High-speed-height-ratio lower frame type reverse scanning compensation imaging method

Abstract

The invention provides a high-speed-height-ratio lower frame type reverse scanning compensation imaging method, and particularly relates to a technology for compensating the motion attitude of an airplane by adopting frame type reverse scanning motion in a high-speed-height-ratio flight mode by an airborne photoelectric reconnaissance system so as to realize high-quality imaging. According to the technology, the motion of the carrier is compensated within the exposure time by utilizing the frame motion of the system to keep the staring of an image scene, mechanisms such as a fast reflecting mirror are not needed, the manufacturing cost is low, the algorithm is simple, the portability is high, the problem of imaging smear under a large speed-height ratio is solved, high-quality imaging is realized, a foundation is laid for accurate detection and identification of a target, and the method is suitable for popularization and application. The method is suitable for various airborne photoelectric systems which use an area array detector to realize clear imaging.

Description

Technical Field

[0001] The present invention belongs to the field of automatic control technology, and mainly relates to a frame-type backsweep compensation imaging technology of an airborne optoelectronic reconnaissance system under a high speed-to-height ratio, and in particular to a technology of using a frame-type backsweep motion to compensate for the motion posture of an aircraft in a high speed-to-height ratio flight mode of an airborne optoelectronic reconnaissance system to achieve high-quality imaging. Background Art

[0002] With the development of science and technology, the imaging quality of airborne optoelectronic systems, as the main way to detect targets, has become an important indicator for measuring equipment performance and an important prerequisite for target identification and attack. Since area array detectors have the characteristics of high sensitivity, environmental adaptability and strong anti-interference ability, in optoelectronic imaging systems, in order to detect long-distance targets and achieve high-quality imaging, area array detectors are often used. However, the exposure time of area array detectors is long. If the picture moves during the exposure time, the image will be blurred, thereby reducing the image quality.

[0003] When an airborne optoelectronic reconnaissance system detects a target in high-speed flight, the optoelectronic imaging system cannot focus on the same image within the exposure time due to the high-speed flight, and therefore cannot complete the high-quality imaging task of the target. Figure 1 As shown in the figure, the photo collection process of the optoelectronic reconnaissance system of the ground scene 1 is performed vertically during the flight of the carrier aircraft. The left and right sides are schematic diagrams without and with frame backscan compensation, respectively. When there is no backscan, the imaging result is the sum of the scene energy during the exposure of the detector from position A to position C, which is different from the energy distribution of scene 1, so a blurred scene appears; after backscan compensation, the line of sight of the detector is maintained at scene 1, and the accumulated energy distribution is approximately scene 1, so the purpose of clear imaging can be achieved.

[0004] Traditional airborne optoelectronic reconnaissance methods for obtaining high-quality images include electronic image stabilization methods and reflector backscanning methods. The patent number 202011425829 applied for by Wuhan Huazhong Tianjing Tongshi Technology Co., Ltd. discloses a method of using an image stabilization platform composed of inertial devices and servo control components to compensate for the relative movement of imaging sensors. This method solves the problem of image shaking caused by irregular jitter of the optoelectronic detection platform with the carrier, but it is only effective when the carrier shakes slightly, and is not applicable when the carrier shakes over a large range; the patent number 202010777312 applied for by the Xi'an Institute of Applied Optics discloses a method of using reflector backscanning to improve scanning efficiency. It is generally composed of a spindle platform carrying the detector and the reflector and a fast reflector mechanism for backscanning compensation. This method has a fast response rate and a small dynamic lag error, but requires an additional reflector mechanism to complete the backscanning compensation process. Summary of the invention

[0005] In view of the problems of complex structure and limited scope of application of existing methods, the present invention proposes a method for an airborne optoelectronic reconnaissance system to achieve high-quality imaging by adopting a frame-type backscan compensation technology under high speed-to-height ratio flight conditions. That is, the motion of the optoelectronic reconnaissance system frame is controlled by calculating the speed-to-height ratio of the carrier aircraft, thereby compensating for the motion of the carrier aircraft, so that the optoelectronic reconnaissance system can maintain its stare at the scene during the exposure time of the detector to achieve clear imaging.

[0006] The technical solution of the present invention is:

[0007] The frame-type backscan compensation imaging method under high speed-height ratio is characterized in that within one imaging cycle, the photoelectric reconnaissance system performs the frame-type backscan compensation action including the following steps:

[0008] Step 1: Initialize the frame position according to the aircraft flight attitude, speed and altitude data, wait for the backscan start signal to be received, and prepare to perform the backscan motion. If the backscan start signal is received, execute step 2, otherwise, maintain the frame position until the backscan start signal is received;

[0009] Step 2: Calculate the backsweep speed in real time according to the carrier aircraft's flight speed-to-height ratio and perform the backsweep movement at the speed;

[0010] Step 3: Determine whether the frame angle meets the start exposure condition. If so, execute step 4. Otherwise, execute step 2 until the start exposure condition is met or timeout occurs.

[0011] Step 4: Send an exposure start signal to the detector and calculate the backscan speed in real time during the exposure time to keep the scene fixed;

[0012] Step 5: Wait for the exposure end signal returned by the detector when the exposure is completed. If the exposure end signal is received, execute step 6; otherwise, keep the reverse scanning motion and continue to wait for the exposure end signal.

[0013] Step 6: Calculate the retrace speed in real time according to the carrier speed-to-height ratio and perform frame retrace motion;

[0014] Step 7: Determine whether the frame reaches the backscan starting position. If it reaches it, execute step 8. If it does not reach it, execute step 6 until it reaches the backscan starting position.

[0015] Step 8: End this frame backsweep and prepare to start the next cycle of backsweep movement.

[0016] Furthermore, the backsweep speed in step 2 and step 4 is:

[0017]

[0018] in:

[0019] V elV is the angular velocity component of the aircraft flying in the pitch direction of the optoelectronic reconnaissance system; rl is the angular velocity component of the aircraft flying in the roll direction of the optoelectronic reconnaissance system; θ is the heading angle of the aircraft; e is the eastward velocity; n is the northward velocity; H is the relative ground height; V is_el V is the pitch frame backsweep angular velocity; is rl is the roll frame backsweep angular velocity.

[0020] Furthermore, the starting exposure condition in step 3 is:

[0021]

[0022] in:

[0023] β t1 is the pitch angle position at time t1; α t1 is the rolling angle position at time t1; σ is a very small number compared to the frame angle; ε t1 is the pitch angle of the aircraft at time t1; t1 is the rolling angle of the aircraft at time t1.

[0024] Furthermore, the retrace speed in step 6 is:

[0025]

[0026] in:

[0027] V el '、V rl ' are the angular velocities of the pitch and roll frame retrace respectively; k is the proportional coefficient, the specific size of which can be changed according to the sending period of the retrace start signal.

[0028] Furthermore, the criterion for judging whether the frame has reached the backsweep starting position in step 7 is whether the angle error between the frame angle after calculating the pitch and roll compensation carrier attitude angle and the backsweep starting position is less than a very small number σ, that is:

[0029]

[0030] in:

[0031] β t2 is the pitch angle position at time t2; α t2 is the rolling angle position at time t2; ε t2 is the pitch angle of the aircraft at time t2; t2 is the roll angle of the aircraft at time t2; β0 is the starting angle position of the pitch backsweep; α0 is the starting angle position of the roll backsweep.

[0032] The beneficial effects of the present invention are embodied in the following aspects:

[0033] 1. The present invention does not require a fast reflector or other mechanism, and has beneficial effects in low-cost manufacturing and miniaturization of structure;

[0034] 2. The present invention utilizes the system's own frame movement to compensate for the carrier movement during the exposure time to maintain the image scene gaze, thereby solving the problem of imaging smear at high speed and high ratio, achieving high-quality imaging, and laying the foundation for accurate target detection and recognition;

[0035] 3. The present invention is implemented by software, has a simple algorithm, and is highly portable, and is applicable to various airborne optoelectronic systems that use area array detectors to achieve clear imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the vertical ground imaging process of the optoelectronic reconnaissance system under high speed and height ratio.

[0037] Figure 2 It is a schematic diagram of the frame-type backsweeping process under high speed and high ratio.

[0038] Figure 3 This is the schematic diagram of frame backscanning. DETAILED DESCRIPTION

[0039] The present invention will be further described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0040] A preferred embodiment of the present invention is a two-axis two-frame optoelectronic reconnaissance system, which are a pitch axis and a roll axis respectively. The system includes a visible light sensor and an infrared sensor for collecting clear images of ground reconnaissance by the optoelectronic reconnaissance system of the carrier aircraft during flight at a high speed ratio. Both the visible light and infrared sensors use array detectors, and the exposure time of the visible light sensor is shorter than that of the infrared sensor.

[0041] In one imaging cycle, the specific steps of the optoelectronic reconnaissance system to perform frame-type backscan compensation are as follows:

[0042] Step 1: Initialize the frame position according to the aircraft flight attitude (heading angle θ, pitch angle ε, roll angle γ), speed data (eastward speed e, northward speed n) and relative ground height H, wait for the reception of the backsweep start signal s1, and prepare to perform the backsweep movement; if s1 is received, record this time as t0 and execute step 2, otherwise, keep the frame backsweep start position until the backsweep start signal is received;

[0043] The angular velocity components of the aircraft motion in the pitch and roll directions of the optoelectronic reconnaissance system are calculated by the aircraft heading angle θ, eastward velocity e, northward velocity n and relative ground height H:

[0044]

[0045] Where V el V is the angular velocity component of the aircraft flying in the pitch direction of the optoelectronic reconnaissance system, rl is the angular velocity component in the rolling direction;

[0046] According to the empirical time T = 0.1s, the pitch backscan starting angle position β0 and the roll backscan starting angle position α0 are calculated respectively:

[0047]

[0048] Step 2: Calculate the backsweep speed in real time according to the aircraft's flight speed-to-height ratio and perform backsweep motion in the pitch and roll directions at the speed;

[0049] The angular velocity component of the aircraft flying on the optoelectronic reconnaissance system frame is calculated by formula (1), and then the frame backscan angular velocity is obtained:

[0050]

[0051] Where V is_el is the pitch frame backsweep angular velocity, V is_rl is the roll frame backsweep angular velocity.

[0052] Step 3: Determine the frame angle β at the current time t1 t1 and α t1 Whether the exposure start condition is met, if so, execute step 4, otherwise, execute step 2 until the exposure start condition is met or step 4 is executed after timeout T1 = 0.4s;

[0053] Calculate the error angle after the optoelectronic reconnaissance system compensates for the carrier's attitude angle. If it is less than σ, it can be considered that the optoelectronic reconnaissance system's line of sight is perpendicular to the ground at this time, that is, the exposure condition is met, and the next step can be taken; if the exposure condition is not met, the next step can be taken when t1-t0>T1, that is, the exposure condition is:

[0054]

[0055] In the formula, β t1 is the pitch angle position at time t1, α t1 is the rolling angle position at time t1, β t1 and α t1 It can be obtained by the angle sensor of the photoelectric reconnaissance system. σ is a very small number compared to the frame angle. In this embodiment, σ=0.0017, ε t1 is the pitch angle of the aircraft at time t1, γ t1 is the aircraft roll angle at time t1, ε t1 and γ t1 Available via external communications.

[0056] Step 4: Send exposure start signals s2 and s2' to the visible light and infrared detectors, and calculate the backsweep speed in real time. Perform backsweep motions in the roll and pitch directions simultaneously so that the scene does not change during the exposure time. The backsweep speed is calculated as shown in equations (1) and (3).

[0057] Step 5: Wait for the exposure end signals s3 and s3' returned by the visible light and infrared detectors when the exposure is completed. Since the infrared exposure time is longer than the visible light, a backscan motion is still required after the visible light exposure is completed, waiting for the infrared exposure to end. If s3' is received, execute step 6, otherwise keep the backscan motion and continue to wait for the exposure end signals s3 and s3'.

[0058] Step 6: Calculate the retrace speed in real time according to the carrier speed-to-height ratio and perform frame retrace motion;

[0059] The angular velocity of the pitch and roll frames of the optoelectronic reconnaissance system is calculated by using formula (1). After the exposure is completed, it is necessary to quickly return to the start position of the backsweep. In order to ensure that the frame is in place before the next s1 signal arrives, the retracement speed must be greater than the backsweep speed. In the formula, k>1. The specific size can be changed according to the transmission period of the s1 signal, that is, the retracement speed is:

[0060]

[0061] Where V el '、V rl ' are the angular velocities of the pitch and roll frame retracement, respectively, and k is a proportional coefficient. In order to quickly reach the retracement starting angle position, the value of k should be greater than 1. In this embodiment, k=2.

[0062] Step 7: Determine whether the frame reaches the backscan starting position. If it reaches it, execute step 8. If it does not reach it, execute step 6 until it reaches the backscan starting position.

[0063] The backscan starting position of pitch and roll is obtained in real time through equations (1) and (2). The angle error between the frame angle after pitch and roll compensation of the carrier attitude angle and the backscan starting position is calculated. If it is less than the minimum number σ, it is considered that the frame has reached the backscan starting position at this time, and the next step can be executed, namely:

[0064]

[0065] In the formula, β t2 is the pitch angle position at time t2, α t2 is the rolling angle position at time t2, ε t2 is the pitch angle of the aircraft at time t2, γ t2is the roll angle of the aircraft at time t2, β0 is the starting angle position of the pitch backsweep, and α0 is the starting angle position of the roll backsweep.

[0066] Step 8: End the current frame backsweep compensation movement and prepare to start the next cycle of backsweep movement.

[0067] When the carrier aircraft was flying at an altitude of 1000m, a speed of 180km / h, and moving at 30° north-east, visible light and infrared photos of the optoelectronic reconnaissance system using the present embodiment and the optoelectronic reconnaissance system not using the method of the present invention were collected respectively. In addition, pictures in a static state were collected as standard images, and the image quality was evaluated using the variance method. After analysis, it was found that the quality of the visible light and infrared images without using the present method could reach 55% and 47% of the standard images, while that using the present method could reach 90% and 85%.

[0068] Finally, it should be noted that the features mentioned and / or shown in the above description of the exemplary embodiments of the present invention may be combined in the same or similar manner into one or more other embodiments, combined with the features in other embodiments or substituted for the corresponding features in other implementations. The technical solutions obtained by these combinations or substitutions shall also be deemed to be included in the protection scope of the present invention.

Claims

1. A frame-type backscanning compensation imaging method under a high speed-to-height ratio, characterized in that: In one imaging cycle, the photoelectric reconnaissance system performs the frame-type backscan compensation action including the following steps: Step 1: Initialize the frame position according to the aircraft flight attitude, speed and altitude data, wait for the backscan start signal to be received, and prepare to perform the backscan motion. If the backscan start signal is received, execute step 2, otherwise, maintain the frame position until the backscan start signal is received; Step 2: Calculate the backsweep speed in real time according to the carrier aircraft's flight speed-to-height ratio and perform the backsweep movement at the speed; Step 3: Determine whether the frame angle meets the start exposure condition. If so, execute step 4. Otherwise, execute step 2 until the start exposure condition is met or timeout occurs. Step 4: Send an exposure start signal to the detector and calculate the backscan speed in real time during the exposure time to keep the scene fixed; Step 5: Wait for the exposure end signal returned by the detector when the exposure is completed. If the exposure end signal is received, execute step 6; otherwise, keep the reverse scanning motion and continue to wait for the exposure end signal. Step 6: Calculate the retrace speed in real time according to the carrier speed-to-height ratio and perform frame retrace motion; Step 7: Determine whether the frame reaches the backscan starting position. If it reaches it, execute step 8. If it does not reach it, execute step 6 until it reaches the backscan starting position. Step 8: End this frame backsweep and prepare to start the next cycle of backsweep movement.

2. The frame-type backscan compensation imaging method under high speed-to-height ratio as claimed in claim 1, characterized in that: The backsweep speed in step 2 and step 4 is: in: V el V is the angular velocity component of the aircraft flying in the pitch direction of the optoelectronic reconnaissance system; rl is the angular velocity component of the aircraft flying in the roll direction of the optoelectronic reconnaissance system; θ is the heading angle of the aircraft; e is the eastward velocity; n is the northward velocity; H is the relative ground height; V is_el V is the reverse sweep angular velocity of the pitch frame; is_rl is the roll frame backsweep angular velocity.

3. The frame-type backscanning compensation imaging method under high speed-to-height ratio as claimed in claim 1, characterized in that: The starting exposure condition in step 3 is: in: β t1 is the pitch angle position at time t1; α t1 is the rolling angle position at time t1; σ is a very small number compared to the frame angle; ε t1 is the pitch angle of the aircraft at time t1; t1 is the rolling angle of the aircraft at time t1.

4. The frame-type backscan compensation imaging method under high speed-to-height ratio as claimed in claim 1, characterized in that: The retrace speed in step 6 is: in, V el '、V rl ' are the angular velocities of the pitch and roll frame retrace respectively; k is the proportional coefficient, the specific size of which can be changed according to the sending period of the retrace start signal.

5. The frame-type backscan compensation imaging method under high speed-to-height ratio as claimed in claim 1, characterized in that: The criterion for judging whether the frame has reached the backscan starting position in step 7 is whether the angle error between the frame angle after calculating the pitch and roll compensation carrier attitude angle and the backscan starting position is less than a very small number σ, that is: in: β t2 is the pitch angle position at time t2; α t2 is the rolling angle position at time t2; ε t2 is the pitch angle of the aircraft at time t2; t2 is the roll angle of the aircraft at time t2; β0 is the starting angle position of the pitch backsweep; α0 is the starting angle position of the roll backsweep.

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