CN108931761A - Ionosphere calibrating method and system based on satellite-borne synthetic aperture radar - Google Patents
Ionosphere calibrating method and system based on satellite-borne synthetic aperture radar Download PDFInfo
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- CN108931761A CN108931761A CN201810572836.7A CN201810572836A CN108931761A CN 108931761 A CN108931761 A CN 108931761A CN 201810572836 A CN201810572836 A CN 201810572836A CN 108931761 A CN108931761 A CN 108931761A
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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
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/40—Means for monitoring or calibrating
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- 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
- G01S7/4052—Means for monitoring or calibrating by simulation of echoes
-
- 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
- G01S7/4052—Means for monitoring or calibrating by simulation of echoes
- G01S7/406—Means for monitoring or calibrating by simulation of echoes using internally generated reference signals, e.g. via delay line, via RF or IF signal injection or via integrated reference reflector or transponder
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- Computer Networks & Wireless Communication (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Radar, Positioning & Navigation (AREA)
- Remote Sensing (AREA)
- Position Fixing By Use Of Radio Waves (AREA)
- Radar Systems Or Details Thereof (AREA)
Abstract
A kind of ionosphere calibrating method and system, this method based on satellite-borne synthetic aperture radar include：Emit double frequency linear FM signal simultaneously same target to be imaged using satellite-borne synthetic aperture radar, and receives double frequency echo-signal；Distance is carried out respectively to the double frequency echo-signal to compress to pulse, obtains the pulse pressure peak position of double frequency echo-signal；Two-frequency signal Range Profile offset deviation is determined according to the pulse pressure peak position of double frequency echo-signal；Ionized layer TEC is acquired according to the relationship of two-frequency signal Range Profile offset deviation and ionized layer TEC.Further provide the ionosphere calibration system for realizing the above method.The present invention uses SAR Whole frequency band echo-signal, establishes the mathematical model between double frequency echo-signal Range Profile offset deviation and ionized layer TEC, improves ionized layer TEC measurement accuracy.
Description
Technical field
The present invention relates to Ionospheric measurement technical field more particularly to a kind of ionospheres based on satellite-borne synthetic aperture radar
Calibrating method and system.
Background technique
Ionosphere is the region that partial ionization state is in earth atmosphere, is extended always since about 50km from the ground
To about 1000km, additional delay is generated to the electromagnetic wave signal passed through, signal is caused to generate amplitude and phase distortion.For
Navigation system will affect navigation accuracy, for satellite-borne synthetic aperture radar (SAR) system, will lead to SAR image quality variation,
Signal frequency is lower, more serious by ionosphere effect.In general, work is in frequency in the 2GHz system (TanDEM of such as L-band
The BIOMASS system and Beidou Navigation System etc. of system and pattern-band) it requires to calibrate ionosphere and compensated.
For Spaceborne SAR System by ionosphere effect, people begin to focus on how to correct and compensate ionosphere effect, a side
Face is based on ionosphere feature and measures to ionized layer TEC (Ionospheric ions concentration total content), and then realizes ionosphere effect
Correction, on the other hand, people are based on satellite-borne SAR echo-signal and realize ionized layer TEC estimation, and then realize that ionosphere effect is mended
It repays.Based on ionosphere feature to ionized layer TEC measure under normal circumstances dependent on ionospheric observatory net (such as GPS system,
Dipper system, meridian engineered system etc.), the object of service is mainly space wave monitoring and satellite navigation, utilizes the party
Method obtains ionized layer TEC and is corrected on satellite-borne SAR influence, and timeliness and precision are difficult to meet satellite-borne SAR ionosphere corrections
Demand.The mathematics that ionized layer TEC estimation influences SAR echo signal using ionized layer TEC is realized based on satellite-borne SAR echo-signal
Model realizes ionized layer TEC estimation, the ionized layer TEC pair estimated using this method by carrying out data processing to echo-signal
In SAR signal processing there is real-time substantially and be SAR propagation path ionized layer TEC, precision is higher, controllability is stronger, compares
Meet ionosphere scaling requirements.
Ionosphere has effect of dispersion, and different frequency signals is caused by ionosphere effect difference in linear FM signal
Linear FM signal pulse width changes, the linear corresponding relation between pulse width variation amount Δ T and ionized layer TEC
For：
Wherein, fcFor linear FM signal centre frequency, BrFor signal bandwidth.
Therefore, Δ T can be obtained by comparing the time width of radar emission signal initial time width and echo-signal
Estimated value, to be finally inversed by ionized layer TEC.
But the satellite-borne SAR ionosphere calibration side compared based on transmitting signal and receives echo-signal pulse temporal width
Case has the following disadvantages：
1) it necessarily requires SAR imaging region that there is strong point scatterer, is otherwise difficult accurately to obtain the pulse width for receiving signal.
2) linear FM signal pulse envelope is unlikely to be ideal rectangular envelope, certainly exists rising edge and failing edge,
It will lead to pulse width measuring error.
3) measurement of pulse signal width is limited by signal sampling rate, and sample rate is higher, and pulse width measuring precision is higher,
Corresponding TEC estimated accuracy is also higher, still, is limited by hardware and data storage capacity, and data sampling rate can not be very high.
4) pulse width is affected by noise leads to measurement error, even if being measured based on strong point scatterer, strong point scatterer week
Other point targets and background enclosed also will affect the pulse width of linear FM signal, and then lead to pulse width measuring error.
To sum up, the satellite-borne SAR ionosphere calibration pair based on transmitting signal and the variation of receives echo-signal pulse temporal width
The requirement of satellite-borne SAR radar performance is very high, more to imaging region point target requirement also very high and error source.
In addition, can also realize that ionized layer TEC is estimated based on the sub- Range Profile offset of same linear FM signal lower sideband, but
It is that the satellite-borne SAR ionosphere calibrating method based on sub- Range Profile offset deviation has the drawback that every sub- Range Profile maximum can only benefit
With 50% bandwidth, sub- Range Profile resolution ratio is reduced, pulse pressure position solving precision is reduced for full bandwidth image, into
And ionized layer TEC estimated accuracy is influenced, measurement accuracy is limited.
Summary of the invention
In view of this, the main purpose of the present invention is to provide a kind of, the ionosphere based on satellite-borne synthetic aperture radar is calibrated
Method and system, at least be partially solved at least one of above-mentioned the technical issues of referring to.
To achieve the above object, technical scheme is as follows：
As one aspect of the present invention, a kind of ionosphere calibrating method based on satellite-borne synthetic aperture radar is provided, is wrapped
Include following steps：
Step A：Using satellite-borne synthetic aperture radar simultaneously emit double frequency linear FM signal come to same target carry out at
Picture, and receive double frequency echo-signal；
Step B：Distance is carried out respectively to the double frequency echo-signal to compress to pulse, obtains the pulse pressure of double frequency echo-signal
Peak position；
Step C：Two-frequency signal Range Profile offset deviation is determined according to the pulse pressure peak position of the double frequency echo-signal；
Step D：According to the relationship of the two-frequency signal Range Profile offset deviation and ionized layer TEC, the ionosphere is acquired
TEC。
It wherein, further include adjusting the distance to carry out distance to data interpolating to pulse compression result to obtain double frequency time in step B
The step of pulse pressure peak position of wave signal.
Wherein, the distance to the multiple of data interpolating be 2nTimes, wherein n is between 5~9.
Wherein, in step D, the relationship of the two-frequency signal Range Profile offset deviation and ionized layer TEC is expressed as by following formula：
Wherein, Δ r is two-frequency signal Range Profile offset deviation；fc1And fc2For double frequency linear FM signal carrier frequency；C is the light velocity；
Δt1For carrier frequency fc1The signal time delay that signal generates；Δt2For carrier frequency fc2The signal time delay that signal generates.
As another aspect of the present invention, a kind of ionosphere calibration system based on satellite-borne synthetic aperture radar is provided,
Including：
Satellite-borne synthetic aperture radar comprising：
Transmitter, for generating double frequency linear FM signal and being transmitted to antenna；
Antenna, for emitting the double frequency linear FM signal, and double frequency echo-signal of the reception after target reflects；
And
Receiver, for being amplified to the received double frequency echo-signal of antenna and being transmitted to data processing unit；
And
Data processing unit, the processing for being followed the steps below to the double frequency echo-signal：
Distance is carried out respectively to the double frequency echo-signal to compress to pulse, obtains the pulse pressure peak value position of double frequency echo-signal
It sets；
Two-frequency signal Range Profile offset deviation is determined according to the pulse pressure peak position of the double frequency echo-signal：
According to the relationship of the two-frequency signal Range Profile offset deviation and ionized layer TEC, the ionized layer TEC is acquired.
Based on the above-mentioned technical proposal, the beneficial effects of the present invention are：
1) pulse width is solved from time domain be transformed into image area (Range compress) measurement pulse pressure peak point position, it is on the one hand logical
It crosses and substantially increases signal-to-noise ratio apart from pulse pressure, reduce the influence of noise, on the other hand avoid what irrational rectangular envelope generated
Pulse width solves error.
2) full bandwidth Range Profile is used, for sub- Range Profile, bandwidth is doubled, and signal-to-noise ratio increases after pulse pressure,
Peak value point position solving precision improves after pulse pressure.
3) by peak value point position after data interpolating measurement pulse pressure, peak value point position solving precision after pulse pressure is greatly improved,
And it is not limited by device hardware sample rate.
Detailed description of the invention
Fig. 1 is ionosphere calibrating method flow chart of the embodiment of the present invention based on satellite-borne synthetic aperture radar；
Fig. 2 (a) is that the embodiment of the present invention carries out pulse pressure result schematic diagram after 10 times of interpolation；
Fig. 2 (b) is that progress of the embodiment of the present invention 512 is interpolated rear pulse pressure result schematic diagram；
Fig. 3 is the relationship of peak point of embodiment of the present invention position precision Yu interpolation multiple and signal-to-noise ratio；
Fig. 4 is ionosphere calibrating method schematic diagram of the embodiment of the present invention based on satellite-borne synthetic aperture radar.
Specific embodiment
To make the objectives, technical solutions, and advantages of the present invention clearer, below in conjunction with specific embodiment, and reference
Attached drawing, the present invention is described in further detail.
In one embodiment of this invention, a kind of ionosphere calibrating method based on satellite-borne synthetic aperture radar is provided,
As shown in Figure 1, including the following steps：
Step A：Using satellite-borne synthetic aperture radar simultaneously emit double frequency linear FM signal come to same target carry out at
Picture, and receive double frequency echo-signal.
In this step, which is respectively carrier frequency fc1Signal and carrier frequency fc2Signal, wherein：
Carrier frequency fc1Signal generate signal time delay be：
Wherein R be SAR between target at a distance from, c is the light velocity,For ionosphere additional time delay.
Carrier frequency fc2Signal generate signal time delay be：
Step B：It carries out distance respectively to double frequency echo-signal to compress to pulse, to obtain the pulse pressure peak of double frequency echo-signal
It is worth position.
This step is transformed into image area by Range compress to measure pulse pressure peak point position, and distance compresses skill to pulse
Art is common sense well known in the art, and therefore not to repeat here, by substantially increasing signal-to-noise ratio apart from pulse pressure, reduces the shadow of noise
It rings.
Preferably, the present embodiment, which improves peak point after pulse is compressed to the method for data interpolating using distance, solves essence
Degree.Fig. 2 (a) and Fig. 2 (b) show pulse pressure result schematic diagram (when system bandwidth 36MHz) after 10 times of interpolation and 512 times of interpolation,
As can be seen that peak value point position solving precision after pulse pressure can be greatly improved by carrying out interpolation to data.
Certainly, peak point position solving precision will not infinitely be improved with the raising of interpolation multiple, with signal-to-noise ratio and
Quantizing noise after interpolation has relationship, is illustrated in figure 3 the pass of peak point position solving precision Yu interpolation multiple and signal-to-noise ratio
System.General interpolation multiple is 2nTimes, wherein n is between 5~9.
Step C：Two-frequency signal Range Profile offset deviation Δ r is determined according to the pulse pressure peak position of double frequency echo-signal.
Peak point solves essence after the solving precision of two-frequency signal Range Profile offset deviation Δ r depends on pulse compression in this step
Degree, can solve double frequency Range Profile offset deviation Δ r by the high precision peak point position after interpolation, this is the known normal of this field
Know, therefore not to repeat here.
Step D：According to the relationship of the two-frequency signal Range Profile offset deviation and ionized layer TEC, the ionosphere is acquired
TEC。
As shown in Figure 4, it is known that two-frequency signal Range Profile is with respect to offset deviation：
Above formula shows that two-frequency signal Range Profile offset deviation and ionized layer TEC are linearly related.Known two-frequency signal carrier frequency fc1,
fc2With double frequency Range Profile offset deviation Δ r, so that it may estimate ionized layer TEC.
In another embodiment of the invention, a kind of ionosphere calibration system based on satellite-borne synthetic aperture radar is provided,
Including satellite-borne synthetic aperture radar and data processing unit, wherein the satellite-borne synthetic aperture radar includes：Transmitter, for generating
Double frequency linear FM signal is simultaneously transmitted to antenna；Antenna for emitting double frequency linear FM signal, and is received and is reflected through target
Double frequency echo-signal afterwards；And receiver, for being amplified to the received double frequency echo-signal of antenna and being transmitted to data
Processing unit；The data processing unit, the processing for being followed the steps below to double frequency echo-signal：To double frequency echo-signal into
Line-spacing descriscent pulse compression, obtains the pulse pressure peak position of double frequency echo-signal；According to the pulse pressure peak value position of double frequency echo-signal
Set determining two-frequency signal Range Profile offset deviation；According to the relationship of two-frequency signal Range Profile offset deviation and ionized layer TEC, ionization is acquired
Layer TEC.
In conclusion the present invention establishes the mathematical model between the difference and ionized layer TEC of double-frequency pulse signal group delay,
A kind of effective, high-precision satellite-borne SAR ionosphere calibrating method is developed；It is compressed, is improved by double-frequency pulse signal distance
Signal-to-noise ratio, while eliminating the influence of non-ideal rectangular envelope；Using SAR Whole frequency band echo-signal, reduce since bandwidth reduces
The decline of the reduction of caused signal-to-noise ratio and peak value of pulse point position solving precision.
Particular embodiments described above has carried out further in detail the purpose of the present invention, technical scheme and beneficial effects
Describe in detail bright, it should be understood that the above is only a specific embodiment of the present invention, is not intended to restrict the invention, it is all
Within the spirit and principles in the present invention, any modification, equivalent substitution, improvement and etc. done should be included in protection of the invention
Within the scope of.
Claims (5)
1. a kind of ionosphere calibrating method based on satellite-borne synthetic aperture radar, includes the following steps：
Step A：Emit double frequency linear FM signal simultaneously same target to be imaged using satellite-borne synthetic aperture radar, and
Receive double frequency echo-signal；
Step B：Distance is carried out respectively to the double frequency echo-signal to compress to pulse, obtains the pulse pressure peak value of double frequency echo-signal
Position；
Step C：Two-frequency signal Range Profile offset deviation is determined according to the pulse pressure peak position of the double frequency echo-signal；
Step D：According to the relationship of the two-frequency signal Range Profile offset deviation and ionized layer TEC, the ionized layer TEC is acquired.
2. ionosphere calibrating method according to claim 1, which is characterized in that further include adjusting the distance to pulse in step B
Compression result carries out the step of distance obtains the pulse pressure peak position of double frequency echo-signal to data interpolating.
3. ionosphere calibrating method according to claim 2, which is characterized in that the distance is to the multiple of data interpolating
2nTimes, wherein n is between 5~9.
4. ionosphere calibrating method according to claim 1, which is characterized in that in step D, the two-frequency signal Range Profile
Offset deviation and the relationship of ionized layer TEC are expressed as by following formula：
Wherein, Δ r is two-frequency signal Range Profile offset deviation；fc1And fc2For double frequency linear FM signal carrier frequency；C is the light velocity；Δt1
For carrier frequency fc1The signal time delay that signal generates；Δt2For carrier frequency fc2The signal time delay that signal generates.
5. a kind of ionosphere calibration system based on satellite-borne synthetic aperture radar, including：
Satellite-borne synthetic aperture radar comprising：
Transmitter, for generating double frequency linear FM signal and being transmitted to antenna；
Antenna, for emitting the double frequency linear FM signal, and double frequency echo-signal of the reception after target reflects；And
Receiver, for being amplified to the received double frequency echo-signal of antenna and being transmitted to data processing unit；And
Data processing unit, the processing for being followed the steps below to the double frequency echo-signal：
Distance is carried out respectively to the double frequency echo-signal to compress to pulse, obtains the pulse pressure peak position of double frequency echo-signal；
Two-frequency signal Range Profile offset deviation is determined according to the pulse pressure peak position of the double frequency echo-signal：
According to the relationship of the two-frequency signal Range Profile offset deviation and ionized layer TEC, the ionized layer TEC is acquired.
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Cited By (3)
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| CN113687313A (en) * | 2021-07-20 | 2021-11-23 | 西安空间无线电技术研究所 | Satellite-borne X + S double-frequency SAR system based on double-reflector antenna |
| CN115580343A (en) * | 2022-11-24 | 2023-01-06 | 北京九天微星科技发展有限公司 | Low-orbit satellite autonomous orbit control method, device and system |
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| CN113687313A (en) * | 2021-07-20 | 2021-11-23 | 西安空间无线电技术研究所 | Satellite-borne X + S double-frequency SAR system based on double-reflector antenna |
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