CN102183743A - Method for calibrating long-wavelength satellite-borne CTLR-mode compact-polarized SAR - Google Patents

Abstract

The invention discloses a method for calibrating long-wavelength satellite-borne CTLR-mode compact-polarized SAR. The method comprises the following steps of: 1, acquiring an estimated value of an unbalanced error of a receiving channel; 2, acquiring an estimated value of a crosstalk coefficient of a circular-polarized transmitting channel; 3, acquiring an estimated value of a crosstalk coefficient of a linear-polarized receiving channel; 4, acquiring an estimated value of a Faraday rotation angle; and 5, acquiring an unambiguous estimated value of the Faraday rotation angle by using total electron content (TEC) data of a global navigation satellite system (GNSS) to finish SAR calibration. By the method, the processing process is simple and the processing precision is high; and the application of the method in processing of the long-wavelength satellite-borne CTLR-mode compact-polarized SAR data represented by a P wave band is very important.

Description

The spaceborne CTLR pattern of a kind of long wavelength is condensed the calibrating method of polarization SAR

Technical field

The present invention relates to the calibrating method that the spaceborne circular polarisation of a kind of long wavelength is launched, the polarization mode synthetic aperture radar (SAR) is condensed in linear polarization reception (CTLR), belong to the signal processing technology field.

Background technology

Forest biomass is one of key link of inverting global carbon model, and is significant to the great basic problem in science such as interaction of research global carbon and climate change.Long wavelength's satellite-borne SAR image has great potential aspect the inverting top biomass (Biomass), has caused the great attention of each main scientific and technological power in the world in recent years.Forest biomass observation SAR becomes one of current international research forward position hot subject.It is that six new survey of the earth of representative are had a high regard for affair that European Space Agency (ESA) has selected with the BIOMASS plan.The measurement that a spaceborne pattern-band SAR satellite is finished global forest biomass will be developed and launch to the BIOMASS plan, realize the monitoring of global land carbon cycle variation is had very important scientific meaning and using value.

The Polarization scattering information of target is the important information amount of forest biomass inverting, complete polarization SAR is than common single polarization SAR, can obtain to lie in the abundanter target information between the different POLARIZATION CHANNEL, have significant advantage, but complete polarization SAR is difficult to realize that the wide swath of single polarization SAR is wide.Therefore, in the Spaceborne SAR System design, there is the contradiction that the mapping bandwidth improves and complete polarization information is obtained.For head it off, the foreign scholar has proposed to condense the polarization SAR mode of operation in recent years, this mode of operation can reach the observation bandwidth of conventional single polarization pattern, and can be finally inversed by the complete polarization pattern and obtain four groups of polarization informations by to two groups of different processing that receive polarization data.

Because long wavelength's satellite-borne SAR performance can be subjected to the influence that ionospheric having a strong impact on, particularly L-band and pattern-band SAR can be subjected to Faraday rotation effect.Faraday rotation effect causes the polarization plane of SAR signal to rotate, and causes the SAR image can not correctly reflect the polarization scattering characteristics of terrain object.The polarization SAR mode of operation of condensing that is suggested the earliest is π/4 patterns, is meant the linear hybrid polarized signal (i.e. 45 ° of linear polarization signals) of emission a kind of H (level)+V (vertically), and receives level and vertical signals having linear polarisation simultaneously.Therefore the spaceborne polarization SAR of condensing of π/4 patterns can be subjected to having a strong impact on of Faraday rotation effect, and Raney in 2007 etc. have proposed a kind of CTLR pattern, are meant the emission circularly polarized signal, receive level and vertical signals having linear polarisation simultaneously.Because Faraday rotation effect do not influence circular polarisation, can weaken the influence of Faraday rotation effect to this pattern, be a kind of mode of operation that development potentiality is arranged very much.Because the polarization plane of the circularly polarized signal of its emission can be owing to Faraday rotation effect produces distortion, so only need proofread and correct the Faraday effect of reflected signal.Freeman in 2008 has proposed to consider that the CTLR of Faraday rotation effect condenses the system model of polarization mode.

Summary of the invention

The present invention proposes the calibrating method that the spaceborne CTLR of a kind of long wavelength condenses polarization mode SAR, this method based on two grid trihedral angle scaler and two polarization initiatively scaler and Global Navigation Satellite System (GNSS) provide high-precision real the time ionosphere total amount of electrons (TEC) Monitoring Data and the 10th generation international geomagnetic reference field model (IGRF10) earth magnetism computation model, be the new method that the spaceborne CTLR of a kind of long wavelength of being applicable to condenses polarization mode SAR calibration.

The spaceborne CTLR of a kind of long wavelength condenses the calibrating method of polarization mode SAR, comprises following step:

Step 1: the estimated value of obtaining the receiving cable unbalanced error;

Step 2: the estimated value of obtaining circular polarisation transmission channel crosstalk coefficient;

Step 3: the estimated value of obtaining linear polarization receiving cable crosstalk coefficient;

Step 4: the estimated value of obtaining faraday's rotation angle;

Step 5: utilizing GLONASS (Global Navigation Satellite System) TEC data to obtain does not have fuzzy faraday's rotation angle estimated value, finishes the SAR calibration.

The invention has the advantages that:

(1) the method treatment scheme of the present invention's proposition is simple, precision is high;

(2) method that proposes of the present invention is to being that the spaceborne CTLR of long wavelength of representative condenses the polarization SAR data processing and has important application with the pattern-band.

Description of drawings

Fig. 1 is a grid trihedral angle scaler of the present invention;

Fig. 2 is a method flow diagram of the present invention;

Fig. 3 is the amplitude Estimation result curve of receiving cable unbalanced error of the present invention;

Fig. 4 is the phase estimation result curve of receiving cable unbalanced error of the present invention;

Fig. 5 is the amplitude Estimation result curve of circular polarisation transmission channel crosstalk coefficient of the present invention;

Fig. 6 is the phase estimation result curve of circular polarisation transmission channel crosstalk coefficient of the present invention;

Fig. 7 is linear polarization receiving cable crosstalk coefficient δ of the present invention ₁The amplitude Estimation result curve;

Fig. 8 is linear polarization receiving cable crosstalk coefficient δ of the present invention ₁The phase estimation result curve;

Fig. 9 is linear polarization receiving cable crosstalk coefficient δ of the present invention ₂The amplitude Estimation result curve;

Figure 10 is linear polarization receiving cable crosstalk coefficient δ of the present invention ₂The phase estimation result curve;

Figure 11 is faraday's rotation angle evaluated error result curve of the present invention;

Embodiment

The present invention is described in further detail below in conjunction with drawings and Examples.

Grid trihedral angle scaler as shown in Figure 1, xyz is a rectangular coordinate system among the figure, three faces of scaler lay respectively at xy face, xz face and yz face, wherein bottom surface (being positioned at the xy face) is the grid face.The CTLR that method of the present invention proposes based on Freeman condenses the error model of polarization mode, as the formula (1):

$\left[\begin{array}{c}{M}_{\mathrm{RH}}\\ M_{\mathrm{RV}}\end{array}\right]=\frac{1}{\sqrt{2}}\left[\begin{array}{cc}1& {\mathrm{\δ}}_2\\ {\mathrm{\δ}}_1& f\end{array}\right]\·\left[\begin{array}{cc}\cos \mathrm{\Ω}& \sin \mathrm{\Ω}\\ -\sin \mathrm{\Ω}& \cos \mathrm{\Ω}\end{array}\right]\·\left[\begin{array}{cc}{S}_{\mathrm{HH}}& S_{\mathrm{HV}}\\ S_{\mathrm{VH}}& S_{\mathrm{VV}}\end{array}\right]\·\left[\begin{array}{c}{e}^{-\mathrm{j\Ω}}+{\mathrm{\δ}}_c{e}^{\mathrm{j\Ω}}\\ -j(e^{-\mathrm{j\Ω}}-{\mathrm{\δ}}_c{e}^{\mathrm{j\Ω}})\end{array}\right]---\left(1\right)$

In the formula, M _RVAnd M _RHExpression is measured the reception vertical polarization component of Scattering of Vector and is received horizontal polarization component, S respectively _HH, S _HV, S _VH, S _VVThe scattering matrix of the matrix representation target that constitutes, S _HH, S _HV, S _VH, S _VVEmission level polarizes and receives the horizontal polarization component, launches vertical polarization and receives horizontal polarization component, emission level polarization reception vertical polarization component, emission vertical polarization reception vertical polarization component in the representing matrix respectively.Ω represents faraday's rotation angle, and f represents receiving cable unbalanced error, δ ₁And δ ₂Expression linear polarization receiving cable crosstalk coefficient, δ _cExpression circular polarisation transmission channel crosstalk coefficient.

Two grid trihedral angle scaler that the present invention is based on are expressed as Gt1 and Gt2, and two polarization active scaler are expressed as X and Y _oThe flow process of method specifically comprises following step as shown in Figure 2.

Step 1: the estimated value of obtaining the receiving cable unbalanced error

Calculate the estimated value of receiving cable unbalanced error according to formula (2)～(4)

$\hat{f}={|{\hat{f}}^{\left(A\right)}\·{\hat{f}}^{\left(B\right)}|}^{\frac{1}{2}}\·\exp \{j\·\frac{\arg ({\hat{f}}^{\left(A\right)}\·{\hat{f}}^{\left(B\right)})}{2}\}---\left(2\right)$

Wherein:

${\hat{f}}^{\left(A\right)}=\frac{M_{\mathrm{RV}}^X+M_{\mathrm{RV}}^Y+j(M_{\mathrm{RV}}^{\mathrm{Gt}1}-M_{\mathrm{RV}}^{\mathrm{Gt}2})}{(M_{\mathrm{RH}}^{\mathrm{Gt}1}-M_{\mathrm{RH}}^{\mathrm{Gt}2})-j(M_{\mathrm{RH}}^X+M_{\mathrm{RH}}^Y)}---\left(3\right)$

${\hat{f}}^{\left(B\right)}=\frac{M_{\mathrm{RV}}^X-M_{\mathrm{RV}}^Y-j(M_{\mathrm{<figure-callout\; id="1"\; label="RV\; Gt"\; filenames="HDA0000048801260000031.png,HDA0000048801260000052.png"\; state="\{\{state\}\}">RV</figure-callout>}}^{\mathrm{Gt}}+M_{\mathrm{RV}}^{\mathrm{Gt}2})}{(M_{\mathrm{<figure-callout\; id="1"\; label="RH\; Gt"\; filenames="HDA0000048801260000031.png,HDA0000048801260000052.png"\; state="\{\{state\}\}">RH</figure-callout>}}^{\mathrm{Gt}}+M_{\mathrm{RH}}^{\mathrm{Gt}2})+j(M_{\mathrm{RH}}^X-M_{\mathrm{RH}}^Y)}---\left(4\right)$

In the formula, j ²=-1, arg represents to ask argument,

With

The reception vertical polarization component of the scaler X Scattering of Vector that measures of expression and receive the horizontal polarization component respectively,

With

The reception vertical polarization component of the scaler Y Scattering of Vector that measures of expression and receive the horizontal polarization component respectively,

With

The reception vertical polarization component of the scaler Gt1 Scattering of Vector that measures of expression and receive the horizontal polarization component respectively,

With

The reception vertical polarization component of the scaler Gt2 Scattering of Vector that measures of expression and receive the horizontal polarization component respectively.

Step 2: the estimated value of obtaining circular polarisation transmission channel crosstalk coefficient

Calculate the estimated value of circular polarisation transmission channel crosstalk coefficient according to formula (5)～(7)

${\widehat{\mathrm{\&delta;}}}_c=\left|{\widehat{\mathrm{\&delta;}}}_c^{\left(B\right)}\right|\&CenterDot;\exp \left\{j\frac{\arg ({\widehat{\mathrm{\&delta;}}}_c^{\left(A\right)}\&CenterDot;{\widehat{\mathrm{\&delta;}}}_c^{\left(B\right)})}{2}\right\}---\left(5\right)$

Wherein

${\widehat{\mathrm{\&delta;}}}_c^{\left(A\right)}=\frac{[M_{\mathrm{RH}}^X-M_{\mathrm{RH}}^Y-j(M_{\mathrm{<figure-callout\; id="1"\; label="RH\; Gt"\; filenames="HDA0000048801260000031.png,HDA0000048801260000052.png"\; state="\{\{state\}\}">RH</figure-callout>}}^{\mathrm{Gt}}+M_{\mathrm{RH}}^{\mathrm{Gt}2})]}{4\hat{f}}\&CenterDot;[j\hat{f}(M_{\mathrm{<figure-callout\; id="1"\; label="RH\; Gt"\; filenames="HDA0000048801260000031.png,HDA0000048801260000052.png"\; state="\{\{state\}\}">RH</figure-callout>}}^{\mathrm{Gt}}+M_{\mathrm{RH}}^{\mathrm{Gt}2})-(M_{\mathrm{<figure-callout\; id="1"\; label="RV\; Gt"\; filenames="HDA0000048801260000031.png,HDA0000048801260000052.png"\; state="\{\{state\}\}">RV</figure-callout>}}^{\mathrm{Gt}}+M_{\mathrm{RV}}^{\mathrm{Gt}2})]---\left(6\right)$

${\widehat{\mathrm{\&delta;}}}_c^{\left(B\right)}=\frac{1}{2}[(M_{\mathrm{RH}}^{\mathrm{Gt}1}-M_{\mathrm{RH}}^{\mathrm{Gt}2})-j(M_{\mathrm{RH}}^X+M_{\mathrm{RH}}^Y)]---\left(7\right)$

Step 3: the estimated value of obtaining linear polarization receiving cable crosstalk coefficient

With

Calculate the estimated value of linear polarization receiving cable crosstalk coefficient according to formula (8)～(9)

With

${\widehat{\mathrm{\&delta;}}}_1=\frac{1}{2}[M_{\mathrm{RV}}^{\mathrm{Gt}1}-M_{\mathrm{RV}}^{\mathrm{Gt}2}+j(M_{\mathrm{RV}}^X+M_{\mathrm{RV}}^Y)]-j\hat{f}---\left(8\right)$

${\widehat{\mathrm{\&delta;}}}_2=\frac{1}{2}[M_{\mathrm{RH}}^X+M_{\mathrm{RH}}^Y-j(M_{\mathrm{RH}}^{\mathrm{Gt}1}-M_{\mathrm{RH}}^{\mathrm{Gt}2})]+j---\left(9\right)$

Step 4: the estimated value of obtaining faraday's rotation angle

Calculate the estimated value of faraday's rotation angle according to formula (10)

$\widehat{\mathrm{\&Omega;}}=\frac{1}{2}\arg \left\{\frac{2\hat{f}}{\hat{f}\&CenterDot;(M_{\mathrm{<figure-callout\; id="1"\; label="RH\; Gt"\; filenames="HDA0000048801260000031.png,HDA0000048801260000052.png"\; state="\{\{state\}\}">RH</figure-callout>}}^{\mathrm{Gt}}+M_{\mathrm{RH}}^{\mathrm{Gt}2})+j\&CenterDot;({\mathrm{<figure-callout\; id="1"\; label="M\; RV\; Gt"\; filenames="HDA0000048801260000031.png,HDA0000048801260000052.png"\; state="\{\{state\}\}">M</figure-callout>}}_{\mathrm{RV}\mathrm{Gt}}^1+M_{\mathrm{RV}}^{\mathrm{Gt}2})}\right\}---\left(10\right)$

Step 5: utilizing GLONASS (Global Navigation Satellite System) TEC data to obtain does not have fuzzy faraday's rotation angle estimated value

Finish the SAR calibration;

For faraday's rotation angle estimated value to trying to achieve in the step 4

Angle fuzzy revise fully, the ionized layer TEC observation data of utilizing Global Navigation Satellite System (GNSS) to provide, and, try to achieve faraday's rotation angle valuation of rough grade according to formula (11) in conjunction with the 10th generation international geomagnetic reference field model (IGRF10) earth magnetism computation model

${\widehat{\mathrm{\&Omega;}}}_{\mathrm{GNSS}}\&ap;\frac{K}{f_0^2}\&CenterDot;{[B\cos \mathrm{\&psi;}\&CenterDot;\sec \mathrm{\&theta;}]}_{400}\&CenterDot;\mathrm{TEC}---\left(11\right)$

In the formula,

Faraday's rotation angle that the ionized layer TEC observation data that expression adopts GNSS to provide estimates roughly.f ₀The frequency of operation of expression SAR system, unit is Hz.K is a constant, and K=2.365 * 10 ⁴, unit is Am ²/ kg.B represents earth magnetic field intensity, and unit is Wb/m ²θ represents the visual angle of borne SAR.ψ represents the angle of magnetic field of the earth direction and the radar electromagnetic wave direction of propagation (being the controlling antenna wave beam to point direction).TEC is illustrated in perpendicular to the ionosphere total electron content on the direction of ground, and unit is TECU, 1TECU=10 ¹⁶m ^-2[Bcos ψ sec θ] ₄₀₀Physical meaning be the magnetic field of the earth factor on expression ground 400 kilometers height.

The angle that employing formula (12) is eliminated faraday's rotation angle estimated value is fuzzy, obtains and does not have fuzzy faraday's rotation angle estimated value

${\widehat{\mathrm{\&Omega;}}}^F=\widehat{\mathrm{\&Omega;}}+\mathrm{round}\left(\frac{{\widehat{\mathrm{\&Omega;}}}_{\mathrm{GNSS}}-\widehat{\mathrm{\&Omega;}}}{\mathrm{\&pi;}/2}\right)\&CenterDot;\frac{\mathrm{\&pi;}}{2}---\left(12\right)$

In the formula,

The fuzzy faraday's rotation angle estimated value of the nothing of expression final output after the over-angle ambiguity solution is handled, immediate round values is got in function round (*) expression.

Through above five steps, the estimation to the receiving cable unbalanced error, the estimation of circular polarisation transmission channel crosstalk coefficient, the estimation of linear polarization receiving cable crosstalk coefficient and the estimation of faraday's rotation angle have been finished respectively, finish the SAR calibration and handle, realize calibration.

Embodiment:

The method that the present invention proposes has been carried out the emulation experiment checking.

According to given parameter, comprise faraday's rotation angle Ω in the emulation experiment, receiving cable unbalanced error f, linear polarization receiving cable crosstalk coefficient δ ₁And δ ₂, circular polarisation transmission channel crosstalk coefficient δ _c, and the scattering matrix of scaler:

${\mathrm{<figure-callout\; id="1"\; label="S\; Gt"\; filenames="HDA0000048801260000031.png,HDA0000048801260000052.png"\; state="\{\{state\}\}">S</figure-callout>}}_{\mathrm{Gt}}=\left[\begin{array}{cc}1& 0\\ 0& 0\end{array}\right]$ $S_{\mathrm{Gt}2}=\left[\begin{array}{cc}0& 0\\ 0& 1\end{array}\right]$ $S_X=\left[\begin{array}{cc}0& 0\\ 1& 0\end{array}\right]$ $S_Y=\left[\begin{array}{cc}0& 1\\ 0& 0\end{array}\right]$

Try to achieve the component of the measurement Scattering of Vector of four scaler by formula (1), be expressed as

And then calibrate processing according to step 1 to step 5.Be specially:

The amplitude of supposing the receiving cable unbalanced error is begun by 0dB, it is increased 0.1dB at every turn, gets arg{f}=π/3, | δ ₁|=| δ ₂|=0.1, | δ _c|=0.32, arg{ δ ₁}=arg{ δ ₂}=arg{ δ _c}=0, the component of the measurement Scattering of Vector of four scaler is tried to achieve by formula (1) in Ω=π/4, has finished simulation calculation 51 times according to step 1, at last the amplitude of the receiving cable unbalanced error of 51 estimations form with curve is presented among Fig. 3.

The phase place of supposing the receiving cable unbalanced error increases by 6 ° with it by-60 ° of beginnings at every turn, gets | f|=1.5, | δ ₁|=| δ ₂|=0.1, | δ _c|=0.32, arg{ δ ₁}=arg{ δ ₂}=arg{ δ _c}=0, the component of the measurement Scattering of Vector of four scaler is tried to achieve by formula (1) in Ω=π/4, has finished simulation calculation 21 times according to step 1, at last the phase place of the receiving cable unbalanced error of 21 estimations form with curve is presented among Fig. 4.

The amplitude of supposing circular polarisation transmission channel crosstalk coefficient is begun by-30dB, it is increased 1dB at every turn, gets | f|=1.5, and arg{f}=π/3, | δ ₁|=| δ ₂|=0.1, arg{ δ ₁}=arg{ δ ₂}=arg{ δ _c}=0, Ω=π/4, try to achieve the component of the measurement Scattering of Vector of four scaler by formula (1), finished simulation calculation 21 times, at last the amplitude of the circular polarisation transmission channel crosstalk coefficient of 21 estimations form with curve is presented among Fig. 5 according to step 1, step 2.

The phase place of supposing circular polarisation transmission channel crosstalk coefficient increases by 6 ° with it by-60 ° of beginnings at every turn, gets | f|=1.5, arg{f}=π/3, { δ ₁|=| δ ₂|=0.1, | δ _c|=0.32, arg{ δ ₁}=arg{ δ ₂; Ω=π/4; try to achieve the component of the measurement Scattering of Vector of four scaler by formula (1), finished simulation calculation 21 times, at last the phase place of the circular polarisation transmission channel crosstalk coefficient of 21 estimations form with curve is presented among Fig. 6 according to step 1, step 2.

Suppose linear polarization receiving cable crosstalk coefficient δ ₁Amplitude begin by-40dB, it is increased 1dB at every turn, get | f|=1.5, arg{f}=π/3, | δ ₂|=0.1, | δ _c|=0.32, arg{ δ ₁}=arg{ δ ₂}=arg{ δ _c}=0, the component of the measurement Scattering of Vector of four scaler is tried to achieve by formula (1) in Ω=π/4, has finished simulation calculation 21 times according to step 1, step 3, at last with the linear polarization receiving cable crosstalk coefficient δ of 21 estimations ₁Amplitude be presented among Fig. 7 with the form of curve.

Suppose linear polarization receiving cable crosstalk coefficient δ ₁Phase place by-60 ° of beginnings, its is increased by 6 ° at every turn, get | f|=1.5, arg{f}=π/3, | δ ₁|=| δ ₂|=0.1, | δ _c|=0.32, arg{ δ ₂}=arg{ δ _c}=0, the component of the measurement Scattering of Vector of four scaler is tried to achieve by formula (1) in Ω=π/4, has finished simulation calculation 21 times according to step 1, step 3, at last with the linear polarization receiving cable crosstalk coefficient δ of 21 estimations ₁Phase place be presented among Fig. 8 with the form of curve.

Suppose linear polarization receiving cable crosstalk coefficient δ ₂Amplitude begin by-40dB, it is increased 1dB at every turn, get | f|=1.5, arg{f}=π/3, | δ ₁|=0.1, | δ _c|=0.32, arg{ δ ₁}=arg{ δ ₂}=arg{ δ _c}=0, the component of the measurement Scattering of Vector of four scaler is tried to achieve by formula (1) in Ω=π/4, has finished simulation calculation 21 times according to step 3, at last with the linear polarization receiving cable crosstalk coefficient δ of 21 estimations ₂Amplitude be presented among Fig. 9 with the form of curve.

Suppose linear polarization receiving cable crosstalk coefficient δ ₂Phase place by-60 ° of beginnings, its is increased by 6 ° at every turn, get | f|=1.5, arg{f}=π/3, | δ ₁|=| δ ₂|=0.1, | δ _c|=0.32, arg{ δ ₁}=arg{ δ _c}=0, the component of the measurement Scattering of Vector of four scaler is tried to achieve by formula (1) in Ω=π/4, has finished simulation calculation 21 times according to step 3, at last with the linear polarization receiving cable crosstalk coefficient δ of 21 estimations ₂Phase place be presented among Figure 10 with the form of curve.

If the frequency of operation of spaceborne linear complete polarization SAR is f ₀=4.35 * 10 ⁸Hz, the radar antenna visual angle is θ=23 °, constant K=2.365 * 10 ⁴Am ²/ kg.Suppose that the date that the SAR satellite obtains data is on January 1st, 2008, the imaging observation zone is positioned at 135 ° of east longitudes, 60 ° in south latitude in above-mentioned parameter substitution IGRF10 earth magnetism computation model, can be B=5.486 * 10 in the hope of the earth magnetic field intensity on the 400 kilometers height in ground ^-5Wb/m ², angle ψ=9.28 of the magnetic field of the earth direction and the radar electromagnetic wave direction of propagation °.According to CODE/GIM TEC data, TEC=9.4TECU is arranged, the formula in the substitution step 5 (11) is tried to achieve

(radian) then has unit conversion for degree

These data can be used for the calibration of actual SAR data and handle.Consider CODE/GIM ionized layer TEC influence of measurement error, measure the precision that is reached according to TEC under the usual conditions, suppose existence ± 5TECU ionized layer TEC random meausrement error, then can calculate faraday's rotation angle estimation error of measuring error introducing thus according to formula (11)

(radian) then has estimation error with unit conversion for degree

Do not surpass 90 °, do not influence the fuzzy elimination shown in the formula (12), so CODE/GIM ionized layer TEC influence of measurement error can be ignored.

Emulation experiment changes in 0 ° of-360 ° of scope in order to realize faraday's rotation angle, and other parameters in the formula (11) are remained unchanged, and supposes that TEC changes in the scope of 0TECU-85.5TECU.Faraday's rotation angle increases by 1 ° with it by 0 ° of beginning at every turn, gets | f|=1.5, and arg{f}=π/3, | δ ₁|=| δ ₂|=0.1, | δ _c|=0.32, arg{ δ ₁}=arg{ δ ₂}=arg{ δ _cThe component of the measurement Scattering of Vector of four scaler is tried to achieve by formula (1) in }=0, has finished simulation calculation 361 times according to step 1, step 4, step 5, at last the error of faraday's rotation angle of 361 estimations form with curve is presented among Figure 11.

Table 1 has provided receiving cable unbalanced error f, the circular polarisation transmission channel crosstalk coefficient δ that Fig. 3 estimates in Figure 10 _c, linear polarization receiving cable crosstalk coefficient δ ₁And δ ₂Range error and the average and the standard deviation of phase error.The average of faraday's rotation angle error of estimating among Figure 11 is 0.892, and standard deviation is 0.445.

Table 1

The method that emulation experiment explanation the present invention proposes is the calibrating method that the spaceborne CTLR pattern of simple, the high-precision long wavelength of a kind of treatment scheme is condensed polarization SAR.

Claims (1)

1. the spaceborne CTLR pattern of long wavelength is condensed the calibrating method of polarization SAR, it is characterized in that, comprises following step:

Step 1: the estimated value of obtaining the receiving cable unbalanced error

Calculate the estimated value of receiving cable unbalanced error according to formula (2)～(4)

$\hat{f}={|{\hat{f}}^{\left(A\right)}\&CenterDot;{\hat{f}}^{\left(B\right)}|}^{\frac{1}{2}}\&CenterDot;\exp \{j\&CenterDot;\frac{\arg ({\hat{f}}^{\left(A\right)}\&CenterDot;{\hat{f}}^{\left(B\right)})}{2}\}---\left(2\right)$

Wherein:

${\hat{f}}^{\left(A\right)}=\frac{M_{\mathrm{RV}}^X+M_{\mathrm{RV}}^Y+j(M_{\mathrm{RV}}^{\mathrm{Gt}1}-M_{\mathrm{RV}}^{\mathrm{Gt}2})}{(M_{\mathrm{RH}}^{\mathrm{Gt}1}-M_{\mathrm{RH}}^{\mathrm{Gt}2})-j(M_{\mathrm{RH}}^X+M_{\mathrm{RH}}^Y)}---\left(3\right)$

${\hat{f}}^{\left(B\right)}=\frac{M_{\mathrm{RV}}^X-M_{\mathrm{RV}}^Y-j(M_{\mathrm{RV}}^{\mathrm{Gt}1}+M_{\mathrm{RV}}^{\mathrm{Gt}2})}{(M_{\mathrm{RH}}^{\mathrm{Gt}1}+M_{\mathrm{RH}}^{\mathrm{Gt}2})+j(M_{\mathrm{RH}}^X-M_{\mathrm{RH}}^Y)}---\left(4\right)$

In the formula, j ²=-1, arg represents to ask argument,

With

The reception vertical polarization component of the scaler X Scattering of Vector that measures of expression and receive the horizontal polarization component respectively, With The reception vertical polarization component of the scaler Y Scattering of Vector that measures of expression and receive the horizontal polarization component respectively,

With

The reception vertical polarization component of the scaler Gt1 Scattering of Vector that measures of expression and receive the horizontal polarization component respectively,

With

The reception vertical polarization component of the scaler Gt2 Scattering of Vector that measures of expression and receive the horizontal polarization component respectively;

Step 2: the estimated value of obtaining circular polarisation transmission channel crosstalk coefficient

Calculate the estimated value of circular polarisation transmission channel crosstalk coefficient according to formula (5)～(7)

${\widehat{\mathrm{\&delta;}}}_c=\left|{\widehat{\mathrm{\&delta;}}}_c^{\left(B\right)}\right|\&CenterDot;\exp \left\{j\frac{\arg ({\widehat{\mathrm{\&delta;}}}_c^{\left(A\right)}\&CenterDot;{\widehat{\mathrm{\&delta;}}}_c^{\left(B\right)})}{2}\right\}---\left(5\right)$

Wherein:

${\widehat{\mathrm{\&delta;}}}_c^{\left(A\right)}=\frac{[M_{\mathrm{RH}}^X-M_{\mathrm{RH}}^Y-j(M_{\mathrm{RH}}^{\mathrm{Gt}1}+M_{\mathrm{RH}}^{\mathrm{Gt}2})]}{4\hat{f}}\&CenterDot;[j\hat{f}(M_{\mathrm{RH}}^{\mathrm{Gt}1}+M_{\mathrm{RH}}^{\mathrm{Gt}2})-(M_{\mathrm{RV}}^{\mathrm{Gt}1}+M_{\mathrm{RV}}^{\mathrm{Gt}2})]---\left(6\right)$

${\widehat{\mathrm{\&delta;}}}_c^{\left(B\right)}=\frac{1}{2}[(M_{\mathrm{RH}}^{\mathrm{Gt}1}-M_{\mathrm{RH}}^{\mathrm{Gt}2})-j(M_{\mathrm{RH}}^X+M_{\mathrm{RH}}^Y)]---\left(7\right)$

Step 3: the estimated value of obtaining linear polarization receiving cable crosstalk coefficient With

Calculate the estimated value of linear polarization receiving cable crosstalk coefficient according to formula (8)～(9) With

${\widehat{\mathrm{\&delta;}}}_1=\frac{1}{2}[M_{\mathrm{RV}}^{\mathrm{Gt}1}-M_{\mathrm{RV}}^{\mathrm{Gt}2}+j(M_{\mathrm{RV}}^X+M_{\mathrm{RV}}^Y)]-j\hat{f}---\left(8\right)$

${\widehat{\mathrm{\&delta;}}}_2=\frac{1}{2}[M_{\mathrm{RH}}^X+M_{\mathrm{RH}}^Y-j(M_{\mathrm{RH}}^{\mathrm{Gt}1}-M_{\mathrm{RH}}^{\mathrm{Gt}2})]+j---\left(9\right)$

Step 4: the estimated value of obtaining faraday's rotation angle

Calculate the estimated value of faraday's rotation angle according to formula (10)

$\widehat{\mathrm{\&Omega;}}=\frac{1}{2}\arg \left\{\frac{2\hat{f}}{\hat{f}\&CenterDot;(M_{\mathrm{RH}}^{\mathrm{Gt}1}+M_{\mathrm{RH}}^{\mathrm{Gt}2})+j\&CenterDot;(M_{\mathrm{RV}}^{\mathrm{Gt}1}+M_{\mathrm{RV}}^{\mathrm{Gt}2})}\right\}---\left(10\right)$

Step 5: utilizing GLONASS (Global Navigation Satellite System) TEC data to obtain does not have fuzzy faraday's rotation angle estimated value

Finish the SAR calibration;

Try to achieve faraday's rotation angle valuation of rough grade according to formula (11)

${\widehat{\mathrm{\&Omega;}}}_{\mathrm{GNSS}}\&ap;\frac{K}{f_0^2}\&CenterDot;{[B\cos \mathrm{\&psi;}\&CenterDot;\sec \mathrm{\&theta;}]}_{400}\&CenterDot;\mathrm{TEC}---\left(11\right)$

In the formula, Faraday's rotation angle that the ionized layer TEC observation data that expression adopts GNSS to provide estimates roughly; f ₀The frequency of operation of expression SAR system, unit is Hz; K is a constant, and K=2.365 * 10 ⁴, unit is Am ²/ kg; B represents earth magnetic field intensity, and unit is Wb/m ²θ represents the visual angle of borne SAR; ψ represents the angle of the magnetic field of the earth direction and the radar electromagnetic wave direction of propagation; TEC is illustrated in perpendicular to the ionosphere total electron content on the direction of ground, and unit is TECU, 1TECU=10 ¹⁶m ^-2

The angle that employing formula (12) is eliminated faraday's rotation angle estimated value is fuzzy, obtains and does not have fuzzy faraday's rotation angle estimated value

${\widehat{\mathrm{\&Omega;}}}^F=\widehat{\mathrm{\&Omega;}}+\mathrm{round}\left(\frac{{\widehat{\mathrm{\&Omega;}}}_{\mathrm{GNSS}}-\widehat{\mathrm{\&Omega;}}}{\mathrm{\&pi;}/2}\right)\&CenterDot;\frac{\mathrm{\&pi;}}{2}---\left(12\right)$

In the formula,

The fuzzy faraday's rotation angle estimated value of the nothing of expression final output after the over-angle ambiguity solution is handled, immediate round values is got in function round (*) expression;

Through above five steps, finished the estimation to the receiving cable unbalanced error, the estimation of circular polarisation transmission channel crosstalk coefficient, the estimation of linear polarization receiving cable crosstalk coefficient and the estimation of faraday's rotation angle respectively, finish the SAR calibration and handle.

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