CN108776341A - Airborne synthetic aperture radar Doppler center offset calculation method - Google Patents
Airborne synthetic aperture radar Doppler center offset calculation method Download PDFInfo
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- CN108776341A CN108776341A CN201810422796.8A CN201810422796A CN108776341A CN 108776341 A CN108776341 A CN 108776341A CN 201810422796 A CN201810422796 A CN 201810422796A CN 108776341 A CN108776341 A CN 108776341A
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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
- G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
- G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
- G01S13/9094—Theoretical aspects
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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
- G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
- G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
- G01S13/9004—SAR image acquisition techniques
- G01S13/9011—SAR image acquisition techniques with frequency domain processing of the SAR signals in azimuth
-
- 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
- G01S7/41—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section
- G01S7/418—Theoretical aspects
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- Remote Sensing (AREA)
- Radar, Positioning & Navigation (AREA)
- Physics & Mathematics (AREA)
- Computer Networks & Wireless Communication (AREA)
- General Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Signal Processing (AREA)
- Radar Systems Or Details Thereof (AREA)
Abstract
The invention discloses a method for calculating Doppler center offset of an airborne synthetic aperture radar, which comprises the steps of firstly reading SAR detection echo data, carrying out azimuth FFT (fast Fourier transform) and obtaining a Doppler power spectrum; then, performing wavelet analysis filtering on the Doppler power spectrum, and determining the Doppler center frequency based on the echo data; reading airborne SAR inertial navigation data and radar performance parameters, and calculating Doppler center frequency based on the inertial navigation data; and finally, determining Doppler center shift according to the Doppler center frequency based on the echo data and the Doppler center frequency based on the inertial navigation data. The calculation method is simple and effective, improves the calculation precision of the Doppler center offset, and provides favorable conditions for future marine environment application.
Description
Technical field
The present invention relates to microwave remote sensing techniques, deviate and count more particularly to a kind of airborne synthetic aperture radar Doppler center
Calculation method.
Background technology
In synthetic aperture radar (Synthetic Aperture Radar, SAR) detection data, doppler centroid
The phase information for representing detection echo directly affects the target location after signal noise ratio (snr) of image, azimuth ambiguity signal ratio and imaging,
It is mainly used in radar imagery field.In recent years, with the raising of carrying platform measuring apparatus measuring speed and precision, Ren Men
It is found when processing SAR detection echo datas, the doppler centroid and marine exploration echo that platform motion state data calculates
Always there are particular differences in the doppler centroid that data calculate, and start to recognize that this species diversity may be from Yu Haiyang table
The influence of layer movement.Based on this it is assumed that scholars are more by SAR marine explorations echo data and the calculating of platform motion state data
General Le centre frequency, which has differences, is defined as Doppler center offset (Doppler Centroid Shift, DCS), and then carries out
The ocean environment parameters inverting such as Ocean Wind-field, sea surface velocities field is studied.
Currently, in terms of doppler centroid calculates research, for platform motion state data, Raney etc. and
[Bezvesilniy O O, the Vavriv D M.Synthetic aperture radar systems for such as Bezvesilniy
small aircrafts:Data processing approaches[M].INTECH Open Access Publisher,
2012, p465-498.] spaceborne, carried SAR doppler centroid computational methods are proposed respectively.For detection echo data,
The different phase that researcher is handled according to detection echo data, it is proposed that a variety of doppler centroid computational methods
[Herland E A.Seasat SAR processing at the Norwegian Defence Research
Establishment(design and operation of a digital process)[J].ESA Appl.of
Remote Sensing Data on the Continental Shelf p 247-253(SEE N 82-14553 05-43),
1981.].But the research for Doppler center calculations of offset method is still fewer, only Hansen etc. utilizes Envisat
ASAR detection datas calculate Doppler center offset, and analyzed handling error [Hansen M W, Collard F,
Dagestad K,et al.Retrieval of sea surface range velocities from Envisat ASAR
Doppler centroid measurements[J].IEEE Transactions on Geoscience and Remote
Sensing,2011,49(10):3582-3592.].However, it is more not to be suitable for carried SAR mainly for satellite-borne SAR for this method
The general calculating for strangling off-centring, and there is the low deficiencies of computational accuracy.
Invention content
Technical problem solved by the invention is to provide a kind of airborne synthetic aperture radar Doppler center calculations of offset
Method.
Realize that the technical solution of the object of the invention is：A kind of airborne synthetic aperture radar Doppler center calculations of offset
Method includes the following steps：
Step 1 reads SAR detection echo datas, carries out orientation FFT, obtains Doppler power spectra；
Step 2 carries out wavelet analysis filtering to Doppler power spectra, determines the Doppler center frequency based on echo data
Rate；
Step 3 reads carried SAR inertial navigation data and radar performance parameter, calculates the Doppler based on inertial guidance data
Centre frequency；
Step 4, the basis doppler centroid based on echo and the doppler centroid based on inertial guidance data, determine
Doppler center deviates.
Compared with prior art, the present invention its remarkable advantage is：1) present invention utilizes the Doppler center frequency based on echo
Rate and doppler centroid based on inertial navigation calculate Doppler center offset, and method is simple and effective；2) present invention is in Doppler
The influence of wavelet analysis removal noise is added in spectrum analysis, improves computational accuracy；3) present invention solves the how general of carried SAR
Off-centring computational problem is strangled, advantage is provided for following marine environment application.
Description of the drawings
Fig. 1 is carried SAR detection geometrical relationship figure of the present invention.
Fig. 2 is the sample calculation figure of doppler centroid of the present invention, wherein figure (a) is the complete polarization of a pulse train
Echo data arranges, and figure (b) is the VV polarization detection echoes read, and figure (c) is the detection echo after FFT, and figure is (d) Doppler
Power spectrum.
Fig. 3 is the posture information figure of detection data 20120726-011 of the present invention, wherein figure (a) is carrier aircraft flight detection
Pitch angle, yaw angle and roll angle, figure (b) is carrier aircraft flying speed, and figure (c) is carrier aircraft flying height.
Fig. 4 is the flow chart of airborne synthetic aperture radar Doppler center calculations of offset method of the present invention.
Specific implementation mode
In the following with reference to the drawings and specific embodiments, the present invention program is further described.
Airborne synthetic aperture radar Doppler center calculations of offset method, includes the following steps：
Step 1 reads SAR detection echo datas, carries out orientation FFT, obtains Doppler power spectra.
If target scene is uniformly (such as ocean, meadow), backscattering coefficient ξ (t, r) meets Gaussian Profile, and orientation is returned
Wave signal is represented by：
In formula, t indicates that receiving time, r indicate detection oblique distance, ha(t, r) is orientation system response function.Above formula is become
Frequency domain is changed to, orientation power spectrum (also known as Doppler power spectra) is represented by：
In formula, f indicates that frequency, r indicate detection oblique distance, ξ0Indicate backscattering coefficient, Ha(f, r) indicates orientation system
Receptance function.
Step 2 carries out wavelet analysis filtering to Doppler power spectra, determines the Doppler center frequency based on echo data
Rate.
Wavelet basis function is normally defined：
In formula, ψa,b(x) be wavelet mother function ψ (x) by Pan and Zoom as a result, a is scale factor, b be scaling because
Son, x indicate independent variable.
Wavelet function choice is problem in science important in wavelet analysis application study.In SAR data processing, it has been found that
Mexican-Hat mother wavelet functions have arbitrary order regularity, while have preferable time domain and frequency localization characteristic and
Signal energy concentrates characteristic, is conducive to remove influence of the noise to Doppler power spectra.Mexican-Hat wavelet functions are Gauss
The second dervative of function, is represented by：
In formula, ψ (x) indicates that wavelet mother function, x indicate independent variable.
Step 3 reads carried SAR inertial navigation data and radar performance parameter, calculates the Doppler based on inertial guidance data
Centre frequency.
The detection geometrical relationship constituted when carried SAR attitudes vibration is as shown in Figure 1.Carrier aircraft is along x-axis with speed V in H high
Degree is parallel to plane (xoy) and carries out survey mission.Radar antenna is directed towardUse vectorIt indicates,For antenna direction
The tangent line of figure and plane (xoy), α is pitch angle, and β is yaw angle, (xR,yR) it is direction of the antenna beam center to detection target
Point.
At this point, coordinate a little is directed toward in antenna beam center to ground is：
Then doppler centroid calculation formula is：
In formula, λ indicates that radar wavelength, V indicate that carrying platform flying speed, r indicate detection oblique distance, xRIndicate antenna beam
It is directed toward the projection in x-axis,Wherein, H indicates to carry
Machine flying height, α indicate that pitch angle, β indicate yaw angle.
Step 4, the doppler centroid based on echo and doppler centroid based on inertial guidance data are made it is poor, really
Determine Doppler center offset：
In formula, fdcsIndicate Doppler center offset,Indicate the doppler centroid calculated based on echo data,Indicate the doppler centroid calculated based on inertial guidance data.
In order to verify the practicability of this patent, is carried out using carried SAR detection data and calculate validity check.
When the flight detection time of carried SAR being 26 days 14 July in 2012 to 21, carrier aircraft flying height is 3000m, is visited
It is 1.5m, 3m to survey resolution ratio, and radar center incidence angle is 30 °, 40 °.Inertial navigation parameter and performance indicator, carried SAR work
Parameter and indexes are respectively as shown in table 1,2.
1 HJG-5 inertial navigation systems output parameter of table and performance indicator
2 carried SAR running parameter of table and index
The detection echo of carried SAR is full polarimetric SAR data, and the present embodiment is calculated using VV polar echo data in Doppler
Frequency of heart.
This patent introduces the computational methods of carried SAR Doppler center offset by taking detection data 20120726-011 as an example.
First, doppler centroid is calculated using detection echo data.It reads carried SAR and detects echo data, a pulse train
The arrangement of complete polarization echo data as shown in Fig. 2 (a), amplitude significant changes part is echo-signal in figure, and polarization mode is successively
For HH, HV, VH and VV, rest part is noise.VV polar echos data (Fig. 2 (b), 512 × 512) are therefrom read, orientation is made
To FFT, shown in gained image such as Fig. 2 (c), light is that region is directed toward at antenna radiation pattern center in figure.By the detection after FFT
Echo is superimposed along orientation, obtains Doppler power spectra (Fig. 2 (d), thin solid-line curve), recycles Mexican-Hat wavelet functions
Filtering, smooth Doppler power spectra (Fig. 2 (d), thick imaginary curve) are final more according to the determination of Doppler power spectra energy central position
General Le centre frequencyAs a result it is 61.5Hz.
Secondly, doppler centroid is calculated using inertial navigation data.The thunder that detection data 20120726-011 is used
It is 40 ° up to incidence angle, the posture informations such as pitch angle, yaw angle, flying speed and height, as shown in Figure 3.
By pitch angle, yaw angle, flying speed, height and radar incidence angle input calculation formula (6) and (8), calculate
Doppler centroidAs a result it is 46.2Hz.
Then, the Doppler center offset of detection data is calculated.UsingIt subtractsCalculate Doppler center offset
fdcs, numerical value 15.3Hz.
As procedure described above, we calculate the Doppler center offset of 9 groups of detection datas on July 26, and with CDOP (C-
Band Doppler Shift) physical geography module function result of calculation is as comparison true value, result of calculation such as 3 institute of table
Show.
3 Doppler center calculations of offset result comparison (unit of table：Hz)
As shown in Table 3,9 groups of detection data Doppler center calculations of offset miss absolute value of the difference and are respectively less than 2Hz, and root mean square misses
Difference is 1.4Hz.It, can by CDOP physical geography module functions result of calculation it is found that when the error of Doppler center offset is less than 2Hz
Meet marine environment application demand.Comparison the result shows that, this patent propose Doppler center calculations of offset method it is effective,
Marine Environmental Elements inversion accuracy requirement can be met.
Claims (5)
1. a kind of airborne synthetic aperture radar Doppler center calculations of offset method, which is characterized in that include the following steps：
Step 1 reads SAR detection echo datas, carries out orientation FFT, obtains Doppler power spectra；
Step 2 carries out wavelet analysis filtering to Doppler power spectra, determines the doppler centroid based on echo data；
Step 3 reads carried SAR inertial navigation data and radar performance parameter, calculates the Doppler center based on inertial guidance data
Frequency；
Step 4, the basis doppler centroid based on echo data and the doppler centroid based on inertial guidance data, determine
Doppler center deviates.
2. airborne synthetic aperture radar Doppler center calculations of offset method according to claim 1, which is characterized in that step
Rapid 1 determines that the formula of Doppler power spectra is：
In formula, Sa(f, r) indicates that Doppler power spectra, f indicate that frequency, r indicate detection oblique distance, ξ0Indicate backscattering coefficient, Ha
(f, r) indicates orientation system response function.
3. airborne synthetic aperture radar Doppler center calculations of offset method according to claim 1, which is characterized in that step
Mexican-Hat wavelet functions are used in the filtering of 2 wavelet analysis, formula is：
In formula, ψ (x) indicates that wavelet mother function, x indicate independent variable.
4. airborne synthetic aperture radar Doppler center calculations of offset method according to claim 1, which is characterized in that step
3 calculating doppler centroids formula be：
In formula,Indicate that the doppler centroid based on inertial guidance data, λ indicate that radar wavelength, V indicate carrying platform flight
Speed, r indicate detection oblique distance, xRIndicate that antenna beam is directed toward the projection in x-axis,Wherein, H indicates that carrier aircraft flying height, α indicate
Pitch angle, β indicate yaw angle.
5. airborne synthetic aperture radar Doppler center calculations of offset method according to claim 1, which is characterized in that step
4, which calculate the formula that Doppler centers deviate, is：
In formula, fdcsIndicate Doppler center offset,Indicate the doppler centroid calculated based on echo data,Table
Show the doppler centroid calculated based on inertial guidance data.
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Cited By (4)
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| CN111381217A (en) * | 2020-04-01 | 2020-07-07 | 上海无线电设备研究所 | Missile-borne SAR motion compensation method based on low-precision inertial navigation system |
| CN113484860A (en) * | 2021-07-06 | 2021-10-08 | 中国科学院空天信息创新研究院 | SAR image ocean front detection method and system based on Doppler center anomaly |
| CN114089339A (en) * | 2022-01-14 | 2022-02-25 | 南京天朗防务科技有限公司 | Real-time processing and displaying system and method for unmanned aerial vehicle-mounted SAR image |
| CN114545390A (en) * | 2021-12-31 | 2022-05-27 | 北京航天自动控制研究所 | Ground detection attitude determination method for radar carried by aircraft |
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
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| CN114545390A (en) * | 2021-12-31 | 2022-05-27 | 北京航天自动控制研究所 | Ground detection attitude determination method for radar carried by aircraft |
| CN114089339A (en) * | 2022-01-14 | 2022-02-25 | 南京天朗防务科技有限公司 | Real-time processing and displaying system and method for unmanned aerial vehicle-mounted SAR image |
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Application publication date: 20181109 |