CN114879197A - Method for calibrating satellite DDM (distributed data management) in real time - Google Patents
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
- G01S13/95—Radar or analogous systems specially adapted for specific applications for meteorological use
- G01S13/955—Radar or analogous systems specially adapted for specific applications for meteorological use mounted on satellite
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/13—Receivers
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- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
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- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/40—Means for monitoring or calibrating
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- Y02A90/10—Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation
Abstract
The invention discloses a method for calibrating a satellite DDM (distributed data management) in real time, which comprises the following steps: acquiring spatial position information required by a satellite-borne GNSS remote sensing detector for GNSS-R observation; obtaining antenna directional pattern information corresponding to the GNSS direct signals and the GNSS reflected signals respectively according to the spatial position information and the geometric relation; reading a GNSS satellite emission antenna directional diagram required for GNSS-R observation and antenna gain information of a satellite-borne GNSS remote sensing detector; calculating the receiving power of the GNSS direct signals according to the coherent integration value of I, Q paths of the satellite-borne GNSS remote sensing detector tracking channel; calculating the transmitting power of the GNSS reflected signal according to the receiving power of the GNSS direct signal; acquiring DDM data obtained by GNSS-R observation of a satellite-borne GNSS remote sensing detector; performing L1A level calibration on the DDM data to obtain L1A DDM data; L1B levels of scaling were performed on L1A DDM data.
Description
Technical Field
The invention relates to the field of GNSS remote sensing technology and application, in particular to a method for calibrating satellite DDM in real time.
Background
The GNSS remote sensing technology is a novel ground remote sensing technology based on a Global Navigation Satellite System (GNSS). The detection of the global sea surface wind field by utilizing the GNSS reflected signal (GNSS-R) is one of the hot spots in the current GNSS remote sensing technology and application field. At present, a satellite-borne GNSS remote sensing detector is a payload for performing GNSS remote sensing detection, and mainly includes a positioning module, a occultation detection module, and a GNSS-R detection module.
The GNSS-R technology mainly depends on a GNSS-R detection module of a satellite-borne GNSS remote sensing detector to obtain DDM data (dimensionless) so as to invert a global sea surface wind field. The inversion process begins by scaling the acquired DDM data (dimensionless). The scaling process can be divided into two stages, L1A level scaling and L1B level scaling. The L1A scale is to convert DDM data (dimensionless) into surface scattered signal power DDM (unit: W), i.e., L1A DDM. The L1B scale further converts the L1A DDM into a Normalized Biradical Radar Cross Section (NBRCS) DDM, L1B DDM. Finally, a global sea surface wind field inversion is performed based on the L1B DDM.
At present, a method for carrying out real-time calibration on DDM data on the satellite is blank at home and abroad.
The satellite DDM real-time calibration is helpful for realizing satellite real-time inversion of the global sea surface wind field, so that real-time detection and forecast of the global sea surface wind field are realized, and the method plays an important role in the field of oceanographic forecast.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, fill the domestic and foreign blank of satellite DDM real-time calibration and provide a satellite DDM real-time calibration method.
In order to achieve the above object, the present invention provides a method for real-time scaling of satellite DDM, wherein the method comprises:
step S101) obtaining space position information required by a satellite-borne GNSS remote sensing detector for GNSS-R observation;
step S102) antenna directional pattern information corresponding to the GNSS direct signal and the GNSS reflected signal respectively is obtained according to the space position information through a geometrical relation;
step S103) reading a GNSS satellite emission antenna directional diagram required for GNSS-R observation and antenna gain information of a satellite-borne GNSS remote sensing detector;
step S104) calculating the receiving power of the GNSS direct signal according to the coherent integration value of the path I, Q tracked by the satellite-borne GNSS remote sensing detector;
step S105) calculating the transmitting power of the GNSS reflected signal according to the receiving power of the GNSS direct signal;
step S106) obtaining DDM data obtained by GNSS-R observation of the satellite-borne GNSS remote sensing detector;
step S107) carrying out L1A-level calibration on the DDM data to obtain L1A DDM data;
step S108) performs L1B-level scaling on the L1A DDM data.
As an improvement of the above method, the step S101) specifically includes:
obtaining space coordinates (X) of satellite-borne GNSS remote sensing detector r ,Y r ,Z r ) Wherein, subscript r represents a satellite-borne GNSS remote sensing detector;
obtaining spatial coordinates (X) of GNSS satellites satisfying a GNSS-R observation geometry g ,Y g ,Z g ) Wherein subscript g denotes the GNSS satellite;
the total distance R that the GNSS reflected signal passes through to be reflected by the specular reflection point in equation (1) is constrained by equation (2) gsr Is minimized to obtain the spatial coordinates (X) of the specular reflection point s ,Y s ,Z s ) Where the subscript s denotes the specular reflection point:
wherein theta is lat 、θ lon And h represents latitude, longitude and altitude corresponding to the specular reflection point, respectively, and intermediate variable
a is the earth's major axis radius and E is the earth's curvature squared.
As an improvement of the above method, the antenna pattern information in step S102) specifically includes:
main beam angle theta of GNSS satellite direct radiation signal corresponding to GNSS satellite transmitting antenna directional diagram g,d And azimuth angle
Main beam angle theta of GNSS satellite reflection signal corresponding to GNSS satellite transmitting antenna directional diagram g,r And azimuth angle
Main beam angle theta of GNSS direct signal received by positioning antenna of satellite-borne GNSS remote sensing detector corresponding to directional diagram of positioning antenna p And azimuth angle
And the main beam angle of the GNSS reflected signal received by the reflection antenna of the satellite-borne GNSS remote sensing detector corresponds to the directional diagram of the reflection antenna θ r and azimuth angle
As an improvement of the above method, the antenna pattern and antenna gain information of step S103) specifically includes:
GNSS satellite transmitting antenna directional diagram measured on ground or on satellite in advance
Satellite-borne GNSS remote sensing detector positioning antenna gain measured on ground through calibration in advance
Gain of reflection antenna of satellite-borne GNSS remote sensing detector
As an improvement of the above method, the step S104) specifically includes:
step S104-1) of reading coherent integration value I of I, Q paths of GNSS direct signal tracking channel of satellite-borne GNSS remote sensing detector d And Q d ；
Step S104-2) for I d And Q d Performing L times of incoherent integration to obtain dimensionless value C d ：
C d ＝∑ L (I d 2 +Qx 2 )
Step S104-3) calculating the received power P of the GNSS direct signal according to the following formula d ：
Wherein G is d The gain of the GNSS direct signal power received by the positioning antenna of the satellite-borne GNSS remote sensing detector in the whole processing process is shown, and is measured by ground calibration in advance.
As a modification of the above method, the step S105) specifically includes:
received power P from GNSS direct signals d Calculating the emission power of the GNSS reflected signal according to the following formula
Wherein the content of the first and second substances,
which represents the GNSS satellite transmit antenna gain, lambda is the carrier wavelength corresponding to the GNSS direct signal,
indicating the gain, R, of the positioning antenna of the satellite-borne GNSS remote sensing detector d The distance between the phase center of the GNSS satellite transmitting antenna and the phase center of the satellite-borne GNSS remote sensing detector positioning antenna is represented,
as a modification of the above method, the DDM data D of step S106) is C (τ, f) satisfies the following formula:
D C (τ,f)＝G n,r (P a,r +P i,r )+G r P r
wherein, P a,r Representing the thermal noise power, P, received by the reflecting antenna of the satellite-borne GNSS remote sensing detector i,r Representing the thermal noise power P of the GNSS-R detection module of the satellite-borne GNSS remote sensing detector r Representing the power, G, of the GNSS reflected signal received by the reflecting antenna of the satellite-borne GNSS remote sensing detector n,r Representing the gain, G, of the overall process on the thermal noise power r And the gain of the whole processing process to the power of the GNSS reflected signal received by the reflection antenna of the satellite-borne GNSS remote sensing detector is shown.
As an improvement of the above method, the step S107) specifically includes:
step S107-1) finding out a DDM data unit corresponding to the mirror reflection point;
step S107-2) calculates average noise in DDM data according to the following formula
Dimensionless:
where n represents the pseudo code delay ordinal number, m represents the Doppler frequency spectral line ordinal number, n 0 The number of pseudo-code delays representing the pseudo-code delay less than the specular reflection point, and M represents the total number of doppler frequency lines.
Step S107-3) calculating L1A DDM data D according to the following formula W (τ, f), completing L1A level scaling:
wherein D W The unit of (tau, f) is W, G r The values of (a) are determined in advance by a surface calibration.
As a modification of the above method, the step S108) specifically includes:
the normalized bistatic radar scattering cross section sigma corresponding to a DDM unit is obtained by calculation according to the following formula 0 ：
Wherein L is gs Representing the atmospheric losses, L, of the earth's surface suffered by GNSS reflected signals during their transmission from GNSS satellites to specular reflection points sr Representing the atmospheric losses on the earth surface suffered by the GNSS reflected signals during their transmission from the specular reflection point to the GNSS remote sensing survey,
represents the effective scattering area corresponding to a certain DDM unit and satisfies the following formula:
wherein A represents the ocean surface scattering region area corresponding to a certain DDM unit, and Λ τ A normalized autocorrelation function value, S, representing the pseudo-code delay corresponding to the DDM unit f A normalized integral gain representing a Doppler frequency corresponding to the DDM unit, s representing an area;
the above calculation is performed for each L1A DDM data unit corresponding to a specular reflection point, thereby completing L1B level scaling.
Compared with the prior art, the invention has the advantages that:
1. the method for real-time calibration of the satellite-borne DDM fills the domestic and foreign blank of real-time calibration of the satellite-borne DDM, and lays a foundation for further enhancing the application capability of the satellite-borne GNSS remote sensing detector and realizing real-time inversion of a global sea surface wind field on the satellite;
2, the method does not increase the complexity of a hardware system of the satellite-borne GNSS remote sensing detector, has lower cost and is easy to realize;
3. the method provided by the invention utilizes the direct signal to carry out calibration, and can well solve the problem of calibration deviation caused by the jitter of the GNSS satellite transmitting power;
4. the method provided by the invention has high real-time performance and is beneficial to realizing the satellite real-time inversion of the global sea surface wind field.
Drawings
FIG. 1 is a flow chart of a method for real-time scaling of an on-board DDM of the present invention;
FIG. 2 is a schematic view of a GNSS-R observation geometry of the present invention;
FIG. 3 is a flow chart illustrating a method for calculating the received power of a GNSS direct signal according to the present invention;
fig. 4 is a flow chart of the method of the present invention for L1A level scaling of DDM data.
Detailed Description
The spatial coordinates described herein are all based on the Earth Centered Earth Fixed coordinate system (ECEF).
A method for real-time scaling of on-board DDM, the method comprising:
step S101) obtaining space position information required by a satellite-borne GNSS remote sensing detector for GNSS-R observation;
step S102) antenna directional pattern information corresponding to the GNSS direct signal and the GNSS reflected signal respectively is obtained according to the space position information through a geometrical relation;
step S103) reading a GNSS satellite emission antenna directional diagram required for GNSS-R observation and antenna gain information of a satellite-borne GNSS remote sensing detector;
step S104) calculating the receiving power of the GNSS direct signal according to the coherent integration value of the path I, Q tracked by the satellite-borne GNSS remote sensing detector;
step S105) calculating the transmitting power of the GNSS reflected signal according to the receiving power of the GNSS direct signal;
step S106) obtaining DDM data obtained by GNSS-R observation of the satellite-borne GNSS remote sensing detector;
step S107) carrying out L1A-level calibration on the DDM data to obtain L1A DDM data;
step S108) performs L1B-level scaling on the L1A DDM data.
The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and examples.
Example 1
As shown in fig. 1, an embodiment of the present invention provides a method for real-time scaling of a satellite DDM, which includes the following specific steps:
step S101) obtaining the spatial location information required for GNSS-R observation is known based on the GNSS-R observation geometry shown in fig. 2, and the spatial location information required for GNSS-R observation includes: (1) space coordinate (X) of satellite-borne GNSS remote sensing detector r ,Y r ,Z r )；
(2) GNSS satellite space coordinates (X) satisfying GNSS-R observation geometry g ,Y g ,Z g )；
(3) Specular reflection point space coordinate (X) s ,Y s ,Z s )。
The positioning module of the GNSS remote sensing detector processes the received GNSS direct signals, on one hand, ephemeris of GNSS satellites emitting corresponding direct signals can be obtained, and therefore the space coordinates of the GNSS satellites can be calculated, and on the other hand, accurate positioning of the satellite-borne GNSS remote sensing detector can be achieved based on the space coordinates of the satellite-borne GNSS remote sensing detector.
The space coordinate of the satellite-borne GNSS remote sensing detector is (X) r ,Y r ,Z r ) Wherein, the subscript r represents a receiver, namely a satellite-borne GNSS remote sensing detector. The corresponding spatial position vector is expressed as
GNSS satellite (hereinafter referred to as GNSS satellite) space satisfying GNSS-R observation geometryThe coordinate is (X) g ,Y g ,Z g ) Wherein the subscript g denotes the GNSS satellite. The corresponding spatial position vector is expressed as
From the GNSS-R observation geometry, there is the following:
wherein R is gs Representing the distance R from the phase center of the GNSS satellite transmitting antenna to the specular reflection point sr Represents the distance R from the mirror reflection point to the phase center of the reflection antenna of the satellite-borne GNSS remote sensing detector gsr Representing the total distance covered by the GNSS reflected signals reflected by the specular reflection point. Vector quantity
Is shown as
(Vector)
Is shown as
There is no question of the specular reflection point being at the earth's surface. Thus, according to WGS84(World Geodetic System1984), there is the following formula:
wherein theta is lat 、θ lon And h respectively represent latitude, longitude and altitude corresponding to the specular reflection point,
a is the radius of the earth's long axis, which is 6378137m, and E is the square of the earth's curvature, which is 0.0066943799901400 m.
Spatial coordinates (X) of specular reflection points s ,Y s ,Z s ) Satisfying R in equation (1) under the constraint of equation (2) gsr The value of (a) is minimal. Based on this, the coordinates (X) can be calculated s ,Y s ,Z s ). Wherein the subscript s denotes the specular reflection point. In addition to this, the present invention is,
and R is d And the distance from the phase center of the GNSS satellite transmitting antenna to the phase center of the positioning antenna of the satellite-borne GNSS remote sensing detector is represented. Vector quantity
Is shown as
Step S102) obtaining antenna pattern information corresponding to the GNSS direct and reflected signals, respectively, is known based on the GNSS-R observation geometry shown in fig. 2, and the antenna pattern information corresponding to the GNSS direct and reflected signals, respectively, includes:
(1) the GNSS satellite direct signal corresponds to a main beam angle (boresight angle) theta of a GNSS satellite transmitting antenna directional diagram g,d And azimuth (azimuth angle)
(2) Main beam angle theta of GNSS satellite reflection signal corresponding to GNSS satellite transmitting antenna directional diagram g,r And azimuth angle
(3) Main beam angle theta of GNSS direct signal received by positioning antenna of satellite-borne GNSS remote sensing detector corresponding to directional diagram of positioning antenna p And azimuth angle
(4) Main beam angle theta of GNSS reflected signal received by reflection antenna of satellite-borne GNSS remote sensing detector and corresponding to directional diagram of reflection antenna r And azimuth angle
Step S103) reading the antenna directional diagram and the antenna gain information required by the GNSS-R observation, wherein the antenna directional diagram and the antenna gain information required by the GNSS-R observation comprise:
(1) GNSS satellite transmitting antenna directional pattern
(2) Positioning antenna gain of satellite-borne GNSS remote sensing detector
(3) Reflection antenna gain of satellite-borne GNSS remote sensing detector
GNSS satellite transmitting antenna directional pattern
Previously measured on the ground or on a star. Positioning antenna gain of satellite-borne GNSS remote sensing detector
Measured in advance by calibration on the ground. Reflection antenna gain of satellite-borne GNSS remote sensing detector
Measured in advance by calibration on the ground.
Step S104) of calculating the received power of the GNSS direct signal
A positioning module of the satellite-borne GNSS remote sensing detector comprises a large number of parallel tracking channels for simultaneously tracking a plurality of paths of GNSS direct signals. A tracking channel is provided for tracking a direct signal transmitted by the GNSS satellite. The specific steps are shown in fig. 3.
Step S104-1) of reading coherent integration value I of I, Q paths of tracking channel d And Q d 。
Reading coherent integration value I of I, Q paths of tracking channel for tracking direct signal emitted by GNSS satellite d And Q d The coherent integration time is 1ms or 10ms, and is determined by factors such as the GNSS signal modulation method.
Step S104-2) of performing L times of non-coherent integration to obtain a numerical value C d (dimensionless) and C d Can be expressed as:
wherein, P a Representing the power, P, of the thermal noise received by the positioning antenna of a satellite-borne GNSS remote sensing probe i Represents the thermal noise power P of the positioning module of the satellite-borne GNSS remote sensing detector d Indicating the power of the GNSS direct signal received by the on-board GNSS remote sensing probe positioning antenna (i.e. the received power of the GNSS direct signal). G n Representing the gain, G, of the overall process on the thermal noise power d And the gain of the whole processing process to the GNSS direct signal power received by the positioning antenna of the satellite-borne GNSS remote sensing detector is shown.
Step S104-3) reading G d The value of (c).
G d The value of (d) is determined in advance by a ground scale.
Step S104-4) of calculating the received power of the GNSS direct signal
According to the GNSS direct signal closed-loop tracking principle, the carrier phase and the pseudo code phase of the GNSS direct signal are stably and accurately estimated in real time by the tracking channel. Under the condition that the integration time is sufficiently long (for example, the integration time is 1s), there are:
G d ＞＞G n (4)
based on equation (4), equation (3) can be simplified to:
thus, there are:
based on equation (6), the received power of the GNSS direct signal can be calculated.
Step S105) calculating the transmitting power of the GNSS reflected signal
According to the bistatic radar signal transmission model, the received power of the GNSS direct signal can be expressed as:
wherein, P g Representing the signal emission power, G, of a GNSS satellite g The gain of the GNSS satellite transmitting antenna is represented, and lambda is the carrier wave wavelength corresponding to the GNSS direct signal.
Based on equation (7), we can derive:
in addition, from the GNSS satellite transmit antenna pattern:
wherein Δ G represents a ratio of antenna gains corresponding to reflected signals and direct signals emitted by GNSS satellites. Therefore, the transmission power of the GNSS reflected signal at this time is:
equation (10) shows that the transmitted power of the GNSS reflected signal can be calculated using the GNSS direct signal.
Step S106) obtaining DDM data obtained by GNSS-R observation
DDM data (dimensionless) D C (τ, f) is N × m (N, m ∈ N) + ) A two-dimensional matrix. Where n represents the pseudo code delay ordinal number, and the interval between two adjacent pseudo code delays represents the pseudo code delay resolution Δ τ (unit: chip). m represents the Doppler frequency line number, and the interval between two adjacent Doppler frequency lines represents the Doppler frequency resolution Δ f (unit: Hz). Each DDM data element corresponds to a different set of values of (τ, f).
For example, n is 61, m is 64, Δ τ is 0.25chip, and Δ f is 500 Hz.
According to the DDM data generation process, equation (3), D C (τ, f) may be expressed as:
D C (τ,f)＝G n,r (P a,r +P i,r )+G r P r (11)
wherein, P a,r Representing the thermal noise power, P, received by the reflecting antenna of the satellite-borne GNSS remote sensing detector i,r Representing the thermal noise power P of the GNSS-R detection module of the satellite-borne GNSS remote sensing detector r Representing the power, G, of the GNSS reflected signal received by the reflecting antenna of the satellite-borne GNSS remote sensing detector n,r Representing the gain, G, of the overall process on the thermal noise power r And the gain of the whole processing process to the power of the GNSS reflected signal received by the reflection antenna of the satellite-borne GNSS remote sensing detector is shown.
Step S107) performs L1A level scaling on the DDM data, and the specific steps are as shown in fig. 4.
Step S107-1) finds out that the DDM data unit corresponding to the mirror reflection point of the DDM data unit corresponding to the mirror reflection point is generally the DDM data unit corresponding to the local pseudo code delay of 0chip and the Doppler frequency of 0 Hz. For example, the unit of DDM data corresponding to the specular reflection point is n-13, and m-32.
Step S107-2) calculating average noise (dimensionless) in DDM data
The delay corresponding to the mirror reflection point is the minimum delay of the satellite-borne GNSS remote sensing detector reflection antenna capable of receiving the GNSS reflection signal. When the delay is less than the minimum delay, it means that the reflection antenna of the satellite-borne GNSS remote sensing detector cannot receive the GNSS reflection signal at this time. Therefore, there are:
D C (τ,f)＝G n,r (P a,r +P i,r ),n∈[1,12] (12)
based on equation (12), the average noise (dimensionless) in the DDM data is represented as:
wherein the content of the first and second substances,
(dimensionless) mean noise in DDM data, n pseudo code delay ordinal, m Doppler frequency line ordinal, n 0 The number of pseudo-code delays representing the pseudo-code delay less than the specular reflection point, and M represents the total number of doppler frequency lines. n is 0 And M is respectively taken as 12 and 64, and the calculation formula is as follows:
wherein 12 and 64 are values set for convenience of description, and in an actual process, the values can be different according to design requirements.
Step S107-3) of scaling the DDM data at level L1A
Based on equations (11), (12), and (13), it can be found that:
based on equation (14), one can obtain:
wherein G is r Is previously given byAnd (5) performing ground calibration measurement. Thus, L1A DDM-D is obtained based on equation (15) W (τ, f) (unit: W).
Step S108) of L1B level scaling of L1A DDM data
Bistatic radar model from GNSS reflected signals, D W (τ, f) is expressed as:
substituting equation (10) into equation (16) may result:
wherein L is gs Representing the atmospheric losses, L, of the earth's surface suffered by GNSS reflected signals during their transmission from GNSS satellites to specular reflection points sr Representing the atmospheric losses, σ, of the earth's surface suffered by the GNSS reflected signal during its transmission from the specular reflection point to the GNSS remote sensing probe 0 To a normalized biradical radar scattering cross-section (NBRCS) corresponding to a certain DDM unit,
represents the effective scattering area for a DDM unit and has:
wherein A represents the marine surface scattering region area corresponding to a DDM unit, and Λ τ A normalized autocorrelation function value, S, representing the pseudo-code delay corresponding to the DDM unit f Which represents the normalized integral gain of the doppler frequency corresponding to the DDM unit.
Combining equations (17), (18) yields:
according to equation (19), NBRCS corresponding to each DDM unit is calculated, and L1B level scaling is completed.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and are not limited. Although the present invention has been described in detail with reference to the embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (9)
1. A method for real-time scaling of on-board DDM, the method comprising:
step S101) obtaining space position information required by a satellite-borne GNSS remote sensing detector for GNSS-R observation;
step S102) antenna directional pattern information corresponding to the GNSS direct signal and the GNSS reflected signal respectively is obtained according to the space position information through a geometrical relation;
step S103) reading a GNSS satellite emission antenna directional diagram required for GNSS-R observation and antenna gain information of a satellite-borne GNSS remote sensing detector;
step S104) calculating the receiving power of the GNSS direct signal according to the coherent integration value of the path I, Q tracked by the satellite-borne GNSS remote sensing detector;
step S105) calculating the transmitting power of the GNSS reflected signal according to the receiving power of the GNSS direct signal;
step S106) obtaining DDM data obtained by GNSS-R observation of the satellite-borne GNSS remote sensing detector;
step S107) carrying out L1A-level scaling on the DDM data to obtain L1A DDM data;
step S108) performs L1B level scaling on the L1ADDM data.
2. The method for real-time scaling of an on-board DDM according to claim 1, wherein the step S101) specifically comprises:
obtaining space coordinates (X) of satellite-borne GNSS remote sensing detector r ，Y r ，Z r ) Wherein, in the process,subscript r represents a satellite-borne GNSS remote sensing detector;
obtaining spatial coordinates (X) of GNSS satellites satisfying a GNSS-R observation geometry g ，Y g ，Z g ) Wherein subscript g represents the GNSS satellite;
the total distance R that the GNSS reflected signal passes through to be reflected by the specular reflection point in equation (1) is constrained by equation (2) gsr Is minimized to obtain the spatial coordinates (X) of the specular reflection point s ，Y s ，Z s ) Wherein subscript s denotes specular reflection point:
wherein theta is lat 、θ lon And h represents latitude, longitude and altitude corresponding to the specular reflection point, respectively, and intermediate variable
a is the earth's major axis radius and E is the earth's curvature squared.
3. The method for real-time calibration of an on-satellite DDM according to claim 2, wherein the antenna pattern information of step S102) specifically includes:
main beam angle theta of GNSS satellite direct radiation signal corresponding to GNSS satellite transmitting antenna directional diagram g，d And azimuth angle
Main beam angle theta of GNSS satellite reflection signal corresponding to GNSS satellite transmitting antenna directional diagram g，r And orientationCorner
Main beam angle theta of GNSS direct signal received by positioning antenna of satellite-borne GNSS remote sensing detector corresponding to directional diagram of positioning antenna p And azimuth angle
And a main beam angle theta of a GNSS reflected signal received by the reflection antenna of the satellite-borne GNSS remote sensing detector corresponding to a directional diagram of the reflection antenna r And azimuth angle
4. The method according to claim 3, wherein the antenna pattern and antenna gain information of step S103) specifically includes:
GNSS satellite transmitting antenna directional diagram measured on ground or on satellite in advance
Satellite-borne GNSS remote sensing detector positioning antenna gain measured on ground through calibration in advance
Gain of reflection antenna of satellite-borne GNSS remote sensing detector
5. The method for real-time scaling of an on-satellite DDM according to claim 4, wherein the step S104) specifically comprises:
step S104-1) of reading coherent integration value I of I, Q paths of GNSS direct signal tracking channel of satellite-borne GNSS remote sensing detector d And Q d ；
Step S104-2) for I d And Q d Performing L times of incoherent integration to obtain dimensionless value C d ：
C d ＝∑ L (I d 2 +Q d 2 )
Step S104-3) calculating the received power P of the GNSS direct signal according to the following formula d ：
Wherein G is d The gain of the GNSS direct signal power received by the positioning antenna of the satellite-borne GNSS remote sensing detector in the whole processing process is shown, and is measured by ground calibration in advance.
6. The method for real-time scaling of an on-satellite DDM according to claim 5, wherein the step S105) specifically comprises:
received power P from GNSS direct signals d Calculating the emission power of the GNSS reflected signal according to the following formula
Wherein the content of the first and second substances,
which represents the GNSS satellite transmit antenna gain, lambda is the carrier wavelength corresponding to the GNSS direct signal,
indicating the gain, R, of the positioning antenna of the satellite-borne GNSS remote sensing detector d The distance from the phase center of the GNSS satellite transmitting antenna to the phase center of the positioning antenna of the satellite-borne GNSS remote sensing detector is represented, and the following formula is satisfied:
7. a method for real-time scaling of an on-satellite DDM as in claim 6, wherein the DDM data D of step S106) is C (τ, f) satisfies the following formula:
D C (τ，f)＝G n，r (P a，r +P i，r )+G r P r
wherein, P a，r Represents the thermal noise power P received by the reflection antenna of the satellite-borne GNSS remote sensing detector i，r Representing the thermal noise power P of the GNSS-R detection module of the satellite-borne GNSS remote sensing detector r Representing the power, G, of the GNSS reflected signal received by the reflecting antenna of the satellite-borne GNSS remote sensing detector n，r Representing the gain, G, of the overall process on the thermal noise power r And the gain of the whole processing process to the power of the GNSS reflected signal received by the reflection antenna of the satellite-borne GNSS remote sensing detector is shown.
8. The method for real-time scaling of an on-satellite DDM according to claim 7, wherein said step S107) specifically comprises:
step S107-1) finding out a DDM data unit corresponding to the mirror reflection point;
step S107-2) calculates average noise in DDM data according to the following formula
Where n represents the pseudo code delay ordinal number, m represents the Doppler frequency spectral line ordinal number, n 0 The number of pseudo-code delays representing the pseudo-code delay is less than the number of pseudo-code delays of the specular reflection points, and M represents the total number of doppler frequency spectral lines.
Step S107-3) according toCalculating to obtain L1ADDM data D W (τ, f), completing L1A level scaling:
wherein D W The unit of (tau, f) is W, G r The values of (a) are determined in advance by a surface calibration.
9. The method for real-time scaling of an on-satellite DDM according to claim 8, wherein the step S108) specifically comprises:
the normalized bistatic radar scattering cross section sigma corresponding to a DDM unit is obtained by calculation according to the following formula 0 ：
Wherein L is gs Representing the atmospheric losses, L, of the earth's surface suffered by GNSS reflected signals during their transmission from GNSS satellites to specular reflection points sr Representing the atmospheric losses on the earth surface suffered by the GNSS reflected signals during their transmission from the specular reflection point to the GNSS remote sensing survey,
represents the effective scattering area corresponding to a certain DDM unit and satisfies the following formula:
wherein A represents the ocean surface scattering region area corresponding to a certain DDM unit, and Λ τ A normalized autocorrelation function value, S, representing the pseudo-code delay corresponding to the DDM unit f A normalized integral gain representing a Doppler frequency corresponding to the DDM unit, s representing an area;
the above calculation is performed for each L1ADDM data element corresponding to a specular reflection point, thereby completing the L1B level scaling.
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