CN114879197B - Real-time calibration method for on-board DDM - Google Patents

Real-time calibration method for on-board DDM Download PDF

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CN114879197B
CN114879197B CN202210389403.4A CN202210389403A CN114879197B CN 114879197 B CN114879197 B CN 114879197B CN 202210389403 A CN202210389403 A CN 202210389403A CN 114879197 B CN114879197 B CN 114879197B
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satellite
ddm
remote sensing
borne
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CN114879197A (en
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仇通胜
王先毅
孙越强
杜起飞
白伟华
蔡跃荣
李伟
王冬伟
吴春俊
刘成
李福�
乔颢
程双双
张�浩
张璐璐
王卓焱
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National Space Science Center of CAS
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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
    • 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
    • G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
    • G01S19/25—Acquisition or tracking or demodulation of signals transmitted by the system involving aiding data received from a cooperating element, e.g. assisted GPS
    • 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
    • G01S19/35—Constructional details or hardware or software details of the signal processing chain
    • G01S19/37—Hardware or software details of the signal processing chain
    • 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
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A90/00—Technologies having an indirect contribution to adaptation to climate change
    • Y02A90/10—Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation

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  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Physics & Mathematics (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • General Physics & Mathematics (AREA)
  • Signal Processing (AREA)
  • Electromagnetism (AREA)
  • Radar Systems Or Details Thereof (AREA)
  • Position Fixing By Use Of Radio Waves (AREA)

Abstract

The invention discloses a real-time calibration method of on-board DDM, which comprises the following steps: acquiring space position information required by a satellite-borne GNSS remote sensing detector for GNSS-R observation; obtaining antenna pattern information corresponding to the GNSS direct signal and the reflected signal respectively according to the space position information and the geometric relation; reading a GNSS satellite transmitting antenna pattern and antenna gain information of a satellite-borne GNSS remote sensing detector required for GNSS-R observation; calculating the receiving power of the GNSS direct signal according to the coherent integral value of the I, Q paths of the tracking channel of the satellite-borne GNSS remote sensing detector; calculating the transmitting power of the GNSS reflected signal according to the receiving power of the GNSS direct signal; acquiring DDM data obtained by performing GNSS-R observation by a satellite-borne GNSS remote sensing detector; performing L1A-level scaling on the DDM data to obtain L1A DDM data; L1B-level scaling is performed on the L1A DDM data.

Description

Real-time calibration method for on-board DDM
Technical Field
The invention relates to the technical and application fields of GNSS remote sensing, in particular to a real-time calibration method for on-board DDM.
Background
The GNSS remote sensing technology is a novel earth remote sensing detection technology based on a global navigation satellite system (Global Navigation SATELLITE SYSTEM, GNSS). The detection of global sea wind fields by using GNSS reflected signals (GNSS-R) is one of hot spots in the current GNSS remote sensing technology and application fields. Currently, a satellite-borne GNSS remote sensing detector is a payload for performing GNSS remote sensing detection, and mainly comprises a positioning module, a occultation detection module and a GNSS-R detection module.
The GNSS-R technology mainly relies on a GNSS-R detection module of a satellite-borne GNSS remote sensing detector to acquire DDM data (dimensionless), and the global sea surface wind field is inverted. This inversion process begins by scaling the acquired DDM data (dimensionless). The scaling process can be divided into two stages, L1A scale and L1B scale, respectively. The L1A scale is to convert DDM data (dimensionless) into surface scattering signal power DDM (unit: W), i.e., L1A DDM. The L1B scale is to further convert the L1A DDM into Normalized double-based radar Cross Section (NBRCS) DDM, i.e., L1B DDM. Finally, global sea surface wind field inversion is performed based on the L1B DDM.
At present, a method for real-time calibration of DDM data on the star is blank at home and abroad.
The real-time calibration of the on-board DDM is beneficial to realizing the on-board real-time inversion of the global sea surface wind field, thereby realizing the real-time detection and forecast of the global sea surface wind field, and playing an important role in the field of marine weather forecast.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, fills the domestic and foreign blank of real-time calibration of on-board DDM, and provides a real-time calibration method of on-board DDM.
In order to achieve the above object, the present invention proposes a method for real-time calibration of on-board DDM, the method comprising:
step S101) acquiring space position information required by a satellite-borne GNSS remote sensing detector for GNSS-R observation;
Step S102), antenna pattern information corresponding to GNSS direct signals and reflected signals respectively is obtained from a geometric relation according to the space position information;
step S103), reading a GNSS satellite transmitting antenna pattern and antenna gain information of a satellite-borne GNSS remote sensing detector required for GNSS-R observation;
Step S104), calculating the receiving power of the GNSS direct signal according to the coherent integral value of the I, Q paths of the tracking channel of the satellite-borne GNSS remote sensing detector;
step S105), according to the received power of the GNSS direct signal, calculating the transmitting power of the GNSS reflected signal;
Step S106), DDM data obtained by performing GNSS-R observation by the satellite-borne GNSS remote sensing detector is obtained;
Step S107), L1A level scaling is carried out 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:
Acquiring space coordinates (X r,Yr,Zr) of a satellite-borne GNSS remote sensing detector, wherein a subscript r represents the satellite-borne GNSS remote sensing detector;
Acquiring space coordinates (X g,Yg,Zg) of a GNSS satellite satisfying the GNSS-R observation geometry, wherein the subscript g represents the GNSS satellite;
Minimizing the total distance R gsr that the GNSS reflected signal passes through by the specular reflection point in equation (1) under the constraint of equation (2), thereby obtaining the spatial coordinates (X s,Ys,Zs) of the specular reflection point, where subscript s represents the specular reflection point:
wherein θ lat、θlon and h respectively represent latitude, longitude and altitude corresponding to the specular reflection point, and an intermediate variable A is the long axis radius of the earth and E is the square of the earth's curvature.
As an improvement of the above method, the antenna pattern information of step S102) specifically includes:
the GNSS satellite direct signal corresponds to the main beam angle theta g,d and azimuth angle of the GNSS satellite transmitting antenna pattern GNSS satellite reflection signals correspond to a main beam angle θ g,r and azimuth/>, of a GNSS satellite transmitting antenna patternMain beam angle theta p and azimuth angle of GNSS direct signal corresponding to positioning antenna pattern received by positioning antenna of satellite-borne GNSS remote sensing detectorMain beam angle θ r and azimuth angle/>, corresponding to reflection antenna pattern, of GNSS reflection signals received by satellite-borne GNSS remote sensing detector reflection antenna
As an improvement of the above method, the antenna pattern and the antenna gain information of step S103) specifically include:
GNSS satellite transmitting antenna pattern pre-determined on the ground or on the satellite Satellite-borne GNSS remote sensing detector positioning antenna gain/>, which is measured on the ground in advance through calibrationAnd satellite-borne GNSS remote sensing detector reflection antenna gain/>
As an improvement of the above method, the step S104) specifically includes:
Step S104-1) reading coherent integration values I d and Q d of a GNSS direct signal tracking channel I, Q of the satellite-borne GNSS remote sensing detector;
Step S104-2) carries out L times of incoherent integration on the I d and the Q d to obtain a dimensionless value C d:
Cd＝∑L(Id 2+Qx2)
Step S104-3) calculates the received power P d of the GNSS direct signal according to the following formula:
The G d represents 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 instrument, and the gain is measured by ground calibration in advance.
As an improvement of the above method, the step S105) specifically includes:
according to the received power P d of the GNSS direct signal, the transmitting power of the GNSS reflected signal is calculated by the following formula
Wherein,Represents the gain of a GNSS satellite transmitting antenna, lambda is the carrier wavelength corresponding to the GNSS direct signal,/>Indicating the gain of a positioning antenna of the satellite-borne GNSS remote sensing detector, R d indicating the distance from the phase center of a transmitting antenna of the GNSS satellite to the phase center of the positioning antenna of the satellite-borne GNSS remote sensing detector,
As an improvement of the above method, the DDM data D C (τ, f) of step S106) satisfies the following formula:
DC(τ,f)＝Gn,r(Pa,r+Pi,r)+GrPr
Wherein, P a,r represents the thermal noise power received by the reflection antenna of the satellite-borne GNSS remote sensing detector, P i,r represents the thermal noise power of the GNSS-R detection module of the satellite-borne GNSS remote sensing detector, P r represents the GNSS reflection signal power received by the reflection antenna of the satellite-borne GNSS remote sensing detector, G n,r represents the gain of the thermal noise power in the whole processing process, and G r represents the gain of the GNSS reflection signal power received by the reflection antenna of the satellite-borne GNSS remote sensing detector in the whole processing process.
As an improvement of the above method, the step S107) specifically includes:
step S107-1), finding out a DDM data unit corresponding to the specular reflection point;
Step S107-2) calculating average noise in DDM data according to Dimensionless:
Where n represents the pseudocode delay ordinal, M represents the Doppler frequency spectral line ordinal, n 0 represents the pseudocode delay number where the pseudocode delay is less than the specular reflection point, and M represents the total Doppler frequency spectral line number.
Step S107-3) calculates L1A DDM data D W (τ, f) according to the following formula, and completes L1A level scaling:
Where D W (τf) is given in W and the value of G r is determined beforehand by ground scaling.
As an improvement of the above method, the step S108) specifically includes:
The normalized bistatic radar cross-section σ 0 corresponding to a certain DDM unit is calculated according to:
Wherein L gs represents the earth surface atmospheric loss suffered by the GNSS reflected signal during transmission from the GNSS satellite to the specular reflection point, L sr represents the earth surface atmospheric loss suffered by the GNSS reflected signal during transmission from the specular reflection point to the GNSS remote sensing probe, Representing the effective scattering area corresponding to a certain DDM unit, satisfying the following equation:
Wherein, A represents the area of the ocean surface scattering area corresponding to a certain DDM unit, Λ τ represents the normalized autocorrelation function value of the pseudo code delay corresponding to the DDM unit, S f represents the normalized integral gain of the Doppler frequency corresponding to the DDM unit, and S represents the area;
And performing the calculation on each L1A DDM data unit corresponding to the specular reflection point, thereby completing L1B-level calibration.
Compared with the prior art, the invention has the advantages that:
1. the real-time calibration method for the on-board DDM fills the domestic and foreign blank of real-time calibration of the on-board DDM, and lays a foundation for further enhancing the application capacity of the on-board GNSS remote sensing detector and realizing the on-board real-time inversion of the global sea surface wind field;
2, the method provided by the invention does not increase the complexity of the 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 uses the direct signal to calibrate, so that the problem of calibration deviation caused by GNSS satellite transmitting power jitter can be well solved;
4. the method provided by the invention has high instantaneity and is beneficial to realizing the on-board real-time inversion of the global sea surface wind field.
Drawings
FIG. 1 is a flow chart of a method of on-board DDM real-time scaling of the present invention;
FIG. 2 is a schematic view of the GNSS-R observation geometry of the present invention;
FIG. 3 is a flow chart of a method of calculating the received power of a GNSS direct signal in accordance with the present invention;
Fig. 4 is a flow chart of a method of L1A scaling DDM data in accordance with the present invention.
Detailed Description
The spatial coordinates described herein are all based on the geocentric Fixed coordinate system (EARTH CENTERED EARTH Fixed, ECEF).
A method of real-time scaling of an on-board DDM, the method comprising:
step S101) acquiring space position information required by a satellite-borne GNSS remote sensing detector for GNSS-R observation;
Step S102), antenna pattern information corresponding to GNSS direct signals and reflected signals respectively is obtained from a geometric relation according to the space position information;
step S103), reading a GNSS satellite transmitting antenna pattern and antenna gain information of a satellite-borne GNSS remote sensing detector required for GNSS-R observation;
Step S104), calculating the receiving power of the GNSS direct signal according to the coherent integral value of the I, Q paths of the tracking channel of the satellite-borne GNSS remote sensing detector;
step S105), according to the received power of the GNSS direct signal, calculating the transmitting power of the GNSS reflected signal;
Step S106), DDM data obtained by performing GNSS-R observation by the satellite-borne GNSS remote sensing detector is obtained;
Step S107), L1A level scaling is carried out on the DDM data to obtain L1A DDM data;
Step S108) performs L1B-level scaling on the L1A DDM data.
The technical scheme of the invention is described in detail below with reference to the accompanying drawings and examples.
Example 1
As shown in fig. 1, the embodiment of the invention provides a real-time calibration method for on-board DDM, which comprises the following specific implementation steps:
Step S101) acquiring spatial location information required for GNSS-R observation based on the GNSS-R observation geometry as shown in fig. 2 includes: (1) Space coordinates (X r,Yr,Zr) of a satellite-borne GNSS remote sensing detector;
(2) GNSS satellite space coordinates (X g,Yg,Zg) that satisfy the GNSS-R observation geometry;
(3) Specular reflection point spatial coordinates (X s,Ys,Zs).
The positioning module of the GNSS remote sensing detector can acquire ephemeris of GNSS satellites transmitting corresponding direct signals to calculate space coordinates of the GNSS satellites by processing the received plurality of GNSS direct signals, and can realize accurate positioning of the satellite-borne GNSS remote sensing detector based on the ephemeris to calculate 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,Yr,Zr), wherein the subscript r represents the receiver-the satellite-borne GNSS remote sensing detector. The corresponding spatial position vector is expressed asThe space coordinates of a GNSS satellite (hereinafter referred to as GNSS satellite) satisfying the GNSS-R observation geometry are (X g,Yg,Zg), wherein the subscript g indicates the GNSS satellite. The spatial position vector corresponding thereto is denoted/>From the GNSS-R observation geometry, there is the following formula:
Wherein, R gs represents the distance from the phase center of the GNSS satellite transmitting antenna to the specular reflection point, R sr represents the distance from the specular reflection point to the phase center of the satellite-borne GNSS remote sensing detector reflecting antenna, and R gsr represents the total distance that the GNSS reflected signal passes through the specular reflection point. Vector quantity Expressed as/>Vector/>Represented asUndoubtedly, the specular reflection point is at the earth's surface. Thus, according to WGS84 (World Geodetic System 1984), there is the following formula:
wherein theta lat、θlon and h respectively represent latitude, longitude and altitude corresponding to the specular reflection point, A is the major axis radius of the earth, the value is 6378107 m, E is the square of the earth's curvature, and the value is 0.0066943799901400m.
The spatial coordinates (X s,Ys,Zs) of the specular reflection point satisfy the constraint of equation (2) such that the value of R gsr in equation (1) is minimized. Based on this, coordinates (X s,Ys,Zs) can be calculated. Wherein the subscript s denotes a specular reflection point. In addition to this, the process is carried out,And R d represents 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. Vector/>Represented as
Step S102) obtaining antenna pattern information corresponding to the direct GNSS signal and the reflected GNSS signal respectively, based on the observation geometry of the GNSS-R shown in fig. 2, the antenna pattern information corresponding to the direct GNSS signal and the reflected GNSS signal respectively includes:
(1) The GNSS satellite direct signal corresponds to a main beam angle (boresight angle) θ g,d and an azimuth angle (azimuth angle) of the GNSS satellite transmitting antenna pattern
(2) GNSS satellite reflection signals correspond to a main beam angle theta g,r and an azimuth angle of a GNSS satellite transmitting antenna pattern
(3) Main beam angle theta p and azimuth angle of GNSS direct signal corresponding to positioning antenna pattern received by positioning antenna of satellite-borne GNSS remote sensing detector
(4) Main beam angle theta r and azimuth angle of GNSS reflected signal received by satellite-borne GNSS remote sensing detector reflection antenna corresponding to reflection antenna pattern
From vector/>Vector/>The geometrical relationship between them is determined.
From vector/>Vector/>The geometrical relationship between them is determined.
From vector/>Vector/>The geometrical relationship between them is determined.
From vector/>Vector/>The geometrical relationship between them is determined.
Step S103) reading the antenna pattern and antenna gain information required for GNSS-R observation, including:
(1) GNSS satellite transmitting antenna pattern
(2) Satellite-borne GNSS remote sensing detector positioning antenna gain
(3) Reflection antenna gain of satellite-borne GNSS remote sensing detectorGNSS satellite transmitting antenna patternMeasured in advance on the ground or on the satellite. Satellite-borne GNSS remote sensing detector positioning antenna gain/>Measured by calibration in advance at the surface. Gain/>, of reflection antenna of satellite-borne GNSS remote sensing detectorMeasured by calibration in advance at the surface.
Step S104) calculating the received power of the GNSS direct signal
The positioning module of the satellite-borne GNSS remote sensing detector comprises a large number of parallel tracking channels for simultaneously tracking multiple GNSS direct signals. Wherein a tracking channel is provided for tracking direct signals transmitted by the GNSS satellites. The specific steps are shown in fig. 3.
Step S104-1) reads the coherent integration values I d and Q d of the track I, Q paths.
And reading coherent integration values I d and Q d of a I, Q path of a tracking channel for tracking the direct signal emitted by the GNSS satellite, wherein the coherent integration time is 1ms or 10ms and the like, and the coherent integration values are determined by factors such as a GNSS signal modulation mode and the like.
Step S104-2) performs L incoherent integrations to obtain a value C d (dimensionless), and C d can be expressed as:
Wherein, P a represents the thermal noise power received by the positioning antenna of the satellite-borne GNSS remote sensing detector, P i represents the thermal noise power of the positioning module of the satellite-borne GNSS remote sensing detector, and P d represents the direct GNSS signal power (i.e. the received power of the direct GNSS signal) received by the positioning antenna of the satellite-borne GNSS remote sensing detector. G n represents the gain of the whole process to the thermal noise power, and G d represents the gain of the whole process to the GNSS direct signal power received by the positioning antenna of the satellite-borne GNSS remote sensing detector.
Step S104-3) reads the value of G d.
The value of G d is determined in advance by ground scaling.
Step S104-4) calculating the received power of the GNSS direct signal
According to the closed loop tracking principle of the GNSS direct signal, the tracking channel carries out stable and accurate estimation on the carrier phase and the pseudo code phase of the GNSS direct signal in real time. Under the condition that the integration time is sufficiently long (for example, the integration time is 1 s), there are:
Gd＞＞Gn (4)
based on equation (4), equation (3) can be simplified as:
therefore, there are:
based on equation (6), the received power of the GNSS direct signal may 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 may be expressed as:
Wherein, P g represents the signal transmitting power of the GNSS satellite, G g represents the gain of the GNSS satellite transmitting antenna, and λ is the carrier wavelength corresponding to the GNSS direct signal.
Based on equation (7), it is possible to:
in addition, from the GNSS satellite transmitting antenna pattern:
where ΔG represents the ratio of the antenna gain corresponding to the reflected signal and the direct signal transmitted by the GNSS satellite. Therefore, the transmit power of the GNSS reflected signal at this time is:
equation (10) shows that the transmit power of the GNSS reflected signal can be calculated using the GNSS direct signal.
Step S106) obtaining DDM data obtained by GNSS-R observations
DDM data (dimensionless) D C (τ, f) is an N m (N, m ε N +) two-dimensional matrix. Where n represents the pseudocode delay ordinal and the spacing of adjacent two pseudocode delays represents the pseudocode delay resolution Δτ (units: chips). m represents the Doppler frequency line number, and the interval between two adjacent Doppler frequency lines represents the Doppler frequency resolution Δf (unit: hz). Each DDM data unit corresponds to a different set of values of (τ, f).
For example, n=61, m=64, Δτ=0.25 chip, Δf=500 Hz.
From the DDM data generation process, equation (3), D C (τ, f) can be expressed as:
DC(τ,f)＝Gn,r(Pa,r+Pi,r)+GrPr (11)
Wherein, P a,r represents the thermal noise power received by the reflection antenna of the satellite-borne GNSS remote sensing detector, P i,r represents the thermal noise power of the GNSS-R detection module of the satellite-borne GNSS remote sensing detector, P r represents the GNSS reflection signal power received by the reflection antenna of the satellite-borne GNSS remote sensing detector, G n,r represents the gain of the thermal noise power in the whole processing process, and G r represents the gain of the GNSS reflection signal power received by the reflection antenna of the satellite-borne GNSS remote sensing detector in the whole processing process.
Step S107) performs L1A-level scaling on DDM data, and the specific steps are shown in fig. 4.
Step S107-1) finds out that the DDM data unit corresponding to the specular reflection point is a DDM data unit corresponding to the DDM data unit with the local pseudo code delay of 0chip and the Doppler frequency of 0 Hz. For example, the DDM data unit corresponding to the specular reflection point is n=13, m=32.
Step S107-2) calculating average noise (dimensionless) in DDM data
The delay corresponding to the specular reflection point is the minimum delay for the satellite-borne GNSS remote sensing detector reflection antenna to receive GNSS reflection signals. When the delay is less than the minimum delay, it means that the satellite-borne GNSS remote sensing detector reflection antenna cannot receive the GNSS reflection signal. Thus, there are:
DC(τ,f)＝Gn,r(Pa,r+Pi,r),n∈[1,12] (12)
based on equation (12), the average noise (dimensionless) in DDM data is expressed as:
Wherein, (Dimensionless) represents average noise in the DDM data, n represents pseudocode delay ordinal, M represents Doppler frequency spectral line ordinal, n 0 represents pseudocode delay number less than specular reflection point, and M represents total Doppler frequency spectral line number. n 0, M are respectively 12 and 64, and the calculation formula is as follows:
wherein, 12, 64 are values set for convenience of description, in actual process, the values can be different according to design requirements.
Step S107-3) L1A-level scaling of DDM data
Based on equations (11), (12) and (13), it is possible to:
based on equation (14), it is possible to obtain:
Wherein the value of G r is determined in advance by ground scaling. Thus, L1A DDM-D W (τ, f) (unit: W) is derived based on equation (15).
Step S108) L1B-level scaling of L1A DDM data
From the bistatic radar model of the GNSS reflected signals, D W (τ, f) is denoted as:
It is possible to take equation (10) into equation (16):
Wherein L gs represents the earth surface atmospheric loss suffered by GNSS reflected signals in the process of transmitting the GNSS reflected signals from the GNSS satellites to the specular reflection points, L sr represents the earth surface atmospheric loss suffered by GNSS reflected signals in the process of transmitting the GNSS reflected signals from the specular reflection points to the GNSS remote sensing detector, sigma 0 is a Normalized Bistatic Radar Cross Section (NBRCS) corresponding to a certain DDM unit, Representing the effective scattering area for a certain DDM cell, and has:
Wherein A represents the area of the ocean surface scattering area corresponding to a certain DDM unit, lambada τ represents the normalized autocorrelation function value of the pseudo code delay corresponding to the DDM unit, and S f represents the normalized integral gain of the Doppler frequency corresponding to the DDM unit.
The joint equations (17), (18) can be obtained:
According to equation (19), NBRCS corresponding to each DDM unit is calculated to complete L1B scale.
Finally, it should be noted that the above embodiments are only for illustrating the technical solution of the present invention and are not limiting. Although the present invention has been described in detail with reference to the embodiments, it should be understood by those skilled in the art that modifications and equivalents may be made thereto without departing from the spirit and scope of the present invention, which is intended to be covered by the appended claims.

Claims (9)

1. A method of real-time scaling of an on-board DDM, the method comprising:
step S101) acquiring space position information required by a satellite-borne GNSS remote sensing detector for GNSS-R observation;
Step S102), antenna pattern information corresponding to GNSS direct signals and reflected signals respectively is obtained from a geometric relation according to the space position information;
step S103), reading a GNSS satellite transmitting antenna pattern and antenna gain information of a satellite-borne GNSS remote sensing detector required for GNSS-R observation;
Step S104), calculating the receiving power of the GNSS direct signal according to the coherent integral value of the I, Q paths of the tracking channel of the satellite-borne GNSS remote sensing detector;
step S105), according to the received power of the GNSS direct signal, calculating the transmitting power of the GNSS reflected signal;
Step S106), DDM data obtained by performing GNSS-R observation by the satellite-borne GNSS remote sensing detector is obtained;
Step S107), L1A level scaling is carried out on the DDM data to obtain L1A DDM data;
Step S108) performs L1B-level scaling on the L1A DDM data.
2. The method for real-time calibration of on-board DDM according to claim 1, wherein said step S101) specifically comprises:
Acquiring space coordinates (X r,Yr,Zr) of a satellite-borne GNSS remote sensing detector, wherein a subscript r represents the satellite-borne GNSS remote sensing detector;
Acquiring space coordinates (X g,Yg,Zg) of a GNSS satellite satisfying the GNSS-R observation geometry, wherein the subscript g represents the GNSS satellite;
Minimizing the total distance R gsr that the GNSS reflected signal passes through by the specular reflection point in equation (1) under the constraint of equation (2), thereby obtaining the spatial coordinates (X s,Ys,Zs) of the specular reflection point, where subscript s represents the specular reflection point:
wherein θ lat、θlon and h respectively represent latitude, longitude and altitude corresponding to the specular reflection point, and an intermediate variable A is the long axis radius of the earth and E is the square of the earth's curvature.
3. The method for real-time calibration of on-board DDM according to claim 2, wherein the antenna pattern information of step S102) specifically includes:
the GNSS satellite direct signal corresponds to the main beam angle theta g,d and azimuth angle of the GNSS satellite transmitting antenna pattern GNSS satellite reflection signals correspond to a main beam angle θ g,r and azimuth/>, of a GNSS satellite transmitting antenna patternMain beam angle theta p and azimuth angle/>, corresponding to positioning antenna directional diagram, of GNSS direct signal received by positioning antenna of satellite-borne GNSS remote sensing detectorMain beam angle theta r and azimuth angle/>, corresponding to reflection antenna pattern, of GNSS reflection signals received by satellite-borne GNSS remote sensing detector reflection antenna
4. The method for real-time calibration of on-board DDM according to claim 3, wherein the antenna pattern and the antenna gain information of step S103) specifically include:
GNSS satellite transmitting antenna pattern pre-determined on the ground or on the satellite Satellite-borne GNSS remote sensing detector positioning antenna gain/>, which is measured on the ground in advance through calibrationAnd satellite-borne GNSS remote sensing detector reflection antenna gain/>
5. The method for real-time calibration of on-board DDM according to claim 4, wherein said step S104) specifically comprises:
Step S104-1) reading coherent integration values I d and Q d of a GNSS direct signal tracking channel I, Q of the satellite-borne GNSS remote sensing detector;
Step S104-2) carries out L times of incoherent integration on the I d and the Q d to obtain a dimensionless value C d:
Cd＝∑L(Id 2+Qd 2)
Step S104-3) calculates the received power P d of the GNSS direct signal according to the following formula:
The G d represents 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 instrument, and the gain is measured by ground calibration in advance.
6. The method for real-time calibration of on-board DDM according to claim 5, wherein said step S105) specifically comprises:
according to the received power P d of the GNSS direct signal, the transmitting power of the GNSS reflected signal is calculated by the following formula
Wherein P g represents the signal transmission power of the GNSS satellite,Represents the gain of the GNSS satellite transmitting antenna, lambda is the carrier wavelength corresponding to the GNSS direct signal, delta G represents the ratio of the reflected signal transmitted by the GNSS satellite to the antenna gain corresponding to the direct signal,/>The gain of the positioning antenna of the satellite-borne GNSS remote sensing detector is represented, and R d represents 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, so that the following formula is satisfied:
7. The method for real-time calibration of on-board DDM according to claim 6, wherein DDM data D C (τ, f) of step S106) satisfies the following formula:
DC(τ,f)＝Gn,r(Pa,r+Pi,r)+GrPr
Wherein, P a,r represents the thermal noise power received by the reflection antenna of the satellite-borne GNSS remote sensing detector, P i,r represents the thermal noise power of the GNSS-R detection module of the satellite-borne GNSS remote sensing detector, P r represents the GNSS reflection signal power received by the reflection antenna of the satellite-borne GNSS remote sensing detector, G n,r represents the gain of the thermal noise power in the whole processing process, and G r represents the gain of the GNSS reflection signal power received by the reflection antenna of the satellite-borne GNSS remote sensing detector in the whole processing process.
8. The method for real-time calibration of on-board DDM according to claim 7, wherein said step S107) specifically comprises:
step S107-1), finding out a DDM data unit corresponding to the specular reflection point;
Step S107-2) calculating average noise in DDM data according to
Wherein n represents a pseudo code delay ordinal number, M represents a Doppler frequency spectral line ordinal number, n 0 represents a pseudo code delay number of which the pseudo code delay is smaller than that of a specular reflection point, and M represents a total Doppler frequency spectral line number;
step S107-3) calculates L1A DDM data D W (τ, f) according to the following formula, and completes L1A level scaling:
Where D W (τf) is given in W and the value of G r is determined beforehand by ground scaling.
9. The method for real-time calibration of on-board DDM according to claim 8, wherein said step S108) specifically comprises:
The normalized bistatic radar cross-section σ 0 corresponding to a certain DDM unit is calculated according to:
Wherein R gs represents the distance from the phase center of the GNSS satellite transmitting antenna to the specular reflection point, R sr represents the distance from the specular reflection point to the phase center of the satellite-borne GNSS remote sensing detector reflecting antenna, Representing the gain of a reflection antenna of a satellite-borne GNSS remote sensing detector, L gs representing the earth surface atmospheric loss suffered in the process of transmitting GNSS reflection signals from GNSS satellites to a specular reflection point, and L sr representing the earth surface atmospheric loss suffered in the process of transmitting GNSS reflection signals from the specular reflection point to the GNSS remote sensing detector,/>Representing the effective scattering area corresponding to a certain DDM unit, satisfying the following equation:
Wherein, A represents the area of the ocean surface scattering area corresponding to a certain DDM unit, Λ τ represents the normalized autocorrelation function value of the pseudo code delay corresponding to the DDM unit, S f represents the normalized integral gain of the Doppler frequency corresponding to the DDM unit, and S represents the area;
And performing the calculation on each L1A DDM data unit corresponding to the specular reflection point, thereby completing L1B-level calibration.
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