A SAR satellite high-resolution imaging mission planning method

Abstract

The present invention discloses a method for SAR satellite high-resolution imaging mission planning. Considering the satellite resource constraints and the imaging mission requirements of high resolution comprehensively, mission planning is carried out in two aspects of attitude maneuver and timing, planning multiple imaging missions at one time, improving the utilization efficiency of satellite resources and the observation speed of the satellite, and being able to meet the imaging mission requirements and achieve the required resolution and swath width indicators; the present invention avoids conflicts between attitude switching, power-on / off times, and storage timing among imaging missions, and completes imaging missions in order from high to low according to the priority. The present invention uses the least squares method to fit the attitude Euler angle curve, and takes the derivative to obtain the attitude Euler angular velocity and the attitude Euler angular acceleration, improving the calculation accuracy. When calculating the timing parameters, the present invention uses simulation to verify whether the segmented variable pulse repetition frequency design result can ensure the effective reception of echoes, ensuring the accuracy of the timing parameters.

Description

Technical Field

[0001] The present invention relates to the technical field of satellite mission planning, and particularly relates to a method for planning high-resolution imaging missions of SAR satellites. Background Art

[0002] Different from the mission planning of traditional satellites, the high-resolution imaging mission planning of SAR satellites needs to comprehensively consider the collaborative planning problem of satellite attitude and pulse transceiver timing. On the one hand, according to the imaging requirements, the mission needs to reasonably design the attitude maneuver trajectory to make the satellite drive the SAR antenna beam to turn a certain angle to ensure a large synthetic aperture bandwidth in the azimuth direction. This is because agile SAR satellites adopt a reflector antenna system, and the beam is fixed relative to the satellite body. To achieve high-resolution imaging, it is necessary to realize the pointing change of the beam in space through attitude maneuvers. When performing multi-target ultra-high-resolution imaging, it is necessary to consider the attitude switching time between different targets to avoid imaging attitude conflicts. On the other hand, during the imaging process, the distance between the satellite and the target will change greatly. Therefore, it is necessary to reasonably design the pulse transceiver timing according to the characteristics of the satellite-ground distance migration during imaging to effectively receive the echoes of the complete scene. The pulse transceiver timing directly affects the satellite's on-board memory occupied by the imaging data. When performing multi-target high-resolution imaging, it is necessary to consider the amount of data occupied by different imaging tasks to store all data completely.

[0003] From the above discussion, it can be seen that the ultra-high-resolution imaging mission planning of agile SAR satellites involves the planning of attitude trajectories and pulse transceiver timing. At present, for the design of attitude trajectories for ultra-high-resolution SAR imaging, the patent "A method for satellite platform attitude maneuver to achieve spaceborne SAR ultra-high-resolution sliding spotlight mode" (Patent No.: CN106291557A) proposes a sliding spotlight attitude trajectory design method. For the design of wave positions for high-resolution SAR imaging, the patent "A method for segmented variable pulse repetition frequency timing design of ultra-high-resolution spaceborne SAR" (Patent No.: CN110208800A) proposes an ultra-high-resolution SAR timing design method. However, the above patents only involve a single aspect of the single-target ultra-high-resolution imaging mission planning and cannot solve the problem of multi-target ultra-high-resolution imaging mission planning for agile SAR satellites. Therefore, there is a need for a mission planning method for multi-target and multi-aspect ultra-high-resolution imaging of agile SAR satellites at present. Summary of the Invention

[0004] In view of this, the present invention provides a method for planning high-resolution imaging missions of SAR satellites, which can efficiently plan multi-target imaging missions by combining attitude maneuvers and timing.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] A method for high-resolution imaging mission planning of SAR satellites, the specific steps include:

[0007] Step 1: Based on satellite orbit prediction, eliminate imaging tasks of invisible targets and calculate the imaging windows of visible targets.

[0008] Step 2: Based on the satellite motion information within the imaging window, calculate the load power-on and power-off times.

[0009] Step 3: Determine whether there is an overlap in the load power-on and power-off times. If there is an overlap, only retain the imaging task with the highest priority.

[0010] Step 4: Calculate the attitude Euler angles, and calculate the angular velocity and angular acceleration based on the attitude Euler angles.

[0011] Step 5: Compare the attitude Euler angles, angular velocity, and angular acceleration of adjacent imaging tasks to determine whether there is an attitude switching conflict. If so, only retain the imaging task with the highest priority.

[0012] Step 6: Calculate the timing parameters of the imaging task.

[0013] Step 7: Calculate the fixed storage amount of the imaging task; sort the imaging tasks and data transmission arcs by time; when the total fixed storage amount of the imaging tasks within adjacent data transmission arcs exceeds the remaining amount of the satellite, arrange the imaging tasks in ascending order of priority and delete them one by one until it does not exceed the remaining amount of the satellite.

[0014] Step 8: Divide the imaging tasks by orbits, calculate the total duration of load imaging per orbit, and determine whether it exceeds the maximum duration per orbit; if it exceeds, delete them one by one in ascending order of priority until it does not exceed the maximum duration per orbit.

[0015] Further, the specific method of Step 2 is:

[0016] Step 2.1: Screen the satellite motion information within the imaging window and calculate the zero Doppler time t m .

[0017] Step 2.2: According to the zero Doppler time t m , calculate the position vector O rot of the equivalent rotation center in the geocentric coordinate system, and then obtain the velocity vector of the satellite relative to the geocentric coordinate system at the zero Doppler time.

[0018] Step 2.3: According to the velocity vector of the satellite relative to the ground and the imaging swath width, calculate the total imaging duration t on :

[0019]

[0020] Among them, D sce is the imaging swath width, VS (t m ) is the velocity vector of the satellite relative to the Earth-fixed coordinate system at the zero Doppler moment, |*| represents the modulus operation, and A = ρ spot / ρ strip is the resolution improvement factor, which is determined by the resolution ρ spot in the sliding spotlight mode and the resolution ρ strip in the stripmap mode.

[0021] Step 2.4: Calculate the imaging start and end times: The imaging start time t start = t m - 0.5 × t on , and the imaging end time t end = t m + 0.5 × t on .

[0022] Step 2.5: Calculate the payload power-on and power-off times: Let the payload imaging power-on preparation duration be denoted as t pre , and the duration from the end of imaging to standby be denoted as t off . Then the payload power-on time is t start - t pre , and the payload power-off time is t end + t off .

[0023] Furthermore, the specific method of Step 4 is as follows:

[0024] Step 4.1: Calculate the theoretical orientations of the x-axis, y-axis, and z-axis of the satellite body coordinate system in the Earth-fixed coordinate system from the imaging start time to the imaging end time.

[0025] Step 4.2: Calculate the attitude matrix C BO (t) from the satellite orbit coordinate system to the satellite body coordinate system:

[0026]

[0027] where C FO (t) is the coordinate transformation matrix from the satellite orbit coordinate system to the Earth-fixed coordinate system; (x1(t), x2(t), x3(t)), (y1(t), y2(t), y3(t)), and (z1(t), z2(t), z3(t)) are the theoretical orientations of the x-axis, y-axis, and z-axis of the satellite body coordinate system in the Earth-fixed coordinate system at time t, respectively.

[0028] Step 4.3: Convert the attitude matrix C BO (t) to Euler angles:

[0029] Denote the component form of C BO (t) as follows:

[0030]

[0031] Then the attitude Euler angle θ(t) is as follows:

[0032]

[0033] where θ pitch and θ roll and θ yaw are the pitch angle, roll angle and yaw angle respectively, and atan(*) and asin(*) are the arctangent and arcsine functions respectively.

[0034] Step 4.4: Using the least squares method, fit the pitch angle, roll angle and yaw angle at each moment from the start to the end of imaging into a polynomial curve.

[0035] Step 4.5: Take the first derivative of the above polynomial curve to obtain the Euler angular velocity at the start and end moments of imaging; take the second derivative of the above polynomial curve to obtain the Euler angular acceleration at the start and end moments of imaging.

[0036] Furthermore, the specific method of step 6 is as follows:

[0037] Step 6.1: Determine the instantaneous maximum slant range span of the scene echo according to the range migration of the scene echo of the target, and design the satisfaction range of the total slant range of each segment in the azimuth direction.

[0038] Step 6.2: Segment the azimuth direction during the echo reception period according to the satisfaction range of the total slant range of each segment in the azimuth direction.

[0039] Step 6.3: Design the length, start and end sampling moments of the echo reception window for each segment in the azimuth direction according to the minimum and maximum slant ranges of the echo in each segment in the azimuth direction.

[0040] Step 6.4: Based on the start and end sampling moments of the echo reception window for each segment in the azimuth direction, search for and match the operating repetition frequency within the time range of the echo reception window.

[0041] Step 6.5: Simulate and verify whether the segmented variable repetition frequency design result can ensure effective echo reception. If it can ensure effective echo reception, the design is completed and the timing parameters are output. Otherwise, return to step 6.3 until the segmented variable repetition frequency design result can ensure effective echo reception.

[0042] Furthermore, the timing parameters include:

[0043] The total number of segments Na in the azimuth direction during one imaging process; the start sampling moment of the azimuth direction of the i-th segment The end sampling moment of the azimuth direction of the i-th segment The start sampling moment of the echo reception window of the i-th segment The echo reception window termination sampling time of the i-th segment The pulse repetition frequency PRF of the i-th segment i ; The total number of pulse transmissions in the i-th segment where i = 1, …, Na.

[0044] Beneficial effects:

[0045] 1. The present invention proposes a method for SAR satellite high-resolution imaging mission planning. Considering the satellite resource constraints and the imaging mission requirements of high resolution comprehensively, it conducts mission planning in two aspects of attitude maneuver and timing, plans multiple imaging missions at one time, improves the utilization efficiency of satellite resources and the observation speed of the satellite, and can meet the imaging mission requirements, achieving the required resolution and swath width indicators; the present invention avoids conflicts between attitude switching, power-on / off times, and storage timing among imaging missions, and completes imaging missions in order from high to low priority.

[0046] 2. The present invention uses the least squares method to fit the attitude Euler angle curve, and obtains the attitude Euler angular velocity and attitude Euler angular acceleration by derivation, improving the calculation accuracy.

[0047] 3. When calculating the timing parameters, the present invention uses simulation to verify whether the segmented variable PRF design result can ensure effective echo reception, ensuring the accuracy of the timing parameters. Brief description of the drawings

[0048] Figure 1 is the flowchart of the method of the present invention.

[0049] Figure 2 is the schematic diagram of the distribution of imaging missions and data transmission arcs. Detailed implementation manners

[0050] The following combines the drawings and gives examples to describe the present invention in detail.

[0051] As Figure 1 shown, the present invention proposes a method for SAR satellite high-resolution imaging mission planning. The specific steps include:

[0052] Step 1. Based on obtaining the initial parameters and constraint conditions for mission planning, including the mission planning period, imaging mission requirements, data transmission arcs, satellite initial orbit, maximum field of view of the payload, initial remaining solid storage capacity, longest cumulative imaging duration per orbit, and maximum attitude maneuverability. The descriptions of each parameter are as follows:

[0053] Mission planning period: including start and end times, used to limit the time range of mission planning;

[0054] Imaging task requirements: target name, target center position coordinates (including longitude, latitude, altitude), imaging resolution and imaging swath to be achieved, imaging period to be simulated, and task priority. The duration of the imaging period to be simulated should not exceed one satellite orbital period;

[0055] Data transmission arc segment: the start time and end time of the satellite transmitting imaging data to the ground. The transmitted imaging data will be deleted by the satellite;

[0056] Maximum field of view of the payload: the maximum angle that the payload beam can point to, restricted by the satellite attitude maneuverability;

[0057] Initial remaining storage capacity: the amount of data that the satellite can store. It should be ensured that it is not less than 0 during the task planning period;

[0058] Longest cumulative imaging duration P0 per orbit: during the task planning period, control the total imaging duration of the satellite per orbit not to exceed this value;

[0059] Maximum attitude maneuverability: the maximum attitude maneuverability provided by the satellite control system, represented by the maximum angular accelerations of the x, y, and z axes in the satellite coordinate system oxyz, denoted as a x_ctrl 、a y_ctrl 、a z_ctrl , from which the maximum field of view of the payload can be calculated.

[0060] Step 2: The satellite performs orbit prediction to obtain the orbit data of the satellite during the task planning period, and deletes the imaging tasks of invisible targets according to the maximum field of view of the payload:

[0061] Step 2.1: The orbit dynamic model extrapolates the orbit prediction data during the task planning period based on the initial orbit of the satellite, including the satellite position and velocity.

[0062] Step 2.2: According to the orbit prediction data and the maximum field of view of the payload, determine whether the satellite can see the target during the simulated observation period of each imaging task, eliminate the imaging tasks of invisible targets, and calculate the imaging window of visible targets (i.e., the time period when the target is within the maximum field of view of the payload).

[0063] Step 3: Based on the satellite motion information within the imaging window, calculate the payload power-on and power-off times for each imaging task:

[0064] Step 3.1: Filter the satellite motion information within the imaging window and calculate the zero Doppler time t m ;

[0065] Step 3.2: According to the zero Doppler time t m , calculate the position vector O rot of the equivalent rotation center in the geocentric coordinate system, and then obtain the velocity vector of the satellite relative to the geocentric coordinate system at the zero Doppler time;

[0066] Step 3.3. Calculate the total imaging duration \(t\) based on the flight speed of the satellite relative to the ground and the imaging swath width. on :

[0067]

[0068] where \(D\) sce is the imaging swath width, \(V\) S \((t\) m ) is the velocity vector of the satellite relative to the Earth-fixed coordinate system at the zero Doppler moment, \(|\cdot|\) represents the modulus operation, and \(A = \rho\) spot / \(\rho\) strip is the resolution improvement factor, which is determined by the resolution \(\rho\) spot of the sliding spotlight mode and the resolution \(\rho\) strip of the strip mode;

[0069] Step 3.4. Calculate the imaging start and end times: The imaging start time \(t\) start \(= t\) m \(- 0.5\times t\) on , and the imaging end time \(t\) end \(= t\) m \(+ 0.5\times t\) on ;

[0070] Step 3.5. Calculate the payload power-on and power-off times: Denote the payload imaging power-on preparation duration as \(t\) pre , and the duration from the end of imaging to standby as \(t\) off . Then the payload power-on time is \(t\) start \(- t\) pre , and the payload power-off time is \(t\) end \(+ t\) off .

[0071] Step 4. Determine whether there is an overlap in the payload power-on and power-off times of the visible targets. If there is an overlap, only retain the imaging task with the highest priority.

[0072] Step 5. Calculate the attitude Euler angles of the imaging task, and calculate the attitude Euler angular velocity and angular acceleration at the start and end times of the imaging task based on the attitude Euler angles:

[0073] Step 5.1. Calculate the theoretical directions of the \(x\)-axis, \(y\)-axis, and \(z\)-axis of the satellite body coordinate system in the Earth-fixed coordinate system from the imaging start time to the imaging end time;

[0074] Step 5.2. Calculate the attitude matrix \(C\) BO (t) from the satellite orbit coordinate system to the satellite body coordinate system:

[0075]

[0076] where \(C\)FO (t) is the coordinate transformation matrix from the satellite orbit coordinate system to the geodetic coordinate system; (x1(t), x2(t), x3(t)), (y1(t), y2(t), y3(t)), and (z1(t), z2(t), z3(t)) are the theoretical directions of the x-axis, y-axis, and z-axis of the satellite body coordinate system at time t in the geodetic coordinate system, respectively.

[0077] Step 5.3: Convert the attitude matrix C BO (t) to Euler angles:

[0078] Denote the component form of C BO (t) as follows:

[0079]

[0080] Then the attitude Euler angle θ(t) is:

[0081]

[0082] where θ pitch , θ roll , θ yaw are the pitch angle, roll angle, and yaw angle respectively, and atan(*) and asin(*) are the arctangent and arcsine functions respectively.

[0083] Step 5.4: Use the least squares method to fit the pitch angle, roll angle, and yaw angle at each moment from the start to the end of imaging to a polynomial curve.

[0084] Step 5.5: Take the first derivative of the above polynomial curve to obtain the Euler angular velocity at the start and end of imaging; take the second derivative of the above polynomial curve to obtain the Euler angular acceleration at the start and end of imaging.

[0085] Step 6: Determine whether the satellite's maneuverability meets the attitude switching requirements of adjacent imaging tasks (compare the attitude Euler angles, angular velocities, and angular accelerations of adjacent imaging tasks to determine whether there are attitude switching conflicts). If it cannot be met, retain the task with the highest priority.

[0086] Step 7: Calculate the timing parameters of the imaging task:

[0087] Step 7.1: Determine the instantaneous maximum slant range span of the scene echo according to the range migration of the scene echo of the target, and design the range that the total slant range of each segment in the azimuth direction should meet accordingly.

[0088] Step 7.2: Segment the azimuth direction during the echo reception period according to the range that the total slant range of each segment in the azimuth direction should meet.

[0089] Step 7.3: Design the length of the echo reception window for each segment in the azimuth direction, as well as the start and end sampling times, based on the minimum and maximum slant ranges of the echoes within each segment in the azimuth direction.

[0090] Step 7.4: Search for the operating pulse repetition frequency (PRF) that can match the time range of the echo reception window based on the start and end sampling times of the echo reception windows for each segment in the azimuth direction.

[0091] Step 7.5: Simulate and verify whether the segmented variable PRF design result can ensure effective reception of the echoes. If it can ensure effective reception of the echoes, the design is completed and the timing parameters are output; otherwise, return to Step 6.3 until the segmented variable PRF design result can ensure effective reception of the echoes.

[0092] Through the above calculation process, the timing parameters required for a single imaging mission of the SAR payload can be obtained, specifically including:

[0093] The total number of segments Na in the azimuth direction during one imaging process; the start sampling time in the azimuth direction of the i-th segment The end sampling time in the azimuth direction of the i-th segment The start sampling time of the echo reception window of the i-th segment The end sampling time of the echo reception window of the i-th segment The transmit pulse repetition frequency PRF of the i-th segment i ; the total number of pulse transmissions of the i-th segment where i = 1, …, Na. Step 8: Calculate the on-board storage requirements for each imaging mission based on the timing parameters, and determine whether the remaining on-board storage capacity of the satellite can meet the requirements for storing imaging data. If not, give priority to retaining high-priority tasks.

[0094] Step 8.1: Calculate the on-board storage capacity for each imaging mission based on the pulse timing obtained in Step 5.

[0095] Step 8.2: Denote that there are N downlink arc segments in total for the satellite during the entire mission planning period, and sort and label them in chronological order. Let the start and end times of the j-th downlink arc segment be respectively. Sort the start and end time periods of each imaging mission and the downlink arc segments retained in Step 6 in chronological order, as Figure 2 shown.

[0096] Step 8.3: Calculate the remaining on-board storage capacity F j .

[0097] Step 8.4: Denote that there are g imaging missions between the (j - 1)-th and j-th downlink resources, as shown in the appendix Figure 2 . Then, delete the g tasks in ascending order of priority one by one, and repeat Step 3) until F juntil it is ≥0.

[0098] Step 9: Divide the imaging tasks according to the number of laps, calculate the total duration of payload imaging for each lap, and determine whether it exceeds the constraint of the total duration of payload imaging per lap; if it exceeds, delete the imaging tasks in order from the lowest to the highest priority until the constraint of the total duration of payload imaging per lap is not exceeded, and end the task planning.

[0099] In summary, the above is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for SAR satellite high-resolution imaging mission planning, characterized by the steps Including: Step 1: Based on the initial parameters and constraints obtained for mission planning, including the mission planning period, imaging mission requirements, data transmission arc segment, satellite initial orbit, maximum field of view angle of the payload, initial remaining storage capacity, longest cumulative imaging duration per orbit, and maximum attitude maneuverability; Based on satellite orbit prediction, eliminate imaging tasks for invisible targets and calculate the imaging windows for visible targets; Step 2: Based on the satellite motion information within the imaging windows, calculate the payload power-on and power-off times; Step 3: Determine whether there is an overlap in the payload power-on and power-off times. If there is an overlap, only retain the imaging task with the highest priority; Step 4: Calculate the attitude Euler angles, and based on the attitude Euler angles, calculate the angular velocity and angular acceleration; Step 5: Compare the attitude Euler angles, angular velocity, and angular acceleration of adjacent imaging tasks to determine whether there is an attitude switching conflict. If so, only retain the imaging task with the highest priority; Step 6: Calculate the timing parameters of the imaging tasks; Step 7: Calculate the storage amount of the imaging tasks; sort the imaging tasks and the data transmission arc segments in time order; when the total storage amount of the imaging tasks within adjacent data transmission arc segments exceeds the satellite's remaining amount, arrange the imaging tasks in ascending order of priority and delete them one by one until it does not exceed the satellite's remaining amount; Step 8: Divide the imaging tasks by orbits, calculate the total imaging duration of the payload per orbit, and determine whether it exceeds the maximum duration per orbit; If it exceeds, delete them one by one in ascending order of priority until it does not exceed the maximum duration per orbit.

2. The method according to claim 1, characterized in that, The specific method of Step 2 is: Step 2.1: Screen the satellite motion information within the imaging window and calculate the zero Doppler moment t m ; Step 2.

2. Calculate the position vector O of the equivalent rotation center in the Earth-fixed coordinate system according to the zero Doppler time t m and then obtain the velocity vector of the satellite relative to the Earth-fixed coordinate system at the zero Doppler time; rot ​ Step 2.3: Calculate the total imaging duration t based on the velocity vector of the satellite relative to the ground and the imaging swath width on : Among them, D sce is the imaging swath width, V S (t m ) is the velocity vector of the satellite relative to the geocentric system at the zero Doppler moment, |*| is the modulus operation, A = ρ spot / ρ strip is the resolution improvement factor, which is determined by the sliding spotlight mode resolution ρ spot and the strip mode resolution ρ strip ; Step 2.4, calculate the imaging start and end times: the imaging start time t start = t m - 0.5×t on , the imaging end time t end = t m + 0.5×t on ; Step 2.5: Calculate the load power-on and power-off times: Denote the load imaging power-on preparation duration as t pre , and the duration from the end of imaging to standby as t off . Then the load power-on time is t start -t pre , and the load power-off time is t end +t off .

3. The method according to claim 1, wherein The specific method of Step 4 is: Step 4.1: Calculate the theoretical directions of the x-axis, y-axis, and z-axis of the satellite body coordinate system in the geodetic coordinate system from the imaging start time to the imaging end time; Step 4.2: Calculate the attitude matrix C BO (t) from the satellite orbital coordinate system to the satellite body coordinate system:(t): Among them, C FO (t) is the coordinate transformation matrix from the satellite orbit coordinate system to the geocentric coordinate system; (x1(t), x2(t), x3(t)), (y1(t), y2(t), y3(t)), and (z1(t), z2(t), z3(t)) are the theoretical directions of the x-axis, y-axis, and z-axis of the satellite body coordinate system at time t in the geocentric coordinate system, respectively; Step 4.

3. Convert the attitude matrix C BO (t) to Euler angles: Denote C BO (t) has the following component form: Then the attitude Euler angle θ(t) is: where θ pitch 、θ roll 、θ yaw are the pitch angle, roll angle and yaw angle respectively, and atan(*), asin(*) are the arctangent and arcsine functions respectively; Step 4.4: Use the least squares method to fit the pitch angle, roll angle, and yaw angle at each moment from the imaging start to the end into a polynomial curve; Step 4.5: Take the first derivative of the above polynomial curve to obtain the Euler angular velocity at the imaging start and end times; take the second derivative of the above polynomial curve to obtain the Euler angular acceleration at the imaging start and end times.

4. The method according to claim 1, characterized in that The specific method of Step 6 is: Step 6.1: Determine the instantaneous maximum slant range span of the scene echo according to the range migration of the scene echo of the target, and design the satisfaction range of the total slant range span of each segment in the azimuth direction; Step 6.2: Segment the azimuth direction during the echo reception period according to the satisfaction range of the total slant range span of each segment in the azimuth direction; Step 6.3: Design the length, start sampling time, and end sampling time of the echo reception window for each segment in the azimuth direction according to the minimum slant range and maximum slant range of the echo within each segment in the azimuth direction; Step 6.4: Search for and match the operating repetition frequency within the time range of the echo reception window based on the start and end sampling times of the echo reception window for each segment in the azimuth direction; Step 6.5: Simulate and verify whether the segmented variable repetition frequency design result can ensure effective echo reception. If it can ensure effective echo reception, the design is completed and the timing parameters are output. Otherwise, return to Step 6.3 until the segmented variable repetition frequency design result can ensure effective echo reception.

5. The method according to claim 1 or 4, characterized in that The said timing parameters include: The total number of azimuth segments Na during the one-shot imaging process; the starting sampling time of the azimuth for the i-th segment The ending sampling time of the azimuth for the i-th segment The starting sampling time of the echo reception window for the i-th segment The ending sampling time of the echo reception window for the i-th segment The pulse repetition frequency PRF of the i-th segment i ; the total number of pulse transmissions for the i-th segment where i = 1, …, Na.

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