Helicopter platform based stripmap sar imaging flight path angle automatic calculation method

Abstract

The present application discloses a method for automatically calculating the track angle of a strip SAR imaging track based on a helicopter platform, comprising: obtaining inertial navigation data of an airborne navigation system by a radar; processing aperture frames to perform frame mapping, aligning the pulse moment of an nth aperture frame Ap_frame(n) with the pulse of an mth processing frame Prc_frame(m); determining a track angle fluctuation range value; identifying a curved track segment and a straight track segment according to the track angle fluctuation range value, presetting a standard range segment, and determining whether the track fluctuation value of the current aircraft is within the standard range segment; if yes, the straight track segment is taken as a straight track segment, and the imaging track angle is processed according to the straight track segment; and if no, the curved track segment is taken as a curved track segment. The method improves the use performance and man-machine interaction performance of the radar, and improves the quality of the radar imaging image.

Description

Technical Field

[0001] This invention belongs to the technical field of radar systems, and particularly relates to an automatic calculation method for the track angle of strip SAR imaging based on a helicopter platform. Background Technology

[0002] With the increasing complexity of radar applications, helicopter-borne surveillance and early warning radars, in addition to traditional detection and surveillance capabilities for ground and low-altitude targets, must also possess high-resolution imaging capabilities for tactical targets such as ground surface targets and missile sites. Within designated mission airspace, helicopters typically need to make multiple round trips to perform reconnaissance and surveillance missions. The helicopter trajectory consists of curves and straight sections; only on the straight sections can the radar output high-quality SAR images. On the straight sections, due to atmospheric disturbances, pilots need to constantly adjust their flight heading to ensure the flight trajectory closely approximates the planned straight route. In strip SAR mode, which consists of multiple consecutive apertures, the imaging track angle must remain constant within each aperture time frame to output high-quality images. Traditional imaging track angle calculation is implemented by the system control module (track angles within the same aperture frame participate in the averaging calculation), using aperture frames to synchronously trigger the averaging track angle instead of updating the imaging track angle. Traditional imaging track angle calculation is mainly suitable for fixed-wing platforms (with stable flight trajectories). Directly applying it to helicopter-borne radar has the following drawbacks:

[0003] 1) The radar lacks the ability to identify straight flight paths for helicopters, which reduces its performance.

[0004] 2) The manually input imaging track angle deviates greatly from the actual track angle, which increases the operator's workload and results in lower image quality from the radar.

[0005] 3) The imaging track angle is automatically calculated based on the processed frame. There are multiple different imaging track angle values ​​within the same aperture, which significantly reduces the imaging quality.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] The purpose of this invention is to provide an automatic calculation method for the track angle of strip SAR imaging based on a helicopter platform, solving the technical problem that existing methods result in low image quality from radar. The technical solution of this invention has many beneficial effects, as described below:

[0008] An automatic calculation method for track angle in strip SAR imaging based on a helicopter platform is provided, the method comprising:

[0009] The radar acquires inertial navigation data from the airborne navigation system, the inertial navigation data including at least the heading angle and the yaw angle, and calculates the track angle using the inertial navigation data;

[0010] The radar aperture frames are processed by frame mapping, aligning the pulse time of the nth aperture frame Ap_frame(n) with the pulse Prc_frame(m) of the mth processing frame;

[0011] Determine the range of track angle fluctuations;

[0012] Based on the track angle fluctuation range value, the turning route segment and the straight route segment are identified. A preset standard range segment is used. If the track fluctuation value of the current aircraft is within the standard range segment, it is regarded as a straight route segment and the imaging track angle is processed based on the straight route segment. If not, it is regarded as a turning route segment.

[0013] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0014] The aim is to calculate the track angle using helicopter-borne inertial navigation heading angle and yaw angle data; identify turning and straight track segments using track angle fluctuation values; synchronize the imaging track angle using the ratio of aperture frames to processing frames; and finally update the imaging track angle using the difference between the imaging track angle and the average track angle. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a flowchart of the method of the present invention;

[0017] Figure 2 Processing frames and aperture frames are aligned and synchronized;

[0018] Figure 3 Helicopter flight path;

[0019] Figure 4 Effect of the range of fluctuation in the thick line segment track;

[0020] Figure 5 The diagram shows the effect of the method for identifying turning sections of a flight path in this invention. Detailed Implementation

[0021] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] To address the shortcomings of traditional imaging track angle calculation functions in high-resolution strip SAR mode for helicopter-borne radar, which fails to identify straight flight segments of the helicopter, thus affecting strip SAR imaging performance,

[0023] The impact of different imaging track angles within the same aperture frame on SAR image quality and the impact of large deviations between the imaging track angle and the actual track angle on SAR image quality.

[0024] This invention provides an automatic calculation method for the track angle of strip SAR imaging based on a helicopter platform, which solves the problems existing in traditional methods. See [link to relevant documentation]. Figure 1 As shown, the method includes:

[0025] S101: The radar acquires inertial navigation data from the airborne navigation system, the inertial navigation data including at least the heading angle and yaw angle, and calculates the track angle using the inertial navigation data. Specifically:

[0026] The heading angle and yaw angle are fused to obtain the track angle. Inertial navigation data from the airborne 429 bus are received in real time. The heading angle Angle_heading and yaw angle Angle_drift are calculated, and the track angle Angle_trace = heading angle Angle_heading + yaw angle Angle_drift is calculated.

[0027] S102: The radar aperture frame is processed by frame mapping, aligning the pulse time of the nth aperture frame Ap_frame(n) with the pulse Prc_frame(m) of the mth processing frame. Specifically:

[0028] like Figure 2 As shown, the radar aperture frames are mapped to processing frames. Based on the timing relationship between the aperture frames and processing frames, the pulse time of the nth aperture frame Ap_frame(n) is aligned with the pulse Prc_frame(m) of the mth processing frame.

[0029] After alignment, process the frame period T.处理帧 and the aperture frame period T 孔径帧 have a proportional relationship of T 孔径帧 =k*T 处理帧 , the system control module of the radar processes the mapping relationship between processing frames and aperture frames, where K is a multiple. As a result, it can be determined which processing frames are included in an aperture frame. For example, the m-th processing frame corresponds to the n-th aperture frame as the starting position, and the m+k-1-th processing frame corresponds to the end position of the n-th aperture frame, that is, Ap_frame(n)-->[prc_frame(m) prc_frame(m+k-1)], where m and n are natural integers.

[0030] S103: Determine the track angle fluctuation range value, specifically:

[0031] In real time, count the maximum track angle Angle_trace_max and the minimum track angle Angle_trace_min within each aperture frame period, and determine the track angle fluctuation range value Angle_trace_zoom, for example, Angle_trace_zoom=Angle_trace_max-Angle_trace_minx.

[0032] S104: Complete the identification of turning flight segments and straight flight segments according to the track angle fluctuation range value. A standard range segment is preset, and it is judged whether the track fluctuation value of the current carrier aircraft is within the standard range segment. If yes, it is regarded as a straight flight segment, and imaging track angle processing is performed according to the straight flight segment; if no, it is regarded as a turning flight segment. Specifically: for the track angle fluctuation range value, generally, when -5°<Angle_trace_zoom<5°, it indicates that the helicopter enters a straight flight segment, and when Angle_trace_zoom≥5° or Angle_trace_zoom≤-5°, it indicates that the helicopter enters a turning flight segment;

[0033] Performing imaging track angle processing on the straight flight segment includes:

[0034] Taking the first average track angle meanAngle_trace(1) calculated in the first aperture frame of the straight flight segment as the imaging track angle SARAngle_trace, which is the initial value;

[0035] For the 2nd to nth aperture frames, calculate the second average track angle values (meanAngle_trace(2) to meanAngle_trace(n)) respectively, compare the initial value with each of the second average track angle values in sequence, and judge whether the absolute value of the difference between the initial value and each of the second average track angle values is greater than the standard track angle difference value. If yes, the initial value is replaced by the second average track angle; if no, the initial value remains unchanged;

[0036] Calculate the imaging track angle for 2-N aperture frames, for example,

[0037] The second average track angle values ​​meanAngle_trace(2) to meanAngle_trace(n) calculated for the 2nd to nth aperture frames of the straight flight segment are compared with the initial value SARAngle_trace, and the difference angle delta_Angle_trace is calculated.

[0038] Difference angle = Second average track angle value - Initial value. When the difference angle is >3° or <-3°, the initial value is replaced by the second average track angle value; otherwise, the imaging track angle remains unchanged.

[0039] This invention provides real-time auxiliary functions to radar based on imaging quality and efficiency through real-time calculations, improving radar performance and human-computer interaction. It ensures automatic alignment and synchronization between the processing frame and the aperture frame, maintains identical track angles within the aperture frame to guarantee SAR image quality, and automatically identifies helicopter entry / exit from straight flight segments using track fluctuation ranges, reducing the radar operator's workload and improving imaging efficiency. Furthermore, it automatically updates the imaging track angle based on the helicopter's trajectory, ensuring SAR image quality. This invention can be applied to helicopter-borne imaging radar, UAV-borne imaging radar, fixed-wing platform imaging radar, and hovering platform imaging radar, etc.

[0040] Figure 3 , Figure 4 , Figure 5 This is a specific implementation example, where the horizontal axis represents longitude and the vertical axis represents latitude. Figure 4 The larger fluctuation range of the track angle in the medium-thick line segment indicates that the helicopter is entering a turning section. Figure 5 Medium-thick line segments are easily identified as turning segments. Results show that the method of this invention achieves accurate detection and identification of helicopter flight paths during turning segments.

[0041] The product provided by this invention has been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are merely for the purpose of helping to understand the core ideas of this invention. It should be noted that those skilled in the art can make various improvements and modifications to the invention without departing from the principles of the invention, and these improvements and modifications also fall within the protection scope of the invention claims.

Claims

1. A method for automatically calculating the track angle of strip SAR imaging based on a helicopter platform, characterized in that, The methods include: The radar acquires inertial navigation data from the airborne navigation system, the inertial navigation data including at least the heading angle and the yaw angle, and calculates the track angle using the inertial navigation data; The radar aperture frames are processed by frame mapping, aligning the pulse time of the nth aperture frame Ap_frame(n) with the pulse Prc_frame(m) of the mth processing frame. Specifically, the radar aperture frames are processed by frame mapping, aligning the pulse time of the nth aperture frame Ap_frame(n) with the pulse Prc_frame(m) of the mth processing frame according to the timing relationship between the aperture frames and the processing frames. After alignment, process the frame period T. 处理帧 With aperture frame period T 孔径帧 The proportional relationship is T 孔径帧 =k T 处理帧 K is a multiple; the aperture frame is determined to include the frame to be processed, where the m-th processing frame corresponds to the n-th aperture frame as the starting position, and the m+k-1-th processing frame corresponds to the ending position of the n-th aperture frame, where m and n are natural integers, and the track angle fluctuation range value is determined. Based on the track angle fluctuation range, the identification of turning and straight flight segments is completed. A preset standard range is defined. If the current aircraft's track fluctuation value is within the standard range, it is considered a straight flight segment, and imaging track angle processing is performed based on the straight flight segment. If not, it is considered a turning flight segment. The first average track angle calculated within the first aperture frame for the straight-line flight segment is used as the imaging track angle e, and is used as the initial value. For 2-n aperture frames, calculate the second average track angle value respectively. The initial value is compared with each of the second average track angle values ​​in turn. Determine whether the absolute value of the difference between the initial value and each of the second average track angle values ​​is greater than the track angle standard deviation. If so, the initial value is replaced by the second average track angle. If not, the initial value remains unchanged. The calculation of the imaging track angle for 2-N aperture frames includes: calculating the difference angle, which is the difference between the second average track angle value and the initial value. When the difference angle is >3° or <-3°, the initial value is replaced by the second average track angle value; otherwise, the imaging track angle remains unchanged.

2. The automatic calculation method for track angle in strip SAR imaging according to claim 1, characterized in that, The track angle is calculated using the inertial navigation data, including: Real-time reception of heading angle and yaw angle transmitted via the airborne 429 bus; The track angle is obtained by combining the heading angle and the yaw angle.

3. The automatic calculation method for track angle in strip SAR imaging according to claim 1, characterized in that, The determination of the track angle fluctuation range includes: Real-time statistics of the maximum and minimum track angles within each aperture frame period; The range of track angle fluctuation is the difference between the maximum and minimum track angle values.

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