A method for calculating normalized bistatic radar cross section based on GNSS-R data

Abstract

The present invention provides a method for calculating a normalized bistatic radar cross section based on GNSS-R data, obtaining detection data collected by GNSS-R technology; performing a first preprocessing on the detection data to obtain required parameters; bringing the required parameters into a forward scattering model, performing a second preprocessing on the required parameters to obtain a normalized bistatic radar cross section; obtaining a first velocity value through the normalized bistatic radar cross section, the first velocity value being a value of the sea surface wind speed; wherein the required parameters include the received power under a delay-Doppler diagram, the total distance loss, the effective isotropic radiated power, the gain of a low-orbit satellite antenna, the unit delay value of a position within a preset distance of a mirror point, and the unit Doppler frequency shift value of a position within a preset distance of a mirror point. By calculating the sea surface wind speed through the normalized bistatic radar cross section based on GNSS-R data, the accuracy and real-time performance of wind speed measurement are improved.

Description

Technical Field

[0001] The present invention relates to the field of normalized bistatic radar cross section calculation, and in particular to a normalized bistatic radar cross section calculation method based on GNSS-R data. Background Art

[0002] At present, in the relevant technologies, sea surface roughness is one of the key parameters of the interaction between the ocean and the atmosphere, and is of great significance to marine meteorological forecasting, wave model construction, marine energy resource assessment, marine environmental monitoring, etc. However, due to the complexity and variability of the marine environment, including the combined effects of wind and waves, tides, currents, temperature changes, and seabed topography, the calculation of sea surface roughness is not accurate enough.

[0003] Therefore, it is particularly important to find a method to improve the calculation accuracy of sea surface roughness. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art or related art.

[0005] To this end, a first aspect of the present invention proposes a normalized bistatic radar cross section calculation method based on GNSS-R data.

[0006] In view of this, a first aspect of the present invention provides a normalized bistatic radar cross section calculation method based on GNSS-R data, characterized in that detection data collected by GNSS-R technology is acquired; a first preprocessing is performed on the detection data to acquire required parameters; the required parameters are brought into a forward scattering model, and a second preprocessing is performed on the required parameters to acquire a normalized bistatic radar cross section; a first velocity value is acquired through the normalized bistatic radar cross section, and the first velocity value is a value of the sea surface wind speed; wherein the required parameters include received power under a delay-Doppler diagram, total range loss, effective isotropic radiated power, low-orbit satellite antenna gain, a unit delay value at a position within a preset distance from a mirror point, and a unit Doppler frequency shift value at a position within a preset distance from a mirror point.

[0007] The present invention provides a calculation method for a normalized bistatic radar cross section based on GNSS-R data, acquires detection data collected by GNSS-R (Global Navigation Satellite System Reflectometry) technology, wherein the detection data is collected by a low-orbit satellite through the GNSS-R technology, performs a first preprocessing on the detection data, and acquires required parameters, wherein the required parameters include received power under a delay-Doppler diagram, total distance loss, effective isotropic radiated power, low-orbit satellite antenna gain, a unit delay value at a position within a preset distance from a mirror point, and a unit Doppler frequency shift value at a position within a preset distance from the mirror point, brings the required parameters into a forward scattering model, performs a second preprocessing on the required parameters through a preset model, acquires a normalized bistatic radar cross section, and acquires a first velocity value through the normalized bistatic radar cross section, wherein the first velocity value is a value of the sea surface wind speed. By calculating the sea surface wind speed based on the normalized bistatic radar scattering cross section of GNSS-R data, human intervention can be reduced. Through multi-parameter joint analysis, the comprehensive accuracy of wind speed measurement can be improved more comprehensively, and the accuracy and real-time performance of wind speed measurement can be improved.

[0008] In addition, the normalized bistatic radar cross section calculation method based on GNSS-R data in the above technical solution provided by the present invention may also have the following additional technical features:

[0009] In some technical solutions of the present invention, optionally, the detection data is first preprocessed to obtain required parameters, including: extracting the detection data to obtain unit delay value and unit Doppler value; based on the unit delay value and unit Doppler value, obtaining the receiving power under the delay-Doppler graph.

[0010] In this technical solution, the detection data is first preprocessed to obtain the required parameters, including extracting the detection data to obtain the unit delay value and the unit Doppler value, and on this basis, based on the unit delay value and the unit Doppler frequency shift value, the received power under the delay Doppler map is obtained. Among them, the detection data is a delay Doppler map, and then based on the unit delay value and the unit Doppler frequency shift value, the received power is extracted from the delay Doppler map. The received power is negatively correlated with the sea surface roughness, so that the change of the sea surface roughness can be indirectly evaluated, laying a foundation for the subsequent detection of the sea surface roughness.

[0011] In some technical solutions of the present invention, optionally, performing a first preprocessing on the detection data to obtain the required parameters further includes: extracting the detection data to obtain navigation satellite coordinates, low-orbit satellite coordinates and mirror point coordinates; obtaining a first distance according to the navigation satellite coordinates and the mirror point coordinates; obtaining a second distance according to the low-orbit satellite coordinates and the mirror point coordinates; obtaining a total distance loss based on the first distance and the second distance; wherein the total distance loss is obtained based on the following formula: ;in, is the total distance loss, is the second distance, is the first distance.

[0012] In this technical solution, the present invention extracts detection data, obtains navigation satellite coordinates, low-orbit satellite coordinates and mirror point coordinates, and obtains the first distance and the second distance based on the navigation satellite coordinates, the low-orbit satellite coordinates and the mirror point coordinates, and then calculates the total distance loss based on the first distance and the second distance. Based on the total distance loss, the influence of the signal transmission process can be estimated, which is convenient for the subsequent correction of the results of the sea surface roughness, improving the accuracy of detection and enhancing the accuracy of measurement.

[0013] In some technical solutions of the present invention, optionally, the navigation satellite coordinates, low-orbit satellite coordinates and mirror point coordinates are all positioned using the ECEF coordinate system, which is an Earth-centered, Earth-fixed coordinate system.

[0014] In this technical solution, the navigation satellite coordinates, low-orbit satellite coordinates and mirror point coordinates are all positioned using the ECEF coordinate system. Among them, the ECEF (Earth-Centered, Earth-Fixed Coordinate system) coordinate system is an earth-centered, earth-fixed rectangular coordinate system, whose origin is the center of mass of the earth, the X-axis extends through the intersection of the prime meridian and the equator, the Z-axis extends through the North Pole and coincides with the earth's rotation axis, and the Y-axis completes the right-hand coordinate system, passing through the equator and 90 degrees of longitude. By selecting the ECEF coordinate system, the three-dimensional position of the navigation satellite and any point on the earth's surface or the three-dimensional position of the low-orbit satellite and any point on the earth's surface can be accurately represented, and because the ECFC coordinates are a coordinate system established with the center of mass of the earth as the origin, it is more convenient to calculate the first distance and the second distance, which simplifies the data processing flow and improves the efficiency of data processing.

[0015] In some technical solutions of the present invention, optionally, the detection data is first preprocessed to obtain the required parameters, and also includes: extracting the detection data to obtain the navigation satellite transmit power and the navigation satellite antenna gain; based on the navigation satellite transmit power and the navigation satellite antenna gain, obtaining the effective isotropic radiated power.

[0016] In this technical solution, the detection data is extracted to obtain the navigation satellite transmission power and the navigation satellite antenna gain, and based on the navigation satellite transmission power and the navigation satellite antenna gain, the effective isotropic radiation power is obtained, so as to understand the signal's propagation ability and anti-interference ability in space, facilitate the correction of the received power when obtaining the sea surface roughness, and improve the accuracy of the acquired data.

[0017] In some technical schemes of the present invention, optionally, a first preprocessing is performed on the detection data to obtain the required parameters, which also includes: based on the low-orbit satellite coordinates and the mirror point coordinates, obtaining the azimuth of the mirror point located on the low-orbit satellite and the incident angle of the mirror point located on the low-orbit satellite; obtaining the antenna gain pattern of the low-orbit satellite; importing the azimuth and the incident angle into the antenna gain pattern of the low-orbit satellite to obtain the antenna gain of the low-orbit satellite.

[0018] In this technical solution, the azimuth and incident angle of the mirror point located on the low-orbit satellite are obtained based on the low-orbit satellite coordinates and the mirror point coordinates, and the antenna gain pattern of the low-orbit satellite is obtained, and then the azimuth and incident angle are imported into the obtained antenna gain pattern of the low-orbit satellite to obtain the antenna gain of the low-orbit satellite. According to the antenna gain of the low-orbit satellite, the amplification factor of the received power can be understood, which is convenient for the subsequent inversion steps, can significantly reduce errors, and improve the accuracy of the acquired data.

[0019] In some technical schemes of the present invention, optionally, based on the low-orbit satellite coordinates and the mirror point coordinates, the azimuth of the mirror point located on the low-orbit satellite and the incident angle of the mirror point located on the low-orbit satellite are obtained, including: converting the low-orbit satellite coordinates and the mirror point coordinates from ECEF coordinates into longitude and latitude coordinates, and obtaining the longitude and latitude coordinates of the low-orbit satellite and the longitude and latitude coordinates of the mirror point; establishing a station-center coordinate system with the mirror point as the origin; converting the longitude and latitude coordinates of the low-orbit satellite and the longitude and latitude coordinates of the mirror point into station-center coordinates, and obtaining the station-center coordinates of the low-orbit satellite and the station-center coordinates of the mirror point; obtaining the altitude of the low-orbit satellite and the distance between the low-orbit satellite and the mirror point based on the low-orbit satellite station-center coordinates; and obtaining the azimuth and incident angle based on the altitude of the low-orbit satellite and the distance between the low-orbit satellite and the mirror point.

[0020] In this technical solution, based on the low-orbit satellite coordinates and the mirror point coordinates, the azimuth of the mirror point located on the low-orbit satellite and the incident angle of the mirror point located on the low-orbit satellite are obtained, including: converting the low-orbit satellite coordinates and the mirror point coordinates from ECEF coordinates into longitude and latitude coordinates, obtaining the longitude and latitude coordinates of the low-orbit satellite and the longitude and latitude coordinates of the mirror point, establishing a station-center coordinate system with the mirror point as the origin, wherein in the station-center coordinate system with the mirror point as the origin, the coordinates are called station-center coordinates, converting the longitude and latitude coordinates of the low-orbit satellite and the longitude and latitude coordinates of the mirror point into station-center coordinates, obtaining the station-center coordinates of the low-orbit satellite and the station-center coordinates of the mirror point, obtaining the altitude of the low-orbit satellite and the distance between the low-orbit satellite and the mirror point based on the station-center coordinates of the low-orbit satellite, and obtaining the azimuth and the incident angle based on the altitude of the low-orbit satellite and the distance between the low-orbit satellite and the mirror point. Because the coordinate values ​​of the ECEF coordinate system are relatively large, it is not convenient to process numerical values ​​for spatial calculations. Converting ECEF coordinates to station center coordinates will facilitate calculations without changing the relative positions of the coordinates, simplifying the data processing process and improving the efficiency of data processing.

[0021] In some technical solutions of the present invention, optionally, the required parameters are brought into the forward scattering model, and the required parameters are subjected to a second preprocessing to obtain a normalized bistatic radar cross section, including: obtaining a carrier signal wavelength; substituting received power, total range loss, effective isotropic radiated power, low-orbit satellite antenna gain, and carrier signal wavelength into the forward scattering model to obtain a bistatic radar cross section; obtaining an effective scattering area based on a unit delay value and a unit Doppler frequency shift value; and obtaining a normalized bistatic radar cross section based on the bistatic radar cross section and the effective scattering area; wherein the bistatic radar cross section is obtained based on the following formula: ;in, is the bistatic radar cross section, is the received power, is the effective isotropic radiated power, is the carrier signal wavelength, is the LEO satellite antenna gain, is the total distance loss.

[0022] In this technical solution, the wavelength of the carrier signal is obtained, and the received power, total distance loss, effective isotropic radiated power, low-orbit satellite antenna gain and carrier signal wavelength are substituted into the forward scattering model to calculate the bistatic radar cross section. According to the unit delay value and the unit Doppler frequency shift value, the effective scattering area is processed and the normalized bistatic radar cross section is obtained based on the bistatic radar cross section and the effective scattering area. Among them, the normalized bistatic radar cross section is a parameter that describes the intensity of the scattered echo after the interaction between the radar wave and the sea surface. It is directly affected by the roughness of the sea surface, because the roughness of the sea surface determines the scattering characteristics of the sea surface to the radar wave. In addition, the normalized bistatic radar cross section is obtained based on the bistatic radar system, which can provide richer scattering information, capture more sea surface scattering characteristics, and thus more accurately reflect the actual situation of the sea surface and improve the calculation accuracy.

[0023] In some technical solutions of the present invention, optionally, based on the unit delay value and the unit Doppler frequency shift value, an effective scattering area is obtained, including: obtaining a delay spread function based on the unit delay value; obtaining a Doppler spread function based on the unit Doppler frequency shift value; and analyzing the delay spread function and the Doppler spread function to obtain the effective scattering area.

[0024] In this technical solution, based on the unit delay value, the delay spread function is obtained, based on the unit Doppler shift value, the Doppler spread function is obtained, and the delay spread function and the Doppler spread function are analyzed to obtain the effective scattering area. Among them, the effective scattering area is a parameter that describes the size of the sea surface area that actually participates in the scattering process when the sea surface interacts with the radar wave. It is directly affected by the roughness of the sea surface, because the roughness determines the scattering intensity and distribution of the radar wave by the sea surface. Therefore, by measuring and analyzing the effective scattering area, the roughness of the sea surface can be indirectly evaluated, and then the actual situation of the interaction between the radar wave and the sea surface can be more accurately reflected, and the roughness of the sea surface can be calculated more accurately.

[0025] In some technical solutions of the present invention, optionally, based on the bistatic radar cross section and the effective scattering area, obtaining a normalized bistatic radar cross section includes: normalizing the bistatic radar cross section of the mirror point and each unit around it to obtain a first normalized value; normalizing the effective scattering area to obtain a second normalized value; and obtaining a normalized bistatic radar cross section based on the first normalized value and the second normalized value; wherein the normalized bistatic radar cross section is obtained based on the following formula: ;in, is the normalized radar cross section, is the first normalized value, is the second normalized value, is the number of time delay units, is the number of Doppler cells, and Used to calculate the first normalized value and the second normalized value.

[0026] In this technical solution, the bistatic radar cross section of the mirror point and each unit around it is normalized to obtain a first normalized value; the effective scattering area corresponding to the bistatic radar cross section is normalized to obtain a second normalized value; based on the first normalized value and the second normalized value, the normalized bistatic radar cross section is obtained. By normalizing the bistatic radar cross section and the effective scattering area, the stability of the data can be improved, which is convenient for data analysis and thus improves the measurement accuracy.

[0027] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0029] Figure 1 The first flowchart of a method for calculating a normalized bistatic radar cross section based on GNSS-R data according to an embodiment of the present invention.

[0030] Figure 2 The second flow chart of the normalized bistatic radar cross section calculation method based on GNSS-R data according to an embodiment of the present invention.

[0031] Figure 3 The third flow chart of the method for calculating the normalized bistatic radar cross section based on GNSS-R data according to an embodiment of the present invention. DETAILED DESCRIPTION

[0032] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0033] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0034] Refer to the following Figures 1 to 3 A method for calculating a normalized bistatic radar cross section based on GNSS-R data according to some embodiments of the present invention is described.

[0035] In one embodiment of the present invention, Figure 1 As shown in FIG, a normalized bistatic radar cross section calculation method based on GNSS-R data is proposed, which is characterized by:

[0036] Step 102, acquiring detection data collected by GNSS-R technology;

[0037] Step 104, performing a first preprocessing on the detection data to obtain required parameters;

[0038] Step 106, bringing the required parameters into the forward scattering model, performing a second preprocessing on the required parameters, and obtaining a normalized bistatic radar cross section;

[0039] Step 108, obtaining a first velocity value by normalizing the bistatic radar cross section, where the first velocity value is a value of the sea surface wind speed;

[0040] Among them, the required parameters include the received power under the delay-Doppler diagram, the total distance loss, the effective isotropic radiated power, the low-orbit satellite antenna gain, the unit delay value at the position within the preset distance of the mirror point, and the unit Doppler frequency shift value at the position within the preset distance of the mirror point.

[0041] The present invention provides a calculation method for a normalized bistatic radar cross section based on GNSS-R data, acquires detection data collected by GNSS-R (Global Navigation Satellite System Reflectometry) technology, wherein the detection data is collected by a low-orbit satellite through the GNSS-R technology, performs a first preprocessing on the detection data, and acquires required parameters, wherein the required parameters include received power under a delay-Doppler diagram, total distance loss, effective isotropic radiated power, low-orbit satellite antenna gain, a unit delay value at a position within a preset distance from a mirror point, and a unit Doppler frequency shift value at a position within a preset distance from the mirror point, brings the required parameters into a forward scattering model, performs a second preprocessing on the required parameters through a preset model, acquires a normalized bistatic radar cross section, and acquires a first velocity value through the normalized bistatic radar cross section, wherein the first velocity value is a value of the sea surface wind speed. By calculating the sea surface wind speed based on the normalized bistatic radar scattering cross section of GNSS-R data, human intervention can be reduced. Through multi-parameter joint analysis, the comprehensive accuracy of wind speed measurement can be improved more comprehensively, and the accuracy and real-time performance of wind speed measurement can be improved.

[0042] It is understandable that the characteristics and advantages of GNSS-R (Global Navigation Satellite System Reflectometry) technology are concentrated in the following aspects: no transmitter is required, and the GNSS constellation is used as a multi-element microwave signal transmission reflection source; there are many signal sources, not only the 24 existing GPS satellites, but also Galileo satellites, GLONASS satellites, BeiDou satellite system, etc.; the gain brought by the spread spectrum communication technology enables the navigation satellite reflection signal receiver to receive weak signals below the background noise; it has strong real-time performance, global coverage, and all-weather performance, etc., making it a very advantageous means of detecting sea surface wind speed.

[0043] It is understandable that the delay Doppler map obtained by GNSS-R technology detection is affected by many factors and cannot directly reflect the change of sea surface roughness. The delay Doppler map needs to be processed and inverted to obtain relevant physical parameters, among which the normalized bistatic radar cross section obtained by considering multiple influencing factors is closely related to the sea surface roughness. Compared with other physical parameters, the normalized bistatic radar cross section has a higher correlation with the sea surface roughness because it considers the influence of the signal propagation process more comprehensively. The present invention obtains the delay Doppler map and processes the relevant parameters one by one, thereby obtaining the normalized bistatic radar cross section.

[0044] In one specific embodiment, the detection data collected by the GNSS-R technology with a time resolution of 1 second includes but is not limited to the delay Doppler map, mirror point coordinates, low-orbit satellite coordinates, navigation satellite coordinates, navigation satellite transmission power, and navigation satellite antenna gain. The received power, mirror point coordinates, low-orbit satellite coordinates, navigation satellite coordinates, navigation satellite transmission power, navigation satellite antenna gain and other information under the delay Doppler map of the corresponding second are extracted from the data of each second.

[0045] In addition, the normalized bistatic radar cross section calculation method based on GNSS-R data in the above embodiment provided by the present invention may also have the following additional technical features:

[0046] In some embodiments of the present invention, optionally, performing a first preprocessing on the detection data to obtain required parameters includes:

[0047] Extract the detection data to obtain the unit delay value and the unit Doppler frequency shift value;

[0048] Based on the unit delay value and the unit Doppler frequency shift value, the received power under the delay-Doppler graph is obtained.

[0049] In this embodiment, the detection data is first preprocessed to obtain the required parameters, including extracting the detection data to obtain the unit delay value and the unit Doppler frequency shift value, and on this basis, based on the unit delay value and the unit Doppler frequency shift value, the received power under the delay Doppler map is obtained. Wherein, the detection data is a delay Doppler map, and then based on the unit delay value and the unit Doppler frequency shift value, the received power is extracted from the delay Doppler map, and the received power is negatively correlated with the sea surface roughness, so that the change of the sea surface roughness can be indirectly evaluated, laying a foundation for the subsequent detection of the sea surface roughness.

[0050] like Figure 2 As shown, in some embodiments of the present invention, optionally, performing a first preprocessing on the detection data to obtain required parameters further includes:

[0051] Extract the detection data to obtain the navigation satellite coordinates, low-orbit satellite coordinates and mirror point coordinates;

[0052] Acquire a first distance according to the navigation satellite coordinates and the mirror point coordinates;

[0053] Obtaining a second distance according to the low-orbit satellite coordinates and the mirror point coordinates;

[0054] Based on the first distance and the second distance, obtaining a total distance loss;

[0055] Among them, the total distance loss is obtained based on the following formula:

[0056] ;

[0057] in, is the total distance loss, is the second distance, is the first distance.

[0058] In this embodiment, the present invention extracts the detection data, obtains the navigation satellite coordinates, the low-orbit satellite coordinates and the mirror point coordinates, and obtains the first distance and the second distance based on the navigation satellite coordinates, the low-orbit satellite coordinates and the mirror point coordinates, and then calculates the total distance loss according to the first distance and the second distance. Based on the total distance loss, we can estimate the impact of the signal sending process, which is convenient for the subsequent correction of the sea surface roughness results, improves the accuracy of detection, and enhances the accuracy of measurement.

[0059] Understandably, and The effective range loss at each delay-Doppler is set in the denominator to calculate the total range loss.

[0060] In one specific embodiment, data of mirror point coordinates, low-orbit satellite coordinates, and navigation satellite coordinates with a time resolution of 1 second are processed, and the distance from the navigation satellite to the mirror point, i.e., the first distance, is calculated using the navigation satellite coordinates and the mirror point coordinates. The distance from the mirror point to the low-orbit satellite, i.e., the second distance, is calculated using the low-orbit satellite coordinates and the mirror point coordinates, and then the total distance loss from the navigation satellite to the mirror point and then to the low-orbit satellite is calculated.

[0061] In some embodiments of the present invention, optionally, the navigation satellite coordinates, low-orbit satellite coordinates and mirror point coordinates are all positioned in the ECEF coordinate system.

[0062] In this embodiment, the navigation satellite coordinates, low-orbit satellite coordinates and mirror point coordinates are all positioned using the ECEF coordinate system. Among them, the ECEF (Earth-Centered, Earth-Fixed Coordinate system) coordinate system is an earth-centered, earth-fixed rectangular coordinate system, whose origin is the center of mass of the earth, the X-axis extends through the intersection of the prime meridian and the equator, the Z-axis extends through the North Pole and coincides with the earth's rotation axis, and the Y-axis completes the right-hand coordinate system, passing through the equator and 90 degrees of longitude. By selecting the ECEF coordinate system, the three-dimensional position of the navigation satellite and any point on the earth's surface or the three-dimensional position of the low-orbit satellite and any point on the earth's surface can be accurately represented, and because the ECFC coordinates are a coordinate system established with the center of mass of the earth as the origin, it is more convenient to calculate the first distance and the second distance, which simplifies the data processing flow and improves the efficiency of data processing.

[0063] Preferably, the first distance is obtained based on the following formula:

[0064] = ;

[0065] in, is the first distance, are the values ​​of the X-axis, Y-axis, and Z-axis of the navigation satellite in the ECEF coordinates, It is the value of the mirror point in the X-axis direction, the Y-axis direction, and the Z-axis direction in the ECEF coordinates.

[0066] Preferably, the second distance is obtained based on the following formula:

[0067] = ;

[0068] in, is the second distance, It is the value of the X-axis direction, Y-axis direction, and Z-axis direction of the low-orbit satellite in the ECEF coordinate. These are the values ​​in the X-axis direction, the Y-axis direction, and the Z-axis direction in the ECEF coordinates of the mirror point.

[0069] In some embodiments of the present invention, optionally, performing a first preprocessing on the detection data to obtain required parameters further includes:

[0070] Extract detection data to obtain navigation satellite transmission power and navigation satellite antenna gain;

[0071] Based on the navigation satellite transmission power and the navigation satellite antenna gain, the effective isotropic radiated power is obtained;

[0072] Among them, the effective isotropic radiated power is obtained based on the following formula:

[0073] ;

[0074] in, is the first power, is the first satellite transmission power, is the first satellite antenna gain.

[0075] In this embodiment, the detection data is extracted to obtain the navigation satellite transmission power and the navigation satellite antenna gain, and based on the navigation satellite transmission power and the navigation satellite antenna gain, the effective isotropic radiation power is obtained, so as to understand the signal's propagation ability and anti-interference ability in space, facilitate the correction of the received power when obtaining the sea surface roughness, and improve the accuracy of the acquired data.

[0076] It can be understood that the effective isotropic radiated power (EIRP) refers to the product of the antenna gain relative to the transmitting antenna gain of the isotropic radiating element and the antenna power supplied by the transmitter in a specific direction.

[0077] In one of the specific embodiments, the data of the navigation satellite transmission power and the navigation satellite antenna gain with a time resolution of 1 second are processed, and the EIRP is calculated based on the obtained navigation satellite transmission power and the navigation satellite antenna gain.

[0078] In some embodiments of the present invention, optionally, performing a first preprocessing on the detection data to obtain required parameters further includes:

[0079] Based on the low-orbit satellite coordinates and the mirror point coordinates, the azimuth of the mirror point located at the low-orbit satellite and the incident angle of the mirror point located at the low-orbit satellite are obtained;

[0080] Obtain antenna gain patterns of low-orbit satellites;

[0081] The azimuth angle and the incident angle are imported into the antenna gain pattern of the low-orbit satellite to obtain the antenna gain of the low-orbit satellite.

[0082] In this embodiment, the azimuth and incident angle of the mirror point located at the low-orbit satellite are obtained based on the low-orbit satellite coordinates and the mirror point coordinates, and the antenna gain pattern of the low-orbit satellite is obtained, and then the antenna gain pattern of the low-orbit satellite is imported based on the azimuth and the incident angle, so as to obtain the antenna gain of the low-orbit satellite. According to the natural gain of the low-orbit satellite, the amplification factor of the received power can be understood, which is convenient for subsequent inversion steps, can significantly reduce errors, and improve the accuracy of the acquired data.

[0083] In one specific embodiment, the data of low-orbit satellite coordinates and mirror point coordinates with a time resolution of 1 second are processed, the antenna gain radiation pattern of the low-orbit satellite that changes with azimuth and elevation is imported, the azimuth and incident angle of the mirror point located on the low-orbit satellite are calculated, and then the low-orbit satellite antenna gain is retrieved based on the acquired azimuth and incident angle.

[0084] In some embodiments of the present invention, optionally, based on the low-orbit satellite coordinates and the mirror point coordinates, the azimuth of the mirror point located on the low-orbit satellite and the incident angle of the mirror point located on the low-orbit satellite are obtained, including: converting the low-orbit satellite coordinates and the mirror point coordinates from ECEF coordinates to longitude and latitude coordinates, and obtaining the longitude and latitude coordinates of the low-orbit satellite and the longitude and latitude coordinates of the mirror point; establishing a station-center coordinate system with the mirror point as the origin; converting the longitude and latitude coordinates of the low-orbit satellite and the longitude and latitude coordinates of the mirror point into station-center coordinates, and obtaining the station-center coordinates of the low-orbit satellite and the station-center coordinates of the mirror point; obtaining the altitude of the low-orbit satellite and the distance between the low-orbit satellite and the mirror point based on the low-orbit satellite station-center coordinates; and obtaining the azimuth and incident angle based on the altitude of the low-orbit satellite and the distance between the low-orbit satellite and the mirror point.

[0085] In this embodiment, based on the low-orbit satellite coordinates and the mirror point coordinates, the azimuth of the mirror point located on the low-orbit satellite and the incident angle of the mirror point located on the low-orbit satellite are obtained, including: converting the low-orbit satellite coordinates and the mirror point coordinates from ECEF coordinates into longitude and latitude coordinates, obtaining the longitude and latitude coordinates of the low-orbit satellite and the longitude and latitude coordinates of the mirror point, establishing a station-center coordinate system with the mirror point as the origin, wherein in the station-center coordinate system with the mirror point as the origin, the coordinates are called station-center coordinates, converting the longitude and latitude coordinates of the low-orbit satellite and the longitude and latitude coordinates of the mirror point into station-center coordinates, obtaining the station-center coordinates of the low-orbit satellite and the station-center coordinates of the mirror point, obtaining the altitude of the low-orbit satellite and the distance between the low-orbit satellite and the mirror point based on the station-center coordinates of the low-orbit satellite, and obtaining the azimuth and the incident angle based on the altitude of the low-orbit satellite and the distance between the low-orbit satellite and the mirror point. Because the coordinate values ​​of the ECEF coordinate system are relatively large, it is not convenient to process numerical values ​​for spatial calculations. Converting ECEF coordinates to station center coordinates will facilitate calculations without changing the relative positions of the coordinates, simplifying the data processing process and improving the efficiency of data processing.

[0086] like Figure 3 As shown, in some embodiments of the present invention, optionally, performing a second preprocessing on the required parameters to obtain a normalized bistatic radar cross section includes:

[0087] Step 202, obtaining the carrier signal wavelength;

[0088] Step 204, substituting the received power, total range loss, effective isotropic radiated power, low-orbit satellite antenna gain and carrier signal wavelength into the forward scattering model to obtain the bistatic radar cross section;

[0089] Step 206, obtaining an effective scattering area based on the unit delay value and the unit Doppler frequency shift value;

[0090] Step 208, obtaining a normalized bistatic radar cross section based on the bistatic radar cross section and the effective scattering area;

[0091] The bistatic radar cross section is based on the following formula:

[0092] ;

[0093] in, is the bistatic radar cross section, is the received power, is the effective isotropic radiated power, is the carrier signal wavelength, is the LEO satellite antenna gain, is the total distance loss.

[0094] In this embodiment, the carrier signal wavelength is obtained, and the received power, total distance loss, effective isotropic radiated power, low-orbit satellite antenna gain and carrier signal wavelength are substituted into the forward scattering model to calculate the bistatic radar cross section, and the effective scattering area is obtained by processing according to the unit delay value and the unit Doppler frequency shift value, and the normalized bistatic radar cross section is obtained based on the bistatic radar cross section and the effective scattering area. Among them, the normalized bistatic radar cross section is a parameter that describes the intensity of the scattered echo after the interaction between the radar wave and the sea surface, which is directly affected by the roughness of the sea surface, because the roughness of the sea surface determines the scattering characteristics of the sea surface to the radar wave, and the normalized bistatic radar cross section is obtained based on the bistatic radar system, which can provide richer scattering information, capture more sea surface scattering characteristics, and thus more accurately reflect the actual situation of the sea surface and improve the calculation accuracy.

[0095] It is understandable that for the sea surface scattered global navigation system signals detected by GNSS-R, Zavorotny and Voronovich conducted a theoretical analysis on the relationship between the reflected signals of the dual-base structure and the sea surface wind field in 2000 and established a forward scattering model (ZV model).

[0096] In one specific embodiment, the data with a time resolution of 1 second is processed, and the total range loss, EIRP, low-orbit satellite antenna gain and received power obtained by calculation or retrieval are used to calculate the bistatic radar cross section using the forward scattering model. On this basis, the unit delay value and unit Doppler frequency shift value of the mirror reflection point are extracted, and the effective scattering area corresponding to the mirror reflection point and the unit value around it is calculated.

[0097] In some embodiments of the present invention, optionally, obtaining the effective scattering area based on the unit delay value and the unit Doppler frequency shift value includes:

[0098] Based on the unit delay value, a delay spread function is obtained;

[0099] Based on the unit Doppler frequency shift value, a Doppler spread spectrum function is obtained;

[0100] Analyze the delay spread function and Doppler spread function to obtain the effective scattering area.

[0101] In this embodiment, based on the unit delay value, the delay spread function is obtained; based on the unit Doppler frequency shift value, the Doppler spread function is obtained; and the delay spread function and the Doppler spread function are analyzed to obtain the effective scattering area. The effective scattering area is a parameter that describes the size of the sea surface area that actually participates in the scattering process when the sea surface interacts with the radar wave. It is directly affected by the roughness of the sea surface, because the roughness determines the scattering intensity and distribution of the radar wave by the sea surface. Therefore, by measuring and analyzing the effective scattering area, the roughness of the sea surface can be indirectly evaluated, thereby more accurately reflecting the actual situation of the interaction between the radar wave and the sea surface, and the roughness of the sea surface can be calculated more accurately.

[0102] In one specific embodiment, the effective scattering area is obtained based on the following formula:

[0103] ;

[0104] in, is the effective scattering area, is the delayed spread function, is the Doppler spread function, is the unit delay value, is the unit Doppler shift value.

[0105] It is understandable that a single delay Doppler zone contains the scattering power captured on one or more physical areas of the ocean surface, and each delay Doppler unit corresponds to a corresponding effective area. The ambiguity function of GPS increases the effective area of ​​each delay Doppler unit, causing the scattering power to spread from the geometrically determined physical scattering area to the adjacent delay Doppler unit, changing the total scattering power, and the physical area and effective area in the entire delay Doppler power map will change. Therefore, the effective surface scattering area of ​​each delay Doppler unit is expressed as the weighted surface integral of the ambiguity function. The delay spread function and the Doppler spread function correspond to the physical surface integral of each delay Doppler unit.

[0106] In some embodiments of the present invention, optionally, obtaining a normalized bistatic radar cross section based on the bistatic radar cross section and the effective scattering area includes:

[0107] Normalizing the bistatic radar cross section of the mirror point and each unit around it to obtain a first normalized value;

[0108] Normalizing the effective scattering area to obtain a second normalized value;

[0109] Obtaining a normalized bistatic radar cross section based on the first normalized value and the second normalized value;

[0110] Among them, the normalized bistatic radar cross section is obtained based on the following formula:

[0111] ;

[0112] in, is the normalized radar cross section, is the first normalized value, is the second normalized value, is the number of time delay units, is the number of Doppler cells, and Used to calculate the first normalized value and the second normalized value.

[0113] In this embodiment, the bistatic radar cross section of the mirror point and each unit around it is normalized to obtain a first normalized value; the effective scattering area corresponding to the bistatic radar cross section is normalized to obtain a second normalized value; based on the first normalized value and the second normalized value, a normalized bistatic radar cross section is obtained. By normalizing the bistatic radar cross section and the effective scattering area, the differences between different measurement conditions can be eliminated, so that the measurement results under different conditions are comparable, the stability of the data is improved, data analysis is facilitated, and the measurement accuracy is improved.

[0114] It can be understood that the area of ​​the delay unit number and the Doppler unit number selected with the mirror point as the center in the delay-Doppler power diagram is used as the effective scattering area.

[0115] In one specific embodiment, normalization processing is performed on the calculated bistatic radar cross section and scattering area values ​​to obtain a normalized bistatic radar cross section corresponding to seconds.

[0116] In the claims, specification and drawings of the present invention, the term "multiple" refers to two or more than two. Unless otherwise clearly defined, the orientation or positional relationship indicated by the terms "upper" and "lower" is based on the orientation or positional relationship shown in the drawings, which is only for the purpose of more conveniently describing the present invention and making the description process simpler, rather than indicating or implying that the device or element referred to must have the specific orientation described, be constructed and operated in a specific orientation, so these descriptions cannot be understood as limiting the present invention; the terms "connect", "install", "fix" and the like should be understood in a broad sense. For example, "connection" can be a fixed connection between multiple objects, or a detachable connection between multiple objects, or an integral connection; it can be a direct connection between multiple objects, or an indirect connection between multiple objects through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood based on the specific circumstances of the above data.

[0117] In the claims, specification and drawings of the present invention, the description of the terms "one embodiment", "some embodiments", "specific embodiments" and the like means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In the claims, specification and drawings of the present invention, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0118] The above description is only a preferred embodiment of the present invention and is 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 method for calculating normalized bistatic radar cross section based on GNSS-R data, characterized in that: Step 102, acquiring detection data collected by GNSS-R technology; Step 104, performing a first preprocessing on the detection data to obtain required parameters, including: Extracting the detection data to obtain navigation satellite coordinates, low-orbit satellite coordinates and mirror point coordinates, wherein the navigation satellite coordinates, the low-orbit satellite coordinates and the mirror point coordinates are all positioned using an ECEF coordinate system, which is an Earth-centered Earth-fixed coordinate system; Acquire a first distance according to the navigation satellite coordinates and the mirror point coordinates; The first distance is obtained based on the following formula: Among them, R T is the first distance, X T , Y T , Z T are the values ​​of the X-axis, Y-axis, and Z-axis of the navigation satellite in the ECEF coordinates. S , Y S , Z S It is the value of the mirror point in the X-axis direction, Y-axis direction, and Z-axis direction in the ECEF coordinates; Acquire a second distance according to the low-orbit satellite coordinates and the mirror point coordinates; The second distance is obtained based on the following formula: Among them, R R is the second distance, X R , Y R , Z R is the value of the X-axis, Y-axis, and Z-axis of the low-orbit satellite in the ECEF coordinates. S , Y S , Z S It is the value of the X-axis direction, the Y-axis direction, and the Z-axis direction in the ECEF coordinates of the mirror point; Obtaining a total distance loss based on the first distance and the second distance; The total distance loss is obtained based on the following formula: in, is the total distance loss, R R is the second distance, R T is the first distance; Step 106, bringing the required parameters into the forward scattering model, performing a second preprocessing on the required parameters, and obtaining a normalized bistatic radar cross section; The required parameters include the received power under the delay-Doppler diagram, the total distance loss, the effective isotropic radiated power, the low-orbit satellite antenna gain, the unit delay value at a position within a preset distance from the mirror point, and the unit Doppler frequency shift value at a position within a preset distance from the mirror point; The normalized bistatic radar cross section is obtained, including: Step 202, obtaining the carrier signal wavelength; Step 204, substituting the received power, the total range loss, the effective isotropic radiated power, the low-orbit satellite antenna gain and the carrier signal wavelength into a forward scattering model to obtain a bistatic radar cross section; Step 206, obtaining an effective scattering area based on the unit delay value and the unit Doppler frequency shift value, including: obtaining a delay spread function based on the unit delay value; Based on the unit Doppler frequency shift value, obtaining a Doppler spread function; Analyzing the delay spread function and the Doppler spread function to obtain the effective scattering area; The effective scattering area is obtained based on the following formula: in, is the effective scattering area, is the delay spread function, is the Doppler spread function, is the unit delay value, is the unit Doppler shift value; Step 208, obtaining a normalized bistatic radar cross section based on the bistatic radar cross section and the effective scattering area; Normalizing the bistatic radar cross section of the mirror point and each unit around it to obtain a first normalized value; Normalizing the effective scattering area to obtain a second normalized value; Acquire the normalized bistatic radar cross section based on the first normalized value and the second normalized value; The bistatic radar cross section is obtained based on the following formula: in, is the bistatic radar cross section, is the received power, P EIRP is the effective isotropic radiated power, λ is the carrier signal wavelength, is the LEO satellite antenna gain, is the total distance loss; The effective isotropic radiated power is based on the following formula: Among them, P EIRP is the first power, P T is the first satellite transmission power, The first satellite antenna gain is based on the navigation satellite transmission power and the navigation satellite antenna gain to obtain the effective isotropic radiation power, understand the signal's propagation ability and anti-interference ability in space, and correct the received power when obtaining the sea surface roughness; Among them, the normalized bistatic radar cross section is obtained based on the following formula: in, is the normalized bistatic radar cross section, is the first normalized value, is the second normalized value, N is the number of time delay units, M is the number of Doppler units, and N and M are used to calculate the first normalized value and the second normalized value; Step 108: Obtain a first velocity value through the normalized bistatic radar cross section, where the first velocity value is a value of the sea surface wind speed.

2. The method for calculating the normalized bistatic radar cross section based on GNSS-R data according to claim 1, characterized in that: The first preprocessing of the detection data to obtain required parameters includes: Extracting the detection data to obtain the unit delay value and the unit Doppler frequency shift value; Based on the unit delay value and the unit Doppler frequency shift value, the received power under the delay-Doppler graph is acquired.

3. The method for calculating normalized bistatic radar cross section based on GNSS-R data according to claim 1, characterized in that: The performing a first preprocessing on the detection data to obtain required parameters further includes: Extracting the detection data to obtain the navigation satellite transmission power and the navigation satellite antenna gain; The effective isotropic radiated power is acquired based on the navigation satellite transmit power and the navigation satellite antenna gain.

4. The method for calculating normalized bistatic radar cross section based on GNSS-R data according to claim 1, characterized in that: The performing a first preprocessing on the detection data to obtain required parameters further includes: Based on the low-orbit satellite coordinates and the mirror point coordinates, obtaining the azimuth of the mirror point located at the low-orbit satellite and the incident angle of the mirror point located at the low-orbit satellite; Obtain antenna gain patterns of low-orbit satellites; The azimuth angle and the incident angle are introduced into the antenna gain pattern of the low-orbit satellite to obtain the antenna gain of the low-orbit satellite.

5. The method for calculating normalized bistatic radar cross section based on GNSS-R data according to claim 1, characterized in that: Based on the low-orbit satellite coordinates and the mirror point coordinates, obtaining the azimuth angle of the mirror point located at the low-orbit satellite and the incident angle of the mirror point located at the low-orbit satellite, including: Convert the low-orbit satellite coordinates and the mirror point coordinates from ECEF coordinates to longitude and latitude coordinates, and obtain the longitude and latitude coordinates of the low-orbit satellite and the mirror point; Establish a station center coordinate system with the mirror point as the origin; Convert the longitude and latitude coordinates of the low-orbit satellite and the longitude and latitude coordinates of the mirror point into station center coordinates to obtain the low-orbit satellite station center coordinates and the mirror point station center coordinates; Acquire the height of the low-orbit satellite and the distance between the low-orbit satellite and the mirror point based on the low-orbit satellite station center coordinates; The azimuth angle and the incident angle are acquired based on the altitude of the low-orbit satellite and the distance between the low-orbit satellite and a mirror point.

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