastal area management. At present, sea surface height monitoring in coastal areas mainly relies on tide gauges, which have high observation accuracy but limited global distribution. Satellite altimetry technology provides a large amount of observation data for sea surface height monitoring, but its cost is high and the temporal and spatial resolution of sea surface height monitoring is low. In recent years, with the continuous development and maturity of GNSS technology, GNSS-R (GNSS reflection) technology has been found to be used for sea surface height inversion, and significant progress has been made so far. GNSS-R technology can provide high stability and continuous free L-band microwave signal resources, enabling low-cost, all-day, all-weather, high-temporal and spatial resolution observation of sea surface height. It has become a new type of sea surface height monitoring method, providing data supplement for current sea surface height monitoring.

[0003] GNSS-IR (GNSS interferometric reflection technology) is a type of GNSS-R technology. It uses an upward single antenna and a positioning receiver to receive signals, and realizes the inversion of sea surface height by analyzing multipath signals at low elevation angles (≤30°). Larson et al. (2008) realized the inversion of sea surface height by using GPS observation data from two observation stations. Compared with tide gauge data, the root mean square difference between the two is at the centimeter level, and the correlation coefficient is better than 0.97. Strandberg et al. used data from the Australian SPBY station and the Swiss GTGU station, and used the Kalman filter method combined with B-spline to realize real-time sea surface height inversion with RMSE of 3.3cm and 1.5cm. Although GNSS-IR sea surface height monitoring technology has developed rapidly in recent years and has achieved remarkable research results, it also has limitations. GNSS-IR is based on the principle of signal interference. It usually receives direct signals and reflected signals from a single antenna. These two signals form an interference signal in the receiver, and the interference signal is used to invert the sea surface height. However, as the elevation angle increases, the interference effect weakens and inversion cannot be achieved. Therefore, the interference effect only exists in the low elevation range. At present, when using GNSS-IR technology to invert sea surface height, only low elevation angle data is used, and high elevation angle data is not available, which limits the sampling rate of sea surface height inversion. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a dual-antenna sea level height monitoring method based on GNSS-IR. The monitoring method of the present invention makes up for the limitation that the traditional GNSS-IR sea level height monitoring can only use low altitude angle data, increases the adoption rate of sea level height, and makes the observation value have the characteristics of high temporal and spatial resolution.

[0005] The present invention adopts the following scheme:

[0006] A dual-antenna sea level height monitoring method based on GNSS-IR, comprising:

[0007] S1. Build a dual-antenna GNSS-IR sea level height monitoring device;

[0008] The monitoring device includes: an upward-looking antenna, a downward-looking antenna and a geodetic receiver, wherein the upward-looking antenna is a right-hand circularly polarized antenna, tilted downward by 30 degrees; the downward-looking antenna is a left-hand circularly polarized antenna, tilted upward by 30 degrees;

[0009] The signals received by the left-hand circularly polarized antenna and the right-hand circularly polarized antenna are combined into one channel by a combiner and connected to the receiver;

[0010] The method for monitoring using the dual-antenna sea level monitoring device comprises the following steps:

[0011] S2. According to the situation at the station, set the effective azimuth observation range; extract the signal-to-noise ratio (SNR) observation values ​​that meet the effective azimuth observation range from the observation file;

[0012] S3: Divide the observation values ​​into segments according to the altitude angle, and then separate the direct and interference signals in each segment;

[0013] S4: Calculate the characteristic value of the reflection surface height in each segment of the data interference signal;

[0014] S5: Long-term observations form a sea surface height observation sequence, which is compared with the sea surface height observations obtained from nearby tide gauges to verify accuracy.

[0015] Furthermore, in step S2, according to the situation at the site of the station establishment, the effective azimuth observation range is set. The signal-to-noise ratio (SNR) observation values ​​that meet the above azimuth observation range are extracted from the observation file respectively; the specific implementation process is as follows:

[0016] According to the azimuth relationship between the observation station and the sea surface, the effective azimuth observation range is set to ensure that the reflected signal comes from the sea surface. The observation values ​​stored in the receiver are saved in the receiver in the form of RINEX format. The elevation angle under the corresponding epoch is calculated based on the recorded direct antenna position and the precise ephemeris file. , azimuth information ; Extract the signal-to-noise ratio (SNR) observation values ​​of GNSS at different frequencies at each epoch within the effective azimuth observation range from the file.

[0017] Furthermore, in step S3, the observation values ​​are segmented according to the altitude angle, and then the direct and interference signals in each segment of data are separated. The specific implementation process is as follows:

[0018] (1) The observation data within the range of 5° to 60° are used for inversion, and the data are divided into four sections according to the altitude angle: 5°~15°, 15°~30°, 30°~45° and 45°~60°;

[0019] (2) For each elevation angle interval, separate the satellite ascending and descending arcs according to the time series;

[0020] (3) For each arc segment data, the received SNR data can be expressed as the direct component , reflection component , Reflection surface height (i.e. the vertical distance from the phase center of the direct antenna to the sea surface) , Satellite altitude angle The relationship is: ;

[0021] In the formula, is the noise power, is the GNSS signal frequency, is the interference phase difference between the direct and reflected signals.

[0022] For observations Perform a second-order polynomial fit and subtract the fitting result from the original data to obtain the interference signal of the direct and reflected signals. : ;

[0023] Among them, Simplified to express.

[0024] Furthermore, in step S4, the calculation of the characteristic value of the reflection surface height in each segment of the interference signal is specifically implemented as follows:

[0025] (1) Calculate the interference signal using the Lomb-Scargle transform method The vibration frequency is: ;

[0026] (2) The height of the reflecting surface can be calculated from the above formula: : ;

[0027] (3) The height of the reflecting surface is corrected for sea surface dynamics and troposphere. The height of the reflecting surface can be expressed as: ;

[0028] In the formula, Indicates the rate of change of satellite altitude angle, obtained through the satellite altitude angle sequence; is the sea surface height change rate, and its value can be expressed as is obtained from step (4); It represents the influence of tropospheric delay on the change of sea surface height, and its value can be obtained by GPT2w model and VMF1 projection function;

[0029] (4) Set the window width and sliding time of the sliding window, and then within the sliding window, and As an unknown parameter, all the reflector height values ​​calculated in step (2) within the sliding window are used to form the following observation equation. The robust regression algorithm is used to calculate the unknown number to obtain the reflector height after dynamic correction and tropospheric correction. :

[0030] ;

[0031] In the formula, For the The height value of the reflecting surface obtained in step (2) within the sliding window, is the middle moment of the sliding window.

[0032] Furthermore, in step S5, a long-term observation forms a sea level observation sequence, which is compared with the sea level observation values ​​obtained by a nearby tide gauge station or other observation means to verify the accuracy. The specific implementation process is as follows:

[0033] (1) Perform the above data processing on all the arc observation data of a certain frequency to obtain the height of the reflection surface. The middle time of the sliding window is taken as the observation time corresponding to the height of the reflection surface. , the height of the reflector calculated within the sliding window , thus forming the reflection surface height observation sequence: ;

[0034] in, is the total number of sliding windows in the observation period;

[0035] (2) Use the sea level height data series obtained from tide gauges near the observation station or other means during the same period to verify the external consistency of the monitoring results; the specific method is to use linear interpolation to obtain the corresponding The sea surface height value is used as the comparison data and is expressed as , statistical data and verify the accuracy, including the correlation coefficient R and root mean square error RMSE obtained by comparing the inversion results of data of different frequencies with the external measured data, and then verify the effectiveness and accuracy of monitoring;

[0036] ;

[0037] .

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] The present invention receives the direct and reflected signals through the upward and downward antennas respectively, and then enters the receiver through the combiner to significantly improve the interference effect of the signal-to-noise ratio at high altitude angles, so that high altitude angle data can also be used for sea surface height inversion, thereby enabling high altitude angle data to be applied to sea surface height inversion work, successfully breaking through the limitation that traditional GNSS-IR sea surface height monitoring can only rely on low altitude angle data. As a result, the sampling rate of sea surface height can be greatly improved, thereby giving the observation value the characteristics of high temporal and spatial resolution, providing more accurate, comprehensive and efficient data support for sea surface height monitoring, and effectively promoting the technical development and application expansion in this field.

[0040] (2) The feasibility and effectiveness of the present invention have been verified through experiments. By conducting specific experiments to collect observations of the signal-to-noise ratio of direct and interference signals, the direct reflection signals at high and low elevation angles are separated and the height of the reflecting surface is calculated, and the sea surface height is further calculated. Combined with the comparative data obtained in the experiment, the inverted sea surface height is analyzed. The results show that the method of the present invention can achieve centimeter-level sea surface height inversion under high wind speed conditions with high accuracy. It has significant application value and advantages, and provides reliable technical support and innovative ideas for the field of sea surface height measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a schematic diagram of the overall process of the present invention;

[0042] Figure 2 It is a schematic diagram of the device composition of the present invention;

[0043] Figure 3 It is a sequence of SNR observation values ​​of GPS satellites at different frequencies from 5° to 60° obtained by the method of the present invention;

[0044] Figure 4 It is the sea surface height result obtained by performing LSP analysis on the segmented dSNR values ​​of the S1C frequency band of GPS PRN20 satellite in step S4 of the method of the present invention;

[0045] Figure 5It is the change of the total number of sea surface height inversions during the entire experimental period using low altitude angle data (≤30°) and adding high altitude angle data in the experiment of the present invention;

[0046] Figure 6 It is a schematic diagram comparing the sea surface height value inverted by the method of the present invention with the data of the tide gauge station. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0049] A dual-antenna sea surface height monitoring method based on GNSS-IR Figure 2 As shown in the figure, a dual-antenna sea level height monitoring device based on GNSS-IR was built, and a monitoring experiment was carried out at Xiaoshi Island, Weihai City (37.5214°N, 122.0092°E). The experimental time was from January 4, 2023 to February 4, 2023. During the experiment, multi-frequency GNSS signals of four systems, GPS, Galileo, GLONASS and BDS, were collected and recorded in RINEX format files, and the calculation method of the present invention was further used to realize the sea level inversion. The specific steps are as follows (refer to Figure 1 shown):

[0050] S1. Build a dual-antenna GNSS-IR sea level height monitoring device:

[0051] (1) The monitoring equipment consists of an upward-looking antenna, a downward-looking antenna, a combiner, and a positioning receiver. The upward-looking antenna is a right-hand circularly polarized antenna, tilted 30° upward; the downward-looking antenna is a left-hand circularly polarized antenna, tilted 30° downward. The vertical distance between the phase center points of the two antennas is 0.304 m.

[0052] (2) The signal received by the right-hand circularly polarized antenna and the signal received by the left-hand circularly polarized antenna are combined into one signal using a combiner and connected to the receiver. The receiver stores the observation data in a RINEX file.

[0053] (3) Obtain the sea level height data of the Xiaoshidao tide gauge station within 5 m of the observation station during the same period (provided by the unit to which the tide gauge station belongs).

[0054] S2. Set the effective azimuth observation range according to the situation at the station. Extract the signal-to-noise ratio (SNR) observation values ​​that meet the effective azimuth observation range from the observation files respectively;

[0055] (1) According to the location of the station and the range of the sea surface, the specular reflection points are calculated. According to the distribution of the specular reflection points, the azimuth angle range corresponding to the observation interval of the station is determined to be 140° to 280°.

[0056] (2) Extract the signal-to-noise ratio of different frequencies within the azimuth range at each epoch from the RINEX format file stored in the receiver. , and calculate the altitude angle of the corresponding epoch based on the recorded direct antenna position and the precise ephemeris file , azimuth information ;

[0057] S3. Divide the observation values ​​into segments according to the altitude angle, and then separate the direct and interference signals in each segment:

[0058] (1) According to the instrument installation angle, the observation values ​​are segmented according to the altitude angle. Considering the characteristics of sampling rate and multipath oscillation, the observation values ​​are divided into four segments according to the following altitude angles, namely 5°~15°, 15°~30°, 30°~45°, and 45°~60°;

[0059] (2) The time series of the original signal-to-noise ratio has an upward and downward trend. According to the changes in its time series, each observation value is further separated into upward and downward segments;

[0060] (3) For each arc segment data, the received SNR data can be expressed as the direct component , reflection component , Reflection surface height (i.e. the vertical distance from the phase center of the direct antenna to the sea surface) , Satellite altitude angle The relationship is: ;

[0061] In the formula, is the noise power, is the GNSS signal frequency, is the interference phase difference between the direct and reflected signals.

[0062] For observations Perform a second-order polynomial fit and subtract the fitting result from the original data to obtain the interference signal of the direct and reflected signals. :

[0063] ;

[0064] Among them, Simplified to express.

[0065] S4. Calculate the characteristic value of the reflection surface height in each segment of the interference signal:

[0066] (1) In accordance with The expression of the reflected component SNR is the vibration frequency f It is linearly related to the height h of the reflecting surface, and the interference signal is calculated using the Lomb-Scargle transformation method. The vibration frequency is: ;

[0067] (2) The height of the reflecting surface can be calculated from the above formula: : ;

[0068] Figure 4 That is, the initial sea surface height result is obtained by performing LSP analysis on the dSNR value of the S1C frequency band of the GPS PRN20 satellite.

[0069] (3) The height of the reflecting surface is corrected for sea surface dynamics and troposphere. The height of the reflecting surface can be expressed as: ;

[0070] In the formula, Indicates the rate of change of satellite altitude angle, obtained through the satellite altitude angle sequence; is the sea surface height change rate, and its value can be expressed as is obtained from step (4); represents the effect of tropospheric delay on sea surface height change and its value can be obtained by the method described in Williams and Nievinski (2017) using the GPT2w model and VMF1 projection function.

[0071] (4) Set the width to 1 hour and the sliding step to 10 minutes, and then in the sliding window, and As an unknown parameter, all the reflector height values ​​calculated in step (2) within the sliding window are used to form the following observation equation. The robust regression algorithm is used to calculate the unknown number to obtain the reflector height after dynamic correction and tropospheric correction. :

[0072] ;

[0073] In the formula, For the The height value of the reflecting surface obtained in step (2) within the sliding window, is the middle moment of the sliding window.

[0074] S5. Long-term observations form a sea surface height observation sequence, which is compared with the sea surface height observations obtained by nearby tide gauges or other observation methods to verify accuracy:

[0075] The tide station data is temporally interpolated according to the inversion results of GNSS-IR to obtain the tide station observation value at the time corresponding to the GNSS-IR inversion value, and form a reflection surface height observation sequence: ;

[0076] Among them, the middle moment of the sliding window is the observation time corresponding to the height of the reflecting surface t , the height of the reflector calculated within the sliding window h , n is the total number of sliding windows in the observation period.

[0077] (2) Use the sea level height data series obtained from the tide gauge station near the observation station during the same period to verify the compliance of the monitoring results. The specific method is to use linear interpolation to obtain the corresponding The sea surface height value is used as the comparison data, expressed as , statistical data and verify the correlation coefficient (R) and root mean square error (RMSE) obtained by comparing the precision inversion results with the external measured data, thereby verifying the effectiveness and accuracy of the monitoring.

[0078] ;

[0079] .

[0080] The effectiveness of this method is verified through the GNSS-IR dual-antenna sea surface monitoring experiment. Figure 3 It is the SNR observation value sequence of GPS satellite at different frequencies from 5° to 60°. Figure 4 The sea surface height results obtained by LSP analysis of the dSNR value of the S1C frequency band of the GPS PRN20 satellite. It can be seen that the LSP spectrum analysis of the four segments of data can obtain better sea surface height results.

[0081] Figure 5 The figure shows the change in the total number of sea surface height inversions during the entire observation period using only low-altitude angle data (≤30°) and adding high-altitude angle data. It can be seen that after adding high-altitude angle data, the number of inversion values ​​in each frequency band has been greatly improved, which verifies the effectiveness of this method.

[0082] Figure 6The sea level height values ​​inverted by this method are compared with the data of the tide gauge station. It can be seen that the inverted values ​​are in good agreement with the observed values ​​of the tide gauge station and have a consistent trend of change. After calculation, the RMSE of the inverted values ​​compared with the observed values ​​of the tide gauge station is 0.077m, and the correlation coefficient R is better than 0.99, which further verifies the effectiveness of the method of the present invention in monitoring sea level height.

[0083] Compared with the GNSS-IR single antenna technology, the dual-antenna sea surface height monitoring method based on GNSS-IR in the present invention is no longer limited to the low elevation angle range, and high elevation angle data can be used simultaneously for sea surface height inversion, thereby increasing the sampling rate of GNSS-IR sea surface height inversion, and thus improving the temporal and spatial resolution of sea surface height observation.

[0084] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A dual-antenna sea level monitoring method based on GNSS-IR, characterized in that: include: S1. Build a dual-antenna GNSS-IR sea level height monitoring device; The monitoring device includes: an upward-looking antenna, a downward-looking antenna and a geodetic receiver, wherein the upward-looking antenna is a right-hand circularly polarized antenna tilted 30 degrees downward; the downward-looking antenna is a left-hand circularly polarized antenna tilted 30 degrees upward; The signals received by the left-hand circularly polarized antenna and the right-hand circularly polarized antenna are combined into one channel by a combiner and connected to the receiver; S2. According to the situation at the station establishment site, set the effective azimuth observation range; respectively extract the signal-to-noise ratio observation values ​​in the observation file that meet the aforementioned azimuth observation range; S3: Divide the observation values ​​into segments according to the altitude angle, and then separate the direct and interference signals in each segment of data; the specific implementation process is as follows: (1) The observation data within the range of 5° to 60° are used for inversion, and the data are divided into four sections according to the altitude angle: 5°~15°, 15°~30°, 30°~45° and 45°~60°; (2) For each elevation angle interval, separate the satellite ascending and descending arcs according to the time series; (3) For each arc segment data, the received SNR data can be expressed as: ; In the formula, is the noise power, is the GNSS signal frequency, is the interference phase difference between the direct and reflected signals, is the direct component, is the reflection component, is the height of the reflecting surface, is the satellite altitude angle; For observations Perform a second-order polynomial fit and subtract the fitting result from the original data to obtain the interference signal of the direct and reflected signals. : ; Among them, Simplified to express; S4: Calculate the characteristic value of the reflection surface height in each segment of the data interference signal; S5: Long-term observations form a sea surface height observation sequence, which is compared with the sea surface height observations obtained from nearby tide gauges to verify accuracy.

2. The dual-antenna sea level monitoring method based on GNSS-IR according to claim 1, characterized in that: The specific implementation process of step S2 is as follows: According to the azimuth relationship between the observation station and the sea surface, the effective azimuth observation range is set to ensure that the reflected signal comes from the sea surface; the receiver generates an observation file in RINEX format with the received observation value and saves it in the receiver; According to the recorded direct antenna position, the altitude angle of the corresponding epoch is calculated in combination with the precise ephemeris file. , azimuth Extract the signal-to-noise ratio (SNR) observation values ​​of GNSS at different frequencies at each epoch within the effective azimuth observation range from the file.

3. The dual-antenna sea level monitoring method based on GNSS-IR according to claim 1, characterized in that: In step S4, the calculation of the characteristic value of the reflection surface height in each segment of the interference signal is specifically implemented as follows: (1) Calculate the interference signal using the Lomb-Scargle transform method The vibration frequency is: ; (2) Calculate the height of the reflecting surface using the above formula: : ; (3) The height of the reflecting surface is corrected for sea surface dynamics and troposphere. The height of the reflecting surface can be expressed as: ; In the formula, Indicates the rate of change of satellite altitude angle, obtained through the satellite altitude angle sequence; is the rate of change of sea surface height, and its value can be expressed as is obtained from step (4); It represents the influence of tropospheric delay on the change of sea surface height, and its value can be obtained by GPT2w model and VMF1 projection function; (4) Set the window width and sliding time of the sliding window, and then within the sliding window, and As an unknown parameter, all the reflector height values ​​calculated in step (2) within the sliding window are used to form the following observation equation. The robust regression algorithm is used to calculate the unknown number to obtain the reflector height after dynamic correction and tropospheric correction. : ； In the formula, For the The height value of the reflecting surface obtained in step (2) within the sliding window, is the middle moment of the sliding window.

4. The dual-antenna sea level monitoring method based on GNSS-IR according to claim 1, characterized in that: In step S5, a long-term observation forms a sea level observation sequence, which is compared with the sea level observation values ​​obtained by a nearby tide gauge station or other observation means to verify the accuracy. The specific implementation process is as follows: (1) Perform the above data processing on all the arc observation data of a certain frequency to obtain the height of the reflection surface. The middle time of the sliding window is taken as the observation time corresponding to the height of the reflection surface. , the height of the reflector calculated within the sliding window , thus forming the reflection surface height observation sequence: ; in, is the total number of sliding windows in the observation period; (2) Use the sea level height data series obtained from tide gauges near the observation station or other means during the same period to verify the external consistency of the monitoring results; the specific method is to use linear interpolation to obtain the corresponding The sea surface height value is used as the comparison data and is expressed as , statistical data and verify the correlation coefficient R and root mean square error RMSE obtained by comparing the precision inversion results with the external measured data, and then verify the effectiveness and accuracy of monitoring; ； 。

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