CN103792535B

CN103792535B - A kind of method utilizing SAR Satellite observation ionized layer TEC value

Info

Publication number: CN103792535B
Application number: CN201410022829.1A
Authority: CN
Inventors: 王伟伟; 王旭艳; 黎薇萍; 李财品; 李光廷; 朱雅琳; 赵泓懿; 刘波
Original assignee: China Academy of Space Technology CAST
Current assignee: China Academy of Space Technology CAST
Priority date: 2014-01-17
Filing date: 2014-01-17
Publication date: 2016-02-10
Anticipated expiration: 2034-01-17
Also published as: CN103792535A

Abstract

The invention discloses a method for measuring ionosphere TEC value by using SAR satellite. After the pulse signal transmitted by spaceborne SAR passes through the ionosphere, its phase contains the complete ionospheric TEC information along the propagation path. This method selects several frequency sub-bands from SAR signals with a certain bandwidth to provide the degree of freedom required for phase deambiguation. By optimizing the design of sub-band parameters and other technical means, while taking into account the estimation accuracy of the TEC value, the influence of the electromagnetic wave propagation distance phase on the phase defuzzification process is eliminated. Finally, the phase deambiguation equation is constructed, and finally the high-precision estimation of the ionospheric TEC value is realized. Using the estimated ionospheric TEC value to compensate the spaceborne SAR echo phase can effectively improve the spaceborne SAR imaging quality and interferometric accuracy.

Description

A Method of Measuring Ionospheric TEC Value Using SAR Satellite

技术领域technical field

本发明涉及一种测量电离层TEC值的方法，尤其涉及一种利用SAR卫星实现高精度测量电离层TEC值的方法，属于地球同步轨道SAR系统研制领域。The invention relates to a method for measuring the TEC value of the ionosphere, in particular to a method for realizing high-precision measurement of the TEC value of the ionosphere by using a SAR satellite, and belongs to the field of geosynchronous orbit SAR system development.

背景技术Background technique

星载SAR发射及接收电磁波在穿越电离层后，会发生群延时、相位漂移、色散及法拉第极化旋转等传播效应，从而对低频段的SAR成像质量造成影响，对于地球同步轨道SAR(GEOSAR)由于其合成孔径时间长，电离层的时空变化对GEOSAR成像造成的影响愈加严重。目前国内外多家研究结构(如美国NASAJPL、英国Cranfield大学、中国空间技术研究院、中科院电子所、北京理工大学)开展了GEOSAR的相关研究。受美国NASA资助开展GEOSAR研究的美国喷气推进实验室（JPL）指出：精确了解大气扰动对SAR信号的影响是得到有意义结论的关键问题。英国克兰菲尔德（Cranfield）大学开展了无源双基GEOSAR系统研究，并指出大气的影响对GEOSAR成像至关重要。After the space-borne SAR transmits and receives electromagnetic waves through the ionosphere, propagation effects such as group delay, phase drift, dispersion, and Faraday polarization rotation will occur, which will affect the imaging quality of low-frequency SAR. For geosynchronous orbit SAR (GEOSAR ) due to its long synthetic aperture time, the spatiotemporal changes of the ionosphere have a more serious impact on GEOSAR imaging. At present, many research institutions at home and abroad (such as NASAJPL in the United States, Cranfield University in the United Kingdom, China Academy of Space Technology, Institute of Electronics of the Chinese Academy of Sciences, and Beijing Institute of Technology) have carried out related research on GEOSAR. The Jet Propulsion Laboratory (JPL), which is funded by NASA to carry out GEOSAR research, pointed out that accurately understanding the influence of atmospheric disturbances on SAR signals is a key issue to draw meaningful conclusions. Cranfield University in the UK carried out research on passive bistatic GEOSAR systems, and pointed out that the influence of the atmosphere is crucial to GEOSAR imaging.

目前国内外针对电离层对GEOSAR影响校正的主要方法包括：基于方位向处理的相位梯度自聚焦（PGA）方法、加权最小二乘方法及最小熵方法等；基于距离向处理的自适应匹配滤波方法及距离多视处理方法；利用现有测量手段对电离层TEC值进行实时测量的方法等。对于方位向处理的PGA方法能够补偿电离层变化对方位聚焦的影响，但是其一方面需要在图像中存在一个孤立的特显点，另一方面该方法只能估计电离层随时间变化的高次项，无法估计电离层TEC值变化的常数项和一次项，因此即使实现图像的方位聚焦，但是对于图像的定位误差及后续干涉测量误差仍无法解决。与PGA方法类似，对于加权最小二乘方法和最小熵方法在一定程度上能够补偿方位向散焦问题，但是均难以精确估计TEC值，从而无法进行精确的相位补偿。同时由于SAR发射信号的带宽通常与其载波频率相比相对较小，针对距离向的自适应匹配滤波方法估计电离层TEC值的精度很低，难以满足高成像质量的要求。对于距离多视方法，其通过将频谱分割成两部分，分别成像后估计二者之间的时延差，进而估计电离层TEC值，该方法同样受到SAR信号带宽的限制，时延差估计精度较低（以载波频率为1GHz，带宽为40M为例，1TECU引起的时延差只有10^-10秒的量级），因此难以精确地估计电离层TEC值的大小。由于电离层对电磁波传播的影响一方面与空间电子密度及其分布有关，另一方面与电磁波的传播路径有关。而SAR所发射与接收的脉冲信号随时间与空间是不断变化的，针对电离层的测量很难保证与SAR发射接收信号的路径和时间相同，因此测量的TEC值存在一定的偏差，从而不能精确补偿电离层对SAR成像质量的影响。At present, the main methods for correcting the impact of the ionosphere on GEOSAR at home and abroad include: phase gradient autofocus (PGA) method based on azimuth processing, weighted least square method and minimum entropy method, etc.; adaptive matched filter method based on range processing And the distance multi-view processing method; the method of real-time measurement of the ionospheric TEC value by using the existing measurement means, etc. The PGA method for azimuth processing can compensate the influence of ionospheric changes on azimuth focusing, but on the one hand, it needs an isolated prominent point in the image, and on the other hand, this method can only estimate the high-order ionospheric changes over time term, the constant term and the first-order term of the ionospheric TEC value change cannot be estimated, so even if the azimuth focusing of the image is realized, the positioning error of the image and the subsequent interferometry error still cannot be solved. Similar to the PGA method, the weighted least squares method and the minimum entropy method can compensate the azimuth defocusing problem to a certain extent, but it is difficult to accurately estimate the TEC value, so that accurate phase compensation cannot be performed. At the same time, because the bandwidth of the SAR transmitted signal is usually relatively small compared with its carrier frequency, the accuracy of the ionospheric TEC value estimated by the adaptive matched filter method for the range direction is very low, and it is difficult to meet the requirements of high imaging quality. For the range multi-look method, it divides the spectrum into two parts, estimates the delay difference between the two after imaging separately, and then estimates the ionospheric TEC value. This method is also limited by the bandwidth of the SAR signal, and the estimation accuracy of the delay difference Low (taking the carrier frequency of 1GHz and the bandwidth of 40M as an example, the delay difference caused by 1TECU is only on the order of ^10-10 seconds), so it is difficult to accurately estimate the value of ionospheric TEC. The impact of the ionosphere on the propagation of electromagnetic waves is related to the density and distribution of electrons in space on the one hand, and the propagation path of electromagnetic waves on the other hand. However, the pulse signal transmitted and received by SAR is constantly changing with time and space. It is difficult to ensure that the measurement of the ionosphere is the same as the path and time of the signal transmitted and received by SAR. Therefore, there is a certain deviation in the measured TEC value, which cannot be accurate. Compensate for the impact of the ionosphere on SAR imaging quality.

目前国内外对于GEOSAR的研究均刚刚起步，而克服电离层对于GEOSAR成像的影响是GEOSAR研究最为关键且必须解决的问题之一。该问题已成为目前国内外SAR领域研究的热点问题。At present, the research on GEOSAR at home and abroad has just started, and overcoming the impact of the ionosphere on GEOSAR imaging is one of the most critical and must-solve problems in GEOSAR research. This problem has become a hot topic in the field of SAR research at home and abroad.

发明内容Contents of the invention

本发明解决的技术问题是：克服现有技术的不足，提供一种利用SAR卫星测量电离层TEC值的方法，利用星载SAR自身信号携带完整电离层信息的特点，提取多个所选子频带的相位信息，通过多频解模糊等技术手段估计电离层TEC值，从而补偿电离层对星载SAR成像及干涉测量的影响，提高成像质量及干涉测量精度。The technical problem solved by the present invention is: to overcome the deficiencies of the prior art, to provide a method for measuring the TEC value of the ionosphere by using SAR satellites, and to extract a plurality of selected sub-frequency bands by utilizing the characteristics of the satellite-borne SAR's own signal to carry complete ionosphere information The phase information of the ionosphere is estimated by multi-frequency defuzzification and other technical means, so as to compensate the ionosphere's influence on spaceborne SAR imaging and interferometry, and improve the imaging quality and interferometry accuracy.

本发明的技术方案是：一种利用SAR卫星测量电离层TEC值的方法，包括如下步骤：Technical scheme of the present invention is: a kind of method utilizing SAR satellite to measure ionospheric TEC value, comprises the steps:

（1）在地面布置SAR信号接收机用于接收SAR卫星发射的脉冲信号；(1) Arrange SAR signal receivers on the ground to receive pulse signals transmitted by SAR satellites;

（2）从步骤（1）接收到的SAR卫星脉冲信号中选取三个子频带信号，分别为子频带1、子频带2与子频带3，子频带1、子频带2与子频带3三个子频带信号的载波频率分别为f₁，f₂，f₃，三个子频带的载波频率满足f₃>f₂>f₁，且f₂-f₁=f₃-f₂=Δf；(2) Select three sub-band signals from the SAR satellite pulse signal received in step (1), which are sub-band 1, sub-band 2 and sub-band 3, sub-band 1, sub-band 2 and sub-band 3 three sub-bands The carrier frequencies of the signal are f ₁ , f ₂ , and f ₃ respectively, and the carrier frequencies of the three sub-bands satisfy f ₃ >f ₂ >f ₁ , and f ₂ -f ₁ =f ₃ -f ₂ =Δf;

（3）将步骤（2）选取的三个子频带信号的频谱分别进行搬移，使其频谱中心频率均位于零频，然后分别利用匹配滤波对三个子频带信号进行脉冲压缩处理，得到三个子频带信号峰值点处的相位Φ_n(n=1,2,3)；(3) Move the spectrum of the three sub-band signals selected in step (2) respectively, so that the center frequency of the spectrum is at zero frequency, and then use matched filtering to perform pulse compression processing on the three sub-band signals to obtain three sub-band signals Phase Φ _n at the peak point (n=1,2,3);

（4）根据步骤（3）得到的三个子频带信号峰值点处的相位Φ_n(n=1,2,3)计算子频带1与子频带2信号峰值点的干涉相位，计算公式为Φ₁₂=angle[exp(jΦ₁)×exp(-jΦ₂)]；计算子频带2与子频带3信号峰值点的干涉相位，计算公式为Φ₂₃=angle[exp(jΦ₂)×exp(-jΦ₃)]；其中定义angle[exp(j(α+2kπ))]=α,α∈[-π,π]，k为整数， (4) According to the phase Φ _n (n=1,2,3) at the peak points of the three sub-band signals obtained in step (3), calculate the interference phase of the peak points of the sub-band 1 and sub-band 2 signals, and the calculation formula is Φ ₁₂ =angle[exp(jΦ ₁ )×exp(-jΦ ₂ )]; calculate the interference phase of the signal peak points of sub-band 2 and sub-band 3, the calculation formula is Φ ₂₃ =angle[exp(jΦ ₂ )×exp(-jΦ ₃ )]; where angle[exp(j(α+2kπ))]=α,α∈[-π,π] is defined, k is an integer,

（5）利用步骤（4）获得的干涉相位Φ₁₂和Φ₂₃求解电离层TEC值，计算公式如下：(5) Using the interferometric phases Φ ₁₂ and Φ ₂₃ obtained in step (4) to solve the ionospheric TEC value, the calculation formula is as follows:

$TEC TEC = = \frac{(((({f f}_{22} - - {f f}_{11})) {Φ Φ}_{23 twenty three} - - (({f f}_{33} - - {f f}_{22})) {Φ Φ}_{1212})) c c}{22 π π 40.3 40.3 (((({f f}_{22} - - {f f}_{11})) ((\frac{11}{{f f}_{22}} - - \frac{11}{{f f}_{33}})) - - (({f f}_{33} - - {f f}_{22})) ((\frac{11}{{f f}_{11}} - - \frac{11}{{f f}_{22}}))))}$

其中，c为光速。where c is the speed of light.

一种利用SAR卫星测量电离层TEC值的方法，其特征在于包括如下步骤：A kind of method utilizing SAR satellite to measure ionospheric TEC value is characterized in that comprising the steps:

（2）从步骤（1）接收到的SAR卫星脉冲信号中选取三个子频带信号，分别为子频带1、子频带2与子频带3，子频带1、子频带2与子频带3三个子频带信号的载波频率分别为f₁，f₂，f₃，三个子频带的载波频率满足f₃>f₂>f₁，f₂-f₁≠f₃-f₂；(2) Select three sub-band signals from the SAR satellite pulse signal received in step (1), which are sub-band 1, sub-band 2 and sub-band 3, sub-band 1, sub-band 2 and sub-band 3 three sub-bands The carrier frequencies of the signal are f ₁ , f ₂ , f ₃ respectively, and the carrier frequencies of the three sub-bands satisfy f ₃ >f ₂ >f ₁ , f ₂ -f ₁ ≠f ₃ -f ₂ ;

（4）利用相关星历信息获取电磁波真实传播距离R的粗估计值利用分别对步骤（3）获得的三个子频带信号峰值点的相位Φ_n(n=1,2,3)进行补偿，可得到补偿后三个子频带信号的相位：(4) Use relevant ephemeris information to obtain a rough estimate of the true propagation distance R of electromagnetic waves use The phases Φ _n (n=1,2,3) of the peak points of the three sub-band signals obtained in step (3) are respectively compensated, and the phases of the three sub-band signals after compensation can be obtained:

${Φ Φ}_{n no}^{' '} = = angle the angle [[exp exp ((j j (({Φ Φ}_{n no} + + \frac{22 π π \overset{^^}{R R} {f f}_{n no}}{c c}))))]],, n no = = 1,2,3 1,2,3;;$

其中，定义angle[exp(j(α+2kπ))]=α,α∈[-π,π]，k为整数， Among them, define angle[exp(j(α+2kπ))]=α,α∈[-π,π], k is an integer,

（5）判断三个子频带的载波频率是否满足如下约束条件：(5) Determine whether the carrier frequencies of the three sub-bands meet the following constraints:

$\{\begin{matrix} - - π π < < {Φ Φ}_{22}^{' '} + + 22 π π \frac{ΔR ΔR}{c c} (({f f}_{22} - - {f f}_{11})) < < π π \\ - - π π < < {Φ Φ}_{22}^{' '} + + 22 π π \frac{ΔR ΔR}{c c} (({f f}_{22} - - {f f}_{33})) < < π π \end{matrix}$

若满足则进入（6），否则重新执行步骤（2）—（5）,其中ΔR是电磁波真实传播距离R与其粗估计值之间的估计误差，c为光速；If it is satisfied, go to (6), otherwise re-execute steps (2)-(5), where ΔR is the real propagation distance R of electromagnetic waves and its rough estimate The estimated error between c is the speed of light;

（6）根据步骤（4）得到的三个子频带信号峰值点处的相位Φ'_n(n=1,2,3)计算子频带1与子频带2信号峰值点的干涉相位，计算公式为Φ₁₂=angle[exp(jΦ'₁)×exp(-jΦ'₂)]；计算子频带2与子频带3信号峰值点的干涉相位，计算公式为Φ₂₃=angle[exp(jΦ'₂)×exp(-jΦ'₃)]；其中定义angle[exp(j(α+2kπ))]=α,α∈[-π,π]，k为整数， (6) According to the phase Φ' _n (n=1,2,3) at the peak points of the three sub-band signals obtained in step (4), calculate the interference phase of the peak points of the sub-band 1 and sub-band 2 signals, and the calculation formula is Φ ₁₂ =angle[exp(jΦ' ₁ )×exp(-jΦ' ₂ )]; Calculate the interferometric phase of the signal peak points of sub-band 2 and sub-band 3, the calculation formula is Φ ₂₃ =angle[exp(jΦ' ₂ )× exp(-jΦ' ₃ )]; where angle[exp(j(α+2kπ))]=α,α∈[-π,π] is defined, k is an integer,

（7）利用步骤（6）获得的干涉相位Φ₁₂和Φ₂₃求解电离层TEC值，计算公式如下：(7) Using the interferometric phases Φ ₁₂ and Φ ₂₃ obtained in step (6) to solve the ionospheric TEC value, the calculation formula is as follows:

其中，c为光速。where c is the speed of light.

本发明与现有技术相比具有如下有益效果：Compared with the prior art, the present invention has the following beneficial effects:

（1）本发明提出两种克服距离相位影响的解决方案，既能兼顾TEC值的估计精度，又有效消除了距离相位的影响；(1) The present invention proposes two solutions to overcome the influence of range and phase, which can not only take into account the estimation accuracy of TEC value, but also effectively eliminate the influence of range and phase;

（2）本发明通过多个子频带信号之间的相位干涉，解决了相位模糊问题，从而能够高精度地估计电离层TEC值；(2) The present invention solves the phase ambiguity problem through the phase interference between multiple sub-band signals, so that the ionospheric TEC value can be estimated with high precision;

（3）本发明所测量的电离层TEC值与SAR发射脉冲的传播路径及时间相同，从而能够准确补偿SAR回波相位误差，提高成像质量和干涉测量精度。(3) The ionospheric TEC value measured by the present invention is the same as the propagation path and time of the SAR emission pulse, so that the SAR echo phase error can be accurately compensated, and the imaging quality and interferometric accuracy can be improved.

附图说明Description of drawings

图1为本发明方法方案1的处理流程图；Fig. 1 is the processing flowchart of method scheme 1 of the present invention;

图2为本发明方法方案2的处理流程图。Fig. 2 is a processing flowchart of the method scheme 2 of the present invention.

具体实施方式detailed description

星载SAR发射脉冲信号穿越电离层后，其相位中包含传播路径上完整的电离层TEC信息。本发明从具有一定带宽的SAR信号中选取若干子频带，以提供相位解模糊所需的自由度。通过优化设计子频带参数等技术手段，在兼顾TEC值估计精度的同时，消除了电磁波传播距离相位对相位解模糊处理的影响。最后构建相位解模糊方程，最终实现对电离层TEC值的高精度估计。利用所估计的电离层TEC值对星载SAR回波相位进行补偿，能够有效提高星载SAR成像质量以及干涉测量精度。本发明完全利用相位信息实现高精度的TEC值测量，实现流程图如图1和图2所示，具体实施方式如下：After the pulse signal transmitted by spaceborne SAR passes through the ionosphere, its phase contains the complete ionospheric TEC information along the propagation path. The invention selects several sub-frequency bands from SAR signals with a certain bandwidth to provide degrees of freedom required for phase defuzzification. By optimizing the design of sub-band parameters and other technical means, while taking into account the estimation accuracy of the TEC value, the influence of the electromagnetic wave propagation distance phase on the phase defuzzification process is eliminated. Finally, the phase deambiguation equation is constructed, and finally the high-precision estimation of the ionospheric TEC value is realized. Using the estimated ionospheric TEC value to compensate the spaceborne SAR echo phase can effectively improve the spaceborne SAR imaging quality and interferometric accuracy. The present invention fully utilizes phase information to realize high-precision TEC value measurement, and the realization flow chart is shown in Figure 1 and Figure 2, and the specific implementation is as follows:

第一步：在地面布置SAR信号接收机，直接接收SAR卫星发射的脉冲信号，以消除地面散射点对TEC值估计的影响。The first step: Arrange the SAR signal receiver on the ground to directly receive the pulse signal transmitted by the SAR satellite, so as to eliminate the influence of ground scattering points on the estimation of TEC value.

第二步：从接收的SAR回波信号中选取三个子频带。Step 2: Select three sub-frequency bands from the received SAR echo signal.

由于接收SAR信号的相位不仅受到电离层影响，而且受到传播距离R的影响。因此在选取子频带过程中，通过合理选择子频带中心频率的方法克服距离相位的影响。下面给出两种子频带中心频率选择方案：The phase of the received SAR signal is not only affected by the ionosphere, but also affected by the propagation distance R. Therefore, in the process of selecting the sub-band, the influence of the range phase is overcome by selecting the center frequency of the sub-band reasonably. Two sub-band center frequency selection schemes are given below:

方案1：假设所选取的三个子频带的中心频率分别为f₁，f₂，f₃，且f₃>f₂>f₁，则选取三个子频带信号时，中心频率之间需要满足约束条件为：f₂-f₁=f₃-f₂=Δf。Solution 1: Assuming that the center frequencies of the selected three sub-bands are f ₁ , f ₂ , f ₃ , and f ₃ >f ₂ >f ₁ , then when selecting three sub-band signals, the center frequencies need to satisfy constraints It is: f ₂ -f ₁ =f ₃ -f ₂ =Δf.

方案2：不选用方案1的约束条件时，即f₃>f₂>f₁，f₂-f₁≠f₃-f₂时，则可采用以下方法消除距离相位的影响：Scheme 2: When the constraints of Scheme 1 are not selected, that is, f ₃ >f ₂ >f ₁ , f ₂ -f ₁ ≠f ₃ -f ₂ , the following methods can be used to eliminate the influence of distance phase:

(1)利用相关星历信息获取电磁波真实传播距离R的粗估计值则估计误差 $ΔR = R - \hat{R} .$ (1) Use the relevant ephemeris information to obtain a rough estimate of the true propagation distance R of electromagnetic waves then the estimated error $ΔR = R - \hat{R} .$

(2)将选取的三个子频带信号的频谱分别进行搬移，使得其频谱中心频率均位于零频，然后分别利用匹配滤波实现脉冲压缩处理，可以得到三个子频带信号峰值点处的相位Φ_n(n=1,2,3)，利用分别对三个子频带信号峰值点的相位进行补偿，补偿峰值点处的距离相位为可得到补偿后三个子频带信号的相位：(2) The spectrums of the selected three sub-band signals are moved separately, so that the center frequency of the spectrum is located at zero frequency, and then the pulse compression process _is realized by using matched filtering respectively, and the phases at the peak points of the three sub-band signals can be obtained. n=1,2,3), using Compensate the phases of the peak points of the three sub-band signals respectively, and the distance phase at the compensated peak points is The phases of the three sub-band signals after compensation can be obtained:

${Φ Φ}_{n no}^{' '} = = angle the angle [[exp exp ((j j (({Φ Φ}_{n no} + + \frac{22 π π \overset{^^}{R R} {f f}_{n no}}{c c}))))]],, n no = = 1,2,3 1,2,3$

其中，定义angle[exp(j(α+2kπ))]=α,α∈[-π,π]，k为整数，此时子频带的中心频率需要满足：Among them, define angle[exp(j(α+2kπ))]=α,α∈[-π,π], k is an integer, At this time, the center frequency of the sub-band needs to satisfy:

因此该方案需要不断调整所选择的f₁，f₂，f₃的大小，直至满足上述约束条件。其中ΔR是电磁波真实传播距离R与其粗估计值之间的估计误差， $ΔR = R - \hat{R}$ c为光速。Therefore, this scheme needs to continuously adjust the selected sizes of f ₁ , f ₂ , and f ₃ until the above constraints are met. Where ΔR is the real propagation distance R of electromagnetic waves and its rough estimate The estimated error between $ΔR = R - \hat{R}$ c is the speed of light.

第三步：计算子频带信号之间的干涉相位。Step 3: Calculate the interference phase between the sub-band signals.

(1)如果采用第二步中方案1的约束条件，将选取的三个子频带信号的频谱分别进行搬移，使得其频谱中心频率均位于零频，然后分别利用匹配滤波实现脉冲压缩处理，可以得到三个子频带信号峰值点处的相位Φ_n(n=1,2,3)，然后计算子频带1与子频带2信号峰值点的干涉相位：Φ₁₂=angle[exp(jΦ₁)×exp(-jΦ₂)]，子频带2与子频带3信号峰值点的干涉相位：Φ₂₃=angle[exp(jΦ₂)×exp(-jΦ₃)]，其中定义angle[exp(j(α+2kπ))]=α,α∈[-π,π]，k为整数，对于方案1中的约束条件，干涉相位Φ₁₂，Φ₂₃分别满足：(1) If the constraints of scheme 1 in the second step are used, the spectrums of the selected three sub-band signals are moved separately so that the center frequencies of their spectrums are all located at zero frequency, and then the pulse compression processing is realized by matched filtering respectively, which can be obtained Phase Φ _n (n=1,2,3) at the peak points of the three sub-band signals, and then calculate the interference phase of the peak points of the sub-band 1 and sub-band 2 signals: Φ ₁₂ =angle[exp(jΦ ₁ )×exp( -jΦ ₂ )], the interference phase of the peak points of sub-band 2 and sub-band 3 signals: Φ ₂₃ =angle[exp(jΦ ₂ )×exp(-jΦ ₃ )], where angle[exp(j(α+2kπ ))]=α,α∈[-π,π], k is an integer, For the constraints in Scheme 1, the interferometric phases Φ ₁₂ and Φ ₂₃ respectively satisfy:

$\{\begin{matrix} {Φ Φ}_{1212} + + 22 Mπ Mπ = = 22 π π \frac{40.3 40.3 TEC TEC}{c c} ((\frac{11}{{f f}_{22} - - Δf Δf} - - \frac{11}{{f f}_{22}})) + + \frac{22 πRΔf πRΔf}{c c} \\ {Φ Φ}_{23 twenty three} + + 22 Mπ Mπ = = 22 π π \frac{40.3 40.3 TEC TEC}{c c} ((\frac{11}{{f f}_{22}} - - \frac{11}{{f f}_{22} + + Δf Δf})) + + \frac{22 πRΔf πRΔf}{c c} \end{matrix} - - - - - - ((11))$

其中M是一个整数，表示模糊数。Wherein M is an integer representing a fuzzy number.

(2)如果采用第二步中方案2的约束条件，经过对所选三个子频带信号频谱中心搬移至零频、匹配滤波及距离相位补偿后，根据得到的Φ'_n(n=1,2,3)计算子频带1与子频带2信号峰值点的干涉相位：Φ₁₂=angle[exp(jΦ'₁)×exp(-jΦ'₂)]，子频带2与子频带3信号峰值点的干涉相位：Φ₂₃=angle[exp(jΦ'₂)×exp(-jΦ'₃)]，其中定义angle[exp(j(α+2kπ))]=α,α∈[-π,π]，k为整数，对于方案2中的约束条件，干涉相位Φ₁₂、Φ₂₃分别满足：(2) If the constraints of scheme 2 in the second step are adopted, after shifting the spectrum center of the selected three sub-band signals to zero frequency, matched filtering and distance phase compensation, according to the obtained Φ' _n (n=1,2 ,3) Calculate the interferometric phase of the peak points of the sub-band 1 and sub-band 2 signals: Φ ₁₂ =angle[exp(jΦ' ₁ )×exp(-jΦ' ₂ )], the signal peak points of sub-band 2 and sub-band 3 Interference phase: Φ ₂₃ =angle[exp(jΦ' ₂ )×exp(-jΦ' ₃ )], where angle[exp(j(α+2kπ))]=α,α∈[-π,π] is defined, k is an integer, For the constraints in Scheme 2, the interferometric phases Φ ₁₂ and Φ ₂₃ respectively satisfy:

$\{\begin{matrix} {Φ Φ}_{1212} = = 22 π π \frac{40.3 40.3 TEC TEC}{c c} ((\frac{11}{{f f}_{11}} - - \frac{11}{{f f}_{22}})) - - \frac{22 πΔR πΔR (({f f}_{11} - - {f f}_{22}))}{c c} \\ {Φ Φ}_{23 twenty three} = = 22 π π \frac{40.3 40.3 TEC TEC}{c c} ((\frac{11}{{f f}_{22}} - - \frac{11}{{f f}_{33}})) - - \frac{22 πΔR πΔR (({f f}_{22} - - {f f}_{33}))}{c c} \end{matrix} - - - - - - ((22))$

第四步：根据公式（1）或（2）可以推导出求解电离层TEC值的公式，如下：Step 4: According to the formula (1) or (2), the formula for solving the TEC value of the ionosphere can be derived, as follows:

利用第三步获得的干涉相位Φ₁₂和Φ₂₃根据上式求得电离层TEC值，其中c为光速。Use the interference phases Φ ₁₂ and Φ ₂₃ obtained in the third step to obtain the ionospheric TEC value according to the above formula, where c is the speed of light.

由于子频带之间的干涉相位计算值有一定的误差，所以按照公式 $TEC = \frac{((f_{2} - f_{1}) Φ_{23} - (f_{3} - f_{2}) Φ_{12}) c}{2 π 40.3 ((f_{2} - f_{1}) (\frac{1}{f_{2}} - \frac{1}{f_{3}}) - (f_{3} - f_{2}) (\frac{1}{f_{1}} - \frac{1}{f_{2}}))}$ 计算得到的实际为电离层TEC的估计值但是本发明提出的两种方案克服了距离相位的影响既能兼顾TEC值的估计精度，又有效消除了距离相位的影响，通过多个子频带信号之间的相位干涉，解决了相位模糊问题，虽然干涉相位有一定的误差，仍然能够高精度地估计电离层TEC值。Since there is a certain error in the calculated value of the interferometric phase between the sub-bands, according to the formula $TEC = \frac{((f_{2} - f_{1}) Φ_{twenty three} - (f_{3} - f_{2}) Φ_{12}) c}{2 π 40.3 ((f_{2} - f_{1}) (\frac{1}{f_{2}} - \frac{1}{f_{3}}) - (f_{3} - f_{2}) (\frac{1}{f_{1}} - \frac{1}{f_{2}}))}$ The calculated value is actually the estimated value of the ionospheric TEC However, the two schemes proposed by the present invention overcome the influence of the range phase, can take into account the estimation accuracy of the TEC value, and effectively eliminate the influence of the range phase, and solve the phase ambiguity problem through the phase interference between multiple sub-band signals, although There is a certain error in the interferometric phase, but the ionospheric TEC value can still be estimated with high precision.

在保证载波频率之间达到一定差异的前提下，子频带信号的频谱可以重叠以增加子频带的带宽，便于提高后续对每个子频带进行匹配滤波处理后的输出峰值信噪比。Under the premise of ensuring a certain difference between the carrier frequencies, the spectrum of the sub-band signals can be overlapped to increase the bandwidth of the sub-bands, which facilitates the improvement of the output peak signal-to-noise ratio after subsequent matching filtering for each sub-band.

本发明未详细描述内容为本领域技术人员公知技术。The content not described in detail in the present invention is well known to those skilled in the art.

Claims

1. utilize a method for SAR Satellite observation ionized layer TEC value, it is characterized in that comprising the steps:

(1) at ground configuration SAR signal receiver for receiving the pulse signal of SAR satellite launch;

(2) from the SAR satellite pulse signal that step (1) receives, choose three sub-band signals, be respectively sub-band 1, sub-band 2 and sub-band 3, sub-band 1, sub-band 2 are respectively f with the carrier frequency of sub-band 3 three sub-band signals ₁, f ₂, f ₃, the carrier frequency of three sub-bands meets f ₃>f ₂>f ₁, and f ₂-f ₁=f ₃-f ₂=Δ f;

(3) frequency spectrum of three sub-band signals step (2) chosen is moved respectively, its spectral centroid frequency is made all to be positioned at zero-frequency, then utilize matched filtering to carry out process of pulse-compression to three sub-band signals respectively, obtain the phase place Φ at three sub-band signal peak point places _n, n=1,2,3;

(4) the phase place Φ at three the sub-band signal peak point places obtained according to step (3) _n, n=1,2,3, calculate the interferometric phase of sub-band 1 and sub-band 2 signal peak value point, computing formula is Φ ₁₂=angle [exp (j Φ ₁) × exp (-j Φ ₂)]; Calculate the interferometric phase of sub-band 2 and sub-band 3 signal peak value point, computing formula is Φ ₂₃=angle [exp (j Φ ₂) × exp (-j Φ ₃)]; Wherein defining angle [exp (j (α+2k π))]=α, α ∈ [-π, π], k is integer,

(5) the interferometric phase Φ that step (4) obtains is utilized ₁₂and Φ ₂₃solve ionized layer TEC value, computing formula is as follows:

T E C = \frac{((f_{2} - f_{1}) Φ_{23} - (f_{3} - f_{2}) Φ_{12}) c}{2 \times π \times 40.3 ((f_{2} - f_{1}) (\frac{1}{f_{2}} - \frac{1}{f_{3}}) - (f_{3} - f_{2}) (\frac{1}{f_{1}} - \frac{1}{f_{2}}))}

Wherein, c is the light velocity.

2. utilize a method for SAR Satellite observation ionized layer TEC value, it is characterized in that comprising the steps:

(2) from the SAR satellite pulse signal that step (1) receives, choose three sub-band signals, be respectively sub-band 1, sub-band 2 and sub-band 3, sub-band 1, sub-band 2 are respectively f with the carrier frequency of sub-band 3 three sub-band signals ₁, f ₂, f ₃, the carrier frequency of three sub-bands meets f ₃>f ₂>f ₁, f ₂-f ₁≠ f ₃-f ₂;

(4) relevant ephemeris information is utilized to obtain the rough estimate evaluation of electromagnetic wave true propagation distance R utilize respectively to the phase place Φ of three sub-band signal peak points that step (3) obtains _n, n=1,2,3, compensates, and can be compensated the phase place of rear three sub-band signals:

Φ_{n}^{'} = a n g l e [\exp (j (Φ_{n} + \frac{2 π \hat{R} f_{n}}{c}))], n = 1, 2, 3;

Wherein, definition angle [exp (j (α+2k π))]=α, α ∈ [-π, π], k are integer,

(5) judge whether the carrier frequency of three sub-bands meets following constraint condition:

\{\begin{matrix} - π < Φ_{2}^{'} + 2 π \frac{Δ R}{c} (f_{2} - f_{1}) < π \\ - π < Φ_{2}^{'} + 2 π \frac{Δ R}{c} (f_{2} - f_{3}) < π \end{matrix}

If meet, enter (6), otherwise re-execute step (2)-(5), wherein Δ R is electromagnetic wave true propagation distance R and its rough estimate evaluation between evaluated error, c is the light velocity;

(6) the phase place Φ ' at three the sub-band signal peak point places obtained according to step (4) _n, n=1,2,3, calculate the interferometric phase of sub-band 1 and sub-band 2 signal peak value point, computing formula is Φ ₁₂=angle [exp (j Φ ' ₁) × exp (-j Φ ' ₂)]; Calculate the interferometric phase of sub-band 2 and sub-band 3 signal peak value point, computing formula is Φ ₂₃=angle [exp (j Φ ' ₂) × exp (-j Φ ' ₃)]; Wherein defining angle [exp (j (α+2k π))]=α, α ∈ [-π, π], k is integer,

(7) the interferometric phase Φ that step (6) obtains is utilized ₁₂and Φ ₂₃solve ionized layer TEC value, computing formula is as follows:

T E C = \frac{((f_{2} - f_{1}) Φ_{23} - (f_{3} - f_{2}) Φ_{12}) c}{2 \times π \times 40.3 ((f_{2} - f_{1}) (\frac{1}{f_{2}} - \frac{1}{f_{3}}) - (f_{3} - f_{2}) (\frac{1}{f_{1}} - \frac{1}{f_{2}}))}

Wherein, c is the light velocity.