CN106093870B - The SAR-GMTI clutter suppression methods of hypersonic aircraft descending branch - Google Patents
The SAR-GMTI clutter suppression methods of hypersonic aircraft descending branch Download PDFInfo
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Abstract
The invention discloses a kind of SAR-GMTI clutter suppression methods of hypersonic aircraft descending branch, thinking is：The radar motion geometrical model of hypersonic aircraft descending branch is established, wherein radar includes N number of antenna channels, and P is radar any one moving target in the scene, and the instantaneous oblique distance between n-th of antenna channels and moving target P is expressed as Rn(ta), obtain the echo-signal in N number of displaced phase center channel；It obtains the echo-signal in N number of displaced phase center channel and carries out phase compensation after frequency domain-orientation time-domain representation form after Range compress, obtain N number of displaced phase center channel after phase compensation apart from frequency domain-orientation time domain echo-signal, calculate N number of displaced phase center channel echo-signal of range-Dopler domain, the noise signal of the echo-signal and range-Dopler domain of the moving target P of range-Dopler domain successively again, the optimum weight coefficient vector for calculating space-time adaptive clutter recognition, finally obtains the echo-signal of moving target P after clutter recognition.
Description
Technical Field
The invention belongs to the technical field of radars, and particularly relates to a synthetic aperture radar-ground moving target detection (SAR-GMTI) clutter suppression method for a descending section of a hypersonic aerocraft, which is suitable for suppressing SAR-GMTI clutter by the descending section of the hypersonic aerocraft so as to finish the detection purpose of a moving target in SAR imaging.
Background
The Synthetic Aperture Radar (SAR) imaging technology was originally developed in the 50 s of the 20 th century, and can simultaneously provide high two-dimensional resolution, including high distance resolution and high azimuth resolution, so as to image a radar target; the synthetic aperture radar-ground moving target detection (SAR-GMTI) combines the clutter suppression technology, can complete the detection of the ground moving target under the influence of strong ground clutter, and has important significance in the fields of battlefield reconnaissance, remote sensing detection and the like.
The existing research is based on satellite-borne or airborne synthetic aperture radar/synthetic aperture radar-ground moving target detection (SAR/SAR-GMTI), the airborne SAR has low flying height, low flying speed and smaller detection range; the space-borne SAR has high flying height, needs larger transmitting energy to detect a ground target, is difficult to meet the transmitting energy requirement required by the space-borne SAR-GMTI due to the limit of the transmitting power of an actual device, and is easy to be detected by an enemy and implement interference or attack due to the fact that the orbit of a satellite is relatively fixed.
In view of the above disadvantages of the airborne SAR and the satellite-borne SAR, the problem of imaging of a synthetic aperture radar (HSV-borne SAR) carried by a hypersonic vehicle (HSV) is studied, and the hypersonic vehicle (HSV) can surround the earth for a circle within 2 hours and has the advantages of high speed and high maneuverability, so that the hypersonic vehicle is difficult to reconnoiter and attack; in addition, hypersonic vehicles (HSV) typically fly in the near-air range, requiring less energy to detect ground targets than space-borne radars; in addition, the hypersonic flight vehicle (HSV) is expected to be used as a weapon platform for performing long-distance battlefield reconnaissance, fire control and precise combat missions, and thus has great research value. However, unlike the conventional platform, the radar in the hypersonic aircraft (HSV) has a complex motion state, usually has a jump motion state, and the acceleration time in the jump phase is usually very short, and only occupies 1/6 or 1/9 of the whole jump phase, so that the synthetic aperture radar (HSV-borne SAR) carried by the hypersonic aircraft (HSV) can be set to work only in the descent phase, and can face strong ground clutter when entering the descent phase, thereby bringing difficulty to detection of a moving target and subsequent tracking, imaging and identification.
Disclosure of Invention
Aiming at the vacancy in the research field and the defects of the research technology, the invention aims to provide the SAR-GMTI clutter suppression method for the descending segment of the hypersonic aerocraft, and the SAR-GMTI clutter suppression method for the descending segment of the hypersonic aerocraft can better solve the influence of strong clutter on SAR-GMTI when synthetic aperture radar (HSV-borne SAR) carried by the hypersonic aerocraft (HSV) faces the descending segment.
In order to achieve the above purpose, the invention is realized by adopting the following scheme.
A SAR-GMTI clutter suppression method for a descending section of a hypersonic aircraft comprises the following steps:
step 1, establishing a radar motion geometric model of a descending section of a hypersonic aircraft, wherein in the radar motion geometric model of the descending section of the hypersonic aircraft, a radar comprises N antenna channels, P is any moving target in a scene where the radar is located, and the instantaneous slant distance between the nth antenna channel and the moving target P is represented as Rn(ta) (ii) a Wherein N belongs to {1,2, …, N }, N represents the number of antenna channels contained in the radar motion geometric model of the descending section of the hypersonic aircraft, N is an odd number larger than 1, and t is an odd number larger than 1aIndicating an azimuth slow time;
step 2, recording N antenna channels contained in the radar as a 1 st channel to an Nth channel in sequence, using the 1 st channel as a reference channel, transmitting a linear frequency modulation signal by the (N +1)/2 nd channel, using the N antenna channels to simultaneously receive an echo signal of a scene where a moving target P is located, and obtaining echo signals s (t) of the N channelsr,ta)，s(tr,ta)＝{s1(tr,ta),…,sn(tr,ta),…,sN(tr,ta)}；sn(tr,ta) Representing the echo signal of the n-th channel, trRepresenting the fast time of distance, taIndicating an azimuth slow time; then, a constant phase compensation factor relative to the reference channel is set, and constant phase compensation is respectively carried out on the echo signals of the N channels to obtain echo signals of N equivalent phase center channels Representing an echo signal of an nth equivalent phase center channel;
step 3, obtaining echo signals of N equivalent phase center channelsRange-compressed range frequency domain-azimuth time domain representation Echo signal representing the nth phase equivalent center channelThe distance frequency domain-azimuth time domain representation form after the distance compression is carried out, and echo signals of N equivalent phase center channels are subjected to echo signal processingRange-compressed range frequency domain-azimuth time domain representationPerforming phase compensation to obtain distance frequency domain-azimuth time domain echo signals of N equivalent phase center channels after phase compensation Distance frequency domain-azimuth time domain echo signal f representing nth equivalent phase center channel after phase compensationrRepresenting the distance frequency, taIndicating azimuth slow time, trRepresenting the distance fast time;
step 4, according to the distance frequency domain-azimuth time domain echo signals of the N equivalent phase center channels after phase compensationSequentially calculating N equivalent phase center channel echo signals s (t) of the range-Doppler domainr,fa) Echo signal st (t) of moving object P in range-Doppler domainr,fa) And clutter signal sc (t) in range-Doppler domainr,fa) Then, solving the weight vector w of the space-time adaptive clutter suppression according to the following formula:
the weight vector satisfying the formula is the optimal weight coefficient vector w of space-time self-adaptive clutter suppressionoptFurther obtaining the echo signal s of the moving target P after clutter suppressionP(tr,fa) (ii) a Wherein,the value of w when the minimum value is obtained is represented, s.t. represents a constraint condition, R represents N equivalent phase center channel echo signals s (t) in a range-Doppler domainr,fa) The covariance matrix, a (f), corresponding to the multi-channel output of the Doppler frequency unita) Steering vector matrix, f, representing N equivalent phase center channelsaRepresenting the doppler frequency of the moving object P.
Compared with the prior art, the invention has the following advantages:
firstly, the method adopts a synthetic aperture radar (HSV-borne SAR) carried by a hypersonic aircraft (HSV), on one hand, compared with a satellite-borne synthetic aperture radar, the method can reduce the power of a transmitted signal and achieve the aim of detecting a moving target without errors; on the other hand, compared with an airborne synthetic aperture radar, the radar has higher flight height and can observe a larger range; in addition, the hypersonic flight vehicle (HSV) has high maneuverability, is difficult to reconnaissance and attack and is more beneficial to battlefield reconnaissance;
secondly, the method can effectively inhibit the strong clutter of the descending section of the hypersonic aircraft (HSV) and detect the moving target from the strong clutter, and has very important significance on subsequent tracking, imaging, identification and the like.
Drawings
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
FIG. 1 is a flow chart of a SAR-GMTI clutter suppression method for the descent segment of a hypersonic aircraft of the present invention;
FIG. 2 is a diagram of a radar motion geometric model of a descent segment of a hypersonic aircraft; in an XYZ three-dimensional coordinate system, a platform where a radar is located makes constant-speed linear motion with a constant speed V along an obliquely downward direction by a constant descending angle gamma (an included angle between the speed direction of the radar and an X axis), a downward viewing angle of the platform where the radar is located is phi, and a nearest slant distance from the platform where the radar is located to a moving target P is R0P is any moving target in the scene where the radar is located, and the horizontal velocity component of the platform where the radar is located is VxThe vertical velocity component of the platform on which the radar is located is Vz；
FIG. 3 is a graph of single channel amplitude results after three phase compensations in the range-Doppler domain after range compression; wherein the horizontal axis represents the range-wise sampling points and the vertical axis represents the Doppler sampling points;
FIG. 4 is a graph of amplitude results after clutter suppression of a three-channel combination; wherein the horizontal axis represents the range-wise sampling points and the vertical axis represents the doppler sampling points.
Detailed Description
Referring to fig. 1, it is a flow chart of the method for suppressing the SAR-GMTI clutter in the descent segment of a hypersonic aircraft according to the present invention; the SAR-GMTI clutter suppression method for the descending segment of the hypersonic aircraft comprises the following steps:
step 1, establishing a radar motion geometric model of a descending section of a hypersonic aircraft, wherein in the radar motion geometric model of the descending section of the hypersonic aircraft, a radar comprises N antenna channels, P is any moving target in a scene where the radar is located, and the instantaneous slant distance between the nth antenna channel and the moving target P is represented as Rn(ta) (ii) a Wherein N is equal to {1,2, …, N }, N represents the number of antenna channels contained in the radar motion geometric model of the descending section of the hypersonic aircraft, and t is equal toaIndicating a slow time to azimuth.
Specifically, referring to fig. 2, a radar motion geometric model diagram of a descent section of a hypersonic aircraft is shown; establishing a radar motion geometric model of a descending section of the hypersonic aircraft, wherein as shown in fig. 2, in a three-dimensional coordinate system XYZ, an X axis points to the right side along a horizontal direction, a Y axis points to the right side, a Z axis is far away from the geocentric direction, the vertical height of a platform where the radar is located is H, the radar platform consists of three antenna channels which are linearly arranged along a track direction, and the distance between every two adjacent antennas is 2 d; in a relevant processing time (CPI), a platform where a radar is located makes constant-speed linear motion with a constant speed V along an oblique downward direction by a constant descending angle gamma (an included angle between the speed direction of the radar and an X axis), the downward viewing angle of the platform where the radar is located is phi, and the nearest slant distance from the platform where the radar is located to a moving target P is R0Then the horizontal velocity component of the platform on which the radar is located is VxThe vertical velocity component of the platform on which the radar is located is Vz(ii) a P is any moving target in the scene where the radar is located, and the moving target P is located at (x) at 0 momentp,yp) Where v is the horizontal velocity component of the moving object P at time 0xpThe vertical velocity component of the moving object P at time 0 is vypThe nearest slope distance from the platform where the radar is located to the moving target P is R0，WgThe width of the strip of the scene observed by the moving object P, and assuming that the radar is operating in front side view (i.e. with an oblique view angle of 0 °); after a radar motion geometric model of a descending section of the hypersonic aircraft is established, representing the instantaneous slope distance between the nth antenna channel and a moving target P as Rn(ta)：
Wherein, VxRepresenting the horizontal velocity component of the platform on which the radar is located, taIndicating azimuth slow time, tcRepresents the time, x, required for the distance between the nth channel and the moving object P to be the nearest slope distancepThe coordinate of the moving object P on the X axis at time 0, vxpRepresents the horizontal velocity component of the moving object P at the moment 0, H represents the vertical height of the platform on which the radar is positioned, VzIndicating the vertical velocity component, y, of the platform on which the radar is locatedpThe coordinate of the moving object P on the Y axis at time 0, vypRepresents the vertical velocity component of the moving object P at time 0,r represents the distance between the platform where the radar is located and the moving target P, phi represents the downward viewing angle of the platform where the radar is located, N belongs to {1,2, …, N }, N represents the number of antenna channels contained in the radar moving geometric model of the descending section of the hypersonic aircraft, and x represents the number of antenna channels contained in the radar moving geometric model of the descending section of the hypersonic aircraftnRepresents the horizontal distance between the nth antenna channel and the origin, znIndicating the vertical distance between the nth antenna channel and the origin.
Step 2, recording N antenna channels contained in the radar as a 1 st channel to an Nth channel in sequenceAnd taking the channel 1 as a reference channel, transmitting a Linear Frequency Modulation (LFM) signal by the channel (N +1)/2, and simultaneously receiving echo signals of a scene where a ground moving target P is located by using N antenna channels to obtain echo signals s (t) of the N channelsr,ta)，s(tr,ta)＝{s1(tr,ta),…,sn(tr,ta),…,sN(tr,ta)}，sn(tr,ta) Representing the echo signal of the n-th channel, trRepresenting the fast time of distance, taIndicating an azimuth slow time; then, a constant phase compensation factor relative to the reference channel is set, and constant phase compensation is respectively carried out on the echo signals of the N channels to obtain echo signals of N equivalent phase center channels Representing the echo signal of the nth phase equivalent center channel.
Specifically, N antenna channels included in the radar are recorded as a channel 1 to a channel N according to the arrangement order, the channel 1 is used as a reference channel, a chirp modulation (LFM) signal is transmitted by a channel (N +1)/2, echo signals of a scene where a moving target P is located are received simultaneously by using the N antenna channels, and echo signals s (t) of the N channels are obtainedr,ta)，s(tr,ta)＝{s1(tr,ta),…,sn(tr,ta),…,sN(tr,ta)}，sn(tr,ta) Representing the echo signal of the n-th channel, trRepresenting the fast time of distance, taIndicating a slow time to azimuth.
Then, a constant phase compensation factor is set with respect to the reference channel, and echoes of the N channels are detectedThe signals are respectively subjected to constant phase compensation to obtain echo signals of N equivalent phase center channels Representing the echo signal of the nth phase equivalent center channel, wherein the set nth phase compensation factor relative to the reference channel is compensated for the echo signal of the nth channelEach two separated transmitting channels and receiving channels are equivalent to the nth self-transmitting and self-receiving channel, the correspondingly received echo signals are also converted into the echo signals of the nth equivalent phase center channel, the distance between the adjacent equivalent phase centers is d, and then the echo signals of the N equivalent phase center channels are respectively obtained Representing the echo signal of the nth phase equivalent center channel,
wherein d isnDenotes the distance between the equivalent phase center of the nth channel and the equivalent phase center of the reference channel, dnN is equal to (N-1) d, N is equal to {1,2, …, N }, N represents the number of antenna channels contained in the radar motion geometric model of the descending section of the hypersonic aircraft, r represents the distance between the platform where the radar is located and the moving target P, and gamma represents the plane where the radar is locatedThe falling angle of the table motion, λ represents the wavelength of the echo signal received by each channel, trRepresenting the fast time of distance, taIndicating a slow time to azimuth.
Step 3, obtaining echo signals of N equivalent phase center channelsRange-compressed range frequency domain-azimuth time domain representation Echo signal representing the nth phase equivalent center channelThe distance frequency domain-azimuth time domain representation form after the distance compression is carried out, and echo signals of N equivalent phase center channels are subjected to echo signal processingRange-compressed range frequency domain-azimuth time domain representationPerforming phase compensation to obtain distance frequency domain-azimuth time domain echo signals of N equivalent phase center channels after phase compensation When the distance frequency domain-azimuth of the nth equivalent phase center channel after phase compensation is expressedDomain echo signal, frRepresenting the distance frequency, taIndicating azimuth slow time, trIndicating the distance fast time.
The specific substeps of step 3 are:
3a) setting a conjugate function s of a replica of a transmitted signalr(tr)，sr(tr)＝Wr(tr)·exp[-jπμtr 2]，Wr(. cndot.) represents a distance-to-rectangular pulse window function, μ represents the modulation frequency of a transmit chirp (LFM) signal, trRepresenting the fast time of the distance and combining the echo signals of N equivalent phase center channelsAre respectively arranged into N1×N2Dimension matrix, obtaining N1×N2Dimension matrix, N1The number of range-direction sampling points contained in the echo signal of each equivalent phase center channel is represented, N2The azimuth sampling point number contained in the echo signal of each equivalent phase center channel is represented; then for N1×N2Each row of the dimensional matrix is subjected to Fast Fourier Transform (FFT) processing and then multiplied by a conjugate function s of a transmitted signal replicar(tr) Further obtaining echo signals of N equivalent phase center channelsRange-compressed range frequency domain-azimuth time domain representation Echo signal representing the nth phase equivalent center channelDistance frequency domain-azimuth time domain representation after distance compression, frRepresenting the distance frequency, taIndicating a slow time to azimuth.
In particular, echo signals at the N equivalent phase center channelsRange-compressed range frequency domain-azimuth time domain representationIn (1),echo signal representing the nth phase equivalent center channelThe distance frequency domain-azimuth time domain representation form after the distance compression is obtained by the following steps:
where N ∈ {1, 2.,. N },. denotes a dot product, FFT denotes a fast Fourier transform operation, and f denotes a fast Fourier transform operationrRepresenting the distance frequency, taIndicating azimuth slow time, trThe distance is represented as a fast time,representing the echo signal of the nth phase equivalent center channel.
Echo signal representing the nth phase equivalent center channelDistance frequency domain-square after distance compressionA bit-time domain representation, whose expression is:
wherein f iscCarrier frequency, W, representing channel echo signala(. represents an azimuthal window function, Wr(. represents a distance-to-rectangular pulse window function, frRepresenting the distance frequency, taIndicating azimuth slow time, tcRepresents the time required for the distance between the nth channel and the moving target P to be the nearest slope distance, R0Representing the closest slope distance between the platform on which the radar is located and the moving target P,h represents the vertical height of the platform on which the radar is located, phi represents the downward viewing angle of the platform on which the radar is located, and xnDenotes the coordinate of the nth channel at time 0 on the X-axis, znDenotes the coordinate, V, of the nth channel at time 0 on the Z axisxRepresenting the horizontal velocity component, V, of the platform on which the radar is locatedzIndicating the vertical velocity component, y, of the platform on which the radar is locatedpRepresenting the coordinates of the moving object P on the Y-axis at time 0, vypRepresenting the horizontal component of the velocity, v, of the moving object PxpRepresents the horizontal velocity component of the moving object P at time 0, anc represents the speed of light, c is 3 × 108(m/s)。
3b) Echo signals to N equivalent phase center channelsRange-compressed range frequency domain-azimuth time domain representationPerforming phase compensation to obtain distance frequency domain-azimuth time domain echo signals of N equivalent phase center channels after phase compensation Distance frequency domain-azimuth time domain echo signal f representing nth equivalent phase center channel after phase compensationrRepresenting the distance frequency, taIndicating a slow time to azimuth.
Specifically, after the phase compensation, distance frequency domain-azimuth time domain echo signals of N equivalent phase center channelsIn (1),the distance frequency domain-azimuth time domain echo signal of the nth equivalent phase center channel after phase compensation is represented, and the obtaining process is as follows:
firstly, setting a quadratic term phase compensation function h of the nth equivalent phase center channeln1And the third order phase compensation function h of the nth equivalent phase center channeln2The expressions are respectively:
then the echo signal of the nth equivalent phase center channel is processedRange-compressed range frequency domain-azimuth time domain representationPhase compensation function h of quadratic term with set nth equivalent phase center channeln1And a third order phase compensation function h of the set nth equivalent phase center channeln2The dot multiplication is carried out in sequence,
namely, it isAnd then calculating to obtain a distance frequency domain-azimuth time domain echo signal of the nth equivalent phase center channel after phase compensationThe expression is as follows:
wherein R is0Representing the closest slope distance between the platform on which the radar is located and the moving target P, fcCarrier frequency, W, representing channel echo signalr(. represents a distance-to-rectangular pulse window function, Wa(. represents an azimuthal window function, frRepresenting the distance frequency, taIndicating azimuth slow time, tcRepresents the time required for the nth channel to reach the nearest slope distance from the moving target P, c represents the speed of light, VxRepresenting the horizontal velocity component, v, of the platform on which the radar is locatedxpRepresenting the horizontal velocity component, v, of the moving object P at time 0ypRepresents the vertical velocity component of the moving object P at the moment 0, phi represents the downward view angle of the platform where the radar is located, VzRepresenting the vertical velocity component, z, of the platform on which the radar is locatednDenotes the vertical distance, x, between the nth channel and the originnRepresenting the horizontal distance between the nth channel and the origin, wherein N belongs to {1, 2.. multidot.N }, and N represents the number of antenna channels contained in the radar motion geometric model of the descending section of the hypersonic aircraft; it can be seen that the distance frequency domain-direction of the nth equivalent phase center channel after phase compensationDomain echo signalThe method is a distance frequency domain-azimuth time domain echo signal of the nth channel after the third phase compensation, and does not contain second and third exponential terms, thereby providing convenience for subsequent clutter suppression processing.
Step 4, according to the distance frequency domain-azimuth time domain echo signals of the N equivalent phase center channels after phase compensationSequentially calculating N equivalent phase center channel echo signals s (t) of the range-Doppler domainr,fa) Echo signal st (t) of moving object P in range-Doppler domainr,fa) And clutter signal sc (t) in range-Doppler domainr,fa) Then, solving the weight vector w of the space-time adaptive clutter suppression according to the following formula:
the weight vector satisfying the formula is the optimal weight coefficient vector w of space-time self-adaptive clutter suppressionoptFurther obtaining the echo signal s of the moving target P after clutter suppressionP(tr,fa) (ii) a Wherein,the value of w when the minimum value is obtained is represented, s.t. represents a constraint condition, R represents N equivalent phase center channel echo signals s (t) in a range-Doppler domainr,fa) The covariance matrix, a (f), corresponding to the multi-channel output of the Doppler frequency unita) Steering vector matrix, f, representing N equivalent phase center channelsaRepresenting the doppler frequency of the moving object P.
The substep of step 4 is:
4a) n equivalent phases after phase compensationRange frequency domain-azimuth time domain echo signal of bit center channelRespectively performing Inverse Fast Fourier Transform (IFFT) on each row, simultaneously respectively performing Fast Fourier Transform (FFT) on each column, and calculating to obtain N equivalent phase center channel echo signals s (t) of a range-Doppler domainr,fa)，
s(tr,fa)＝{s1(tr,fa),…,sn(tr,fa),…,sN(tr,fa)}，sn(tr,fa) Representing the nth equivalent phase center channel echo signal of the range-Doppler domain, and the expression is as follows:
wherein f isrRepresenting the distance frequency, faIndicating the Doppler frequency, t, of a moving object PrThe method is characterized in that the method represents the fast time of the distance, N belongs to {1, 2.,. N }, N represents the number of antenna channels contained in a radar motion geometric model of a hypersonic aircraft descending section, and t represents the number of antenna channels contained in the radar motion geometric model of the hypersonic aircraft descending sectionaIndicating azimuth slow time, FFT indicating fast fourier transform operation, IFFT indicating inverse fast fourier transform operation,and (3) representing distance frequency domain-azimuth time domain echo signals of N equivalent phase center channels after phase compensation.
4b) N equivalent phase center channel echo signals s (t) according to range-Doppler domainr,fa) Separately calculating the echo signal st (t) of the moving target P in the range-Doppler domainr,fa) And clutter signal sc (t) in range-Doppler domainr,fa) The expressions are respectively:
wherein, BrRepresenting the range-wise bandwidth, t, of a Linear Frequency Modulated (LFM) signalrRepresenting the fast time of distance, sinc [. C]Denotes the sinc function, faIndicating the Doppler frequency of the moving object P, c the speed of light, tcRepresents the time required for the nth channel to reach the nearest slope distance from the moving target P, R0The nearest slope distance between the platform where the radar is located and a moving target P is represented, lambda represents the wavelength of an echo signal received by each channel, and fdccRepresents the doppler center frequency of the clutter signals,Wa(. represents an azimuthal window function, KacRepresents the doppler shift frequency of the clutter signals,fdctrepresenting the doppler center frequency of the moving object P,Katrepresenting the doppler shift frequency of the moving object P,Vxrepresenting the horizontal velocity component, v, of the platform on which the radar is locatedxpRepresenting the horizontal velocity component, v, of the moving object P at time 0ypRepresents the vertical velocity component of the moving object P at the moment 0, phi represents the downward view angle of the platform where the radar is located, VzRepresenting the vertical velocity component of the platform on which the radar is located.
N equivalent phase center channel echo signals s (t) of the range-Doppler domainr,fa) Echo signal st (t) of moving object P in range-Doppler domainr,fa) And clutter signal sc (t) in range-Doppler domainr,fa) And (4) summing.
4c) Based on the maximum output signal-to-noise ratio criterion, solving the weight vector w of the space-time self-adaptive clutter suppression according to the following formula:
the weight vector satisfying the formula is the optimal weight coefficient vector w of space-time self-adaptive clutter suppressionoptThe expression is as follows:
wherein, wnThe space-time self-adaptive clutter suppression optimal weight coefficient vector of the nth equivalent phase center channel is represented, and R represents the echo signals s (t) of the N equivalent phase center channels in the range-Doppler domainr,fa) The multi-channel output of the Doppler frequency unit corresponds to a covariance matrix, and R ═ E { s (t)r,fa)sH(tr,fa)}，s(tr,fa) N equivalent phase center channel echo signals representing the range-Doppler domain, (.)-1Inverse matrix of expression [ ·]HConjugate transpose of expression [ ·]TRepresents the transposition of a, represents the dot product, a (f)a) The method comprises the steps of representing a guide vector matrix of N equivalent phase center channels, wherein N belongs to {1, 2., N }, and N represents the number f of antenna channels contained in a radar motion geometric model of a hypersonic aircraft descending sectionaIndicating the Doppler frequency, t, of a moving object PrIndicating the distance to the fast time, (.)-1An inverse matrix representing a, E {. The } represents an averaging operation, the phase difference between the echo signal received by the nth equivalent phase center channel and the reference channel is represented by the following expression:
fashowing the Doppler frequency of the moving target P, gamma the falling angle of the platform on which the radar is located, VxRepresenting the horizontal velocity component, v, of the platform on which the radar is locatedxpRepresenting the horizontal velocity component, d, of the moving object P at time 0nDenotes the distance, v, between the equivalent phase center of the nth channel and the equivalent phase center of the reference channelypRepresents the vertical velocity component of the moving object P at the moment 0, phi represents the downward view angle of the platform where the radar is located, VzThe vertical velocity component of the platform where the radar is located is shown, and lambda represents the wavelength of the echo signal received by each channel.
4d) N equivalent phase center channel echo signals s (t) according to range-Doppler domainr,fa) Optimal weight coefficient vector w for sum space-time adaptive clutter suppressionoptCalculating to obtain an echo signal s of the moving target P after clutter suppressionP(tr,fa) (ii) a Wherein f isaIndicating the Doppler frequency, t, of a moving object PrIndicating the distance fast time.
Specifically, a channel echo signal s (t) in the range-Doppler domain is extractedr,fa) The channel echo signals of the same distance direction, the same Doppler unit but different antenna channels are subjected to point multiplication with the optimal weight coefficient vector of space-time adaptive clutter suppression of the channel corresponding to the distance direction, so that space-domain adaptive clutter suppression is completed, and the echo signal s of the moving target P after clutter suppression is obtainedP(tr,fa) The expression is as follows:
sP(tr,fa)＝s(tr,fa)·wopt，
wherein, s (t)r,fa) N equivalent phase center channel echo signals, f, representing the range-Doppler domainaIndicating the Doppler frequency, t, of a moving object PrRepresenting the fast time of distance, woptRepresenting an optimal weight coefficient vector of space-time adaptive clutter suppression; obtaining an echo signal s of the moving target P after clutter suppressionP(tr,fa) And then, the echo signal of the moving target P can be extracted to the maximum extent, and the amplitude of the clutter signals except the echo signal of the moving target P is greatly reduced to 0, so that the clutter signals are filtered, and the echo signal of the moving target P is reserved.
The effect of the present invention can be further illustrated by the following simulation experiments:
simulation parameter(s)
The carrier frequency of the channel echo signal is 5.405GHz, the bandwidth of transmitting Linear Frequency Modulation (LFM) signals is 50MHz, the pulse width is 10us, the pulse repetition frequency is 3000Hz, the number of radar antenna channels is 3, the distance between adjacent channels is 1m, and the horizontal velocity component V of the platform where the radar is locatedx3000m/s, the vertical velocity component V of the platform on which the radar is locatedyThe vertical height H of the platform where the radar is located is 30km, the azimuth speed of the moving target P is 10m/s, and the range speed of the moving target P is 20 m/s.
(II) simulation content
Simulation content 1, adopting the method of the invention to perform distance compression on radar echo, and adopting a range-doppler result graph after three times of phase compensation in a range frequency domain-azimuth time domain, referring to fig. 3, which is a single-channel amplitude result graph after three times of phase compensation in a range-doppler domain after distance compression; wherein the horizontal axis represents the range-wise sampling points and the vertical axis represents the Doppler sampling points; the distance compression result of the moving object is the middle oblique line, and the other 4 oblique lines are the compressed images of clutter.
Simulation content 2, an image result graph after the result is further subjected to clutter suppression by adopting the method of the invention, and an amplitude result graph after three channels are jointly subjected to clutter suppression with reference to fig. 4; wherein the horizontal axis represents the range-wise sampling points and the vertical axis represents the doppler sampling points.
(III) analysis of simulation results
As can be seen from fig. 3, the echoes and clutter of the moving target occupy different doppler ranges, thereby providing a theoretical basis for the subsequent clutter suppression processing.
As can be seen from fig. 4, after the method of the present invention is used for clutter suppression, clutter can be suppressed well, and only the result of the moving target is retained.
In conclusion, the simulation experiment verifies the correctness, the effectiveness and the reliability of the method.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention; thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (10)
1. A SAR-GMTI clutter suppression method for a descending segment of a hypersonic aircraft is characterized by comprising the following steps:
step 1, establishing a radar motion geometric model of a descending section of a hypersonic aircraft, wherein in the radar motion geometric model of the descending section of the hypersonic aircraft, a radar comprises N antenna channels, P is any moving target in a scene where the radar is located, and the instantaneous slant distance between the nth antenna channel and the moving target P is represented as Rn(ta) (ii) a Wherein N is equal to {1,2, …, N }, and N represents the hypersonic aerocraftThe number of antenna channels contained in the radar motion geometric model of the descending section is N which is an odd number greater than 1, taIndicating an azimuth slow time;
step 2, recording N antenna channels contained in the radar as a 1 st channel to an Nth channel in sequence, using the 1 st channel as a reference channel, transmitting a linear frequency modulation signal by the (N +1)/2 nd channel, using the N antenna channels to simultaneously receive an echo signal of a scene where a moving target P is located, and obtaining echo signals s (t) of the N channelsr，ta)，s(tr，ta)＝{s1(tr，ta)，…，sn(tr，ta)，…，sN(tr，ta)}，sn(tr，ta) Representing the echo signal of the n-th channel, trRepresenting the fast time of distance, taIndicating an azimuth slow time;
then, a constant phase compensation factor relative to the reference channel is set, and constant phase compensation is respectively carried out on the echo signals of the N channels to obtain echo signals of N equivalent phase center channels Representing an echo signal of an nth equivalent phase center channel;
step 3, obtaining echo signals of N equivalent phase center channelsRange-compressed range frequency domain-azimuth time domain representation Echo signal representing the nth phase equivalent center channelThe distance frequency domain-azimuth time domain representation form after the distance compression;
and for echo signals of N equivalent phase center channelsDistance-compressed distance frequency domain-azimuth time domain representation s (f)r，ta) Performing phase compensation to obtain distance frequency domain-azimuth time domain echo signals of N equivalent phase center channels after phase compensation Distance frequency domain-azimuth time domain echo signal f representing nth equivalent phase center channel after phase compensationrRepresenting the distance frequency, taIndicating azimuth slow time, trRepresenting the distance fast time;
step 4, according to the distance frequency domain-azimuth time domain echo signals of the N equivalent phase center channels after phase compensationSequentially calculating N equivalent phase center channel echo signals s (t) of the range-Doppler domainr，fa) Echo signal st (t) of moving object P in range-Doppler domainr，fa) And clutter signal sc (t) in range-Doppler domainr，fa) Then, solving a weight vector w of the space-time adaptive clutter suppression according to formula 1:
the weight vector satisfying the formula 1 is the optimal weight coefficient vector w of the space-time self-adaptive clutter suppressionoptFurther obtaining the echo signal s of the moving target P after clutter suppressionP(tr，fa) (ii) a Wherein,the value of w when the minimum value is obtained is represented, s.t. represents a constraint condition, R represents N equivalent phase center channel echo signals s (t) in a range-Doppler domainr，fa) The covariance matrix, a (f), corresponding to the multi-channel output of the Doppler frequency unita) Steering vector matrix, f, representing N equivalent phase center channelsaRepresenting the doppler frequency of the moving object P.
2. The SAR-GMTI clutter suppression method for the descent segment of the hypersonic flight vehicle as claimed in claim 1, wherein in step 1, the radar motion geometric model of the descent segment of the hypersonic flight vehicle is specifically:
in a three-dimensional coordinate system XYZ, an X axis points to the right side along the horizontal direction, a Y axis points to the right side, a Z axis is far away from the geocentric direction, the vertical height of a platform where a radar is located is H, the radar platform is composed of three antenna channels which are linearly arranged along the track direction, and the distance between every two adjacent antennas is 2 d; in a relevant processing time, a platform where the radar is located makes constant linear motion with constant speed V along an oblique downward direction at a constant descending angle gamma between the speed direction of the radar and an X axis, the downward viewing angle of the platform where the radar is located is phi, and the nearest slant distance from the platform where the radar is located to a moving target P is R0Then the horizontal velocity component of the platform on which the radar is located is VxThe vertical velocity component of the platform on which the radar is located is Vz(ii) a P is any moving object in the scene where the radar is locatedThe moving object P is at (x) at the time 0p，yp) Where v is the horizontal velocity component of the moving object P at time 0xpThe vertical velocity component of the moving object P at time 0 is vyp，WgThe width of the band of the scene observed by the moving object P and the radar operating in a front view.
3. The SAR-GMTI clutter suppression method for the descent segment of hypersonic flight vehicle as claimed in claim 1, wherein in step 1, the instantaneous slope distance between the nth antenna channel and the moving target P is expressed as Rn(ta)：
Wherein, VxRepresenting the horizontal velocity component of the platform on which the radar is located, taIndicating azimuth slow time, tcRepresents the time, x, required for the distance between the nth channel and the moving object P to be the nearest slope distancepThe coordinate of the moving object P on the X axis at time 0, vxpRepresents the horizontal velocity component of the moving object P at the moment 0, H represents the vertical height of the platform on which the radar is positioned, VzIndicating the vertical velocity component, y, of the platform on which the radar is locatedpThe coordinate of the moving object P on the Y axis at time 0, vypRepresents the vertical velocity component of the moving object P at time 0,r represents the distance between the platform where the radar is located and the moving target P, phi represents the downward viewing angle of the platform where the radar is located, N belongs to {1,2, …, N }, N represents the number of antenna channels contained in the radar moving geometric model of the descending section of the hypersonic aircraft, and x represents the number of antenna channels contained in the radar moving geometric model of the descending section of the hypersonic aircraftnRepresents the horizontal distance between the nth antenna channel and the origin, znIndicating the vertical distance between the nth antenna channel and the origin.
4. A height as defined in claim 1Method for suppressing SAR-GMTI clutter in the descent segment of a supersonic aircraft, characterized in that in step 2, said method is used for suppressing SAR-GMTI clutter in the descent segment of a supersonic aircraftThe echo signal of the nth equivalent phase center channel is represented, and the obtaining process is as follows: setting a constant phase compensation factor for the nth phase with respect to the reference channelThen calculating to obtain the echo signal of the nth equivalent phase center channelThe expression is as follows:
wherein d isnThe method comprises the steps of representing the distance between the equivalent phase center of the nth channel and the equivalent phase center of a reference channel, wherein N belongs to {1,2, …, N }, N represents the number of antenna channels contained in a radar motion geometric model of a descending section of the hypersonic aircraft, r represents the distance between a platform where the radar is located and a moving target P, gamma represents the descending angle of the platform where the radar is located, lambda represents the wavelength of echo signals received by each channel, t represents the distance between the platform where the radar is located and the moving target P, and the number of the antenna channels is NrRepresenting the fast time of distance, taIndicating a slow time to azimuth.
5. The SAR-GMTI clutter suppression method for the descent segment of hypersonic flight vehicles according to claim 1, characterized in that the substep of step 3 is:
3a) setting a conjugate function s of a replica of a transmitted signalr(tr) And the echo signals of N equivalent phase center channels are combinedAre respectively arranged into N1×N2Dimension matrix, obtaining N1×N2Dimension matrix, N1The number of range-direction sampling points contained in the echo signal of each equivalent phase center channel is represented, N2The azimuth sampling point number contained in the echo signal of each equivalent phase center channel is represented; then for N1×N2Each row of the dimensional matrix is subjected to fast Fourier transform processing and then multiplied by a conjugate function s of a transmission signal replicar(tr) Further obtaining echo signals of N equivalent phase center channelsRange-compressed range frequency domain-azimuth time domain representation Echo signal representing the nth phase equivalent center channelDistance frequency domain-azimuth time domain representation after distance compression, trRepresenting the fast time of distance, frRepresenting the distance frequency, taIndicating an azimuth slow time;
3b) echo signals to N equivalent phase center channelsRange-compressed range frequency domain-azimuth time domain representationPerforming phase compensation to obtain distance frequency domain-azimuth time domain echo signals of N equivalent phase center channels after phase compensation Distance frequency domain-azimuth time domain echo signal f representing nth equivalent phase center channel after phase compensationrRepresenting the distance frequency, taIndicating a slow time to azimuth.
6. The SAR-GMTI clutter suppression method for the descent segment of hypersonic aircraft as claimed in claim 5, wherein the conjugate function s of the replica of the transmitted signalr(tr) The expression is as follows: sr(tr)＝Wr(tr)·exp[-jπμtr 2]，trIndicating the fast time of distance, Wr(. cndot.) represents the distance to rectangular pulse window function, μ represents the frequency modulation rate of the transmitted chirp:
echo signals at the N equivalent phase center channelsRange-compressed range frequency domain-azimuth time domain representationIn (1),echo signal representing the nth phase equivalent center channelThe distance frequency domain-azimuth time domain representation form after the distance compression is obtained by the following steps:
where N ∈ {1, 2.,. N },. denotes a dot product, FFT denotes a fast Fourier transform operation, and f denotes a fast Fourier transform operationrRepresenting the distance frequency, taIndicating azimuth slow time, trThe distance is represented as a fast time,representing the echo signal of the nth phase equivalent center channel.
7. The SAR-GMTI clutter suppression method for the descent segment of hypersonic aircraft as claimed in claim 5, wherein said method is characterized in thatEcho signal representing the nth phase equivalent center channelThe distance frequency domain-orientation time domain representation form after distance compression is as follows:
wherein f iscCarrier frequency, W, representing channel echo signala(. represents an azimuthal window function, Wr(. represents a distance-to-rectangular pulse window function, frRepresenting the distance frequency, taIndicating azimuth slow time, tcRepresents the time required for the distance between the nth channel and the moving target P to be the nearest slope distance, R0Representing the closest slope distance between the platform on which the radar is located and the moving target P,h represents the vertical height of the platform on which the radar is located, phi represents the downward viewing angle of the platform on which the radar is located, and xnIndicating that the nth channel is on the X-axis at time 0Coordinate of (2), znDenotes the coordinate, V, of the nth channel at time 0 on the Z axisxRepresenting the horizontal velocity component, V, of the platform on which the radar is locatedzIndicating the vertical velocity component, y, of the platform on which the radar is locatedpRepresenting the coordinates of the moving object P on the Y-axis at time 0, vypRepresenting the horizontal component of the velocity, v, of the moving object PxpRepresents the horizontal velocity component of the moving object P at time 0, anAnd c represents the speed of light.
8. The SAR-GMTI clutter suppression method for the descent segment of hypersonic vehicles according to claim 5, characterized in that the distance frequency domain-azimuth time domain echo signals of N equivalent phase center channels after the phase compensationIn (1),the distance frequency domain-azimuth time domain echo signal of the nth equivalent phase center channel after phase compensation is represented, and the obtaining process is as follows:
firstly, setting a quadratic term phase compensation function h of the nth equivalent phase center channeln1And the third order phase compensation function h of the nth equivalent phase center channeln2And according to the distance frequency domain-azimuth time domain echo signal of the nth equivalent phase center channel after distance compressionThen the echo signal of the nth equivalent phase center channel is processedRange-compressed range frequency domain-azimuth time domain representationPhase compensation function h of quadratic term with set nth equivalent phase center channeln1And a third order phase compensation function h of the set nth equivalent phase center channeln2Dot multiplication in turn, i.e.And then calculating to obtain a distance frequency domain-azimuth time domain echo signal of the nth equivalent phase center channel after phase compensationThe expressions are respectively:
wherein R is0Representing the closest slope distance between the platform on which the radar is located and the moving target P, fcCarrier frequency, W, representing channel echo signalr(. represents a distance-to-rectangular pulse window function, Wa(. represents an azimuthal window function, frRepresenting the distance frequency, taIndicating azimuth slow time, tcRepresents the time required for the nth channel to reach the nearest slope distance from the moving target P, c represents the speed of light, VxRepresenting the horizontal velocity component, v, of the platform on which the radar is locatedxpRepresenting the horizontal velocity component, v, of the moving object P at time 0ypRepresents the vertical velocity component of the moving object P at the moment 0, phi represents the downward view angle of the platform where the radar is located, VzRepresenting the vertical velocity component, z, of the platform on which the radar is locatednDenotes the vertical distance, x, between the nth channel and the originnRepresenting between the nth channel and the originAnd the horizontal distance N belongs to {1, 2.,. N }, wherein N represents the number of antenna channels contained in the radar motion geometric model of the descending section of the hypersonic aircraft.
9. The SAR-GMTI clutter suppression method for the descent segment of hypersonic flight vehicles according to claim 1, characterized in that the substep of step 4 is:
4a) distance frequency domain-azimuth time domain echo signals of N equivalent phase center channels after phase compensationRespectively carrying out inverse fast Fourier transform on each row, simultaneously respectively carrying out fast Fourier transform FFT on each column, and calculating to obtain N equivalent phase center channel echo signals s (t) of a range-Doppler domainr，fa)，s(tr，fa)＝{s1(tr，fa)，…，sn(tr，fa)，…，sN(tr，fa)}，sn(tr，fa) An nth equivalent phase center channel echo signal representing a range-doppler domain;
4b) n equivalent phase center channel echo signals s (t) according to range-Doppler domainr，fa) Separately calculating the echo signal st (t) of the moving target P in the range-Doppler domainr，fa) And clutter signal sc (t) in range-Doppler domainr，fa)；
4c) Solving a weight vector w of space-time self-adaptive clutter suppression according to the following formula:
the weight vector satisfying the formula is the optimal weight coefficient vector w of space-time self-adaptive clutter suppressionopt；
4d) N equivalent phase center channel echo signals s (t) according to range-Doppler domainr，fa) And space-time adaptationOptimal weight coefficient vector w for clutter suppressionoptCalculating to obtain an echo signal s of the moving target P after clutter suppressionP(tr，fa) (ii) a Wherein f isaIndicating the Doppler frequency, t, of a moving object PrIndicating the distance fast time.
10. The method of claim 9, wherein s is the SAR-GMTI clutter suppression method for the descent segment of hypersonic vehiclesn(tr，fa) An nth equivalent phase center channel echo signal representing a range-Doppler domain, an echo signal st (t) of a moving object P of said range-Doppler domainr，fa) A clutter signal sc (t) of the range-Doppler domainr，fa) The optimal weight coefficient vector w of the space-time self-adaptive clutter suppressionoptAnd the echo signal s of the moving target P after clutter suppressionP(tr，fa) The expressions are respectively:
sP(tr，fa)＝s(tr，fa)·wopt
wherein f isrRepresenting the distance frequency, faIndicating the Doppler frequency, t, of a moving object PrThe method is characterized in that the method represents the fast time of the distance, N belongs to {1, 2.,. N }, and N represents a radar motion geometric model of a descending section of the hypersonic aircraftThe radar in (1) includes the number of antenna channels, taIndicating azimuth slow time, FFT indicating fast fourier transform operation, IFFT indicating inverse fast fourier transform operation,distance frequency domain-azimuth time domain echo signals representing N equivalent phase center channels after phase compensation, BrRepresenting the range-wise bandwidth of the chirp signal, sinc ·]Denotes the sinc function, c denotes the speed of light, tcRepresents the time required for the nth channel to reach the nearest slope distance from the moving target P, R0The nearest slope distance between the platform where the radar is located and a moving target P is represented, lambda represents the wavelength of an echo signal received by each channel, and fdccRepresents the doppler center frequency of the clutter signals,Wa(. represents an azimuthal window function, KacRepresents the doppler shift frequency of the clutter signals,fdctrepresenting the doppler center frequency of the moving object P,Katrepresenting the doppler shift frequency of the moving object P,Vxrepresenting the horizontal velocity component, v, of the platform on which the radar is locatedxpRepresenting the horizontal velocity component, v, of the moving object P at time 0ypRepresents the vertical velocity component of the moving object P at the moment 0, phi represents the downward view angle of the platform where the radar is located, VzRepresenting the vertical velocity component, w, of the platform on which the radar is locatednRepresenting the optimal weight coefficient vector of the space-time self-adaptive clutter suppression of the nth equivalent phase center channel, R representing the echo signals of the N equivalent phase center channels in the range-Doppler domains(tr，fa) The covariance matrix corresponding to the multi-channel output of the Doppler frequency unit, (-)-1Inverse matrix of expression [ ·]HConjugate transpose of expression [ ·]TRepresents the transposition of a, represents the dot product, a (f)a) A steering vector matrix representing N equivalent phase center channels, representing the phase difference between the echo signal received by the n-th equivalent phase center channel and the reference channel, s (t)r，fa) N equivalent phase center channel echo signals representing the range-doppler domain.
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