A monte carlo based range-gated imaging simulation method

Abstract

The application provides a Monte Carlo-based range-gating imaging simulation method, and belongs to the field of scattering medium imaging. In the simulation process, the delay time T of a detector in a range-gating system is replaced by a delay range S0, and the opening time of a gating gate of the detector in the range-gating system is replaced by a range S1. The transmission characteristics of photons in a scattering medium are calculated by using a Monte Carlo method, including scattering and absorption of the scattering medium to light. The photons emitted from the scattering medium are screened by using a range-gating method, and the number and spatial distribution of the photons reaching the detector are counted, i.e. a range-gating image. The application provides a theoretical basis for researching target information obtained by penetrating a scattering medium, and provides a theoretical basis for researches such as feature extraction and target identification of the scattering medium imaging, and has important scientific research significance and value.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of scattering medium imaging technology, and particularly relates to a Monte Carlo-based range-gated imaging simulation method. BACKGROUND

[0002] At present, underwater imaging detection technologies mainly include acoustic detection and photoelectric detection. The acoustic detection technology has a long detection distance, but has poor spatial resolution. The underwater photoelectric imaging technology has high resolution and can intuitively and quickly transfer two-dimensional or three-dimensional information of targets and scenes. However, due to the rapid attenuation of light in water along the transmission path, the underwater photoelectric imaging needs auxiliary illumination. In addition, the illumination and imaging systems of the underwater photoelectric imaging equipment are often in the same direction, and therefore, the backscattering of the illumination light becomes an important factor affecting the effective distance of the underwater photoelectric imaging system. Therefore, reducing backscattering and improving image contrast become the focus of the research on underwater photoelectric imaging technology. The range-gated technology can suppress backscattering, and significantly improve the imaging distance, so that the underwater laser range-gated imaging technology becomes one of the most effective photoelectric imaging technologies for underwater carrier platforms.

[0003] For the underwater range-gated photoelectric imaging system, some scientific and technical institutions have carried out effective research and development. For example, the LUCIE series products of DRDC Valcartier (Institute of Defense Research) in Canada can work under the sea at a depth of 200 m on ROVs, and can be used for detection and monitoring of ports and deep seas. The product has developed three generations (2006-2009) so far. Since 2006, Beijing Institute of Technology has carried out a lot of research on underwater range-gated imaging technology, including the use of a range-gated ICCD imaging system with a pulse width of 5 ns and a DPLNd:YAG high-power pulsed laser, the development of an underwater range-gated imaging experimental system, the realization of direct detection of targets at a distance of 40 m underwater, and a large number of improvements to handheld or table-type real-time underwater range-gated imaging instruments. The relevant work is also carried out by Electronic Institute 1411 and Weapon Institute 205. The working environment of the underwater range-gated imaging system is mostly the sea, and the sea environment itself is very complex. In addition, the design and manufacture of each link of the underwater range-gated imaging system cannot be idealized, and these factors together lead to the degradation of the quality of the obtained images. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a Monte Carlo-based range-gated imaging simulation method, which realizes active light illumination reflection type optical imaging simulation.

[0005] To achieve the above object, the application adopts the following technical scheme: a distance-gated imaging simulation method based on Monte Carlo, comprising: the simulation process is as follows: the photons emitted by a pulsed laser propagate in a scattering medium, a target object is located in the scattering medium, when the photons reach the target object, diffuse reflection occurs, then the photons are transmitted reversely in the scattering medium, and finally reach a detector on the same side of the light source; the position and distance of each movement of the photons are recorded, and the total path S of the photons is obtained by accumulation; the time when the laser pulse is emitted is set as 0, the detector gate is opened at time T and closed at time T+T; only when the photons reach the detector and the total path S is greater than the delay distance S0 and less than the sum of the delay distance S0 and the distance range S1, the photons are collected by the detector; the above process is repeated, and the number and spatial distribution of the photons reaching the detector are counted, which are the distance-gated images of the delay time T and the gate width T; whether the photons irradiate on the target object is determined by judging whether the position of the photons is located in the range of the target object; the light intensity of the photons after diffuse reflection is equal to the light intensity of the incident photons multiplied by the reflectivity of the target object at the position, and the reflection angle is randomly selected in the range of 0-180 degrees; the delay distance S0 is used to replace the delay time T of the detector in the distance-gated system, and the distance range S1 is used to replace the opening time of the gate of the detector in the distance-gated system, i.e. the gate width T. . .

[0006] In a preferred embodiment, in the simulation process, the delay distance S0 is set, S0=C*T, C is the speed of light, to replace the delay time T of the detector in the distance-gated system.

[0007] In a preferred embodiment, in the simulation process, the distance range S1 is used to replace the opening time of the gate of the detector in the distance-gated system, i.e. the gate width T, S1=C*T. .

[0008] In a preferred embodiment, in the distance-gated system, the time when the laser pulse is emitted is set as 0, the detector gate is opened at time T and closed at time T+T; in the simulation process, the total path S of the photons in the whole propagation process is recorded based on Monte Carlo simulation; if S<S0, it is known that the photons reach the detector before the gate is opened, at this time the photons are not counted; if S0<S<(S0+S1), it is known that the photons reach the detector in the opening of the gate, at this time the photons are counted; if (S0+S1)<S, it is known that the photons reach the detector after the gate is closed, at this time the photons are not counted. Compared with the prior art, the application has the following beneficial effects: the method provides a distance-gated optical imaging simulation method based on Monte Carlo, which is used to simulate the imaging results of the distance-gated system in the scattering medium.

[0009] ​​​BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 is a method implementation flowchart of an embodiment of the present application.

[0011] Figure 2 is a Monte Carlo-based range-gated imaging simulation model schematic diagram in an embodiment of the present application. DETAILED DESCRIPTION

[0012] The present application is further described below in conjunction with the accompanying drawings and embodiments.

[0013] It should be noted that the following detailed description is illustrative only, and is intended to provide further description in order to provide a fuller enabling teaching of the exemplary embodiments according to the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application pertains. In addition, it should be understood that descriptions, as used herein, are intended to be illustrative and are not intended to be limiting, as the spirit and scope of the present application is to be limited solely by the claims.

[0014] It should be noted that the terms used herein are merely for the purpose of describing particular embodiments and are not intended to limit the exemplary embodiments according to the present application; as used herein, the singular form is intended to include the plural form, unless the context clearly indicates otherwise, and it should be further understood that the terms "comprise" and / or "include" as used herein specify the presence of features, steps, operations, devices, components and / or combinations thereof.

[0015] Reference Figure 1 , 2 A Monte Carlo-based range-gated imaging simulation method,

[0016] Figure 1 The embodiment provided by the present application shows the implementation steps of the Monte Carlo-based range-gated imaging simulation method, which includes:

[0017] 1) Delay distance S0 instead of delay time T simulation.

[0018] 2) Distance range S1 instead of gate width Simulation.

[0019] 3) Transmission characteristic simulation.

[0020] 4) Receive reflected photon simulation

[0021] Wherein, the delay distance S0 instead of delay time T simulation step,

[0022] In the simulation, a delay distance S0 is used to replace the detector delay time T in the range-gated system. In a range-gated imaging system, imaging a target at a distance L requires the detector to wait for the pulsed laser to travel from emission to the target position and then back to the detector after a delay of T. At this point, the detector's gating gate is open, and the speed of light is C, so L = CT / 2. In the simulation, a delay distance S0, where S0 = CT, is used to replace the detector delay time T. S0 is precisely the total path S that the pulsed laser travels from emission to the target position and back to the detector without scattering. If the pulsed laser fails to reach the target and is scattered prematurely by the scattering medium, the total path S traveled by this portion of the laser will be less than S0. This non-target light will affect the system's imaging quality. During the simulation, the total path S of the pulsed laser is used to determine if it is less than S0. If S < S0, it indicates that the pulsed laser is not the target light and will not be received by the detector.

[0023] Where, the distance range S1 replaces the gate width. Simulation steps,

[0024] In the simulation, the range S1 is used to replace the gate opening time, i.e., the gate width, of the detector in the range gating system. In a range-gated imaging system, the imaging depth of field... It is determined by the width of the door The range resolution of a range-gated imaging system is determined by the laser pulse width and the gate width; on the other hand, the range resolution of a range-gated imaging system is determined by the laser pulse width and the gate width. The laser pulse width and gate width are determined. The smaller the value, the less backscattered light the detector receives, and the higher the signal-to-noise ratio of its imaging. During the simulation, a distance range S1 is set, where S1 = To replace the gate width in the distance gating system Assuming the laser pulse emission time is 0, the detector gating gate opens at time T, and at time T+ The detector is closed at all times. At this point, (S0+S1) is exactly the total distance S traveled by the pulsed laser in the gating system from the start of emission until the detector gating gate closes. If the pulsed laser reaches the target but is scattered by the scattering medium and returns to the detector, the total distance S traveled by this part of the laser will be greater than (S0+S1). By judging the total distance S traveled by the pulsed laser, if the total distance S>(S0+S1), it can be known that the pulsed laser is scattered light and is not received by the detector.

[0025] Among them, the transmission characteristic simulation steps,

[0026] First, according to the characteristics of the pulsed laser source, the wavelength of the incident photon is set to 532 nm, and the polarization state is linear polarization. The random sampling method is used to randomly generate the position, scattering angle and azimuth angle parameters of the incident photon according to the spatial light intensity distribution, emission angle and other properties of the pulsed laser source. The statistical characteristics of a large number of photons meet the light intensity distribution, emission angle and other properties of the pulsed laser source. The photon enters the scattering medium and scatters with the scattering particles. The scattering phase function is calculated using Mie scattering theory, and the probability distribution of the scattering angle is determined. Through the random sampling method, the position and distance information of each step in the transmission process of the photon are obtained and recorded. When the photon irradiates the target object, that is, the position of the photon is located within the range of the target object, reflection occurs, and the light intensity of the photon is equal to the light intensity of the photon before reflection multiplied by the reflectivity of the target object at that point. The reflection direction when the photon is reflected is randomly generated in the range of 0~180° using the rejection sampling method. The reflected photon is transmitted in the scattering medium again until the photon leaves the scattering medium. The position and distance of the photon at each movement are recorded during the transmission characteristic simulation process, and the total path S of the photon is obtained by accumulation.

[0027] wherein the receiving reflected photon simulation step,

[0028] is based on the distance gating principle to screen the photons entering the detector, so that the detector only collects photons within the gate width, thereby reducing the influence of backscattered light in active light illumination reflection imaging and improving the imaging quality. If the total path S of the photon in the transmission process

Claims

1. A Monte Carlo-based range-gated imaging simulation method, characterized in that, include; The simulation process is as follows: Photons emitted by the pulsed laser propagate in the scattering medium. The target object is located within the scattering medium. When the photon reaches the target object, diffuse reflection occurs. Subsequently, the photon propagates in the opposite direction in the scattering medium and finally reaches the detector on the same side as the light source. The position and distance of the photon's movement each time are recorded, and the total path S of the photon is calculated by summing these values. The laser pulse emission time is set to 0, and the detector gating gate opens at time T. At time T+... The detector is closed at all times; a photon is only collected by the detector if it reaches the detector and its total path S is greater than the delay distance S0 and less than the sum of the delay distance S0 and the distance range S1. This process is repeated to count the number of photons reaching the detector and their spatial distribution, which are the delay time T and the gate width. The distance-gated image; whether a photon illuminates the target object is determined by whether the photon's position is within the target object's range; the intensity of the photon after diffuse reflection is equal to the intensity of the incident photon multiplied by the reflectivity of the target object at that position, with the reflection angle randomly selected within the range of 0-180 degrees; the delay distance S0 is used to replace the detector's delay time T in the distance-gated system, and the distance range S1 is used to replace the gate opening time (i.e., gate width) of the detector in the distance-gated system. .

2. The Monte Carlo-based range-gated imaging simulation method according to claim 1, characterized in that, During the simulation, the delay distance S0, where S0 = C × T and C is the speed of light, is used to replace the detector delay time T in the distance gating system.

3. The Monte Carlo-based range-gated imaging simulation method according to claim 1, characterized in that, In the simulation, the distance range S1 is used to replace the gating gate opening time, i.e., the gate width, of the detector in the distance gating system. S1=C× .

4. The Monte Carlo-based range-gated imaging simulation method according to claim 1, characterized in that, In a range-gating system, let the laser pulse emission time be 0, the detector gating gate open at time T, and close at time T + ; during the simulation, based on Monte Carlo simulation, record the total distance S of photons during the entire propagation process; if S < S0, it can be known that the photons reach the detector before the gating gate opens, and at this time the photons are not counted; if S0 < S < (S0 + S1), it can be known that the photons reach the detector during the opening of the gating gate, and at this time the photons are counted; if (S0 + S1) < S, it can be known that the photons reach the detector after the gating gate closes, and at this time the photons are not counted.

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