Method and system for improving sea surface height measurement accuracy based on atmospheric delay error correction

Abstract

The present invention discloses a method and system for improving the accuracy of sea surface height measurement based on atmospheric delay error correction, the method comprising: constructing an ionosphere correction model and a troposphere correction model; according to the ionosphere correction model, respectively calculating the ionosphere delay of the reflected signal and the ionosphere delay of the direct signal; according to the troposphere correction model, calculating the difference between the troposphere delay of the reflected signal and the troposphere delay of the direct signal; calculating the influence of the ionosphere and troposphere on the height measurement process, correcting and outputting the inverted sea surface height, so as to improve the accuracy of sea surface height measurement. The present invention eliminates the influence of the atmospheric delay error (ionosphere and troposphere) on the height measurement process, and improves the accuracy of sea surface height measurement.

Description

Technical Field

[0001] The present invention belongs to the cross-technical fields of satellite altimetry, oceanographic mapping, etc., and in particular relates to a method and system for improving the accuracy of sea surface altimetry based on atmospheric delay error correction. Background Art

[0002] Sea surface height is the basic data for studying ocean dynamics, meteorology, geodesy, geophysics and other fields. Global sea surface height data can be used to monitor global climate change, obtain the geoid, determine ocean circulation, invert the ocean gravity field, establish ocean tide models, and conduct mesoscale climate model research. Monitoring changes in sea level height is of great significance. At present, sea surface height can be obtained from traditional ship measurements, tide stations, to current medium-resolution imaging spectrometers, synthetic aperture radars, radar altimeters and other methods. However, ship measurements and tide station modes are limited by space and data sampling efficiency. They are suitable for local observations and cannot achieve global ocean coverage. Both synthetic aperture radar altimeters and radar altimeters can only measure the target height of the sub-satellite point, and the conditions of use are relatively limited. Although radar altimeters can obtain high-precision global sea surface height, their lack of mesoscale spatial resolution means that surface water information at this scale cannot be observed stably for a long time, and cannot meet the current application needs of new ocean observations.

[0003] Global Navigation Satellite System Reflection Remote Sensing (GNSS-R) is a new generation of altimetry technology, which uses the reflection of GNSS signals on the sea surface to achieve altimetry. In GNSS navigation and positioning, while receiving direct signals, reflected signals are generally considered harmful as multipath interference and need to be suppressed and eliminated. However, from the perspective of electromagnetic wave propagation theory, the reflected signal carries the physical characteristics of the reflecting surface. The changes in the reflected signal waveform, polarization characteristics, amplitude, phase, frequency and other parameters can directly reflect the physical characteristics of the reflecting surface. Therefore, accurate estimation and reception processing of the reflected signal can achieve the estimation and inversion of the physical characteristics of the reflecting surface. Based on this theory, in 1993, Martin-Neira, a scientist at the European Space Agency, first proposed and described the concept of PARIS (passive reflectometry and interferometry system) for altimetry using sea surface reflection signals. The main idea is to use the GPS sea surface reflection wave as a ranging signal to perform ocean altimetry. In 1994, French scientist Auber accidentally discovered through flight tests that the receiver could receive GPS sea surface reflection signals. NASA's Langley Research Center in the United States conducted experiments on August 6, 8, and 27, 1996, respectively, and concluded that a special receiver is needed to receive GPS reflected signals. Martin-Neira conducted the PARIS altimeter bridge I, bridge II, and bridge III tests in the Netherlands in September 1997, June 2001, and February 2003, respectively, and verified the feasibility of GNSS-R altimeter measurement using the C / A code correlation function delay and phase measurement methods. In 2003, the UK-DMC satellite of the United Kingdom successfully obtained surface physical coefficients such as sea surface roughness using the GNSS-R equipment on board. In 2014, the first GNSS-R satellite (TDS-1) was launched. These achievements have aroused the interest of many researchers in GPS reflected signals, prompting countries to begin exploring and researching GNSS-R technology, and GNSS-R technology has developed rapidly.

[0004] As a new and effective dual (multi) base radar passive remote sensing technology, GNSS-R effectively makes up for the shortcomings of existing marine remote sensing technology with its advantages of rich signal sources, low cost, wide coverage, low power consumption, all-weather, and high real-time performance compared with traditional remote sensing technology. At present, global navigation satellite system reflection remote sensing technology (GNSS-R) has been widely used in the fields of sea surface wind measurement, sea surface height measurement, sea ice detection, ocean salinity detection, soil moisture detection, and mobile target detection. Among them, there are five main methods of GNSS-R sea surface height measurement technology, namely code-based height measurement, carrier phase height measurement, carrier frequency change height measurement, interferometric height measurement, delay Doppler map (DDM) height measurement, signal-to-noise ratio height measurement, etc.

[0005] The realization of GNSS-R sea surface height measurement depends on the transmission of GPS electromagnetic wave signals in space. Signal propagation in space will be affected by the ionosphere, troposphere, multipath, etc. These factors, as error terms, will affect the accuracy of GPS sea surface height measurement, so it is necessary to eliminate the influence of these errors as much as possible. The ionosphere has a distance error of tens of centimeters on the high-frequency band signal used by the satellite altimeter. The single-frequency altimeter is still useful in the low electron concentration area. With the needs of scientific research, high-precision ionospheric correction is an inevitable requirement, and the installation of dual-frequency altimeters on spacecraft brings cost and other complexity problems. The present invention proposes to use GNSS-R technology to determine the ionospheric electron density near the satellite, and analyzes the feasibility of this technology. The literature studies the feasibility of using satellite-borne GNSS-R technology to study the ionosphere. Through simulation experiments, the results show that GNSS dual-frequency or multi-frequency signals can be used to estimate the ionospheric delay using GNSS-R technology, and dual-frequency pseudorange measurement and model prediction are used to obtain the result of improving the measurement accuracy by 2m after 1s integration. In terms of ionospheric detection, Chen Biyan proposed an improved ionospheric tomography method, which uses the observation data of ground-based GPS receivers to establish a regional ionospheric model, and interpolates to obtain sufficient TEC data, overcoming the shortcomings of the empirical ionospheric model being distorted by the space environment. The literature proposes a method for using DDM to invert the total electron content of the ionosphere over the ocean. The results are well consistent with the IRI-2012 model value. Ren Xiaodong established an ionospheric model based on multi-system GNSS observation data based on the data of the four major satellite systems of GPS, GLNOASS, BDS and Galileo, combined with the MGEX network and IGS network, and conducted an accuracy analysis of the model. The results show that the accuracy is comparable to the products released by the IGS center. At the same time, it is proposed to use the non-difference ambiguity fixation technology to extract TEC. Compared with the traditional carrier phase smoothed pseudorange, the accuracy of the ionospheric TEC extracted by this method is significantly improved, which is of great value for extracting TEC using short-term low-orbit satellite data in the future. In other studies on GNSS-R applications, researchers used models to correct atmospheric delay errors. Single-frequency navigation receivers use global ionosphere models for correction, such as the Klobuchar model, and dual-frequency navigation receivers use a linear combination of carrier phase and pseudorange code to eliminate ionospheric errors. There is no systematic study of the changing laws of atmospheric delay. In the study of the airborne GNSS-R reflection signal altimetry model, Zhang Yun only theoretically excluded the influence of the ionosphere on the experimental results, and did not give in-depth actual results. Some of the above experiments were subject to conditions and only analyzed the possibility of GNSS-R ionosphere detection from a simulation perspective, while others used ionosphere models to reduce the impact of atmospheric delay. But as we all know, the ionosphere model is greatly affected by changes in the space environment and cannot reflect the actual measurement situation well. Summary of the invention

[0006] The technology of the present invention solves the problem: Overcoming the shortcomings of the prior art, providing a method and system for improving the accuracy of sea surface height measurement based on atmospheric delay error correction, aiming to eliminate the influence of atmospheric delay error (ionosphere and troposphere) on the height measurement process and improve the accuracy of sea surface height measurement.

[0007] In order to solve the above technical problems, the present invention discloses a method for improving the sea surface height measurement accuracy based on atmospheric delay error correction, comprising:

[0008] Construct ionosphere correction model and troposphere correction model;

[0009] According to the ionospheric correction model, the ionospheric delay of the reflected signal is calculated respectively. and the ionospheric delay of the direct signal

[0010] According to the tropospheric correction model, the tropospheric delay of the reflected signal is calculated. Tropospheric delay from direct signal The difference Δρ tro ;

[0011] According to the calculated and Δρ tro , the influence of ionosphere and troposphere on the altimetry process is solved and obtained;

[0012] According to the calculated H, the inverted sea surface height is corrected and output to improve the accuracy of sea surface height measurement.

[0013] In the above method for improving the accuracy of sea surface height measurement based on atmospheric delay error correction, the influence of ionosphere and troposphere on the height measurement process is expressed as follows:

[0014]

[0015] Where θ represents the GNSS satellite altitude angle at the mirror reflection point.

[0016] In the above method for improving the sea surface height measurement accuracy based on atmospheric delay error correction, the ionospheric delay of the reflected signal is calculated according to the ionospheric correction model. and the ionospheric delay of the direct signal include:

[0017] The ionospheric delay of the reflected signal is calculated by the following equation (2):

[0018]

[0019] The ionospheric delay of the direct signal is calculated by the following equation (3):

[0020]

[0021] Where f is the GPS signal carrier frequency, STEC r Indicates the total electron content contained in the propagation path of the reflected signal, STEC d Represents the total electron content contained in the direct signal propagation path.

[0022] In the above method for improving the sea surface height measurement accuracy based on atmospheric delay error correction, the ionospheric delay of the reflected signal is calculated according to the ionospheric correction model. and the ionospheric delay of the direct signal Also includes:

[0023] STEC is calculated by using equations (4) and (5) below: r and STEC d :

[0024]

[0025]

[0026] Among them, VTEC r Indicates the electron content in the vertical direction of the reflected signal propagation path, VTEC d Represents the electron content in the vertical direction of the direct signal propagation path, R e represents the radius of the earth, h represents the height of the ionosphere single layer model, and θ represents the GNSS satellite altitude angle at the mirror reflection point.

[0027] In the above method for improving the sea surface height measurement accuracy based on atmospheric delay error correction, the ionospheric delay of the reflected signal is calculated according to the ionospheric correction model. and the ionospheric delay of the direct signal Also includes:

[0028] Determine the ionospheric puncture point;

[0029] The expression of VTEC in the zenith direction at the ionospheric piercing point is as follows:

[0030]

[0031] in, represents the VTEC value at the ionospheric piercing point j, represents the VTEC value at the ionospheric grid point i in the vicinity of the ionospheric puncture point, d ij It represents the distance between ionospheric piercing point j and ionospheric grid point i, and DR represents the distance threshold.

[0032] In the above method for improving the accuracy of sea surface height measurement based on atmospheric delay error correction, the coordinates of the ionospheric puncture point The solution formula is as follows:

[0033]

[0034] Among them, γ represents the geocentric angle, represents the longitude of the puncture point, λ m represents the latitude of the puncture point, φ n represents the longitude of the receiver, λ n represents the latitude of the receiver and A represents the satellite azimuth.

[0035] In the above method for improving the accuracy of sea surface height measurement based on atmospheric delay error correction, the tropospheric delay of the reflected signal is calculated according to the tropospheric correction model. Tropospheric delay from direct signal The difference Δρ tro ,include:

[0036] The tropospheric delay of the reflected signal is calculated by the following equation (8): Tropospheric delay from direct signal The difference Δρ tro :

[0037]

[0038] Among them, h r represents the height of the receiver relative to the reference ellipsoid, and θ represents the GNSS satellite altitude angle at the mirror reflection point.

[0039] In the above method for improving the sea surface height measurement accuracy based on atmospheric delay error correction, the reflected signal refers to: the GPS signal from the mirror reflection point to the receiver; the direct signal refers to: the GPS signal from the GNSS satellite to the receiver.

[0040] Correspondingly, the present invention also discloses a system for improving the accuracy of sea surface height measurement based on atmospheric delay error correction, comprising:

[0041] Model building module, used to build ionosphere correction model and troposphere correction model;

[0042] The first solution module is used to solve the ionospheric delay of the reflected signal according to the ionospheric correction model and the ionospheric delay of the direct signal

[0043] The second solution module is used to solve the tropospheric delay of the reflected signal according to the tropospheric correction model Tropospheric delay from direct signal The difference Δρ tro ;

[0044] The third solution module is used to obtain the and Δρ tro , we can get the influence of ionosphere and troposphere on the altimetry process H;

[0045] The correction module is used to correct and output the inverted sea surface height according to H to improve the accuracy of sea surface height measurement.

[0046] In the above-mentioned system for improving the accuracy of sea surface altimetry based on atmospheric delay error correction, the influence of the ionosphere and troposphere on the altimetry process is expressed as follows:

[0047]

[0048] Where θ represents the GNSS satellite altitude angle at the mirror reflection point.

[0049] The present invention has the following advantages:

[0050] (1) The present invention discloses a method for improving the accuracy of sea surface height measurement based on atmospheric delay error correction. The method takes into account the atmospheric delay error in the GNSS-R sea surface height measurement process, and reduces the influence of atmospheric propagation delay on the sea surface height measurement result through a geometric angle algorithm, thereby improving the accuracy of sea surface height measurement.

[0051] (2) The present invention discloses a method for improving the accuracy of sea surface height measurement based on atmospheric delay error correction. Through experiments, it is concluded that low satellite altitude angle has a greater impact on the height measurement result, and the satellite cut-off altitude angle should be increased in practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is a flowchart of the steps of a method for improving sea surface height measurement accuracy based on atmospheric delay error correction in an embodiment of the present invention;

[0053] Figure 2 is a flight trajectory diagram in an embodiment of the present invention;

[0054] Figure 3 Schematic diagram of a GNSS-R height measurement geometric path delay model in an embodiment of the present invention;

[0055] Figure 4 is a schematic diagram of global ionospheric VTEC distribution in an embodiment of the present invention;

[0056] Figure 55(a) is a schematic diagram of the atmospheric delay of each satellite in an embodiment of the present invention; wherein 5(a) is the atmospheric delay of the PRN1 satellite, 5(b) is the atmospheric delay of the PRN11 satellite, 5(c) is the atmospheric delay of the PRN14 satellite, and 5(d) is the atmospheric delay of the PRN32 satellite;

[0057] Figure 6 6(a) is a schematic diagram of the atmospheric delay results of a satellite-borne experiment in an embodiment of the present invention; wherein, 6(a) is the delay and altitude angle change of satellite-borne platform A at 0333 hours, 6(b) is the delay and altitude angle change of satellite-borne platform B at 0348 hours, 6(c) is the delay and altitude angle change of satellite-borne platform A at 2048 hours, and 6(d) is the delay and altitude angle change of satellite-borne platform B at 2103 hours. DETAILED DESCRIPTION

[0058] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments disclosed in the present invention will be further described in detail below with reference to the accompanying drawings.

[0059] Starting from the mathematical point of view, the present invention uses ionospheric products and subdivides the signal path, studies the influence of ionosphere and troposphere on the altitude measurement accuracy from the actual spatial changes of the receiver, GPS satellite and mirror reflection point, explores the connection between satellite altitude angle and error delay, and expands the study of atmospheric delay error in GNSS-R experiments on space-borne platforms based on airborne experiments, providing the possibility of improving the altitude measurement accuracy of space-borne GNSS-R.

[0060] GNSS signals propagate through the ionosphere and troposphere in space, causing atmospheric delay. Therefore, the observed pseudorange ρ e The actual distance ρ p The distance relationship is: e =ρ p +ρ ion +ρ tro , ρ ion represents the ionospheric delay, ρ tro Represents the tropospheric delay. Further, combined with the geometric path of signal propagation, the influence of the ionosphere and troposphere on the altimetry process can be expressed as follows:

[0061]

[0062] in, represents the ionospheric delay of the reflected signal, represents the ionospheric delay of the direct signal, Δρ tro Indicates the ionospheric delay of the reflected signal and the ionospheric delay of the direct signal The reflected signal may specifically refer to: the GPS signal from the mirror reflection point to the receiver; the direct signal may specifically refer to: the GPS signal from the GNSS satellite to the receiver.

[0063] In this embodiment, if Figure 1 The method for improving the sea surface height measurement accuracy based on atmospheric delay error correction includes:

[0064] Step 101, constructing an ionosphere correction model and a troposphere correction model.

[0065] Step 102: Calculate the ionospheric delay of the reflected signal according to the ionospheric correction model. and the ionospheric delay of the direct signal

[0066] The ionosphere is a diffuse medium. Electromagnetic waves of different frequencies have different propagation paths and speeds in the ionosphere. This effect is called ionospheric delay. For GNSS signals, the distance difference of the electromagnetic wave propagation path caused by ionospheric refraction can reach up to 50m in the vertical gradient direction and up to 150m in the horizontal gradient direction. The ionosphere has the highest electron content in the space 130 to 500km above the ground. Therefore, for the convenience of research, the present invention regards the ionosphere as a compressed single layer 450km above the ground, called the ionosphere single layer model, and the height of the ionosphere single layer model is h.

[0067] The point where the GPS signal passes through the ionosphere single layer model is called the ionosphere puncture point. The coordinates of the ionosphere puncture point are The solution formula is as follows:

[0068]

[0069] Among them, γ represents the geocentric angle, represents the longitude of the puncture point, λ m represents the latitude of the puncture point, φ n represents the longitude of the receiver, λ n represents the latitude of the receiver and A represents the satellite azimuth.

[0070] Since 1988, IGS (International Gnss Services) has released the precision product Global Ionospheric TEC Grid Map (GIM) to the world, which has provided great help for ionospheric research and application. Currently, the IAAC (Ionosphere Associate Analysis Center) that provides GIM products to IGS includes the European Orbit Determination Center (CODE), the Jet Propulsion Laboratory (JPL) of the United States, the European Space Agency (ESA), the Polytechnic University of Catalonia (UPC) of Spain, the Natural Resources Canada (NRCan / EMR), the Chinese Academy of Sciences (CAS) and Wuhan University (WHU). The ionospheric grid model divides the space into several grids according to certain longitude and latitude, and the intersection of each grid is called a grid point. At present, IGS divides the world into 5183 grids with a longitude interval of 5° from -180° to 180° and a latitude interval of 2.5° from -87.5° to 87.5°. The VTEC value of the grid point can be interpolated to get the VTEC at any location. Compared with other ionospheric models, GIM can provide a wide range of ionospheric data and is not limited by the base station environment. The ionospheric products of the CODE analysis center are of high accuracy, and the present invention uses the ionospheric products provided by CODE. Figure 4 The global ionospheric vertical total electron content VTEC (Vertical Total Electron Content) distribution map obtained by the GIM product provided by CODE at 10:00 on December 3, 2015 is given. The present invention uses the inverse distance weighting method (IDW) to interpolate the grid points to obtain the VTEC value at the ionospheric puncture point, and then calculates the total electron concentration TEC (Total Electron Content) in the direction of the signal path through geometric relationships, that is, the slant total electron concentration STEC (Slant Total Electron Content), thereby obtaining the ionospheric delay in the path direction. The inverse distance weighting method is a method for obtaining the attribute value of the point to be determined by determining the correlation between the point to be determined and the surrounding known points and determining the size of the weight coefficient based on the distance between the point to be determined and the surrounding known points. The closer the point to be determined is to the known point, the greater the weight it occupies. Using the inverse distance weighting method, the expression of VTEC in the zenith direction at the ionospheric puncture point is as follows:

[0071]

[0072] in, represents the VTEC value at the ionospheric piercing point j, represents the VTEC value at the ionospheric grid point i in the vicinity of the ionospheric puncture point, d ij It represents the distance between ionospheric piercing point j and ionospheric grid point i, and DR represents the distance threshold.

[0073] Preferably, based on equations (6) and (7), the electron content VTEC in the vertical direction of the reflected signal propagation path can be calculated: r The electron content VTEC in the direction perpendicular to the direct signal propagation path d .

[0074] Furthermore, STEC can be solved by the following equations (4) and (5): r and STEC d :

[0075]

[0076]

[0077] Among them, R e represents the radius of the earth, and θ represents the GNSS satellite altitude angle at the mirror reflection point.

[0078] The present invention studies the influence of atmospheric delay on the altimetry accuracy during GNSS-R sea surface altimetry. By interpolating the global ionospheric TEC grid map (GIM) provided by IGS (International GNSS Services), the VTEC at the ionospheric puncture point is obtained, which is then converted into the path direction STEC through a projection function. Finally, the ionospheric delay of the reflected signal is solved by the following equations (2) and (3), respectively. and the ionospheric delay of the direct signal

[0079]

[0080]

[0081] Where f is the GPS signal carrier frequency, STEC r Indicates the total electron content contained in the propagation path of the reflected signal, STEC d Represents the total electron content contained in the direct signal propagation path.

[0082] Step 103: Calculate the tropospheric delay of the reflected signal according to the tropospheric correction model Tropospheric delay from direct signal The difference Δρ tro .

[0083] In this embodiment, the earth's atmosphere ranges from the ground to a height of about 60 km. When electromagnetic waves pass through the atmosphere, the signal propagation is delayed due to changes in medium density, of which about 80% of the atmospheric delay occurs in the troposphere, which is called tropospheric delay. According to the different molecular gases in the air, the tropospheric delay can be divided into wet delay and hydrostatic delay. The hydrostatic delay is mainly related to the atmospheric pressure and temperature on the ground, also known as dry delay, accounting for 90% of the total delay. The wet delay is related to the atmospheric humidity and altitude of the propagation path. In the GNSS-R experiment, the dry delay component is mainly considered.

[0084] Preferably, the tropospheric delay of the reflected signal can be calculated by the following formula (8): Tropospheric delay from direct signal The difference Δρ tro :

[0085]

[0086] Among them, h r Indicates the height of the receiver relative to the reference ellipsoid.

[0087] Step 104, according to the solution and Δρ tro , and the influence of ionosphere and troposphere on the altimetry process H is solved.

[0088] In this embodiment, by combining the above formulas (1) to (8), the influence H of the ionosphere and troposphere on the altimetry process can be calculated.

[0089] Step 105, based on the calculated H, the inverted sea surface height is corrected and output to improve the sea surface height measurement accuracy.

[0090] On the basis of the above-mentioned embodiments, the method for improving the sea surface height measurement accuracy based on atmospheric delay error correction is further described below in combination with specific experimental data, verification and results.

[0091] Experimental data

[0092] (1) Airborne GNSS-R sea surface height measurement experimental data

[0093] The data for this airborne experiment was collected by an airborne experiment conducted in the Baltic Sea of ​​Finland. The sampling rate of the signal for this airborne experiment was 80MHz. During the experiment, the aircraft flew at an altitude of about 3km and a speed of about 50m / s. The antenna for collecting direct signals (RHCP, right-hand circular polarization) pointed to the zenith, and the antenna for collecting reflected signals (LHCP, left-hand circular polarization) pointed to the ground. The direct signal and the reflected signal were each obtained through an antenna array of eight elements. The signal was down-converted to a 35MHz intermediate frequency signal through the RF module and then quantized and stored at a rate of 80MHz for 1bit. The instrument control and data recording system consists of an industrial computer running Linux. The original data recording was turned off when the aircraft turned, and the spectrum analysis of the signals collected during the interval could not be performed.

[0094] The time period of the airborne experimental data is 384702-386364s. In order to avoid the impact of the aircraft turning, the time period of 385121-385542s is removed, and only the data of the aircraft flying in a straight line is selected as the experimental analysis data. The flight trajectory of the aircraft is as follows: Figure 2 As shown, the flight altitude changes as Figure 3 As shown, Pseudo Random Noise code (PRN) satellites 1, 11, 19 and 32 are selected as signal sources.

[0095] (2) Satellite-borne GNSS-R sea surface altimetry data

[0096] The onboard experimental data is the onboard GNSS-R altimetry data product on June 27, 2019, with a satellite orbit altitude of 580 km. Data from different onboard platforms at different times of the day were selected for analysis. The selected data were created at 3:33 and 20:48 UTC on June 27, 2019 for the onboard A platform, and 3:48 and 21:03 UTC on June 27, 2019 for the onboard B platform.

[0097] Verification and Results

[0098] (1) Correction results of airborne experiments

[0099] In the airborne GNSS-R sea surface height measurement experiment, the spatial process of the signal can be divided into three parts. The first part is the path of the signal between the GPS satellite and the airborne receiver, that is, the direct signal transmission path. The signal passes through the ionosphere and troposphere during the transmission process and is delayed by the ionosphere and troposphere. The second part is the path of the signal between the GPS satellite and the mirror reflection point. The signal also passes through the ionosphere and troposphere during this process. The third part is the path of the signal between the airborne receiver and the mirror reflection point. Since the aircraft is flying at an altitude of only about 3km, the signal does not pass through the ionosphere during this process, and only the influence of the troposphere is considered. Figure 5 shown.

[0100] (2) Correction results of onboard experiments

[0101] In the satellite-borne GNSSS-R altimetry experiment, the transmission path of the electromagnetic wave signal is the same as that in the airborne experiment. The difference is that in the satellite-borne experiment, because the receiver is carried on a satellite operating at an altitude of 580km, the direct signal only passes through the ionosphere and is not affected by the troposphere, while the reflected signal not only passes through the ionosphere, but also through the troposphere. Figure 6 As shown in FIG. 1 , the atmospheric delay suffered by the signal and its relationship with the satellite altitude angle at the mirror reflection point in the experiments in the above-mentioned time periods are shown respectively.

[0102] (3) Discussion

[0103] By analyzing the signal delay results obtained by using six satellites as observation satellites, it can be clearly found that in the airborne platform GNSS-R altimetry experiment, since the platform height is too low relative to the ionosphere height, the altitude angles at the receiver and the mirror reflection point are very close, and the path similarity of the signal through the ionosphere is high, so the delay effect of the ionosphere on the signal can offset each other, and the final impact on the altimetry result can be ignored. The troposphere produces a meter-level delay on the signal, which must be corrected. The present invention uses the mean absolute error (MAE) and its standard deviation (STD) as the evaluation criteria for the experiment, and at the same time calculates the average value of the impact of the tropospheric delay on the altimetry result during this period, expressed as mean:

[0104]

[0105]

[0106]

[0107] in, represents the tropospheric delay value; x a Represents the average tropospheric delay, which is used as a reference value.

[0108] In the case of low elevation angles, the signal is relatively greatly affected by the troposphere, the obtained tropospheric results have high discreteness, and the inverted sea surface height results are relatively unstable; in the case of high elevation angles, the signal is less affected by the troposphere, the calculated tropospheric results have low discreteness, and the influence of the troposphere on the height measurement results can be eliminated through averaging processing, achieving sub-meter accuracy.

[0109] For the satellite-borne experimental results, the present invention divides the elevation angle of the mirror reflection point into 10° intervals, and statistically calculates the average value of the altitude measurement error caused by each part of the atmospheric delay, wherein the average value of the ionosphere effect is Iono_mean, and the average value of the troposphere effect is Tro_mean.

[0110] Zhang Qiuyang analyzed the corresponding ionospheric delay measurement values ​​of eight different regions around the world in the satellite-borne GNSS-R experiment, and the results showed meter-level accuracy, among which the ionospheric delay results close to the experimental site fluctuated by about 6m. In the experiment, Zhang Yun used the international reference ionosphere model to perform ionospheric correction on the satellite-borne GNSS-R altimetry experiment, and the delay error was about 15m. The present invention studied the data of six time periods of the satellite-borne GNSS-R experiment, and found that the satellite-borne platform GNSS-R altimetry is greatly affected by the ionosphere and troposphere, which is an error term that must be considered to improve the accuracy of altimetry. Similar to the airborne experiment, the larger the incident angle of the reflected signal, that is, the altitude angle at the mirror reflection point, the smaller the atmospheric delay. Figure 6 As shown in Figure 1, the tropospheric delay varies between 10 and 20 meters, and the ionospheric delay generally does not exceed 6 meters. By correcting the atmospheric delay error, the GNSS-R sea surface height measurement accuracy can be improved by 5 to 7 meters.

[0111] On the basis of the above embodiments, the present invention further discloses a system for improving the sea surface height measurement accuracy based on atmospheric delay error correction, comprising: a model building module, used to build an ionosphere correction model and a troposphere correction model; a first solving module, used to solve the ionosphere delay of the reflected signal according to the ionosphere correction model and the ionospheric delay of the direct signal The second solution module is used to solve the tropospheric delay of the reflected signal according to the tropospheric correction model Tropospheric delay from direct signal The difference Δρ tro ; The third solution module is used to obtain the and Δρ tro , and obtain the influence H of the ionosphere and troposphere on the height measurement process; the correction module is used to correct the inverted sea surface height according to H and output it to improve the accuracy of sea surface height measurement.

[0112] As for the system embodiment, since it corresponds to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the description of the method embodiment part.

[0113] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

[0114] The contents not described in detail in the specification of the present invention belong to the common knowledge of the professionals in this field.

Claims

1. A method for improving sea surface height measurement accuracy based on atmospheric delay error correction, characterized in that: include: Construct ionosphere correction model and troposphere correction model; According to the ionospheric correction model, the ionospheric delay of the reflected signal is calculated respectively. and the ionospheric delay of the direct signal According to the tropospheric correction model, the tropospheric delay of the reflected signal is calculated. Tropospheric delay from direct signal The difference Δρ tro ; According to the calculated and Δρ tro , the influence of ionosphere and troposphere on the altimetry process is solved and obtained; According to the calculated H, the inverted sea surface height is corrected and output to improve the sea surface height measurement accuracy; The influence of ionosphere and troposphere on the altimetry process is expressed as follows: Where θ represents the GNSS satellite altitude angle at the mirror reflection point; According to the ionospheric correction model, the ionospheric delay of the reflected signal is calculated respectively. and the ionospheric delay of the direct signal include: The ionospheric delay of the reflected signal is calculated by the following equation (2): The ionospheric delay of the direct signal is calculated by the following equation (3): Where, f represents the GPS signal carrier frequency, STEC r Indicates the total electron content contained in the propagation path of the reflected signal, STEC d Indicates the total electron content contained in the direct signal propagation path; According to the ionospheric correction model, the ionospheric delay of the reflected signal is calculated respectively. and the ionospheric delay of the direct signal Also includes: STEC is calculated by using equations (4) and (5) below: r and STEC d : Among them, VTEC r Indicates the electron content in the vertical direction of the reflected signal propagation path, VTEC d Represents the electron content in the vertical direction of the direct signal propagation path, R e represents the radius of the earth, h represents the height of the ionosphere single layer model, and θ represents the GNSS satellite altitude angle at the mirror reflection point; According to the tropospheric correction model, the tropospheric delay of the reflected signal is calculated. Tropospheric delay from direct signal The difference Δρ tro ,include: The tropospheric delay ρ of the reflected signal is calculated by the following equation (8): t r ro Tropospheric delay from direct signal The difference Δρ tro : Among them, h r represents the height of the receiver relative to the reference ellipsoid, and θ represents the GNSS satellite altitude angle at the mirror reflection point.

2. The method for improving sea surface height measurement accuracy based on atmospheric delay error correction according to claim 1 is characterized in that: According to the ionospheric correction model, the ionospheric delay of the reflected signal is calculated respectively. and the ionospheric delay of the direct signal Also includes: Determine the ionospheric puncture point; The expression of VTEC in the zenith direction at the ionospheric piercing point is as follows: Among them, VTEC ion represents the VTEC value in the zenith direction at the ionospheric piercing point, represents the VTEC value at the ionospheric piercing point j, represents the VTEC value at the ionospheric grid point i in the vicinity of the ionospheric puncture point, d ij It represents the distance between ionospheric piercing point j and ionospheric grid point i, and DR represents the distance threshold.

3. The method for improving sea surface height measurement accuracy based on atmospheric delay error correction according to claim 2 is characterized in that: Coordinates of the ionospheric piercing point The solution formula is as follows: Among them, γ represents the geocentric angle, represents the longitude of the puncture point, λ m represents the latitude of the puncture point, φ n represents the longitude of the receiver, λ n represents the latitude of the receiver and A represents the satellite azimuth.

4. The method for improving sea surface height measurement accuracy based on atmospheric delay error correction according to claim 1, characterized in that: The reflected signal refers to the GPS signal from the mirror reflection point to the receiver; the direct signal refers to the GPS signal from the GNSS satellite to the receiver.

5. A system for improving sea surface height measurement accuracy based on atmospheric delay error correction for implementing the method as claimed in claim 1, characterized in that: include: Model building module, used to build ionosphere correction model and troposphere correction model; The first solution module is used to solve the ionospheric delay of the reflected signal according to the ionospheric correction model and the ionospheric delay of the direct signal The second solution module is used to solve the tropospheric delay of the reflected signal according to the tropospheric correction model Tropospheric delay from direct signal The difference Δρ tro ; The third solution module is used to obtain the and Δρ tro , we can get the influence of ionosphere and troposphere on the altimetry process H; The correction module is used to correct and output the inverted sea surface height according to H to improve the accuracy of sea surface height measurement.

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