Method for suppressing atmospheric scattered light in active laser imaging through fog

Abstract

The present invention discloses a method for suppressing atmospheric scattered light in laser active fog-penetrating imaging, which relates to the field of laser imaging technology. The method comprises the following steps: placing a laser light source and a CCD image sensor separately; calculating the relationship between the atmospheric scattered light energy received by the CCD and the discrete distance L under different conditions; calculating the target energy received by the CCD under different conditions; calculating the signal-to-noise ratio (SNR) of the image based on the atmospheric scattered light energy and the target energy, and obtaining the discrete distance L when SNR=1 based on the relationship between the atmospheric scattered light energy and the discrete distance L. SNR＝1 ; Set the discrete distance L>L SNR＝1 This method significantly suppresses background light noise caused by scattered light from fog particles in the atmosphere, significantly improving the signal-to-noise ratio of active imaging in foggy conditions and providing a simple and applicable method for active imaging through fog.

Description

Technical Field

[0001] The present invention relates to the technical field of atmospheric laser imaging, in particular to a method for suppressing atmospheric scattered light in active laser fog-penetrating imaging. Background Art

[0002] Active optical imaging is gaining popularity in areas such as criminal investigation, scientific research, safety, and navigation, and its impact on people's lives is growing. However, in foggy conditions, the quality and detection range of active imaging are significantly reduced. This is primarily due to the strong scattering of laser light by fog particles in the atmosphere, which increases the background light in the image. This results in a lower signal-to-noise ratio and a shorter detection range, severely impacting the effectiveness of active imaging.

[0003] Currently, the technologies for improving the quality of active optical imaging mainly include polarized light imaging technology and range-gated imaging technology.

[0004] Polarized light imaging through fog technology primarily acquires multi-dimensional active optical polarization images and applies image processing methods to enhance fog-penetrating imaging capabilities. This technology's unique advantages lie in increasing the image dimension and applying image processing techniques without suppressing the intensity of laser light scattered by atmospheric fog particles as detected by the CCD image sensor. This technology is effective in light fog, but less effective in dense fog.

[0005] Range-gated imaging technology suppresses atmospheric scattered light from the active laser beam by controlling the exposure start and duration of the CCD image sensor, thereby improving the signal-to-noise ratio and image quality. Range-gated imaging significantly reduces the intensity of laser beam scattered light from atmospheric fog particles, improving the image signal-to-noise ratio. This technology is effective in both light and dense fog. However, its disadvantage is the high hardware cost, requiring an enhanced ICCD and a high-power pulsed laser. Summary of the Invention

[0006] In order to overcome the defects in the above-mentioned prior art, the present invention provides a method for suppressing atmospheric scattered light in laser active fog-penetrating imaging. By increasing the distance between the laser light source and the CCD image detector, the background light noise caused by the scattered light of fog particles in the atmosphere can be greatly suppressed, and the signal-to-noise ratio of active imaging in foggy conditions can be significantly improved, thus finding a simple and applicable method for active fog-penetrating imaging.

[0007] To achieve the above object, the present invention adopts the following technical solutions, including:

[0008] A method for suppressing atmospheric scattered light in laser active fog-penetrating imaging includes the following steps:

[0009] S1, the laser light source and the CCD image sensor are placed separately, and the separation distance is recorded as L;

[0010] S2, calculating the relationship between the energy of the atmospheric scattered light received by the CCD image sensor and the discrete distance L under specific conditions; wherein the conditions are composed of the atmospheric visibility and the target distance; the target distance refers to the distance between the laser light source and the target;

[0011] S3, calculates the target energy received by the CCD image sensor under specific conditions;

[0012] S4, calculate the signal-to-noise ratio (SNR) of the image based on the energy of the atmospheric scattered light and the target energy, and according to the relationship between the energy of the atmospheric scattered light and the discrete distance L obtained in step S2, the discrete distance when SNR=1 is obtained as L SNR＝1 ;

[0013] S5, set the discrete distance between the laser light source and the CCD image sensor L>L SNR＝1 , thereby achieving the suppression of atmospheric scattered light in laser active fog-penetrating imaging under this specific condition.

[0014] Preferably, in step S1, the radius of the spot irradiated by the laser on the target is D, the distance between the laser and the target, i.e., the target distance is R2, the line connecting the center of the spot on the target and the CCD forms an intersection with the laser beam, and the distance between the intersection and the CCD is R1; wherein,

[0015] .

[0016] Preferably, the specific process of step S2 is as follows:

[0017] S21, within the distance from R1 to R2, the total atmospheric scattered light energy received by the CCD image sensor is:

[0018]

[0019] Where P0 is the laser emission power; τ is the exposure time; ηr and ηt are the optical transmittances of the emitting and receiving parts, respectively; Ar is the effective receiving area of ​​the CCD image sensor; R is the distance variable, i.e., the integral variable; β is the atmospheric backscattering coefficient; α is the atmospheric extinction coefficient;

[0020] S22, the atmospheric scattered energy received by a single pixel is E a，pix =E a / N, N is the number of pixels occupied by the target;

[0021]

[0022]

[0023] The relationship between the atmospheric extinction coefficient α and the atmospheric visibility V is:

[0024]

[0025] Where q is a constant related to the atmospheric visibility V, and λ is the laser wavelength;

[0026] S23, according to the formula of step S22, simulate E under different atmospheric visibility V and different target distance R2 a，pix The relationship between the distance R1 and the target distance R2 is obtained by converting the distance R1 into a discrete distance L according to the formula in step S1. a，pix Relationship with the discrete distance L.

[0027] Preferably, the specific process of step S3 is as follows:

[0028] S31, the target energy received by the CCD image sensor, that is, the diffuse reflection energy received by the target is:

[0029]

[0030] Where P0 is the emission power of the laser; τ is the exposure time; ηr and ηt are the optical transmittances of the emitting and receiving parts, respectively; Ar is the effective receiving area of ​​the CCD image sensor; G is the normalized reflectivity of the target; α is the atmospheric extinction coefficient;

[0031] S32, the target energy received by a single pixel is E t，pix =E t / N, N is the number of pixels occupied by the target;

[0032]

[0033]

[0034] The relationship between the atmospheric extinction coefficient α and the atmospheric visibility V is:

[0035]

[0036] Where q is a constant related to the atmospheric visibility V, and λ is the laser wavelength.

[0037] Preferably, in step S4, the signal-to-noise ratio (SNR) of the image is:

[0038]

[0039] Among them, E t，pix is the target energy received by a single pixel, E t,pix =Et / N,E t is the target energy received by the CCD image sensor, N is the number of pixels occupied by the target; E a,pix is the atmospheric scattered energy received by a single pixel, E a,pix =E a / N,E a The CCD image sensor receives atmospheric scattered energy.

[0040] A linked scanning device, suitable for the above-mentioned method of suppressing atmospheric scattered light in laser active fog-penetrating imaging, includes two turntables and a turntable control unit; the laser and the CCD image sensor are placed on the two turntables respectively, and the turntable control unit controls the two turntables respectively to perform synchronous scanning control on the separately placed laser and CCD image sensor.

[0041] The advantages of the present invention are:

[0042] (1) The present invention proposes a method for nearly suppressing atmospheric scattered light in laser active imaging in foggy weather. That is, by increasing the distance between the laser light source and the CCD image detector, the background light noise caused by the scattered light of fog particles in the atmosphere can be greatly suppressed, and the signal-to-noise ratio of active imaging in foggy weather can be significantly improved, thus finding a simple and applicable method for active imaging through fog.

[0043] (2) In the method proposed in the present invention, a non-enhanced CCD and a continuous semiconductor laser of several tens of watts are used, but the effect of suppressing scattered light in active optical imaging in foggy weather is equivalent to that of the range gating technology, and the hardware requirements are low, simple and convenient. At the same time, the scanning detection of aerial targets is achieved through the linkage of the laser and the CCD image sensor.

[0044] (3) The present invention proposes a method for suppressing scattered light from active optical imaging in foggy weather by separately placing a laser and a CCD image sensor and a linked scanning method.

[0045] (4) The present invention quantitatively simulates the relationship between the discrete distance and the atmospheric scattered light received by the CCD under different fog visibility conditions and different target distances.

[0046] (5) The present invention proposes a criterion for selecting the discrete distance. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 Schematic diagram of the discrete infrared active imaging structure.

[0048] Figure 2 is the atmospheric scattering energy E of a single pixel under different conditions a,pix Relationship curve with R1.

[0049] Figure 3The atmospheric scattering energy E of a single pixel when R2 = 200m, 2D = 10m, and V = 100m a,pix Graph showing the relationship between the discrete distance L.

[0050] Figure 4 is the diffuse reflection energy E of a single pixel under different conditions t,pix , and the atmospheric scattered energy E a,pix Relationship curve with R1.

[0051] Figure 5 Schematic diagram of the linkage scanning device.

[0052] Figure 6 This is a flow chart of a method for suppressing atmospheric scattered light in active laser fog-penetrating imaging according to the present invention. DETAILED DESCRIPTION

[0053] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0054] Example 1

[0055] The present invention provides a method for suppressing atmospheric scattered light in active laser fog-penetrating imaging. The laser light source (laser) and the CCD image sensor are placed separately, and the relationship between the atmospheric scattered light energy received by the CCD image sensor and the discrete distance L (the discrete distance between the laser light source and the CCD image sensor) is obtained through simulation calculation, thereby providing a theoretical basis for determining the discrete distance.

[0056] Depend on Figure 6 As shown, the method of the present invention comprises the following steps:

[0057] S1, place the laser light source and the CCD image sensor separately, and the separation distance is recorded as L.

[0058] In general active optical imaging devices, the distance between the laser light source and the CCD image sensor (abbreviated as CCD) is on the order of centimeters, so it can be considered that the two are placed together. The present invention proposes to place the two separately, as shown in the schematic diagram of the separate placement. Figure 1As shown in the figure. Among them, the spot radius of the laser beam irradiated on the target is D, the distance between the laser (Laser) and the target, i.e., the target distance, is R2 (R2 >> L), the separation distance between the CCD and the laser is L, the divergence angle of the laser beam is θ1, the angle between the line connecting the center point of the spot on the target and the CCD and the vertical direction is θ2, and the line connecting the center point of the spot on the target and the CCD intersects with the laser beam, and the distance between this intersection point and the CCD is R1 (R1 >> L). Since R2 >> L and R1 >> L, therefore Figure 1 the distances R2 and R1 shown in it are approximate distances.

[0059] According to the above geometric relationships, in the two cases of L < D and L > D, as Figure 1 shown in (a) and (b) in it, there is always

[0060]

[0061] From Figure 1 it can be seen that for the center point of the illuminated area on the target (the center point of the spot on the target), the atmospheric scattered light of the laser beam within the distance of R1 is suppressed, but the atmospheric scattered light of the laser beam within the distance from R2 to R1 is still received by the CCD image sensor. For different points in the illuminated area on the target, the distances of the suppressed atmospheric scattered light are different; by changing the separation distance L, the atmospheric scattered light of the laser beam suppressed for the same point in the target is also different, and the larger the separation distance L, the more the atmospheric scattered light of the laser beam is suppressed.

[0062] S2. Through simulation, calculate the relationship between the energy of the atmospheric scattered light received by the CCD image sensor and the separation distance L, which is specifically as follows:

[0063] S21. The scattered light at different distances within the divergence angle of the CCD image sensor will be received by the CCD. The energy of the atmospheric scattered light on the laser beam received by the CCD within the distance from R to R + dR is:

[0064]

[0065] Among them, P0 is the emission power of the laser (unit: W), T is the exposure time, ηr and ηt are the optical transmittances of the emission part and the receiving part respectively, A r is the effective receiving area of the CCD (unit: m 2 [[ID=三十一]]),β为大气后向散射系数(单位为km-1Sr-1), is the two-way transmittance of the atmosphere, α is the atmospheric extinction coefficient (unit: km-1).

[0066] Therefore, within the distance from R1 to R2, the total energy of the atmospheric scattered light received by the CCD image sensor is:

[0067]

[0068] Among them, R is the distance variable or the integral variable;

[0069] S22, the atmospheric scattered energy received by a single pixel is E a，pix =E a / N, where N is the number of pixels occupied by the target. Substituting this into the equation, we get:

[0070]

[0071]

[0072] Where C is the system constant. When the system constant C is constant, the atmospheric scattered energy E received by a single pixel is a，pix It is a function of the distances R1, R2, the atmospheric extinction coefficient α, and the atmospheric backscatter coefficient β. Extinction-backscatter ratio S = α / β.

[0073] Among them, the relationship between the atmospheric extinction coefficient α and the atmospheric visibility V is:

[0074]

[0075] Where q is a constant related to the atmospheric visibility V, and λ is the laser wavelength.

[0076] In this embodiment, the wavelength of the laser irradiated is 1064 nm. Under the three conditions of light fog, medium fog and thick fog (the atmospheric visibility V is 1500 m, 400 m and 100 m respectively), and at different target distances R2 (R2 is 1500 m, 500 m and 200 m respectively), the E simulated by formula (4) is a，pix The relationship curve with R1 is as follows Figure 2 shown.

[0077] from Figure 2 It can be seen that the atmospheric scattered energy E received by a single pixel a，pix As the distance R1 increases, it rapidly attenuates, and the greater the atmospheric visibility V, the greater the E a，pix The faster the decay.

[0078] For the center point of the light spot on the target (special point), according to formula (1), converting R1 into a discrete distance L can simulate the atmospheric scattered energy E received by a single pixel. a，pix The relationship curve with the discrete distance L, specifically, under R2 = 200m, 2D = 10m, V = 100m, the simulation results are as follows Figure 3 As shown, from Figure 3 It can be seen that the atmospheric scattering energy E a，pixIt decays rapidly with the increase of the discrete distance L, from which we can conclude that increasing the discrete distance L can greatly suppress the atmospheric scattered light of the laser beam.

[0079] S3, calculating the target energy received by the CCD image sensor.

[0080] S31, within the target distance R2, that is, from 0 to R2, the target is irradiated by the laser and diffusely reflects outward. The target energy received by the CCD, that is, the diffusely reflected energy received by the target is:

[0081]

[0082] Among them, P0 is the emission power of the laser, τ is the exposure time, η r and η t are the transmittance of the transmitting part and the receiving part respectively, Ar is the effective receiving area of ​​CCD, G is the normalized reflectivity of the target (unit is Sr- 1 ), when the target is larger than the light spot, G = ρ / π, where ρ is the reflectivity of the target; is the two-way transmittance of the atmosphere, and α is the atmospheric extinction coefficient.

[0083] S32, the target energy received by a single pixel is E t，pix =E t / N, where N is the number of pixels occupied by the target; substituting this into:

[0084]

[0085]

[0086] Where C is the system constant, which is the same as the system constant in formula (4).

[0087] The relationship between the atmospheric extinction coefficient α and the atmospheric visibility V is:

[0088]

[0089] Where q is a constant related to the atmospheric visibility V, and λ is the laser wavelength.

[0090] In this embodiment, the wavelength of the laser irradiated is 1064 nm. Under the three conditions of light fog, medium fog and thick fog (the atmospheric visibility V is 1500 m, 400 m and 100 m respectively), and at different target distances R2 (R2 is 1500 m, 500 m and 200 m respectively), the E simulated by formula (6) is t，pix like Figure 4 shown, and Figure 4 The E simulated by formula (4) is also shown in a，pix The relationship curve with R1 (i.e. Figure 2 ) for comparison.

[0091] S4, calculate the signal-to-noise ratio (SNR) of the image based on the energy of the atmospheric scattered light and the target energy, and according to the relationship between the energy of the atmospheric scattered light and the discrete distance L obtained in step S2, obtain the discrete distance L when SNR=1 under specific conditions. SNR =1.

[0092] As an approximation, only the interference of atmospheric scattered light is considered while ignoring the interference caused by random errors and dark current, then the signal-to-noise ratio of the image is:

[0093]

[0094] In this embodiment, according to Figure 4 Under certain weather conditions (atmospheric visibility V) and target distance R2, the distance R1 when SNR = 1 is obtained. Combined with formula (1), the discrete distance between the laser and the CCD image sensor at this time can be calculated, that is, the discrete distance L when SNR = 1 SNR＝1 .

[0095] S5, selecting a discrete distance L between the CCD image sensor and the laser, wherein the backscattered light is less than or equal to the target reflected light.

[0096] If the signal-to-noise ratio is defined as greater than or equal to 1 as the condition for image recognition, then the discrete distance between the laser light source and the CCD image sensor is set to L>L SNR＝1 , thus achieving the suppression of atmospheric scattered light in laser active fog-penetrating imaging. When L>L SNR＝1 When , the target image on the CCD is considered to be recognizable.

[0097] Example 2

[0098] Based on the formula (2) and formula (7) of the above embodiment 1, and combined with Figure 3 and Figure 4 It can be seen that when the target distance R2 is more than 100 meters, the separation distance between the laser and the CCD image sensor must be more than 10 meters. In this way, it is difficult to place the laser and the CCD image sensor on a rotating platform.

[0099] Depend on Figure 5 As shown, the present invention also provides a linkage scanning device, which is suitable for the method of suppressing atmospheric scattered light in the above-mentioned laser active fog-penetrating imaging, including two turntables and a turntable control unit; the laser and the CCD image sensor are placed on the two turntables respectively, and the turntable control unit controls the two turntables respectively, and performs synchronous scanning control on the separately placed lasers and CCD image sensors, thereby realizing scanning detection of space targets.

[0100] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for suppressing atmospheric scattered light in active laser fog-penetrating imaging, characterized in that: The following steps are involved: S1, the laser light source and the CCD image sensor are placed separately, and the separation distance is recorded as L; S2, calculating the relationship between the energy of the atmospheric scattered light received by the CCD image sensor and the discrete distance L under specific conditions; wherein the conditions are composed of the atmospheric visibility and the target distance; the target distance refers to the distance between the laser light source and the target; S3, calculates the target energy received by the CCD image sensor under specific conditions; S4, calculate the signal-to-noise ratio (SNR) of the image based on the energy of the atmospheric scattered light and the target energy, and according to the relationship between the energy of the atmospheric scattered light and the discrete distance L obtained in step S2, the discrete distance when SNR=1 is obtained as L SNR＝1 ; S5, set the discrete distance between the laser light source and the CCD image sensor L>L SNR＝1 , thereby achieving the suppression of atmospheric scattered light in laser active fog-penetrating imaging under this specific condition.

2. The method for suppressing atmospheric scattered light in active laser fog-penetrating imaging according to claim 1, characterized in that: In step S1, the radius of the laser spot irradiated on the target is D, the distance between the laser and the target, i.e., the target distance, is R2, and the line connecting the center of the laser spot on the target and the CCD forms an intersection with the laser beam, and the distance between the intersection and the CCD is R1; in, 3. The method for suppressing atmospheric scattered light in active laser fog-penetrating imaging according to claim 2, characterized in that: The specific process of step S2 is as follows: S21, within the distance from R1 to R2, the total atmospheric scattered light energy received by the CCD image sensor is: Where P0 is the laser emission power; τ is the exposure time; η r and η t are the optical transmittances of the transmitting and receiving parts respectively; A r is the effective receiving area of ​​the CCD image sensor; R is the distance variable, i.e., the integral variable; β is the atmospheric backscattering coefficient; α is the atmospheric extinction coefficient; S22, the atmospheric scattered energy received by a single pixel is E a,pix =E a / N, N is the number of pixels occupied by the target; The relationship between the atmospheric extinction coefficient α and the atmospheric visibility V is: Where q is a constant related to the atmospheric visibility V, and λ is the laser wavelength; S23, according to the formula of step S22, simulate E under different atmospheric visibility V and different target distance R2 a,pix The relationship between the distance R1 and the target distance R2 is obtained by converting the distance R1 into a discrete distance L according to the formula in step S1. a,pix Relationship with the discrete distance L.

4. The method for suppressing atmospheric scattered light in active laser fog-penetrating imaging according to claim 2, characterized in that: The specific process of step S3 is as follows: S31, the target energy received by the CCD image sensor, that is, the diffuse reflection energy received by the target is: Where P0 is the laser emission power; τ is the exposure time; η r and η t are the optical transmittances of the transmitting and receiving parts respectively; A r is the effective receiving area of ​​the CCD image sensor; G is the normalized reflectivity of the target; α is the atmospheric extinction coefficient; S32, the target energy received by a single pixel is E t,pix =E t / N, N is the number of pixels occupied by the target; The relationship between the atmospheric extinction coefficient α and the atmospheric visibility V is: Where q is a constant related to the atmospheric visibility V, and λ is the laser wavelength.

5. The method for suppressing atmospheric scattered light in active laser fog-penetrating imaging according to claim 1, characterized in that: In step S4, the signal-to-noise ratio (SNR) of the image is: Among them, E t,pix is the target energy received by a single pixel, E t,pix =E t / N,E t is the target energy received by the CCD image sensor, N is the number of pixels occupied by the target; E a,pix is the atmospheric scattered energy received by a single pixel, E a,pix =E a / N,E a The CCD image sensor receives atmospheric scattered energy.

6. A linked scanning device, applicable to the method for suppressing atmospheric scattered light in active laser fog-penetrating imaging according to any one of claims 1 to 5, characterized in that: It includes two turntables and a turntable control unit; the laser and the CCD image sensor are placed on the two turntables respectively, and the turntable control unit controls the two turntables respectively to perform synchronous scanning control on the separately placed laser and CCD image sensor.

Images