Synthetic Aperture Radar Imaging Method and Device Based on Adaptive Digital Beamforming

Abstract

This disclosure provides a synthetic aperture radar (SAR) imaging method and apparatus based on adaptive digital beamforming, applicable to the field of radar technology. The method includes: transmitting a signal to a wide-area scene using an array antenna; acquiring the SAR's downward viewing angle and side-view direction, the array antenna's mounting angle, and the heading angle, pitch angle, roll angle, and position information of a mobile device; calculating the oblique viewing angle of the mobile device based on the downward viewing angle, side-view direction, heading angle, and pitch angle; determining the initial pitch in-pulse scanning angle based on the oblique viewing angle, a preset number of sampling points, position information, and sampling delay, wherein the sampling delay characterizes the time delay between transmitting the signal and starting to receive the echo signal corresponding to the transmitted signal; calculating the target pitch in-pulse scanning weight based on the initial pitch in-pulse scanning angle, roll angle, and mounting angle; and obtaining the target image of the target area based on the target pitch in-pulse scanning weight.

Description

Technical Field

[0001] This disclosure relates to the field of radar technology, and specifically to a synthetic aperture radar imaging method and apparatus based on adaptive digital beamforming. Background Technology

[0002] Synthetic Aperture Radar (SAR) imaging systems, as a high-resolution, all-weather, all-day active microwave imaging radar, are widely used in topographic mapping, resource exploration, disaster monitoring, and other fields. Mountainous areas, as typical natural targets, are covered with numerous distributed targets that are highly sensitive to temporal decorrelation. The undulations of the terrain can cause inaccurate beam pointing of the SAR receiving beam.

[0003] In the process of realizing this disclosure, the inventors discovered that due to the undulating terrain in mountainous areas, the pointing accuracy of the received beam based on adaptive digital beamforming received by synthetic aperture radar is poor, resulting in low imaging quality of synthetic aperture radar. Summary of the Invention

[0004] In view of the above problems, this disclosure provides a synthetic aperture radar imaging method and apparatus based on adaptive digital beamforming.

[0005] According to a first aspect of this disclosure, a synthetic aperture radar (SAR) imaging method based on adaptive digital beamforming is provided, comprising: transmitting a transmitted signal to a wide-field scene using an array antenna; acquiring the SAR's downward viewing angle and side-view direction, the array antenna's mounting angle, and the heading angle, pitch angle, roll angle, and position information of a mobile device; calculating the oblique viewing angle of the mobile device based on the downward viewing angle, side-view direction, heading angle, and pitch angle; determining an initial pitch in-pulse scanning angle based on the oblique viewing angle, a preset number of sampling points, position information, and sampling delay, wherein the sampling delay characterizes the time delay between transmitting the transmitted signal and starting to receive the echo signal corresponding to the transmitted signal; calculating the target pitch in-pulse scanning weight based on the initial pitch in-pulse scanning angle, roll angle, and mounting angle; and obtaining a target image of the target region based on the target pitch in-pulse scanning weight, wherein the target region characterizes the region corresponding to the wide-field scene.

[0006] According to embodiments of this disclosure, the transmitted signal includes multiple pulses. The initial pitch in-pulse scanning angle is determined based on the oblique angle, a preset number of sampling points, position information, and sampling delay. This includes: determining the elevation information of the target area based on the oblique angle, the preset number of sampling points, position information, and sampling delay; and determining the initial pitch in-pulse scanning angle based on the elevation information, sampling delay, and pulse width, wherein the pulse width characterizes the width of a single pulse in the transmitted signal.

[0007] According to embodiments of this disclosure, the location information includes longitude, latitude, and altitude. Determining the elevation information of the target area based on the oblique angle, a preset number of sampling points, the location information, and a sampling delay includes: performing Gaussian projection processing on the longitude and latitude information to obtain first location information and second location information that are related to both the longitude and latitude information; calculating the start point and end point of the target area based on the oblique angle, the preset number of sampling points, the first location information, the second location information, the altitude information, and the sampling delay; and obtaining the elevation information of the target area from a preset external digital elevation model based on the start point and end point.

[0008] According to embodiments of this disclosure, determining the initial pitch-to-intra-pulse scanning angle based on elevation information, sampling delay, and pulse width includes: determining the number of intra-pulse scanning angles based on a preset number of sampling points; calculating the slant range corresponding to each preset sampling point based on the sampling delay and pulse width; calculating the beam pointing angle of each preset sampling point based on the slant range and elevation information corresponding to each preset sampling point; and determining the initial pitch-to-intra-pulse scanning angle based on the beam pointing angle of each preset sampling point and the number of intra-pulse scanning angles.

[0009] According to an embodiment of this disclosure, determining the initial pitch-to-pulse scanning angle based on the beam pointing angle of each preset sampling point and the number of intra-pulse scanning angles includes: determining the scanning angle range based on the beam pointing angle of each preset sampling point; and dividing the scanning angle range based on the number of intra-pulse scanning angles to obtain the initial pitch-to-pulse scanning angle.

[0010] According to an embodiment of this disclosure, obtaining a target image of a target region based on the target pitch intra-pulse scanning weight includes: generating a target receiving beam based on the target pitch intra-pulse scanning weight; and performing two-dimensional compression processing on the echo of the target receiving beam to obtain a target image of the target region.

[0011] According to embodiments of this disclosure, generating a target receiving beam based on the target pitch intra-pulse scanning weights includes: determining a range gate start point and a range gate end point based on an initial pitch intra-pulse scanning angle; determining a range gate segment corresponding to the initial pitch intra-pulse scanning angle based on the range gate start point and the range gate end point; and generating a target receiving beam based on the target pitch intra-pulse scanning weights and the range gate segments.

[0012] According to embodiments of this disclosure, the target pitch-to-pulse scanning weight is calculated based on the initial pitch-to-pulse scanning angle, roll angle, and mounting angle, including: determining the target pitch-to-pulse scanning angle based on the initial pitch-to-pulse scanning angle, roll angle, and mounting angle; and determining the target pitch-to-pulse scanning weight based on the target pitch-to-pulse scanning angle.

[0013] A second aspect of this disclosure provides an imaging apparatus for synthetic aperture radar, comprising: a transmitting module, an acquiring module, a first calculation module, a determining module, a second calculation module, and a obtaining module.

[0014] The transmitting module is used to transmit signals to a wide-area scene using an array antenna.

[0015] The acquisition module is used to acquire the downward and side-view directions of the synthetic aperture radar, the mounting angle of the array antenna, and the heading, pitch, roll, and position information of the mobile device.

[0016] The first calculation module is used to calculate the oblique angle of the mobile device based on the downward angle, the side view direction, the heading angle, and the pitch angle.

[0017] The determination module is used to determine the initial pitch in-pulse scanning angle based on the oblique angle, the preset number of sampling points, the position information, and the sampling delay. The sampling delay represents the time delay between sending the transmitted signal and starting to receive the echo signal corresponding to the transmitted signal. The transmitted signal represents the transmitted pulse sent by the synthetic aperture radar using a multi-channel array antenna.

[0018] The second calculation module is used to calculate the target pitch in-pulse scanning weight based on the initial pitch in-pulse scanning angle, roll angle, and mounting angle.

[0019] The module is used to obtain the target image of the target region based on the target pitch intrapulse scan weights, wherein the target region represents the region corresponding to the wide-angle scene.

[0020] According to the synthetic aperture radar imaging method based on adaptive digital beamforming provided in this disclosure, the oblique viewing angle of the mobile device can be obtained by acquiring the downward viewing angle, side-looking direction, heading angle, and pitch angle. Combined with the preset number of sampling points, sampling delay, and acquired position information, the initial pitch in-pulse scanning angle can be determined. Then, combined with the acquired roll angle and mounting angle, the target pitch in-pulse scanning weight can be obtained, thereby acquiring the target image of the target area. Since the echo of the adaptive target receiving beam generated based on the target pitch in-pulse scanning weight is avoided from undergoing range compression processing on the mobile device, the processing complexity is reduced, achieving real-time in-pulse adaptive target receiving beamforming. Furthermore, it overcomes the influence of terrain undulations within the target area, improving the accuracy of the target receiving beam and thus improving the signal-to-noise ratio of the target image. Because the heading angle, pitch angle, roll angle, and position information of the mobile device are recorded in real time, the target receiving beam is not affected by the motion error and attitude of the mobile device, making the target receiving beam formation more robust and improving the image quality of the target image. Attached Figure Description

[0021] The foregoing contents, as well as other objects, features, and advantages of this disclosure, will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0022] Figure 1 A flowchart illustrating a synthetic aperture radar imaging method based on adaptive digital beamforming according to an embodiment of the present disclosure is shown schematically.

[0023] Figure 2 This schematically illustrates an adaptive target receiving beam of an elevation antenna array based on a preset external digital elevation model according to an embodiment of the present disclosure.

[0024] Figure 3 The illustration shows a schematic diagram of the imaging result of a synthetic aperture radar receiving echoes in a single pitch channel according to an embodiment of the present disclosure;

[0025] Figure 4 The diagram illustrates the imaging results of a synthetic aperture radar receiving echoes at 0 degrees DBF using an elevation array antenna according to an embodiment of the present disclosure.

[0026] Figure 5 The schematic diagram illustrates the imaging results of a synthetic aperture radar receiving echoes using an elevation array antenna adaptive DBF according to an embodiment of the present disclosure.

[0027] Figure 6 This schematically illustrates a signal-to-noise ratio comparison of synthetic aperture radar imaging results under different echo reception methods of an elevation array antenna according to embodiments of the present disclosure;

[0028] Figure 7 A schematic block diagram of a synthetic aperture radar imaging apparatus based on adaptive digital beamforming according to an embodiment of the present disclosure is shown. Detailed Implementation

[0029] The embodiments of the present disclosure will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the disclosure. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the present disclosure for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of the present disclosure.

[0030] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0031] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0032] When using expressions such as "at least one of A, B and C", they should generally be interpreted in accordance with the meaning that is commonly understood by those skilled in the art (e.g., "a system having at least one of A, B and C" should include, but is not limited to, a system having A alone, a system having B alone, a system having C alone, a system having A and B, a system having A and C, a system having B and C, and / or a system having A, B and C, etc.).

[0033] In the technical solution disclosed herein, the user information (including but not limited to user personal information, user image information, user device information, such as location information) and data (including but not limited to data used for analysis, stored data, and displayed data) involved are all information and data authorized by the user or fully authorized by all parties. Furthermore, the collection, storage, use, processing, transmission, provision, disclosure, and application of related data all comply with relevant laws, regulations, and standards, necessary confidentiality measures have been taken, and they do not violate public order and good morals. Corresponding operation entry points are provided for users to choose to authorize or refuse.

[0034] In the process of developing this invention, it was discovered that with the increasing demand for imaging regions of interest (ROIs), it is necessary to obtain high-resolution two-dimensional images of ROIs to achieve the goal of "clear visibility and accurate measurement" in order to detect and identify high-value targets within ROIs. The azimuth resolution of a single-channel Synthetic Aperture Radar (SAR) imaging system in related technologies depends on the Doppler bandwidth of the echo signal, which is determined by the antenna size. To avoid azimuth ambiguity, the Pulse Repetition Frequency (PRF) of the SAR imaging system needs to be greater than the Doppler bandwidth of the echo; otherwise, false targets will appear in the image. However, an excessively high PRF will lead to a reduction in the window range of the echo signal, thereby reducing the maximum unambiguous range of the SAR imaging system, i.e., reducing the mapping band width, which contradicts the purpose of wide-swath imaging. Furthermore, to meet the requirements of high resolution and wide mapping band, smaller antenna sizes are needed in both the azimuth and range directions, resulting in a significantly increased demand for transmission power, which is difficult to achieve in engineering.

[0035] In related technologies, to simultaneously achieve high resolution and wide swath imaging, High-Resolution Wide-Swath (HRWS) synthetic aperture radar technology has been proposed. This technology employs a pitch-oriented multi-channel system, setting intra-pulse varying weighting coefficients between different pitch channels to spatially generate a narrow, high-gain beam to track and receive echo arrival directions. In practical implementation, the echo angle at different times can be calculated based on the geometric relationship between the aircraft and the ground, and then the intra-pulse scanning weighting vector can be calculated based on the array element spacing to achieve the goal of pitch-oriented adaptive scanning digital beamforming (DBF). To improve the accuracy of wide-pulse signal processing, a method of first compressing the range of each pitch channel data and then weighting and synthesizing it intra-pulse can be adopted. However, the on-board range compression in related technologies requires a significant amount of processing time, increasing the data processing volume and implementation difficulty of the real-time system.

[0036] When the region of interest is mountainous, the terrain is more complex, and the undulation of the surface will cause inaccurate pointing of the SAR receiving beam, thus degrading the DBF performance of the imaging system and consequently reducing the signal-to-noise ratio of the image. Furthermore, the large variations in the attitude of the airborne radar platform, and the difficulty of measurement, also significantly affect the pointing of the DBF. Large changes or errors in attitude will also lead to degraded DBF performance, resulting in image quality that does not meet expectations. Among related technologies, there are few imaging systems that achieve real-time pitch-oriented DBF reception. Imaging systems that achieve real-time pitch-oriented DBF reception require data post-processing, resulting in a large data storage burden on the airborne platform and limited practicality. Aircraft motion errors, attitude changes, and terrain undulations within the mapping zone greatly affect DBF accuracy, leading to low signal-to-noise ratios in wide-swath images.

[0037] In view of this, embodiments of the present disclosure provide a synthetic aperture radar imaging method based on adaptive digital beamforming, comprising: transmitting a transmitted signal to a wide-field scene using an array antenna; acquiring the downward viewing angle and side-view direction of the synthetic aperture radar, the mounting angle of the array antenna, and the heading angle, pitch angle, roll angle, and position information of the mobile device; calculating the oblique viewing angle of the mobile device based on the downward viewing angle, side-view direction, heading angle, and pitch angle; determining the initial pitch in-pulse scanning angle based on the oblique viewing angle, a preset number of sampling points, position information, and sampling delay, wherein the sampling delay characterizes the time delay between transmitting the transmitted signal and receiving the echo signal corresponding to the transmitted signal; calculating the target pitch in-pulse scanning weight based on the initial pitch in-pulse scanning angle, roll angle, and mounting angle; and obtaining a target image of the target region based on the target pitch in-pulse scanning weight, wherein the target region characterizes the region corresponding to the wide-field scene.

[0038] Figure 1 A flowchart illustrating a synthetic aperture radar imaging method based on adaptive digital beamforming according to an embodiment of the present disclosure is shown schematically.

[0039] like Figure 1 As shown, the synthetic aperture radar imaging method 100 based on adaptive digital beamforming in this embodiment includes operations S110 to S160.

[0040] When operating S110, the array antenna is used to transmit signals to a wide field of view.

[0041] During operation of S120, the downward and side-view directions of the synthetic aperture radar, the mounting angle of the array antenna, and the heading, pitch, roll, and position information of the mobile device are acquired.

[0042] When operating S130, the oblique angle of the mobile device is calculated based on the downward angle, side view direction, heading angle, and pitch angle.

[0043] In operation S140, the initial pitch-to-pulse scanning angle is determined based on the oblique angle, the preset number of sampling points, the position information, and the sampling delay.

[0044] In operation S150, the target pitch in-pulse scanning weight is calculated based on the initial pitch in-pulse scanning angle, roll angle, and mounting angle.

[0045] In operation S160, the target image of the target region is obtained according to the target pitch pulse scanning weight.

[0046] According to embodiments of this disclosure, synthetic aperture radar is a high-resolution, all-weather, all-time radar imaging system that utilizes the motion of a radar platform to synthesize a smaller actual antenna aperture into a larger equivalent antenna aperture, thereby achieving high-resolution imaging of the ground or targets. The radar motion platform can be a mobile device, such as an aircraft, satellite, or drone.

[0047] According to embodiments of this disclosure, an array antenna can characterize an antenna system composed of multiple antenna elements, which can be called array elements. Multiple array elements are combined together in a certain geometric arrangement. By controlling the signal phase and amplitude of each array element, beam directivity and gain control can be achieved. The structure and types of array antennas can include various types, such as linear array antennas, planar array antennas, and circular array antennas.

[0048] According to embodiments of this disclosure, the transmitted signal can be a periodic pulse signal, or a beam of synthetic aperture radar. A wide swath scene can characterize a large geographical area that can be covered during imaging or observation; it can also be called a wide mapping strip.

[0049] In one embodiment, a synthetic aperture radar (SAR) may include various angular parameters, such as the SAR's downward viewing angle, azimuth angle, and oblique viewing angle. The SAR's downward viewing angle characterizes the angle between the SAR's beam direction and the vertical axis of the radar's moving platform. The SAR's side-looking direction characterizes the SAR's beam transmission and reception directions, and is typically perpendicular to the radar's moving platform's direction of motion.

[0050] According to embodiments of this disclosure, a mobile device can represent a movable device on which a synthetic aperture radar can be mounted, such as an aircraft, a drone, or a satellite. The angular parameters of the mobile device can include multiple parameters, such as the heading angle, pitch angle, and roll angle of the mobile device. The heading angle of the mobile device can represent the angle between the mobile device and a reference direction, and the pitch angle of the mobile device can represent the upward or downward tilt angle of the mobile device. The position information of the mobile device can represent its current location.

[0051] In one embodiment, the oblique angle of the mobile device can be calculated based on the downward angle, the side view direction, the heading angle, and the pitch angle, as shown in the following formula (1).

[0052] (1)

[0053] in, This indicates the oblique view of a mobile device. This indicates the downward field of view of the synthetic aperture radar. Indicates the heading angle of the mobile device. Indicates the pitch angle of a mobile device. Indicates the side-looking direction of the synthetic aperture radar. Represents a symbolic function.

[0054] In one embodiment, once the synthetic aperture radar (SAR) is installed on the mobile device, it can determine the SAR's downward viewing angle and side-looking direction, as well as the mounting angle of the array antenna. The mobile device's heading angle, pitch angle, roll angle, and position information can be acquired in real time using a real-time navigation, positioning, and orientation subsystem (POS). When the SAR's side-looking direction is left-side, When the side-looking direction of the synthetic aperture radar is the right side-looking direction of the radar, .

[0055] According to embodiments of this disclosure, the echo signal can characterize the signal emitted by the transmitted signal to the target area and reflected back to the synthetic aperture radar (SAR). When the number of elevation channels is M, since the distance difference between the echo signals of the SAR and different elements in the array antenna is much smaller than the distance between the mobile device and the target area, it can be approximated that the echo envelopes of each elevation channel are the same. Therefore, after the SAR transmits the signal, the echo signal received by each elevation channel is as follows (2).

[0056] (2)

[0057] in, This represents the echo signal received by the m-th pitch channel, where m represents the pitch channel number and the value of m ranges from [1, M]. Indicates the carrier frequency. Indicates location and time. Indicates a fast time interval. express Echo delay at time, This indicates the modulation frequency of a linear frequency modulated signal. This represents the period, or pulse width, of a linear frequency modulated signal. Represents a rectangular window function. Indicates the interval between pitch and tilt directions in the channel. This indicates the angle between the direction of the echo signal and the normal of the antenna array. This indicates the wavelength of the echo signal.

[0058] In one embodiment, the receive steering vector of the antenna array with M elevation channels As shown in formula (3).

[0059] (3)

[0060] In one embodiment, the angle between the directions of the echo signals from the M pitch channels and the normal of the antenna array is... Since it is a fixed value, the receive steering vector of the antenna array with M elevation channels is not adaptive.

[0061] According to embodiments of this disclosure, the sampling delay can characterize the time delay between transmitting a transmitted signal and starting to receive the echo signal corresponding to the transmitted signal. The preset number of sampling points can be set according to requirements or experience. The transmitted signal and the echo signal can be sampled based on the preset number of sampling points. Given a fixed oblique viewing angle and a fixed number of sampling points, the initial pitch-to-pulse scanning angle can be determined by combining position information and the sampling delay.

[0062] In one embodiment, the mounting angle of the array antenna may include an azimuth angle and a downward viewing angle. The azimuth angle of the array antenna is used to determine the direction of the array antenna in the horizontal plane. The downward viewing angle of the array antenna can characterize the angle between the beam direction and the height vector of the synthetic aperture radar, which is the vertical direction of the radar platform.

[0063] In one embodiment, given a fixed initial pitch in-pulse scanning angle, the target pitch in-pulse scanning angle can be calculated by combining the roll angle and the mounting angle, thereby obtaining the target pitch in-pulse scanning weight.

[0064] In one embodiment, the mounting angle of the array antenna can be the downward viewing angle of the array antenna. The target elevation intra-pulse scan weight, compared with the receive steering vector of the antenna array of M elevation channels, can be adaptively varied based on different target regions.

[0065] According to embodiments of this disclosure, the target area can characterize the area corresponding to a wide-angle scene. Based on the target pitch-to-pulse scanning weight, the target receiving beam can be formed. The echo of the target receiving beam is subjected to two-dimensional compression processing on the ground to obtain a target image of the target area. The two-dimensional compression processing of the echo of the target receiving beam can include range compression and azimuth compression of the echo of the target receiving beam.

[0066] According to embodiments of this disclosure, the oblique viewing angle of the mobile device can be obtained by acquiring the downward viewing angle, side viewing direction, heading angle, and pitch angle. Combined with the preset number of sampling points, sampling delay, and acquired position information, the initial pitch in-pulse scanning angle can be determined. Furthermore, by combining the acquired roll angle and mounting angle, the target pitch in-pulse scanning weight can be obtained, thereby acquiring the target image of the target area. Since the distance compression processing of the echo of the adaptive target receiving beam generated based on the target pitch in-pulse scanning weight is avoided on the mobile device, the processing complexity is reduced, achieving real-time intra-pulse adaptive target receiving beamforming. In addition, the influence of terrain undulations within the target area is overcome, improving the accuracy of the target receiving beam and thus improving the signal-to-noise ratio of the target image. Because the heading angle, pitch angle, roll angle, and position information of the mobile device are recorded in real time, the target receiving beam is not affected by the motion error and attitude of the mobile device, making the formation of the target receiving beam more robust and improving the image quality of the target image.

[0067] According to embodiments of this disclosure, determining the initial pitch-in-pulse scanning angle based on the oblique angle, the preset number of sampling points, location information, and sampling delay includes: determining the elevation information of the target area based on the oblique angle, the preset number of sampling points, location information, and sampling delay; and determining the initial pitch-in-pulse scanning angle based on the elevation information, sampling delay, and pulse width.

[0068] In one embodiment, the transmitted signal may include multiple pulses, and the waveform of the transmitted signal may be composed of periodic pulses. The location information may include longitude, latitude, and altitude. Determining the elevation information of the target area based on the oblique angle, a preset number of sampling points, location information, and sampling delay includes: performing Gaussian projection processing on the longitude and latitude information to obtain first location information and second location information that are related to both longitude and latitude information; calculating the start point and end point of the target area based on the oblique angle, the preset number of sampling points, the first location information, the second location information, altitude information, and sampling delay; and obtaining the elevation information of the target area from a preset external digital elevation model based on the start point and end point.

[0069] In one embodiment, by performing Gaussian projection processing on the longitude and latitude information, first position information and second position information that are related to both longitude and latitude information can be obtained. Then, by combining the oblique angle, the preset number of sampling points, the height information and the sampling delay, the starting point and the ending point of the target area are calculated as shown in the following formula (4).

[0070] (4)

[0071] in, Indicates the starting point of the target region in the x-direction. Indicates the endpoint in the x-direction of the target region. Indicates the starting point of the target region in the y-direction. Indicates the endpoint in the y-direction of the target region. This indicates the height information of the mobile device. This indicates the first location information of the mobile device. This indicates the second location information of the mobile device. This indicates the shortest slant range at which the synthetic aperture radar receives the echo signal. This represents the longest slant range at which the synthetic aperture radar receives the echo signal.

[0072] In one embodiment, the shortest slant range at which the synthetic aperture radar receives the echo signal is... The longest slant range for receiving echo signals by synthetic aperture radar The formulas are (5) and (6) respectively.

[0073] (5)

[0074] (6)

[0075] in, Indicates the center sampling delay of the echo signal. , This represents the sampling delay, where c represents the speed of light. Indicates the preset number of sampling points. Indicates the sampling frequency.

[0076] In one embodiment, by... , By performing Gaussian back projection, the longitude information of the endpoint in the x-direction of the target region can be obtained. Latitude and longitude information ,right , By performing Gaussian back projection, the longitude information of the starting point in the y-direction of the target region can be obtained. Latitude and longitude information .

[0077] In one embodiment, with the starting point and the ending point determined, the elevation information of the target area can be obtained from a preset external digital elevation model (DEM) based on the starting point and the ending point.

[0078] According to embodiments of this disclosure, the pulse width can characterize the width of a single pulse in the transmitted signal, and the initial pitch-to-pulse scanning angle can be determined based on elevation information, sampling delay, and pulse width.

[0079] According to embodiments of this disclosure, by performing Gaussian projection processing on longitude and latitude information, first position information and second position information can be obtained. By combining oblique angle, preset number of sampling points, height information and sampling delay, the starting point and ending point of the target area can be obtained, thereby obtaining the elevation information of the target area. By combining sampling delay and pulse width, the initial pitch in-pulse scanning angle can be determined, improving the accuracy of the elevation information of the target area, and thus improving the accuracy of the initial pitch in-pulse scanning angle.

[0080] According to embodiments of this disclosure, determining the initial pitch-to-intra-pulse scanning angle based on elevation information, sampling delay, and pulse width includes: determining the number of intra-pulse scanning angles based on a preset number of sampling points; calculating the slant range corresponding to each preset sampling point based on the sampling delay and pulse width; calculating the beam pointing angle of each preset sampling point based on the slant range and elevation information corresponding to each preset sampling point; and determining the initial pitch-to-intra-pulse scanning angle based on the beam pointing angle of each preset sampling point and the number of intra-pulse scanning angles.

[0081] In one embodiment, the number of intrapulse scanning angles can be determined based on a preset number of sampling points. For example, the preset number of sampling points is... The number of intrapulse scanning angles is Q. The number of intrapulse scanning distance gate segments can also be determined based on the preset number of sampling points, i.e., the preset number of sampling points is... The number of segments in the intrapulse scan distance gate is also Q. For example, the preset number of sampling points. The number of intrapulse scanning angles is 20, and the number of intrapulse scanning distance gates can also be 20.

[0082] In one embodiment, the slope distance corresponding to each preset sampling point can be calculated based on the sampling delay and pulse width, and the slope distance corresponding to the nth preset sampling point can be calculated. As shown in formula (7).

[0083] (7)

[0084] Where n represents the number of the preset sampling point, and the value range of n is: .

[0085] In one embodiment, the elevation information of the nth preset sampling point can be determined using the following formula (8). .

[0086] (8)

[0087] in, This represents the elevation value of the nth preset sampling point.

[0088] In one embodiment, the beam pointing angle of each preset sampling point can be calculated based on the slant range and elevation information corresponding to each preset sampling point, and the beam pointing angle of the nth preset sampling point can be calculated. As shown in formula (9).

[0089] (9)

[0090] In one embodiment, when there are a large number of preset sampling points, the preset sampling points can be grouped. For example, the preset sampling points can be grouped... Divide into equal parts Groups can be considered to have the same slope distance in each group.

[0091] According to an embodiment of this disclosure, determining the initial pitch-to-pulse scanning angle based on the beam pointing angle of each preset sampling point and the number of intra-pulse scanning angles includes: determining the scanning angle range based on the beam pointing angle of each preset sampling point; and dividing the scanning angle range based on the number of intra-pulse scanning angles to obtain the initial pitch-to-pulse scanning angle.

[0092] According to embodiments of this disclosure, the range of scanning angles can be determined based on the beam pointing angle of each preset sampling point and the number of preset sampling points. Based on the number of intra-pulse scanning angles, the range of scanning angles can be divided to determine the initial pitch intra-pulse scanning angle.

[0093] According to embodiments of this disclosure, the number of intrapulse scanning angles can be determined by preset sampling points. Based on the sampling delay and pulse width, the slant distance corresponding to each preset sampling point can be obtained. Combined with elevation information, the beam pointing angle of each preset sampling point can be obtained, thereby determining the range of scanning angles. By dividing the range of scanning angles according to the number of intrapulse scanning angles, the initial pitch to intrapulse scanning angle can be determined, improving the accuracy of the initial pitch to intrapulse scanning angle.

[0094] According to embodiments of this disclosure, the target pitch-to-pulse scanning weight is calculated based on the initial pitch-to-pulse scanning angle, roll angle, and mounting angle, including: determining the target pitch-to-pulse scanning angle based on the initial pitch-to-pulse scanning angle, roll angle, and mounting angle; and determining the target pitch-to-pulse scanning weight based on the target pitch-to-pulse scanning angle.

[0095] In one embodiment, given that the initial pitch-in-pulse scanning angle is determined, the target pitch-in-pulse scanning angle can be calculated by combining the roll angle and the mounting angle, as shown in the following formula (10), and then the target pitch-in-pulse scanning weight can be obtained, as shown in the following formula (11).

[0096] (10)

[0097] (11)

[0098] in, Indicates the target's pitch angle within the pulse. Indicates the mounting angle of the array antenna. Indicates the roll angle of a movable platform. This indicates the initial pitch angle within the pulse. This indicates the target pitch scan weights within the pulse.

[0099] In one embodiment, considering the complex terrain of mountainous areas, the target area may be obstructed. The target pitch in-pulse scanning angle (DBF angle) of the obstructed target area is the same as the angle of the corresponding obstructed area.

[0100] According to embodiments of this disclosure, obtaining a target image of a target region based on the target pitch-in-pulse scanning weights includes: generating a target receiving beam based on the target pitch-in-pulse scanning weights, including: determining a range gate start point and a range gate end point based on an initial pitch-in-pulse scanning angle; determining range gate segments corresponding to the initial pitch-in-pulse scanning angle based on the range gate start point and the range gate end point; generating a target receiving beam based on the target pitch-in-pulse scanning weights and the range gate segments; and performing two-dimensional compression processing on the echo of the target receiving beam to obtain a target image of the target region.

[0101] In one embodiment, the range gate start point and range gate end point can be directly determined based on the initial pitch angle intra-pulse scan angle, and the range gate range can be determined based on the range gate start point and end point. The range gate range is then divided based on the target pitch angle to obtain range gate segments corresponding to the initial pitch angle intra-pulse scan angle. In another embodiment, the generated target receiving beam can be determined based on the target pitch angle intra-pulse scan weight and the range gate segments. As shown in formula (12).

[0102] (12)

[0103] in, This represents the q-th distance gate segment. This represents the target pitch pulse scan weight corresponding to the q-th distance gate segment. The target pitch pulse scanning angle of the qth distance gate segment is represented by M, and M represents the number of pitch channels.

[0104] In one embodiment, the range gate segment and the target pitch intra-pulse scanning weight corresponding to the range gate segment change continuously over time. Therefore, different range gate segments and the target pitch intra-pulse scanning weight corresponding to the range gate segments are time-varying, thus obtaining a target receiving beam that changes over time. The target receiving beam that changes over time can be called adaptive digital beamforming (adaptive DBF for short).

[0105] In one embodiment, the two-dimensional compression processing of the echo of the target received beam may include range compression and azimuth compression, thereby obtaining a target image of the target area. For example, range compression may employ the Range-Doppler Algorithm (RDA), Chirp Scaling (CSA), and BackProjection Algorithm (BPA).

[0106] In one embodiment, where the antenna array includes only a pitch channel, the array antenna can be referred to as a pitch array antenna.

[0107] Figure 2 The diagram illustrates an adaptive target receiving beam of an elevation antenna array based on a preset external digital elevation model according to an embodiment of the present disclosure.

[0108] like Figure 2 As shown, the antenna array can include M elevation channels, with a channel spacing of d. r The normal direction of the array antenna is perpendicular to the array antenna, and the mounting angle of the array antenna is... The elevation changes in the target area can be correlated with the array antenna to form the target elevation angle within the pulse scan, such as... Figure 2 As shown, it can include two target pitch intrapulse scanning angles, which are the target pitch intrapulse scanning angles of the first range gate. And the target pitch in the pulse scan angle of the second distance gate .

[0109] According to embodiments of this disclosure, a target receiving beam can be generated based on the target pitch intra-pulse scanning weight, and then the echo of the target receiving beam can be compressed in range and azimuth to obtain a target image of the target area. Since the target pitch intra-pulse scanning weight is adaptive, the quality of the target image is improved. Figure 3 The illustration schematically shows the imaging result of a synthetic aperture radar receiving echoes in a single elevation channel according to an embodiment of the present disclosure. Figure 5 The diagram illustrates the imaging results of a synthetic aperture radar receiving echoes at 0 degrees DBF using an elevation array antenna according to an embodiment of the present disclosure. Figure 6 The diagram illustrates the imaging results of a synthetic aperture radar with an adaptive DBF receiving echo from an elevation array antenna according to an embodiment of the present disclosure.

[0110] like Figure 3 and Figure 4 As shown, compared to the imaging results of a synthetic aperture radar with a single elevation channel, the imaging results of a synthetic aperture radar with an array antenna receiving echoes at 0 degrees DBF show better signal-to-noise ratio in the central region. Figure 4 The right side of the imaging image has poorer image quality, which indicates that the energy distribution of the imaging image is relatively uneven. Compared to... Figure 3 and Figure 4 , Figure 5 The imaging results shown have a higher signal-to-noise ratio, especially in the central region. Figure 4 The array antenna shown is similar to the synthetic aperture radar imaging results obtained by receiving echoes at 0 degrees DBF, but with a more uniform energy distribution.

[0111] In one embodiment, to verify the effectiveness of the synthetic aperture radar imaging method based on adaptive digital beamforming, the signal-to-noise ratio (SNR) can be used to evaluate image quality. In one embodiment, the imaging system parameters can be set to a bandwidth of 600MHz, a mobile device altitude of approximately 6000m, a pulse repetition frequency of 1000Hz, a mobile device speed of approximately 122m / s, 12 elevation channels, a pulse width of 100 microseconds, and a time interval... It can be 1 microsecond, and the sampling rate can be 800MHz.

[0112] Figure 6 The diagram schematically illustrates the signal-to-noise ratio comparison of synthetic aperture radar imaging results under different echo reception modes of an elevation array antenna according to embodiments of the present disclosure.

[0113] like Figure 6 As shown, the horizontal axis represents the preset number of sampling points, and the vertical axis represents the signal-to-noise ratio (SNR). The adaptive DBF result characterizes the SNR of the synthetic aperture radar imaging result of the array antenna receiving echoes using adaptive DBF. The fixed 0-degree result DBF characterizes the SNR of the synthetic aperture radar imaging result of the array antenna receiving echoes using 0-degree DBF. The single-channel result characterizes the SNR of the synthetic aperture radar imaging result of the single elevation channel receiving echoes. Synthetic Aperture Radar (SAR) imaging results with adaptive DBF (Digital Difference Filter) of the array antenna receive echoes show higher signal-to-noise ratio (SNR) and better image quality. Compared to SAR imaging results with a single elevation channel receiving echoes, the SNR improvement generally exceeds 6dB, with the maximum SNR improvement reaching 9dB. Compared to SAR imaging results with the array antenna receiving echoes at 0 degrees DBF, due to the larger pulse width, the SNR near the center position of the 0-degree DBF cannot be the same as that of SAR imaging results with the array antenna receiving echoes at 0 degrees DBF. However, in other parts, the SNR of SAR imaging results with adaptive DBF of the array antenna receiving echoes is much higher than that of SAR imaging results with the array antenna receiving echoes at 0 degrees DBF, with the maximum SNR improvement reaching 15dB.

[0114] Based on the aforementioned synthetic aperture radar (SAR) imaging method, this disclosure also provides a SAR imaging device based on adaptive digital beamforming. The following will be combined with... Figure 7 The device is described in detail.

[0115] Figure 7 A schematic block diagram of a synthetic aperture radar imaging apparatus based on adaptive digital beamforming according to an embodiment of the present disclosure is shown.

[0116] like Figure 7 As shown, the synthetic aperture radar imaging device 700 based on adaptive digital beamforming in this embodiment includes a transmitting module 710, an acquiring module 720, a first calculation module 730, a determining module 740, a second calculation module 750, and an obtaining module 760.

[0117] The transmitting module 710 is used to transmit a signal to a wide-area scene using an array antenna. In one embodiment, the transmitting module 710 can be used to perform the operation S210 described above, which will not be repeated here.

[0118] The acquisition module 720 is used to acquire the downward viewing angle and side-looking direction of the synthetic aperture radar, the mounting angle of the array antenna, and the heading angle, pitch angle, roll angle, and position information of the mobile device. In one embodiment, the acquisition module 720 can be used to perform the operation S220 described above, which will not be repeated here.

[0119] The first calculation module 730 is used to calculate the oblique viewing angle of the mobile device based on the downward viewing angle, the side viewing direction, the heading angle, and the pitch angle. In one embodiment, the first calculation module 730 can be used to perform the operation S230 described above, which will not be repeated here.

[0120] The determining module 740 is used to determine the initial pitch in-pulse scanning angle based on the oblique viewing angle, the preset number of sampling points, position information, and sampling delay. The sampling delay represents the time delay between transmitting the transmitted signal and starting to receive the echo signal corresponding to the transmitted signal. The transmitted signal represents the transmitted pulse transmitted by the synthetic aperture radar using a multi-channel array antenna. In one embodiment, the determining module 740 can be used to perform the operation S240 described above, which will not be repeated here.

[0121] The second calculation module 750 is used to calculate the target pitch in-pulse scanning weight based on the initial pitch in-pulse scanning angle, roll angle, and mounting angle. In one embodiment, the second calculation module 750 can be used to perform the operation S250 described above, which will not be repeated here.

[0122] The obtaining module 760 is used to obtain a target image of the target region based on the target pitch intra-pulse scan weights, wherein the target region represents the region corresponding to the wide-angle scene. In one embodiment, the obtaining module 760 can be used to perform the operation S260 described above, which will not be repeated here.

[0123] According to an embodiment of this disclosure, the transmitted signal includes multiple pulses, and the determination module 740 includes: a first determination submodule and a second determination submodule.

[0124] The first determination submodule is used to determine the elevation information of the target area based on the oblique angle, the preset number of sampling points, the location information, and the sampling delay.

[0125] The second determining submodule is used to determine the initial pitch-to-pulse scanning angle based on elevation information, sampling delay, and pulse width, wherein the pulse width represents the width of a single pulse in the transmitted signal.

[0126] According to embodiments of this disclosure, the location information includes longitude information, latitude information, and altitude information. The first determining submodule includes: a first determining unit, a second determining unit, and a third determining unit.

[0127] The first determining unit is used to perform Gaussian projection processing on the longitude and latitude information to obtain first position information and second position information that are related to both the longitude and latitude information.

[0128] The second determining unit is used to calculate the starting point and the ending point of the target area based on the oblique angle, the preset number of sampling points, the first position information, the second position information, the height information, and the sampling delay.

[0129] The third determining unit is used to obtain the elevation information of the target area from the preset external digital elevation model based on the starting point and the ending point.

[0130] According to embodiments of this disclosure, the second determining submodule includes: a fourth determining unit, a fifth determining unit, a sixth determining unit, and a seventh determining unit.

[0131] The fourth determining unit is used to determine the number of intrapulse scanning angles based on the preset number of sampling points.

[0132] The fifth determining unit is used to calculate the slant distance corresponding to each preset sampling point based on the sampling delay and pulse width.

[0133] The sixth determining unit is used to calculate the beam pointing angle of each preset sampling point based on the slant range and elevation information corresponding to each preset sampling point.

[0134] The seventh determining unit is used to determine the initial pitch to intrapulse scanning angle based on the number of beam pointing angles and intrapulse scanning angles for each preset sampling point.

[0135] According to embodiments of this disclosure, the seventh determining unit includes: a first determining subunit and a second determining subunit.

[0136] The first determining subunit is used to determine the scanning angle range based on the beam pointing angle of each preset sampling point.

[0137] The second determining subunit is used to divide the scanning angle range based on the number of intrapulse scanning angles to obtain the initial pitch intrapulse scanning angle.

[0138] According to embodiments of this disclosure, module 760 includes: a first obtaining submodule and a second obtaining submodule.

[0139] The first submodule is used to generate the target receiving beam based on the target pitch intra-pulse scanning weight.

[0140] The second submodule is used to perform two-dimensional compression processing on the echo of the target receiving beam to obtain the target image of the target area.

[0141] According to embodiments of this disclosure, the first obtaining submodule includes: a first obtaining unit, a second obtaining unit, and a third obtaining unit.

[0142] The first unit determines the range gate start point and range gate end point based on the initial pitch-in-pulse scanning angle.

[0143] The second obtaining unit is used to determine the range gate segment corresponding to the initial pitch pulse scanning angle based on the range gate start point and range gate end point.

[0144] The third unit is used to generate the target receiving beam based on the target pitch intra-pulse scanning weight and range gate segmentation.

[0145] According to an embodiment of this disclosure, the second calculation module 750 includes: a first calculation submodule and a second calculation submodule.

[0146] The first calculation submodule is used to determine the target pitch in-pulse scanning angle based on the initial pitch in-pulse scanning angle, roll angle, and mounting angle.

[0147] The second calculation submodule is used to determine the target pitch-in-pulse scanning weight based on the target pitch-in-pulse scanning angle.

[0148] According to embodiments of this disclosure, any plurality of modules among the sending module 710, acquiring module 720, first calculation module 730, determining module 740, second calculation module 750, and obtaining module 760 can be combined into one module, or any one of these modules can be split into multiple modules. Alternatively, at least part of the functionality of one or more of these modules can be combined with at least part of the functionality of other modules and implemented in one module. At least one of the sending module 710, acquiring module 720, first calculation module 730, determining module 740, second calculation module 750, and obtaining module 760 can be at least partially implemented as a computer program module, which can perform corresponding functions when the computer program module is run.

Claims

1. A synthetic aperture radar imaging method based on adaptive digital beamforming, characterized in that, The method includes: Transmit signals to a wide-area scene using an array antenna; The synthetic aperture radar's downward and side-view directions, the array antenna's mounting angle, and the mobile device's heading, pitch, roll, and position information are obtained. The oblique angle of the mobile device is calculated based on the downward viewing angle, the side viewing direction, the heading angle, and the pitch angle. The initial pitch intrapulse scanning angle is determined based on the oblique angle, the preset number of sampling points, the position information, and the sampling delay, wherein the sampling delay represents the time delay between sending the transmitted signal and starting to receive the echo signal corresponding to the transmitted signal; The target pitch in-pulse scanning weight is calculated based on the initial pitch in-pulse scanning angle, the roll angle, and the mounting angle. Based on the target pitch intra-pulse scan weights, a target image of the target region is obtained, wherein the target region represents the region corresponding to the wide-angle scene.

2. The method according to claim 1, characterized in that, The transmitted signal includes multiple pulses. Determining the initial pitch-in-pulse scanning angle based on the oblique angle, the preset number of sampling points, the position information, and the sampling delay includes: The elevation information of the target area is determined based on the oblique angle, the preset number of sampling points, the location information, and the sampling delay. Based on the elevation information, the sampling delay, and the pulse width, the initial pitch in-pulse scanning angle is determined, wherein the pulse width characterizes the width of a single pulse in the transmitted signal.

3. The method according to claim 2, characterized in that, The location information includes longitude, latitude, and altitude information. Determining the elevation information of the target area based on the oblique angle, the preset number of sampling points, the location information, and the sampling delay includes: Gaussian projection processing is performed on the longitude information and the latitude information to obtain first location information and second location information that are related to both the longitude information and the latitude information; The starting point and the ending point of the target area are calculated based on the oblique angle, the preset number of sampling points, the first position information, the second position information, the height information, and the sampling delay. Based on the starting point and the ending point, the elevation information of the target area is obtained from a preset external digital elevation model.

4. The method according to claim 3, characterized in that, Determining the initial pitch-in-pulse scanning angle based on the elevation information, the sampling delay, and the pulse width includes: The number of intrapulse scanning angles is determined based on the preset number of sampling points; Based on the sampling delay and the pulse width, the slant distance corresponding to each preset sampling point is calculated; Based on the slant distance and elevation information corresponding to each preset sampling point, the beam pointing angle of each preset sampling point is calculated. The initial pitch-to-pulse scanning angle is determined based on the beam pointing angle of each preset sampling point and the number of intra-pulse scanning angles.

5. The method according to claim 4, characterized in that, The step of determining the initial pitch-to-pulse scanning angle based on the beam pointing angle of each preset sampling point and the number of intra-pulse scanning angles includes: The scanning angle range is determined based on the beam pointing angle of each preset sampling point; Based on the number of intrapulse scanning angles, the scanning angle range is divided to obtain the initial pitch intrapulse scanning angle.

6. The method according to claim 4, characterized in that, The step of obtaining the target image of the target region based on the target pitch intrapulse scanning weight includes: Based on the target pitch intra-pulse scanning weights, a target receiving beam is generated; The echo of the target receiving beam is subjected to two-dimensional compression processing to obtain a target image of the target area.

7. The method according to claim 6, characterized in that, The step of generating a target receiving beam based on the target pitch intra-pulse scanning weight includes: Based on the initial pitch-in-pulse scanning angle, determine the range gate start point and range gate end point; Based on the starting point and ending point of the distance gate, determine the distance gate segment corresponding to the initial pitch intrapulse scanning angle; The target receiving beam is generated based on the target pitch intra-pulse scanning weights and the range gate segmentation.

8. The method according to claim 1, characterized in that, The step of calculating the target pitch intrapulse scan weight based on the initial pitch intrapulse scan angle, the roll angle, and the mounting angle includes: The target pitch in-pulse scanning angle is determined based on the initial pitch in-pulse scanning angle, the roll angle, and the mounting angle. The target pitch-in-pulse scanning weight is determined based on the target pitch-in-pulse scanning angle.

9. An imaging device for synthetic aperture radar, characterized in that, The device includes: The transmitting module is used to transmit signals to a wide-area scene using an array antenna; The acquisition module is used to acquire the downward viewing angle and side-view direction of the synthetic aperture radar, the mounting angle of the array antenna, and the heading angle, pitch angle, roll angle, and position information of the mobile device; The first calculation module is used to calculate the oblique angle of the mobile device based on the downward angle, the side view direction, the heading angle and the pitch angle. The determination module is used to determine the initial pitch in-pulse scanning angle based on the oblique angle, the preset number of sampling points, the position information, and the sampling delay. The sampling delay represents the time delay between sending a transmitted signal and starting to receive the echo signal corresponding to the transmitted signal. The transmitted signal represents the transmitted pulse sent by the synthetic aperture radar using a multi-channel array antenna. The second calculation module is used to calculate the target pitch in-pulse scanning weight based on the initial pitch in-pulse scanning angle, the roll angle, and the mounting angle. The module is used to obtain a target image of the target region based on the target pitch intrapulse scan weight, wherein the target region represents the region corresponding to the wide-angle scene.

Images