CN109490881A - Interference SAR measurement of higher degree system and measurement method based on vortex electromagnetic wave - Google Patents

Abstract

The invention discloses an interferometric SAR elevation measurement system based on a vortex electromagnetic wave and a measurement method. The system includes: a vortex electromagnetic wave antenna with different modes; a transmission channel for controlling the frequency of the vortex electromagnetic wave antenna to transmit the vortex electromagnetic wave; The channel receives the echo data corresponding to the vortex electromagnetic wave emitted by the vortex electromagnetic wave antenna in different modes; the acquisition unit processes the echo data received by the receiving channel and outputs the measurement result. Based on the principle of vortex electromagnetic wave SAR imaging, this scheme inverts the target elevation information by interfering phase processing on the multi-modal vortex electromagnetic wave echoes, which fundamentally avoids the dependence of traditional InSAR on the baseline, greatly reduces the system complexity and The requirements of the flying platform are beneficial to the popularization and application of the interferometric SAR elevation measurement technology; at the same time, the invention fundamentally avoids the problems of baseline decoherence and the like, and the signal coherence is better.

Description

Interferometric SAR Elevation Measurement System and Measurement Method Based on Vortex Electromagnetic Waves

technical field

The invention belongs to the technical field of radar, and in particular relates to an interferometric SAR elevation measurement system and measurement method based on vortex electromagnetic waves.

Background technique

Synthetic Aperture Radar (SAR) has been widely used in military and civilian fields such as reconnaissance, surveying and mapping, agriculture and forestry because of its all-weather, all-weather and long-distance imaging capabilities. At present, the demand for 3D information of targets in production activities and military activities is getting higher and higher. Accurately obtaining 3D information of targets including elevation information is of great value in military reconnaissance, terrain mapping, oil exploration, building roads, building bridges, etc. However, traditional SAR can only obtain two-dimensional images of distance and azimuth, but cannot obtain elevation information, and is affected by overlapping and perspective shrinkage, so traditional SAR imaging systems can no longer fully meet the requirements of practical applications. Interferometric Synthetic Aperture Radar (InSAR) uses the echo data obtained by multiple receiving antennas or multiple observations from a single antenna for interferometric processing. It can estimate ground elevation information and has the ability to generate a large area surface height model. It has been widely used in recent years. .

In recent years, vortex electromagnetic waves carrying orbital angular momentum (OAM) have received extensive attention from scholars at home and abroad. Vortex electromagnetic waves have great potential in wireless communications, radio astronomy, and radar imaging. The staring imaging based on vortex electromagnetic wave can realize two-dimensional imaging of the target, but in staring imaging, the radar and the target are relatively stationary, and the synthetic aperture technology is not used. In the prior art, the main technical defects also include: a. InSAR system needs to have an interferometric baseline of a certain length to achieve elevation estimation. The longer the baseline, the higher the elevation accuracy, but the long baseline increases the complexity of the system. The flight platform puts forward higher requirements, and the system development and use costs are high, which limits the popularization and application of the InSAR system; b. InSAR elevation estimation accuracy depends on high-quality interferometric phase, and long baselines will lead to serious baseline decoherence problems. Affecting signal coherence, this is a pair of contradictions that are difficult to reconcile, which greatly limits the improvement of the InSAR system's elevation measurement capability.

SUMMARY OF THE INVENTION

In view of this, the present invention provides an interferometric SAR elevation measurement system and measurement method based on vortex electromagnetic waves to at least partially solve the above problems.

The present invention provides an interferometric SAR elevation measurement system based on vortex electromagnetic waves, comprising:

Vortex electromagnetic wave antenna with different modes;

The transmitting channel controls the frequency of the vortex electromagnetic wave antenna to transmit the vortex electromagnetic wave;

The receiving channel receives the echo data corresponding to the vortex electromagnetic wave emitted by the vortex electromagnetic wave antenna in different modes;

The acquisition unit processes the echo data received by the receiving channel and outputs the measurement results.

Further, the system also includes a switch assembly to control the operating state of the system.

Further, the vortex electromagnetic wave antenna is a uniform circular array antenna, a parabolic antenna or a metasurface material antenna.

Further, the transmitting channel includes a frequency device and a transmitter, which controls the frequency of the vortex electromagnetic wave antenna to transmit the vortex electromagnetic wave.

Further, there may be one receiving channel, which is used for time-sharing to receive echo data corresponding to the vortex electromagnetic wave emitted by the vortex electromagnetic wave antenna in different modes.

Further, there may also be at least two receiving channels for simultaneously receiving echo data corresponding to the vortex electromagnetic waves emitted by the vortex electromagnetic wave antenna in all modes.

The present invention also provides an interferometric SAR elevation measurement method based on vortex electromagnetic waves, comprising:

The vortex electromagnetic wave antenna transmits vortex electromagnetic waves of different modes to the target to be measured;

After the vortex electromagnetic wave is reflected by the target to be measured, the echo data of the corresponding modal vortex electromagnetic wave is obtained;

SAR imaging using vortex electromagnetic waves;

Calculate target elevation information.

Further, the vortex electromagnetic wave antenna transmits vortex electromagnetic waves of different modes to the target to be measured at the same time or in time division.

Further, SAR imaging uses the RD imaging algorithm or the ωK algorithm.

Further, calculating the target elevation information includes:

The received echo data of the corresponding modal vortex electromagnetic wave is as follows:

where t _m is the azimuth slow time, t is the fast time, 1 is the vortex electromagnetic wave mode, ω _a is the azimuth envelope, ω _r is the range envelope, r(t _m ) is the target slant range, and c is the vacuum medium speed of light, K _r is the frequency modulation frequency of the chirp signal, J _l is the first-order Bessel function, and the phase term of the After approximation with the slant distance term r(t _m ), we can get:

s(t _m , t, l)≈Aω _a (t _m -x ₀ /v)ω _r (t-2r(t _m )/c)exp{iπK _r [t-2r(t _m )/c] ² }

exp{-iπK _a (t _m -x ₀ /v) ² }exp{i2lφ+i2lvt _m /y ₀ } (2)

in,

A=σN ² J _l ² [k(t _m )asinθ(t _m )]exp{ilπ}exp(-i4πR ₀ /λ) (3)

_A is the echo amplitude, Ka is the azimuth modulation frequency, and R ₀ is the reference slope distance;

Perform range compression and range migration correction on the echo:

s(t _m , t, l)≈Aω _a (t _m -x ₀ /v)p _r (t-2R ₀ /c)

exp{-iπK _a (t _m -x ₀ /v) ² }exp{i2lφ+i2lvt _m /y ₀ } (4)

where _pr is the envelope after distance compression;

Taking the center of the target to be measured as a reference, that is, y ₀ =R ₀ sinθ _c , where θ _c is the incident angle of the center of the scene, in the azimuth time domain, compensate the OAM phase term that varies with ground distance:

s(t _m , t, l)≈Aω _a (t _m -x ₀ /v)p _r (t-2R ₀ /c)

exp{-iπK _a (t _m -x ₀ /v) ² }exp{i2lφ} (5)

Azimuth Compression:

Interferometric processing is performed on the echo phase to invert the target elevation information.

The present invention has the following beneficial effects:

a. Based on the principle of vortex electromagnetic wave SAR imaging, this scheme inverts the target elevation information by performing interference phase processing on the echoes of the multi-modal vortex electromagnetic waves. In the embodiment of the present invention, the dual-mode vortex electromagnetic waves can use a single antenna phase center Transceiver, without interference baseline, fundamentally avoids the dependence of traditional InSAR on baseline, greatly reduces system complexity and requirements for flight platform, and is conducive to the popularization and application of interferometric SAR elevation measurement technology;

b. In the embodiment of this solution, a single antenna phase center and a single transceiver channel are used to realize the transmission and reception of dual-mode vortex electromagnetic waves, which fundamentally avoids problems such as baseline decoherence, and has better signal coherence.

Description of drawings

Fig. 1 is the composition block diagram of the embodiment of the present invention based on the vortex electromagnetic wave interference height measurement system;

2 is a flowchart of an elevation measurement method involved in an embodiment of the present invention;

3 is a geometric model of vortex electromagnetic wave SAR imaging according to an embodiment of the present invention;

Fig. 4 is the interference phase result of the embodiment of the present invention;

FIG. 5 is a target elevation model according to an embodiment of the present invention.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

Aiming at the problems existing in InSAR elevation measurement, the present invention proposes an interferometric SAR elevation measurement system and measurement method based on vortex electromagnetic waves. Different from the traditional method, the present invention avoids the dependence of the traditional InSAR on the baseline, and obtains the target elevation information through the interference processing of the multi-mode vortex electromagnetic wave echo.

An embodiment of the present invention provides an interferometric SAR elevation measurement system based on vortex electromagnetic waves, including:

Vortex electromagnetic wave antenna with different modes;

The transmitting channel controls the frequency of the vortex electromagnetic wave antenna to transmit the vortex electromagnetic wave;

The receiving channel receives the echo data corresponding to the vortex electromagnetic wave emitted by the vortex electromagnetic wave antenna in different modes;

The acquisition unit processes the echo data received by the receiving channel and outputs the measurement results.

In some embodiments, the system further includes a switch assembly to control the operating state of the system.

In some embodiments, the vortex electromagnetic wave antenna is a uniform circular array antenna, a parabolic antenna or a metasurface material antenna.

In some embodiments, the transmission channel includes a frequency generator and a transmitter, and controls the frequency of the vortex electromagnetic wave antenna to transmit the vortex electromagnetic wave.

In some embodiments, there may be one receiving channel, which is used for time-sharing to receive echo data corresponding to the vortex electromagnetic wave emitted by the vortex electromagnetic wave antenna in different modes.

In some embodiments, there may also be at least two receiving channels for simultaneously receiving echo data corresponding to the vortex electromagnetic waves emitted by the vortex electromagnetic wave antenna in all modes.

Referring to FIG. 1 , the present invention adopts dual-mode vortex electromagnetic waves as a specific embodiment. The whole system is composed of dual-mode vortex electromagnetic wave antenna, switch components, transmitting channel, receiving channel, acquisition unit and so on. Under the timing control, the system transmits different vortex electromagnetic waves in a time-sharing manner, and the echo data of the corresponding modal vortex electromagnetic waves are obtained after being reflected by the target. In this way, one mode of echo data is obtained in one pulse, and another mode of echo data is obtained in the next pulse, and finally two modes of vortex electromagnetic wave echo data can be obtained. It is worth noting that, although the system described in this embodiment uses dual-mode vortex electromagnetic waves and outputs echoes in time division, further, multi-mode vortex electromagnetic waves can also be used, and multiple receiving channels can be used to obtain all the signals at the same time. The modal echo data, the method is the same, and will not be repeated.

Another embodiment of the present invention provides an interferometric SAR elevation measurement method based on vortex electromagnetic waves, including:

The vortex electromagnetic wave antenna transmits vortex electromagnetic waves of different modes to the target to be measured;

After the vortex electromagnetic wave is reflected by the target to be measured, the echo data of the corresponding modal vortex electromagnetic wave is obtained;

SAR imaging using vortex electromagnetic waves;

Calculate target elevation information.

In some embodiments, the vortex electromagnetic wave antenna transmits vortex electromagnetic waves of different modes to the target to be measured at the same time or in time division.

In some embodiments, SAR imaging uses the RD imaging algorithm or the ωK algorithm.

In some embodiments, referring to FIG. 2 , calculating the target elevation information includes the following steps:

Step 1, the present invention transmits a dual-mode vortex electromagnetic wave, and uses the dual-mode vortex electromagnetic wave SAR imaging, then its SAR echo expression is as follows:

where t _m is the azimuth slow time, t is the fast time, 1 is the vortex electromagnetic wave mode, ω _a is the azimuth envelope, ω _r is the range envelope, r(t _m ) is the target slant range, and c is the vacuum In the speed of light, K _r is the frequency modulation frequency of the chirp signal, and J _l is the first-order Bessel function. for the phase term After approximation with the slant distance term r(t _m ), we can get:

s(t _m , t, l)≈Aω _a (t _m -x ₀ /v)ω _r (t-2r(t _m )/c)exp{iπK _r [t-2r(t _m )/c] ² }

exp{-iπK _a (t _m -x ₀ /v) ² }exp{i2lφ+i2lvt _m /y ₀ } (2)

in,

A=σN ² J _l ² [k(t _m )asinθ(t _m )]exp{ilπ}exp(-i4πR ₀ /λ) (3)

_A is the echo amplitude, Ka is the azimuth modulation frequency, and R ₀ is the reference slant range.

Step 2, after performing range compression and range migration correction on the echo, we can obtain:

s(t _m , t, l)≈Aω _a (t _m -x ₀ /v)p _r (t-2R ₀ /c)

exp{-iπK _a (t _m -x ₀ /v) ² }exp{i2lφ+i2lvt _m /y ₀ } (4)

where _pr is the envelope after distance compression.

Step 3, taking the center of the scene as a reference, that is, y ₀ =R ₀ sinθ _c , where θ _c is the incident angle of the center of the scene, after compensating the OAM phase term that varies with ground distance in the azimuth time domain, we can obtain:

s(t _m , t, l)≈Aω _a (t _m -x ₀ /v)p _r (t-2R ₀ /c)

exp{-iπK _a (t _m -x ₀ /v) ² }exp{i2lφ} (5)

Step 4, after azimuth compression, the two-dimensional time domain echo expression can be obtained:

Step 5. At this time, the initial azimuth angle φ of the target is in a dual relationship with the OAM mode 1. If the dual-mode SAR echo phase is subjected to interference processing, the initial azimuth angle φ of the target can be solved. According to the geometric relationship in Figure 3, we can obtain:

sinβ=sinθcosφ (7)

Among them, β=x ₀ /R ₀ is the azimuth angle corresponding to the azimuth position of the target, and θ is the initial incident angle of the target.

According to the geometric relationship in Figure 3, it can be obtained:

h=H-rcosθ (8)

Where H is the flight height, r is the initial slope distance of the target, and finally the target elevation information can be obtained.

The effect of the present invention will be further described below in conjunction with the simulation data experiments. The simulation parameters are shown in the table below and assume that there are two point targets in the scene.

Figure 4 shows the results of the interference phase. Finally, according to the interference phase and the imaging geometry, the target elevation estimation results are shown in Figure 5. The elevation accuracy of both targets is better than 1m. The simulation results preliminarily verify the effectiveness of the method. This method breaks through the traditional InSAR system, overcomes the requirements for the baseline, thereby reducing the requirements for the flight platform; at the same time, it avoids problems such as baseline decoherence, and the signal coherence is better; for the subsequent three-dimensional imaging based on multi-modal vortex electromagnetic waves Foundation.

Based on the above embodiment, the present invention has the following alternative technical solutions:

(1) In the form of the vortex electromagnetic wave transceiver antenna, the uniform circular array antenna form can be replaced by a parabolic antenna or a metasurface material antenna;

(2) The RD imaging algorithm can be replaced by the ωK algorithm in the process of vortex electromagnetic wave SAR imaging;

(3) In the mode selection of vortex electromagnetic wave, it is not limited to +1 and -1 modes, and can be replaced by vortex electromagnetic waves of any two different modes.

The specific embodiments described above further describe the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above-mentioned specific embodiments are only specific embodiments of the present invention, and are not intended to limit the present invention. Within the spirit and principle of the present invention, any modifications, equivalent replacements, improvements, etc. made should be included within the protection scope of the present invention.

Claims (10)

1. An interference SAR elevation measurement system based on vortex electromagnetic waves is characterized by comprising:

vortex electromagnetic wave antennas having different modes;

the emission channel controls the frequency of the vortex electromagnetic wave emitted by the vortex electromagnetic wave antenna;

the receiving channel is used for receiving echo data corresponding to the vortex electromagnetic waves emitted by the vortex electromagnetic wave antenna in different modes;

and the acquisition unit is used for processing the echo data received by the receiving channel and outputting a measurement result.

2. The interferometric SAR elevation measurement system based on vortex electromagnetic waves as claimed in claim 1, further comprising a switch assembly for controlling the operation state of the system.

3. The interferometric SAR elevation measurement system based on vortex electromagnetic waves of claim 1, wherein the vortex electromagnetic wave antenna is a uniform circular array antenna, a parabolic antenna or a super surface material antenna.

4. The interferometric SAR elevation measurement system based on vortex electromagnetic waves as claimed in claim 1, wherein the transmission channel comprises a frequency device and a transmitter, and the frequency of the vortex electromagnetic waves transmitted by the vortex electromagnetic wave antenna is controlled.

5. The interferometric SAR elevation measurement system based on vortex electromagnetic waves according to claim 1, wherein the number of the receiving channels is 1, and the receiving channels are used for receiving echo data corresponding to the vortex electromagnetic waves emitted by the vortex electromagnetic wave antenna in different modes in a time-sharing manner.

6. The interferometric SAR elevation measurement system based on vortex electromagnetic waves according to claim 1, wherein the number of the receiving channels is at least two, and the receiving channels are used for simultaneously receiving echo data corresponding to the vortex electromagnetic waves emitted by the vortex electromagnetic wave antenna in all modes.

7. An interference SAR elevation measurement method based on vortex electromagnetic waves is characterized by comprising the following steps:

the vortex electromagnetic wave antenna transmits vortex electromagnetic waves of different modes to a target to be detected;

the vortex electromagnetic wave is reflected by a target to be measured to obtain echo data of the corresponding modal vortex electromagnetic wave;

imaging by utilizing vortex electromagnetic waves SAR;

and calculating target elevation information.

8. The interferometric SAR elevation measurement method based on the vortex electromagnetic waves as claimed in claim 7, wherein the vortex electromagnetic wave antenna transmits vortex electromagnetic waves of different modes to a target to be measured simultaneously or in a time-sharing manner.

9. The interferometric SAR elevation measurement method based on eddy electromagnetic waves as claimed in claim 7, characterized in that the SAR imaging uses RD imaging algorithm or ω K algorithm.

10. The interferometric SAR elevation measurement method based on eddy electromagnetic waves according to claim 7, wherein the calculating target elevation information comprises:

the echo data of the corresponding modal vortex electromagnetic wave is received as follows:

wherein t is_mIs azimuth slow time, t is fast time, 1 is vortex electromagnetic wave mode, omega_aIs the azimuthal envelope, ω_rIs the distance envelope, r (t)_m) Is the target slant distance, c is the speed of light in vacuum, K_rFor frequency modulation of a chirp signal, J_lIs a first order Bessel function to which the phase termAnd the skew term r (t)_m) After approximate treatment, the following can be obtained:

s(t_m，t，l)≈Aω_a(t_m-x₀/v)ω_r(t-2r(t_m)/c)exp{iπK_r[t-2r(t_m)/c]²}

exp{-iπK_a(t_m-x₀/v)²}exp{i2lφ+i2lvt_m/y₀} (2)

wherein,

A＝σN²J_l ^２[k(t_m)asinθ(t_m)]expilπ}exp(-i4πR₀/λ) (3)

a is the amplitude of the echo, K_ａFrequency modulation of azimuth, R₀Is a reference slope distance;

performing range compression and range migration correction on the echo:

s(t_m，t，l)≈Aω_a(t_m-x₀/v)p_r(t-2R₀/c)

exp{-iπK_a(t_m-x₀/v)²}exp{i2lφ+i2lvt_m/y₀} (4)

wherein p is_rEnvelope after distance compression;

with reference to the centre of the object to be measured, i.e. y₀＝R₀sinθ_cWherein theta_cCompensating an OAM phase term which is changed along with the space of the ground distance in an azimuth time domain for a scene center incidence angle:

s(t_m，t，l)≈Aω_a(t_m-x₀/v)p_r(t-2R₀/c)

exp{-iπK_a(t_m-x₀/v)²}exp{i2lφ} (5)

azimuth compression:

and performing interference processing on the echo phase to invert the target elevation information.