Shock wave free field overpressure measurement method and system based on high-speed photography of unmanned aerial vehicle

Abstract

The application discloses a shock wave free field overpressure measurement method and system based on high-speed photography of a UAV, and relates to the field of shock wave measurement. Based on the refraction phenomenon of light caused by a wave front during propagation of a shock wave in air, high-speed photography of a ground explosion process is performed by using a high-speed camera of a UAV, an image difference value algorithm and an edge recognition algorithm are used to determine the wave front of each frame of shock wave image, the propagation speed of the wave front in air is obtained, analysis and measurement of the shock wave wave front are realized, and then the shock wave free field overpressure is obtained.

Description

Technical Field

[0001] This invention relates to the field of shock wave measurement, and in particular to a method and system for measuring free-field overpressure of shock waves based on high-speed photography by unmanned aerial vehicles. Background Technology

[0002] Explosives generate high speed and high pressure at the moment of explosion, forming a shock wave that is several times stronger than normal atmospheric pressure. When the shock wave from a physical explosion propagates through the air as sound energy from the explosion source (sound source), it is a series of spherical waves centered on the explosion's epicenter. Wherever it reaches, it causes abrupt changes in the air's pressure, density, and other physical properties. The interface between the original state and the disturbed state of the air medium is the shock wave front. The refractive index of the air at the location of the shock wave front will change significantly, such as... Figure 1 As shown.

[0003] In most cases, the destructive effect of a shock wave is caused by the overpressure on the wavefront. The overpressure of a physical explosion can reach several or even tens of atmospheres. Therefore, the peak overpressure of a physical explosion shock wave is one of the important indicators for measuring its destructive effect. Currently, the common method for testing and measuring shock wave overpressure is to use highly sensitive sensors to receive the pressure signal generated by the physical explosion, which is then digitized, recorded, and analyzed by a data acquisition unit. This method requires the deployment of a large number of sensors during testing, and the shock wave can also damage the sensors and their connecting cables. Summary of the Invention

[0004] The purpose of this invention is to provide a method and system for measuring shock wave free field overpressure based on high-speed photography by unmanned aerial vehicles (UAVs), which can realize the analysis and measurement of shock wave front through UAV photography.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] A method for measuring shock wave free-field overpressure based on high-speed UAV photography includes:

[0007] Setting up markers at the explosion test site;

[0008] The drone was hovered in the air, and the high-speed camera mounted on the drone was aimed at the explosion test site at a preset shooting frame rate;

[0009] The high-speed camera continuously captures images of the shock wave generated by the explosion at the test site from the air, forming a sequence of shock wave images reflecting the propagation process of the wave front in the air; the calibration object is captured on the shock wave images.

[0010] The initial wavefront of each frame of the shock wave image sequence is determined by image difference algorithm and edge recognition algorithm respectively, and the intersection of the two initial wavefronts is taken as the wavefront of each frame of the shock wave image.

[0011] Based on the position of the wavefront, the calibration object, and the preset shooting frame rate, the wavefront propagation velocity at the corresponding moment of each frame of shock wave image is determined;

[0012] Based on the propagation velocity of the wavefront, the overpressure at the wavefront position at each moment is obtained, which serves as the free-field overpressure of the shock wave propagating in the air at each moment.

[0013] Optionally, hovering the drone in the air and positioning the high-speed camera mounted on the drone at a preset frame rate to aim at the explosion test site specifically includes:

[0014] Adjust the focal length, aperture, exposure time, shooting frame rate, shooting time, and triggering method of the high-speed camera mounted on the drone;

[0015] Adjust the drone's position in the air according to the shooting direction;

[0016] Adjust the gimbal mounted on the drone so that the high-speed camera is aimed at the test site.

[0017] Optionally, an image interpolation algorithm is used to determine the initial wavefront of each frame of the shock wave image sequence, specifically including:

[0018] Subtract the pixel values ​​of each pixel in any two frames of the shock wave images in the (n-2)th, nth, and (n+2)th frames to obtain the first difference image between the (n-2)th and nth frames, the second difference image between the nth and (n+2)th frames, and the third difference image between the (n-2)th and (n+2)th frames; where n is a positive integer greater than 2.

[0019] In the first difference image, the second difference image, and the third difference image, pixel values ​​greater than or equal to the pixel threshold are assigned a value of 1, and pixel values ​​less than the pixel threshold are assigned a value of 0, thus obtaining the first binarized difference image, the second binarized difference image, and the third binarized difference image.

[0020] Select pixels whose pixel values ​​are both 1 in the first and second binarized difference images and whose pixel values ​​are 0 in the third binarized difference image, and construct the initial wavefront from all selected pixels.

[0021] Optionally, an edge recognition algorithm is used to determine the initial wavefront of each frame of the shock wave image sequence, specifically including:

[0022] Edge extraction operators are applied to the shock wave images of frame (n-2), frame (n), and frame (n+2) respectively to extract edges, resulting in edge images of frame (n-2), frame (n), and frame (n+2).

[0023] Compare the edge images of frame n, frame n-2, and frame n+2 at the same location, and construct the initial wavefront from the position in frame n that is different from both frame n-2 and frame n+2.

[0024] Optionally, the wavefront propagation velocity at the corresponding moment of each frame of the shock wave image is determined based on the position of the wavefront, the calibration object, and the preset shooting frame rate, specifically including:

[0025] Determine the pixel Euclidean distance L from the wavefront to the explosion center in each frame of the shock wave image. n ;

[0026] Measure the length l of the marker on each frame of the shock wave image;

[0027] Based on the pixel Euclidean distance and the length of the calibration object, the formula is used. Calculate the actual distance R from the wavefront to the explosion center on each frame of the shock wave image. n In the formula, H is the actual height of the calibration object;

[0028] in accordance with The formula calculates the wavefront propagation velocity at the corresponding moment for each frame of the shock wave image; where Vel n R represents the wavefront propagation velocity at the corresponding moment in the nth frame of the shock wave image. n-2 and R n+2 These are the actual distances from the wavefront to the explosion center in the shock wave images of frames n-2 and n+2, respectively, where Fps is the shooting frame rate.

[0029] Optionally, the formula for calculating the overpressure at the wavefront position at each time step is as follows:

[0030]

[0031] In the formula, ΔP n Let P be the overpressure at the wavefront position at the corresponding moment in the nth frame of the shock wave image, c be the speed of sound at standard atmospheric pressure, and P be the overpressure. atm Standard atmospheric pressure.

[0032] Optionally, an image interpolation algorithm and an edge recognition algorithm are used to determine the initial wavefront of each frame of the shock wave image sequence, and the intersection of the two initial wavefronts is taken as the wavefront of each frame of the shock wave image. This is followed by:

[0033] Visual enhancement of the wavefront in each frame of the shock wave image is performed, and the visually enhanced shock wave images of each frame are combined to obtain an image of the wavefront propagation process.

[0034] Optionally, based on the wavefront propagation velocity, the overpressure at the wavefront position at each moment is obtained as the free-field overpressure of the shock wave propagating in the air at each moment, and the process further includes:

[0035] Compare the overpressure at the wavefront position at each time point with the overpressure measured by the pressure sensor;

[0036] If the difference between the overpressure at the wavefront position and the overpressure measured by the pressure sensor at any given time is greater than the threshold, then the overpressure measured by the pressure sensor is determined to be an abnormal overpressure value.

[0037] By analyzing the shock wave image sequence at the measurement points where abnormal overpressure values ​​are located, the cause of the abnormal overpressure values ​​can be determined.

[0038] A shock wave free field overpressure measurement system based on high-speed photography by UAV includes: a calibration object, a UAV, a high-speed camera, and a host computer;

[0039] The calibration object was set up at the explosion test site; a high-speed camera was mounted on a drone.

[0040] The drone is used to carry a high-speed camera to continuously capture shock wave images of the explosion process from the air at a preset frame rate; the target object is captured on the shock wave images.

[0041] The host computer is used to determine the wavefront propagation velocity and wavefront position overpressure at each moment during the explosion process based on the continuously acquired shock wave images, the calibration object, and the preset shooting frame rate.

[0042] Optionally, the host computer includes:

[0043] The wavefront determination module is used to determine the initial wavefront of each frame of shock wave image by using image difference algorithm and edge recognition algorithm respectively, and take the intersection of the two initial wavefronts as the wavefront of each frame of shock wave image.

[0044] The wavefront propagation velocity determination module is used to determine the wavefront propagation velocity at the corresponding moment of each frame of shock wave image based on the position of the wavefront, the calibration object, and the preset shooting frame rate.

[0045] The wavefront position overpressure determination module is used to obtain the wavefront position overpressure at each moment based on the wavefront propagation speed, which serves as the free field overpressure of the shock wave propagating in the air at each moment.

[0046] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0047] This invention discloses a method and system for measuring the free-field overpressure of shock waves based on high-speed photography by unmanned aerial vehicles (UAVs). Based on the phenomenon of light refraction caused by the wavefront when a shock wave propagates in the air, the method uses high-speed photography by UAVs to capture the ground explosion process. Image difference algorithms and edge recognition algorithms are used to determine the wavefront of each frame of the shock wave image, obtain the propagation speed of the wavefront in the air, realize the analysis and measurement of the shock wave wavefront, and thus obtain the free-field overpressure of the shock wave. Attached Figure Description

[0048] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments 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.

[0049] Figure 1 A schematic diagram of existing spherical wave propagation;

[0050] Figure 2 A flowchart of a shock wave free field overpressure measurement method based on high-speed UAV photography provided in an embodiment of the present invention;

[0051] Figure 3 A schematic diagram of the shock wave free field overpressure measurement method based on high-speed photography by UAV provided in an embodiment of the present invention;

[0052] Figure 4 This is a schematic diagram of the structure for measuring shock wave free field overpressure based on high-speed photography by a drone, provided as an embodiment of the present invention. Detailed Implementation

[0053] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] The purpose of this invention is to provide a method and system for measuring shock wave free field overpressure based on high-speed photography by unmanned aerial vehicles (UAVs), which enables the analysis and measurement of the shock wave front through UAV photography.

[0055] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0056] This invention provides a method for measuring free-field overpressure of shock waves based on high-speed photography by unmanned aerial vehicles (UAVs). By utilizing the light refraction phenomenon caused by the wavefront when the shock wave propagates in the air, high-speed photography of ground explosions is performed to obtain the propagation process of the wavefront in the air. This is a non-contact measurement method.

[0057] This invention provides a method for measuring shock wave free-field overpressure based on high-speed UAV photography, such as... Figure 2 and Figure 3 As shown, it includes:

[0058] Step S1: Set up a calibration object at the explosion test site.

[0059] Set up a marker at the site in terms of height and mark its height.

[0060] Step S2: Hover the drone in the air and point the high-speed camera mounted on the drone at the explosion test site at a preset shooting frame rate.

[0061] Experiment preparation process: Based on the site conditions and required shooting position, deploy the high-speed camera (high-speed camera) of the UAV, adjust the gimbal to point it at the test site, adjust parameters such as focal length, aperture, exposure time, shooting frame rate, and shooting time, and select the trigger mode.

[0062] It is important to note that the drone's position height relative to its distance from the blast center should not be too large; otherwise, the projection of the spherical wavefront will not approximate a circular expanding wavefront, and the calibration error in the height direction will be too large, resulting in a significant decrease in accuracy.

[0063] Step S3: Use a high-speed camera to continuously collect images of the shock wave generated by the explosion at the explosion test site from the air, forming a sequence of shock wave images that reflect the propagation process of the wave front in the air; the shock wave images include a marker.

[0064] During the testing phase: During the explosion, the high-speed camera of the drone will trigger and capture images according to the selected triggering method.

[0065] Shock waves travel at speeds exceeding 1000 m / s in the air. The high-speed camera used in this invention operates at 3000 fps, or 3000 images per second. Only a high-speed camera can capture the wavefront of a shock wave, while cameras operating on flat ground cannot.

[0066] Steps S4 to S6 are the post-processing stage: the captured image sequence is analyzed. First, the image sequence is analyzed using image difference algorithm and edge recognition algorithm to find the wavefront position on each frame image. Using height direction calibration objects, the actual distance between the wavefront and the explosion center on each frame image is determined. Based on the actual distance between the wavefront and the explosion center on each frame image, the relationship between the wavefront velocity and time is further generated by combining the frame rate, thereby calculating the overpressure magnitude at the wavefront position.

[0067] Step S4: The image difference algorithm and the edge recognition algorithm are used to determine the initial wavefront of each frame of the shock wave image sequence, and the intersection of the two initial wavefronts is taken as the wavefront of each frame of the shock wave image.

[0068] Image interpolation algorithm: This algorithm analyzes and processes the shock wave front generated by a ground explosion by analyzing all the intermediate frames of the captured image sequence.

[0069] First, select the position of the explosive or projectile on the image and determine its pixel coordinates as the blast center position coordinates. When processing the nth frame, take the (n-2)th frame and the (n+2)th frame for joint analysis.

[0070] Since the background at the wavefront location in frame n has almost the same pixel values ​​and edge features in frames n-2 and n+2, and none of them are the same as in frame n, based on the above analysis, the pixel values ​​of each pixel in frames n-2, n, and n+2 are subtracted pairwise. Considering the layering and contrast of the background, a higher threshold is set for backgrounds with stronger layering and contrast, and a lower threshold is used for backgrounds with lower layering and contrast. The difference image obtained by pairwise subtraction is binarized using this threshold as a boundary. Pixels greater than or equal to the threshold are assigned a value of 1, and others are assigned a value of 0. The smaller closed regions of the binarized image are filtered out, thus removing image noise caused by the threshold setting. Pixels that meet the following condition—with a value of 1 in the binarized difference images of frames n and n-2, and frames n and n+2, and a value of 0 in the binarized difference image of frames n+2 and n-2—are identified as the wavefront location.

[0071] Edge recognition algorithm: Edge extraction is performed on three frames of images n-2, n, and n+2. Based on the comparison of the edge extraction results, the part of the edge image in the nth frame that is different from the other two frames at the same position is identified as the wavefront.

[0072] The wavefront is obtained by calculating the three images using the two methods described above and taking the intersection of the calculation results.

[0073] Step S5: Determine the wavefront propagation velocity at the corresponding moment of each frame of shock wave image based on the position of the wavefront, the calibration object, and the preset shooting frame rate.

[0074] Calculate the position of the wavefront on the n-frame image and its pixel Euclidean distance from the explosion center. Based on this Euclidean distance, calculate the corresponding wavefront velocity and overpressure for the wavefronts at the following medium-to-long distance positions.

[0075] Because in the mid-to-far field, the free-field wavefront approximately expands spherically around the explosion center, the projection of this spherical wavefront onto the image can be considered as a two-dimensional circular wavefront perpendicular to the ground and the plane containing the explosion center. Therefore, the distance from any point on this circular wavefront to the explosion center can be considered the distance from the wavefront to the explosion center. Furthermore, since this two-dimensional circular wavefront is parallel to the projection plane (e.g., ...), Figure 4 As shown in the figure, there will be no other velocity components outside this plane, and the influence of the projection angle during imaging does not need to be considered.

[0076] Therefore, a ruler (calibrator) is erected at the explosion center beforehand, and its height H is calibrated during shooting. Its length l on the image is measured. From equation (1), combined with the pixel Euclidean distance L from the explosion center obtained from the previous image processing, the distance is calculated. n The actual distance R between the wavefront and the blast center can be obtained. n And by taking advantage of this, its propagation speed Vel is derived from equation (2). n .

[0077]

[0078]

[0079] Fps represents the shooting frame rate.

[0080] Step S6: Based on the wavefront propagation velocity, obtain the overpressure at the wavefront position at each moment, which serves as the free field overpressure of the shock wave propagating in the air at each moment.

[0081] Therefore, the free-field overpressure ΔP of the shock wave propagating in the air in the nth frame can also be calculated from equation (3). n Wavefront propagation velocity and free-field overpressure are both important factors in analyzing and evaluating the explosive force field.

[0082]

[0083] Where c is the speed of sound under standard atmospheric pressure, P atm Standard atmospheric pressure.

[0084] Visual enhancement of the wavefront position in each frame of the image is achieved by multiplying the value of each pixel at that position by 3-10 times the pixel ratio when it is undisturbed, and then combining the frames of the image to generate a video, which can produce a clear image of the wavefront propagation process (wavefront dilatation image).

[0085] This method provides a reference for analyzing the propagation patterns of explosion shock waves and the damage they cause to targets. Based on high-speed UAV photography, the free-field overpressure measurement method for shock waves can obtain the free-field overpressure in the air, even in the far field or at higher altitudes—an advantage unmatched by ground-based sensors. This provides a reference for analyzing the propagation patterns of explosion shock waves and the damage they cause to targets.

[0086] Meanwhile, the shock wave free-field overpressure measurement method based on UAV high-speed photography can also assist in analyzing the causes of abnormal values ​​in ground overpressure sensors. Compared with ground-based high-speed photography, UAV aerial photography produces a stronger sense of background layering, more pronounced background distortion caused by the wavefront, and easier extraction of wavefront position and propagation speed information. In terms of actual field setup, UAV high-speed photography offers faster setup speed, fewer restrictions on shooting positions, and lower difficulty in shooting in complex terrain environments compared to ground-based high-speed photography.

[0087] This invention calibrates the length of relevant reference objects at the test site, captures images using high-speed photography by a drone, and obtains the wavefront velocity of the explosion field by setting the frame rate. Regarding the analysis of overpressure anomalies generated by near-field overpressure sensors, the image sequence from high-speed aerial drone photography is used to examine the measurement points where anomalies are found in ground-based DPR (device pixel ratio) overpressure sampling. This allows for the interpretation of ground-based measurement point anomalies caused by direct fragment impact, fragment ballistic waves, and ground reflection overpressure. Specifically, the overpressure value at the location of the anomaly is obtained using a shock wave free-field overpressure measurement method based on high-speed drone photography (its accuracy has been proven through free-field overpressure calculations), and compared with the results measured by the ground sensor at the measurement point to determine whether the sensor's measurement result is abnormal. This method, due to its superior ground monitoring capabilities compared to traditional high-speed ground photography, can be widely applied in the fields of explosion testing and damage assessment for wavefront velocity measurement and result analysis in explosion tests.

[0088] This invention also provides a shock wave free field overpressure measurement system based on high-speed photography by a drone, comprising: a calibration object, a drone, a high-speed camera, and a host computer.

[0089] The calibration object was set up at the explosion test site; a high-speed camera was mounted on a drone. The drone was used to continuously capture shock wave images of the explosion process from the air at a preset frame rate; the calibration object was captured on the shock wave images. The host computer was used to determine the wavefront propagation velocity and overpressure position of the wavefront at each moment during the explosion process based on the continuously acquired shock wave images, the calibration object, and the preset frame rate.

[0090] For example, the host computer includes: a wavefront determination module, a wavefront propagation velocity determination module, and a wavefront position overpressure determination module.

[0091] The wavefront determination module is used to determine the initial wavefront of each frame of shock wave image by using image difference algorithm and edge recognition algorithm respectively, and take the intersection of the two initial wavefronts as the wavefront of each frame of shock wave image.

[0092] The wavefront propagation velocity determination module is used to determine the wavefront propagation velocity at the corresponding moment of each frame of shock wave image based on the position of the wavefront, the calibration object, and the preset shooting frame rate.

[0093] The wavefront position overpressure determination module is used to obtain the wavefront position overpressure at each moment based on the wavefront propagation speed, which serves as the free field overpressure of the shock wave propagating in the air at each moment.

[0094] The specific implementation process of the host computer determining the wavefront propagation velocity and wavefront position overpressure at each moment during the explosion is similar in working principle and beneficial effect to the shock wave free field overpressure measurement method based on UAV high-speed photography described in the above embodiment. Therefore, it will not be described in detail here. For details, please refer to the introduction of the above method embodiment.

[0095] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple; relevant parts can be referred to the method section.

[0096] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for measuring shock wave free-field overpressure based on high-speed UAV photography, characterized in that, include: Setting up markers at the explosion test site; The drone was hovered in the air, and the high-speed camera mounted on the drone was aimed at the explosion test site at a preset shooting frame rate; The high-speed camera continuously captures images of the shock wave generated by the explosion at the test site from the air, forming a sequence of shock wave images reflecting the propagation process of the wave front in the air; the calibration object is captured on the shock wave images. The initial wavefront of each frame of the shock wave image sequence is determined using image interpolation and edge recognition algorithms, respectively. The intersection of two initial wavefronts is taken as the wavefront of each frame of the shock wave image sequence. Specifically, the image interpolation algorithm is used to determine the initial wavefront of each frame of the shock wave image sequence, which includes: subtracting the pixel values ​​of each pixel point in any two frames of the (n-2)th, nth, and (n+2)th shock wave images to obtain the first difference image between the (n-2)th and nth frames, the second difference image between the nth and (n+2)th frames, and the nth... -2 frames and the third difference image of the (n+2)th frame; where n is a positive integer greater than 2; assign 1 to the pixel values ​​greater than or equal to the pixel threshold in the first difference image, the second difference image and the third difference image, and assign 0 to the pixel values ​​less than the pixel threshold to obtain the first binarized difference image, the second binarized difference image and the third binarized difference image; select the pixels with pixel values ​​of 1 in the first binarized difference image and the second binarized difference image and pixel values ​​of 0 in the third binarized difference image, and form the initial wavefront with all the selected pixels; Based on the position of the wavefront, the calibration object, and the preset shooting frame rate, the wavefront propagation velocity at the corresponding moment of each frame of shock wave image is determined; Based on the propagation velocity of the wavefront, the overpressure at the wavefront position at each moment is obtained, which serves as the free field overpressure of the shock wave propagating in the air at each moment.

2. The method for measuring shock wave free-field overpressure based on high-speed UAV photography according to claim 1, characterized in that, The process of hovering the drone in the air and having a high-speed camera mounted on the drone aimed at the explosion test site at a preset frame rate specifically includes: Adjust the focal length, aperture, exposure time, shooting frame rate, shooting time, and triggering method of the high-speed camera mounted on the drone; Adjust the drone's position in the air according to the shooting direction; Adjust the gimbal mounted on the drone so that the high-speed camera is aimed at the test site.

3. The method for measuring shock wave free-field overpressure based on high-speed UAV photography according to claim 1, characterized in that, An edge recognition algorithm is used to determine the initial wavefront of each frame of the shock wave image sequence, specifically including: Edge extraction operators are applied to the shock wave images of frame (n-2), frame (n), and frame (n+2) respectively to extract edges, resulting in edge images of frame (n-2), frame (n), and frame (n+2). Compare the edge images of frame n, frame n-2, and frame n+2 at the same location, and construct the initial wavefront from the position in frame n that is different from both frame n-2 and frame n+2.

4. The method for measuring shock wave free-field overpressure based on high-speed UAV photography according to claim 1, characterized in that, Based on the position of the wavefront, the calibration object, and the preset frame rate, the wavefront propagation velocity at the corresponding moment of each frame of the shock wave image is determined, specifically including: Determine the pixel Euclidean distance L from the wavefront to the explosion center in each frame of the shock wave image. n ; Measure the length l of the marker on each frame of the shock wave image; Based on the pixel Euclidean distance and the length of the calibration object, the formula is used. Calculate the actual distance R from the wavefront to the explosion center on each frame of the shock wave image. n In the formula, H is the actual height of the calibration object; in accordance with The formula calculates the wavefront propagation velocity at the corresponding moment for each frame of the shock wave image; where Vel n R represents the wavefront propagation velocity at the corresponding moment in the nth frame of the shock wave image. n-2 and R n+2 These are the actual distances from the wavefront to the explosion center in the shock wave images of frames n-2 and n+2, respectively, where Fps is the shooting frame rate.

5. The method for measuring shock wave free-field overpressure based on high-speed UAV photography according to claim 4, characterized in that, The formula for calculating the overpressure at the wavefront position at each time step is as follows: In the formula, ΔP n Let P be the overpressure at the wavefront position at the corresponding moment in the nth frame of the shock wave image, c be the speed of sound at standard atmospheric pressure, and P be the overpressure. atm Standard atmospheric pressure.

6. The method for measuring shock wave free-field overpressure based on high-speed UAV photography according to claim 1, characterized in that, The initial wavefront of each frame of the shock wave image sequence is determined using image interpolation and edge recognition algorithms, respectively. The intersection of the two initial wavefronts is taken as the wavefront of each frame of the shock wave image. This is followed by: Visual enhancement of the wavefront in each frame of the shock wave image is performed, and the visually enhanced shock wave images of each frame are combined to obtain an image of the wavefront propagation process.

7. The method for measuring shock wave free-field overpressure based on high-speed UAV photography according to claim 1, characterized in that, Based on the wavefront propagation velocity, the overpressure at the wavefront position at each moment is obtained, which serves as the free-field overpressure of the shock wave propagating in the air at each moment. This is followed by: Compare the overpressure at the wavefront position at each time point with the overpressure measured by the pressure sensor; If the difference between the overpressure at the wavefront position and the overpressure measured by the pressure sensor at any given time is greater than the threshold, then the overpressure measured by the pressure sensor is determined to be an abnormal overpressure value. By analyzing the shock wave image sequence at the measurement points where abnormal overpressure values ​​are located, the cause of the abnormal overpressure values ​​can be determined.

8. A shock wave free-field overpressure measurement system based on high-speed UAV photography, characterized in that, include: Calibration equipment, drones, high-speed cameras, and host computers; The calibration object was set up at the explosion test site; High-speed cameras are mounted on drones; The drone is used to carry a high-speed camera to continuously capture shock wave images of the explosion process from the air at a preset frame rate; the target object is captured on the shock wave images. The host computer is used to determine the wavefront propagation velocity and wavefront position overpressure at each moment during the explosion process based on the continuously acquired shock wave images, the calibration object, and the preset shooting frame rate. The host computer includes: The wavefront determination module is used to determine the initial wavefront of each frame of the shock wave image using an image difference algorithm and an edge recognition algorithm, respectively, and to take the intersection of the two initial wavefronts as the wavefront of each frame of the shock wave image. Specifically, the image difference algorithm for determining the initial wavefront of each frame of the shock wave image sequence includes: subtracting the pixel values ​​of each pixel point from any two frames in the (n-2)th, nth, and (n+2)th frames of the shock wave image to obtain the first difference image between the (n-2)th and nth frames, the second difference image between the nth and (n+2)th frames, and the... The third difference image between frame n-2 and frame n+2; where n is a positive integer greater than 2; assigning a value of 1 to pixels greater than or equal to a pixel threshold in the first, second, and third difference images, and assigning a value of 0 to pixels less than the pixel threshold, to obtain the first, second, and third binarized difference images; selecting pixels with a value of 1 in both the first and second binarized difference images, and a value of 0 in the third binarized difference image, and constructing the initial wavefront from all selected pixels; The wavefront propagation velocity determination module is used to determine the wavefront propagation velocity at the corresponding moment of each frame of shock wave image based on the position of the wavefront, the calibration object, and the preset shooting frame rate. The wavefront position overpressure determination module is used to obtain the wavefront position overpressure at each moment based on the wavefront propagation speed, which serves as the free field overpressure of the shock wave propagating in the air at each moment.

Images