Cloud particle parameter measuring device and method based on digital holographic imaging

Abstract

The invention belongs to the technical field of flight test photoelectric testing, and particularly relates to a cloud particle parameter measuring device and method based on digital holographic imaging. The device comprises a device pneumatic shell (100), a signal transmitting end arm (300), a signal receiving end arm (200), a measuring module and a data processing module, the device pneumatic shell (100) is integrally provided with a columnar pneumatic appearance, the signal transmitting end arm (300) and the signal receiving end arm (200) are arranged at the same end of the device pneumatic shell in parallel, and the opposite sides of the signal transmitting end arm (300) and the signal receiving end arm (200) are provided with a transparent transmitting light window (301) and a transparent receiving light window (201) respectively. The measuring module is arranged in the pneumatic shell of the device, the measuring module generates an emission light beam, the emission light beam is emitted through the signal emission end arm and then received through the signal receiving end arm to form holographic image information, and the holographic image information is transmitted to the data processing module; and the data processing module analyzes the image and calculates to obtain a particle median volume diameter MVD and an atmosphere liquid water content LWC. Accurate measurement of geometric quantities such as three-dimensional morphology, particle size distribution and the like, motion quantities such as three-dimensional speed, rotation characteristics and the like, and statistical quantity information such as median volume diameter (median volume diameter), liquid water content (liquid water content) and the like of ice crystal / water drop particles in multi-scale complex-form cloud can be realized; and autonomous control of the core test equipment for the icing flight test of the aircraft is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of photoelectric testing of flight tests, and in particular relates to a cloud and fog particle parameter measurement device and method based on digital holographic imaging. Background Art

[0002] Aircraft natural icing test flight is one of the test flight subjects that all large and medium-sized aircraft must conduct. The key is to use the onboard meteorological parameter measurement equipment to obtain meteorological data that meets the airworthiness standards, predict and identify supercooled cloud areas and ice-water mixed cloud areas, so as to realize the test and verification of the functional performance of the aircraft anti-icing system under standard meteorological conditions.

[0003] When laser is irradiated on particles, a variety of complex optical phenomena such as transmission, refraction, reflection, scattering, diffraction and interference will occur. Digital holographic imaging technology is a real three-dimensional photography technology, which includes two steps: hologram recording and wavefront reconstruction. Hologram recording uses the principle of light interference to interfere the object light wave carrying object information with the reference light and record their interference fringes to implicitly record the amplitude and phase of the object light wave. Wavefront reconstruction uses reference light to illuminate the hologram, reproduce the object light wave and thus reconstruct the three-dimensional object, thereby realizing the accurate measurement of geometric quantities such as the three-dimensional morphology and particle size distribution of ice crystals / water droplets in multi-scale complex clouds, motion quantities such as three-dimensional velocity and rotation characteristics, and statistical information such as median volume diameter (median volume diameter) and liquid water content (liquid water content). Summary of the invention

[0004] The purpose of the present invention is to solve the problem that the measurement range and accuracy of the current type of test flight icing measurement equipment cannot fully meet the measurement requirements of natural icing test, and propose a cloud particle parameter measurement device and method based on digital holographic imaging to achieve the measurement of key meteorological parameters of high-speed cloud particles in the high-altitude atmospheric environment.

[0005] Technical solution of the present invention: In order to achieve the above-mentioned purpose of the invention, according to the first aspect of the present invention, a cloud particle parameter measurement device based on digital holographic imaging is proposed, comprising a device pneumatic shell (100), a signal transmitting end arm (300), a signal receiving end arm (200), a measurement module, and a data processing module; the device pneumatic shell (100) as a whole has a cylindrical pneumatic shape, the signal transmitting end arm (300) and the signal receiving end arm (200) are arranged in parallel at the same end of the device pneumatic shell, and the signal transmitting end arm (300) and the signal receiving end arm (200) are respectively provided with a transparent transmitting light window (301) and a transparent receiving light window (201) on opposite sides; the measurement module is arranged in the device pneumatic shell, the measurement module generates an emitting light beam which is emitted through the signal transmitting end arm, and then is received by the signal receiving end arm to form holographic image information, and the image information is transmitted to the data processing module; the data processing module calculates and obtains the measurement parameter to be measured by analyzing the image.

[0006] Preferably, the measurement parameters to be measured include particle median volume diameter (MVD) and atmospheric liquid water content (LWC).

[0007] A laser beam is used to illuminate the cloud particle field between the signal transmitting arm and the signal receiving arm. The object light affected by the particles and the reference light not affected by the particles interfere with each other to form a hologram and is recorded by a digital camera. The hologram contains not only the amplitude information of the fringes, but also the phase information of the fringes. The focal cross section of the particles can be inverted through numerical reconstruction. By analyzing the focal cross section, information such as the particle size, morphology and three-dimensional position of the particles can be obtained, which can be used for imaging measurement of parameters of naturally frozen high-speed cloud particles.

[0008] In a possible embodiment, the measurement module comprises a pulse laser (1), a microscope objective lens (2), a convex lens (4), a signal transmitting reflector (6), a signal receiving reflector (9), an imaging lens (10), and a camera (11); the monochromatic laser emitted by the pulse laser (1) is filtered by the microscope objective lens (2), collimated into parallel light by the convex lens (4), passes through the signal transmitting reflector (6), passes through the cloud particle measurement area, and then is changed in direction by the signal receiving reflector (9) to reach the target surface of the camera (11) arranged at the end of the light path through the imaging lens (10). When the cloud particles pass through the holographic measurement area between the measurement arms, the particles irradiated by the parallel laser generate scattered light, which is called object light in holographic measurement, and the laser that does not interact with the cloud particles is used as reference light. The object light and the reference light interfere to generate a holographic image, which is recorded by the camera and transmitted to the data processing module. The digital delay generator (12) is mainly used to control the synchronous operation of the pulse laser and the camera, and can set the emission frequency of the pulse laser and the acquisition frequency of the camera.

[0009] In high-altitude flight tests or wind tunnel icing and fog tests, the ambient temperature can be as low as -40°C. In order to ensure the normal operation of the device in the low temperature and high humidity environment of the icing wind tunnel, a thermal control system needs to be designed to ensure the normal operation of the laser, camera and other devices in the measurement module, and prevent the end position and optical window from icing and fogging.

[0010] In a possible embodiment, the signal transmitting end arm, the signal receiving end arm, and the pneumatic housing of the device are also provided with a heating device, and the heating device is connected to the temperature controller in communication, and the most suitable heating element is selected according to the structural characteristics of each required part. The temperature signal is collected by the thermocouple and transmitted to the temperature controller. When the surface temperature of the heated device is lower than the temperature set by the temperature controller, the system automatically turns on the heating device. When the surface temperature of the heated device is higher than the temperature set by the temperature controller, the heating device automatically turns off. The temperature controller signal is collected and transmitted to the industrial computer through the serial communication protocol, thereby realizing remote control.

[0011] In a possible embodiment, a rectangular ceramic heating plate is arranged inside the pneumatic shell of the device to keep the ambient temperature inside the pneumatic shell of the device at 15-30° C., ensuring that the energy of the measurement module inside the pneumatic shell of the device is sufficiently stable.

[0012] In a possible embodiment, a rectangular heating film is arranged on the surface of the pulse laser (1) and the camera (11), and the pulse laser (1) and the camera (11) are appropriately wrapped according to their appearance characteristics. The equipment is heated evenly by means of heat insulation cotton or other components, thereby ensuring that the pulse laser (1) and the camera (11) can operate normally.

[0013] In a possible embodiment, an annular ceramic heating plate is arranged around the transparent emitting light window and the transparent receiving light window to ensure the passage of light while preventing the light window surface from fogging or even icing during the operation of the device, thereby ensuring the stability of the optical path in the instrument measurement area.

[0014] In one possible embodiment, heating rods are arranged at the heads of the signal transmitting end arm and the signal receiving end arm to prevent the heads of the two end arms from freezing under low temperatures and the presence of droplets, thereby ensuring that the flow field in the instrument measurement area is not affected by the freezing of the end arms and reducing measurement errors.

[0015] In a possible embodiment, the front ends of the signal transmitting end arm and the signal receiving end arm, i.e., the end away from the end connected to the pneumatic housing of the device, are respectively fixed with sharp wedges for guiding the flow field passing through the head outward, thereby guiding the droplets hitting the head outward, so as to avoid splashing of the droplets hitting the tip and affecting the measurement accuracy of the droplets.

[0016] According to a second aspect of the present invention, a method for measuring cloud and fog particle parameters based on digital holographic imaging is proposed, using the above-mentioned cloud and fog particle parameter measuring device based on digital holographic imaging, comprising the following steps:

[0017] Step 1: Obtain a holographic image of cloud particles;

[0018] Step 2: Preprocessing of holographic images; taking the hologram recorded when there are no target particles as the background of the system, removing the background from the particle hologram by background subtraction or background division, and then performing brightness uniformization to remove the interference of external noise, improve the signal-to-noise ratio of the particle hologram, and thus improve the accuracy of data processing;

[0019] Step 3: Three-dimensional reconstruction of the holographic image; by numerically reconstructing the holographic pre-processed image, reconstructed cross-sectional images at different positions along the axial direction are obtained;

[0020] Step 4: Reconstruct the holographic three-dimensional image fusion; expand the depth of field of the reconstructed section, synthesize all particles in the focused state into the same image, and extract the morphology and size information of all particles in the same hologram;

[0021] Step 5: Reconstruct the cloud and fog particle image recognition; in view of the obvious difference in brightness between particles and background in the depth of field extension image, the local multi-threshold judgment method is used to identify particles, and the data such as the number of particles in the reconstructed cloud and fog particle image and the number of pixels occupied by a single particle are obtained;

[0022] Step 6: Three-dimensional positioning of cloud particles: Apply the brightness gradient local variance method to perform additional calculations on the coordinates of the cloud particles in the axial direction to obtain the three-dimensional spatial coordinates of the cloud particles;

[0023] Step 7: According to the number of particles N in the sampling volume p , shape, number of pixels occupied N pixel As well as the three-dimensional position information, the particle median volume diameter (MVD) and atmospheric liquid water content (LWC) are calculated.

[0024] In a possible embodiment, in step 7, the specific calculation process of the particle median volume diameter MVD includes:

[0025] Calculate the size of individual cloud particles;

[0026] According to the number of pixels occupied by the cloud particles, under a certain camera target surface and lens, the length and width of a single pixel can be obtained. The focal area of ​​the cloud particles in the hologram is converted to the diameter of the same circle area to obtain the particle size of the cloud particles. The calculation formula is as follows:

[0027] A=P h ×Pv ×N pixel

[0028]

[0029] Where A is the focal area of ​​a single cloud particle in the hologram, N pixel is the number of pixels occupied by a single cloud particle in the hologram, P h , P v are the pixel sizes in the horizontal and vertical directions respectively;

[0030] Calculate the median volume diameter (MVD) of the particles

[0031] According to the definition of median volume diameter, removing the constant term in the calculation of spherical volume, we can get

[0032]

[0033] Among them, N p is the number of particles in the sampling volume, Vs is the volume of all cloud particles, and Vp is the volume of all cloud particles after eliminating the constant term; D i is the diameter of the ith cloud particle;

[0034] Arrange the particle sizes in ascending order and add them up. <N p satisfy

[0035]

[0036] When this condition is met, there is

[0037] MVD=D j .

[0038] In one possible embodiment, the specific process of calculating the atmospheric liquid water content (LWC) includes:

[0039] According to the frame size and equivalent pixel size of the hologram, the resolution and reconstruction distance of the hologram can be obtained, and the sampling volume of the device can be obtained as

[0040] V=MP h ×NP v ×Z

[0041] The liquid water content measured by the equipment is

[0042]

[0043] Where: the hologram resolution is M×N, the reconstruction distance is Z, N f is the number of frames of the sampled image, ρ is the density of water, N p is the number of particles in the sampling volume.

[0044] The beneficial effects of the present invention are:

[0045] 1. The present invention proposes a cloud particle parameter measurement method based on digital holographic imaging, which can realize the accurate measurement of geometric quantities such as the three-dimensional morphology and particle size distribution of ice crystals / water droplet particles in multi-scale complex morphology clouds, kinetic quantities such as three-dimensional velocity and rotation characteristics, and statistical quantity information such as median volume diameter (median volume diameter) and liquid water content (liquid water content), so as to realize the autonomous control of the core test equipment of the aircraft icing flight test.

[0046] 2. The main application direction of the present invention is the measurement of cloud and fog environment parameters in which the aircraft is flying, and it provides a technical basis and support for the subsequent development of multiphase flow particle flow field environment measurement instruments, and further provides technical support for the design of aircraft anti-icing and de-icing systems and icing airworthiness certification.

[0047] 3. The method proposed in the present invention can be applied to the measurement of multiphase flow particle flow field parameters in the fields of aerospace and so on, and has broad application prospects and urgent social needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a schematic structural diagram of a cloud particle parameter measurement device based on digital holographic imaging according to a preferred embodiment of the present invention;

[0049] Figure 2 is a schematic diagram of the structure of a measurement module in a preferred embodiment of the present invention;

[0050] Among them: 1: pulse laser; 2: microscope objective lens; 3: pinhole; 4: convex lens; 5: laser light; 6: signal transmitting reflector; 7: cloud particles to be measured; 8: particle scattered light; 9: signal receiving reflector; 10: imaging lens; 11: camera; 12: digital delay generator

[0051] Figure 3 is a schematic diagram of the distribution of the heating device of a preferred embodiment of the present invention;

[0052] Figure 4 It is a schematic diagram of the hologram recording and numerical three-dimensional reconstruction principle of the cloud and fog particle hologram measurement method according to the preferred embodiment of the present invention. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are 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 work are within the scope of protection of the present invention.

[0054] The features and illustrative embodiments of various aspects of the present invention will be described in detail below. In the detailed description below, many specific details are proposed to provide a comprehensive understanding of the present invention. However, it is obvious to those skilled in the art that the present invention can be implemented without the need for some of these specific details. The following description of the embodiments is only to provide a better understanding of the present invention by illustrating examples of the present invention. The present invention is by no means limited to any specific settings and methods proposed below, but covers any improvements, replacements and modifications of structures, methods, devices without departing from the spirit of the present invention. In the accompanying drawings and the following description, known structures and technologies are not shown to avoid unnecessary ambiguity in the present invention.

[0055] Example 1

[0056] like Figure 1 As shown, a cloud and fog particle parameter measurement device based on digital holographic imaging comprises a device pneumatic shell (100), a signal transmitting end arm (300), a signal receiving end arm (200), a measurement module, and a data processing module; the device pneumatic shell (100) as a whole has a columnar pneumatic shape, the signal transmitting end arm (300) and the signal receiving end arm (200) are arranged in parallel at the same end of the device pneumatic shell, and the opposite sides of the signal transmitting end arm (300) and the signal receiving end arm (200) are respectively provided with a transparent transmitting light window (301) and a transparent receiving light window (201); the measurement module is arranged in the device pneumatic shell, the measurement module generates an emitting light beam which is emitted through the signal transmitting end arm, and then is received by the signal receiving end arm to form holographic image information, and the image information is transmitted to the data processing module; the data processing module calculates and obtains the measurement parameters to be measured by analyzing the image, including the particle median volume diameter (MVD) and the atmospheric liquid water content (LWC).

[0057] The bottom or top of the pneumatic housing (100) of the device is provided with a mounting interface (400), and a network cable interface and a power supply interface are arranged at the bottom of the main body to provide interfaces for external communication and instrument power supply.

[0058] like Figure 2As shown, the measurement module comprises a pulse laser (1), a microscope objective lens (2), a convex lens (4), a signal transmitting reflector (6), a signal receiving reflector (9), an imaging lens (10), a camera (11), and a digital delay generator (12); the monochromatic laser emitted by the pulse laser (1) is filtered by the microscope objective lens (2), collimated into parallel light by the convex lens (4), passes through the signal transmitting reflector (6), passes through the cloud particle measurement area, and then is changed in light path direction by the signal receiving reflector (9) and passes through the imaging lens (10) to reach the target surface of the camera (11) arranged at the end of the light path. When fog particles pass through the holographic measurement area between the measuring arms, the particles irradiated by the parallel laser generate scattered light, which is called object light in holographic measurement, and the laser that does not interact with the fog particles serves as reference light. The object light and the reference light interfere with each other to generate a holographic image, which is recorded by a camera and transmitted to a data processing module. The digital delay generator (12) is mainly used to control the synchronous operation of the pulse laser and the camera, and can set the emission frequency of the pulse laser and the acquisition frequency of the camera.

[0059] like Figure 3 As shown, the signal transmitting end arm, the signal receiving end arm, and the pneumatic housing of the device are also provided with a heating device, which is connected to the temperature controller in communication. The most suitable heating element is selected according to the structural characteristics of each required part. The temperature signal is collected by the thermocouple and transmitted to the temperature controller. When the surface temperature of the heated device is lower than the temperature set by the temperature controller, the system will automatically turn on the heating device. When the surface temperature of the heated device is higher than the temperature set by the temperature controller, the heating device will automatically turn off. The temperature controller signal is collected and transmitted to the industrial computer through the serial communication protocol, thereby realizing remote control.

[0060] A rectangular ceramic heating plate is arranged inside the pneumatic shell of the device to keep the ambient temperature inside the pneumatic shell of the device at 15-30° C., ensuring that the energy of the measurement module inside the pneumatic shell of the device is sufficiently stable.

[0061] A rectangular heating film is arranged on the surface of the pulse laser (1) and the camera (11), and the pulse laser (1) and the camera (11) are appropriately wrapped according to their appearance characteristics. The equipment is heated evenly by heat insulation cotton or other components, thereby ensuring that the pulse laser (1) and the camera (11) can operate normally.

[0062] Annular ceramic heating plates are arranged around the transparent emitting light window and the transparent receiving light window to ensure the passage of light while preventing the light window surface from fogging or even icing during the operation of the device, thereby ensuring the stability of the optical path in the instrument measurement area.

[0063] Heating rods are arranged at the heads of the signal transmitting arm and the signal receiving arm to prevent the heads of the two arms from freezing when the temperature is low and liquid droplets are present, thereby ensuring that the flow field in the instrument measurement area is not affected by the freezing of the arms and reducing measurement errors.

[0064] The front ends of the signal transmitting end arm and the signal receiving end arm, i.e., the ends away from the end connected to the pneumatic housing of the device, are respectively fixed with sharp wedges, which are used to guide the flow field flowing through the head outward, and can guide the droplets hitting the head outward, so as to avoid the droplets hitting the tip from splashing and affecting the measurement accuracy of the droplets.

[0065] The outer shape of the device's pneumatic shell is a cylindrical structure. This is because the cylindrical shape has little effect on the flow field, which is beneficial to reducing the resistance generated by the device's pneumatic shell itself and reducing the vibration generated during actual use; the front and rear end covers of the device's pneumatic shell adopt an ellipsoidal structure design, which can reduce the overall size and flow field resistance; the signal transmitting end arm and the signal receiving end arm are designed to be tilted outward, which has an outward diversion effect on the flow field flowing through the head, and can guide the droplets hitting the head outward to avoid splashing of droplets hitting the tip and affecting the measurement accuracy of the droplets; effective sealing measures are taken on the outside of the device to ensure that the instrument can operate normally in a high-humidity, low-pressure environment; hard aluminum alloy is used for material processing, and anodizing is used for oxidation blackening. The hard aluminum alloy has a low density but sufficient strength to meet the quality and strength requirements of the instrument during flight. The oxidation treatment can prevent the HACPI instrument from rusting, and the black surface can absorb stray light, which is beneficial to improve the stability of the optical system.

[0066] The installation position of a cloud particle parameter measurement device based on digital holographic imaging is determined by the following process analysis:

[0067] The following requirements are imposed on the installation location of the equipment:

[0068] a) The equipment should be installed away from water droplet shielding areas;

[0069] b) The liquid water content at the equipment installation location should be as close as possible to the liquid water content of the distant atmospheric flow, and the change trend should be gentle;

[0070] c) The equipment should be installed away from the propeller slipstream influence area;

[0071] d) After installation, the equipment should not have a significant impact on the aerodynamic characteristics of the aircraft itself.

[0072] Referring to the typical installation positions of meteorological parameter measurement equipment for civil aircraft at home and abroad, according to the shell characteristics of the instrument and the mission requirements of natural icing test flight, the installation position of the equipment is usually selected on the back of the aircraft fuselage or the lower wing surface of the left and right wings. The advantages and disadvantages of the two typical positions are as follows:

[0073] The equipment is installed on the back of the fuselage: The advantage is that the equipment support bracket can be installed stably, the equipment detection area can avoid the water droplet shielding area, the atmospheric parameters in this range are less affected by distant airflow or the aircraft's own engine or aerodynamic shape, and the change trend is relatively mild; the disadvantage is that there are many antennas installed on the back of the aircraft fuselage, including TCAS directional antennas, L-band omnidirectional antennas, etc. The space for equipment installation is very limited. Under icing conditions, ice may fall off the equipment bracket and probe area, causing certain damage to the antenna and fuselage structure.

[0074] The equipment is installed on the lower surface of the wing: The advantage is that the water droplet shielding area at this location is low, the height of the equipment hanging bracket is short, and it is far away from the flow field interference of the aircraft itself. The atmospheric parameters in this range are less affected by distant flow or the aircraft's own engine or aerodynamic shape, and the change trend is relatively mild. The disadvantage is that the lower surface of the aircraft wing is close to the aircraft's engine, and the impact of the equipment on the aerodynamic characteristics of the wing needs to be considered.

[0075] Step 1: Import the geometric model of the aircraft. According to the equipment installation location requirements, input the clean configuration of a certain type of aircraft, and use a 1:1 full-size model for calculation.

[0076] Step 2: Select the corresponding computational grid according to the structural characteristics of different positions in the geometric model of the aircraft. Since the structure of the aircraft is usually more complex, a hybrid grid is often used.

[0077] Step 3: Set critical calculation conditions to examine the working state of the equipment under critical conditions. According to the common flight speed, altitude, angle of attack and other parameters of this type of aircraft under critical icing conditions, design appropriate calculation conditions to examine the working state of the equipment under critical flight conditions such as critical icing conditions, large water droplets under maximum icing conditions, and aircraft angle of attack.

[0078] Step 4: Simulation calculation. Use flow field simulation software (such as FENSAP-ICE software) to simulate the working state of the equipment under the above working conditions. The flow field can be solved by FENSAP module, the control equation can be the Reynolds average NS equation, the turbulence model can be the SA model, and the water drop impact calculation can be done by DROP3D module.

[0079] Example 2

[0080] A method for measuring cloud and fog particle parameters based on digital holographic imaging comprises the following steps:

[0081] Step 1: Obtain a holographic image of cloud particles;

[0082] Step 2: Preprocessing of holographic images. The hologram recorded when there are no target particles is used as the background of the system. The background is removed from the particle hologram by background subtraction or background division, and then the brightness is uniformed to remove the interference of external noise and improve the signal-to-noise ratio of the particle hologram, thereby improving the accuracy of data processing;

[0083] Step 3: If Figure 4 As shown, the three-dimensional reconstruction of the holographic image. By numerically reconstructing the holographic pre-processing image, the reconstructed cross-sectional images at different positions along the axial direction are obtained;

[0084] Step 4: Reconstruct holographic 3D image fusion. Expand the depth of field of the reconstructed section, synthesize all particles in the focused state into the same image, and extract the morphology, size and other information of all particles in the same hologram;

[0085] Step 5: Reconstruct the cloud and fog particle image recognition. In view of the obvious difference in brightness between particles and background in the depth of field extension image, the local multi-threshold judgment method is used to identify particles, and the data such as the number of particles in the reconstructed cloud and fog particle image and the number of pixels occupied by a single particle are obtained;

[0086] Step 6: Three-dimensional positioning of cloud particles. The brightness gradient local variance method is used to perform additional calculations on the coordinates of the cloud particles in the axial direction to obtain the three-dimensional spatial coordinates of the cloud particles.

[0087] Step 7: According to the number of particles N in the sampling volume p , shape, number of pixels occupied N pixel The natural icing test flight subjects mainly focus on the working status of the aircraft's anti-icing and de-icing system under icing conditions. The parameters for measuring the icing conditions of the atmospheric environment mainly include the particle median volume diameter (MVD) and the atmospheric liquid water content (LWC). The larger the particle median volume diameter and the higher the atmospheric liquid water content, the more severe the atmospheric environment in which the aircraft is located, and the more likely it is that ice will form on the fuselage surface.

[0088] In step 7, the specific calculation process of the particle median volume diameter MVD includes:

[0089] Calculate the size of individual cloud particles;

[0090] According to the number of pixels occupied by the cloud particles, under a certain camera target surface and lens, the length and width of a single pixel can be obtained. The focal area of ​​the cloud particles in the hologram is converted to the diameter of the same circle area to obtain the particle size of the cloud particles. The calculation formula is as follows:

[0091] A=P h ×Pv ×N pixel

[0092]

[0093] Where A is the focal area of ​​a single cloud particle in the hologram, N pixel is the number of pixels occupied by a single cloud particle in the hologram, P h , P v are the pixel sizes in the horizontal and vertical directions respectively;

[0094] Calculate the median volume diameter (MVD) of the particles

[0095] According to the definition of median volume diameter, removing the constant term in the calculation of spherical volume, we can get

[0096]

[0097] Among them, N p is the number of particles in the sampling volume, V s is the volume of all cloud particles, V p D is the volume of all cloud particles after eliminating the constant term; i is the diameter of the ith cloud particle;

[0098] Arrange the particle sizes in ascending order and add them up. <N p satisfy

[0099]

[0100] When this condition is met, there is

[0101] MVD=D j .

[0102] The specific process of calculating atmospheric liquid water content (LWC) includes:

[0103] According to the frame size and equivalent pixel size of the hologram, the resolution and reconstruction distance of the hologram can be obtained, and the sampling volume of the device can be obtained as

[0104] V=MP h ×NP v ×Z

[0105] The liquid water content measured by the equipment is

[0106]

[0107] Among them, the hologram resolution is M×N, the reconstruction distance is Z, N f is the number of frames of the sampled image, ρ is the density of water, N pis the number of particles in the sampling volume.

[0108] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other, and the embodiments can refer to and quote each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

Claims

1. A cloud particle parameter measurement device based on digital holographic imaging, characterized in that: The invention comprises a pneumatic shell (100) of the device, a signal transmitting end arm (300), a signal receiving end arm (200), a measuring module and a data processing module; the pneumatic shell (100) of the device as a whole has a columnar pneumatic shape; the signal transmitting end arm (300) and the signal receiving end arm (200) are arranged in parallel at the same end of the pneumatic shell of the device; the opposite sides of the signal transmitting end arm (300) and the signal receiving end arm (200) are respectively provided with a transparent transmitting light window (301) and a transparent receiving light window (201); the measuring module is arranged in the pneumatic shell of the device, the measuring module generates an emitting light beam which is emitted through the signal transmitting end arm, and then is received by the signal receiving end arm to form holographic image information, and the image information is transmitted to the data processing module; the data processing module calculates the particle median volume diameter MVD and the atmospheric liquid water content LWC by analyzing the image.

2. The cloud particle parameter measurement device based on digital holographic imaging according to claim 1 is characterized in that: The measurement module comprises a pulse laser (1), a microscope objective lens (2), a convex lens (4), a signal emission reflector (6), a signal receiving reflector (9), an imaging lens (10), and a camera (11); the monochromatic laser emitted by the pulse laser (1) is filtered by the microscope objective lens (2), collimated into parallel light by the convex lens (4), passes through the signal emission reflector (6), passes through the cloud particle measurement area, and then is changed in light path direction by the signal receiving reflector (9) to pass through the imaging lens (10) to reach the target surface of the camera (11) arranged at the end of the light path; the digital delay generator (12) is mainly used to control the synchronous operation of the pulse laser and the camera, and can set the emission frequency of the pulse laser and the acquisition frequency of the camera.

3. The cloud particle parameter measurement device based on digital holographic imaging according to claim 1 is characterized in that: The signal transmitting end arm, the signal receiving end arm and the pneumatic housing of the device are also provided with a heating device, and the heating device is communicatively connected with the temperature controller.

4. The cloud and fog particle parameter measurement device based on digital holographic imaging according to claim 3 is characterized in that: A rectangular ceramic heating plate is arranged inside the pneumatic shell of the device to keep the ambient temperature inside the pneumatic shell of the device at 15-30°C.

5. The cloud particle parameter measurement device based on digital holographic imaging according to claim 3 is characterized in that: A rectangular heating film is arranged on the surface of the pulse laser (1) and the camera (11), and the pulse laser (1) and the camera (11) are appropriately wrapped according to their appearance characteristics. The equipment is heated evenly by heat insulation cotton or other components, thereby ensuring that the pulse laser (1) and the camera (11) can operate normally.

6. The cloud particle parameter measurement device based on digital holographic imaging according to claim 3 is characterized in that: An annular ceramic heating plate is arranged around the transparent emitting light window (301) and the transparent receiving light window (201), which ensures the passage of light while preventing the light window surface from fogging or even icing during the operation of the device, thereby ensuring the stability of the light path in the instrument measurement area.

7. The cloud particle parameter measurement device based on digital holographic imaging according to claim 3 is characterized in that: Heating rods are arranged at the heads of the signal transmitting end arm (300) and the signal receiving end arm (200) to prevent the heads of the two end arms from freezing under low temperature and the presence of liquid droplets, thereby ensuring that the flow field in the instrument measurement area is not affected by the freezing of the end arms and reducing measurement errors.

8. A method for measuring cloud and fog particle parameters based on digital holographic imaging, using a cloud and fog particle parameter measuring device based on digital holographic imaging as claimed in any one of claims 1 to 7, characterized in that: The steps include: Step 1: Obtain a holographic image of cloud particles; Step 2: Preprocessing of the holographic image; taking the hologram recorded when there are no target particles as the background of the system, removing the background from the particle hologram by background subtraction or background division, and then performing brightness uniformization; Step 3: Three-dimensional reconstruction of the holographic image; by numerically reconstructing the holographic pre-processed image, reconstructed cross-sectional images at different positions along the axial direction are obtained; Step 4: Reconstruct the holographic three-dimensional image fusion; expand the depth of field of the reconstructed section, synthesize all particles in the focused state into the same image, and extract the morphology and size information of all particles in the same hologram; Step 5: Reconstruct the cloud and fog particle image recognition; in view of the obvious difference in brightness between particles and background in the depth of field extension image, the local multi-threshold criterion method is used to identify particles, and the number of particles in the reconstructed cloud and fog particle image and the number of pixels occupied by a single particle are obtained; Step 6: Three-dimensional positioning of cloud particles: Apply the brightness gradient local variance method to perform additional calculations on the coordinates of the cloud particles in the axial direction to obtain the three-dimensional spatial coordinates of the cloud particles; Step 7: According to the number of particles N in the sampling volume p , shape, number of pixels occupied N pixel As well as the three-dimensional position information, the particle median volume diameter MVD and the atmospheric liquid water content LWC are calculated.

9. The method for measuring cloud and fog particle parameters based on digital holographic imaging according to claim 8, characterized in that: In step 7, the specific calculation process of the particle median volume diameter MVD includes: Calculate the size of individual cloud particles; According to the number of pixels occupied by the cloud particles, under a certain camera target surface and lens, the length and width of a single pixel can be obtained. The focal area of ​​the cloud particles in the hologram is converted to the diameter of a circle with the same area, thereby obtaining the particle size of the cloud particles. The calculation formula is as follows: A=P h ×P v ×N pixel Where A is the focal area of ​​a single cloud particle in the hologram, N pixel is the number of pixels occupied by a single cloud particle in the hologram, P h , P v are the pixel sizes in the horizontal and vertical directions respectively; Calculate the median volume diameter (MVD) of the particles According to the definition of median volume diameter, removing the constant term in the calculation of spherical volume, we can get Among them, N p is the number of particles in the sampling volume, Vs is the volume of all cloud particles, and Vp is the volume of all cloud particles after eliminating the constant term; D i is the diameter of the ith cloud particle; Arrange the particle sizes in ascending order and add them up. <N p satisfy When this condition is met, there is MVD=D j 。 10. The method for measuring cloud and fog particle parameters based on digital holographic imaging according to claim 8, characterized in that: The specific process of calculating atmospheric liquid water content (LWC) includes: According to the frame size and equivalent pixel size of the hologram, the resolution and reconstruction distance of the hologram can be obtained, and the sampling volume of the device can be obtained as V=MP h ×NP v ×Z The liquid water content measured by the equipment is Where: the hologram resolution is M×N, the reconstruction distance is Z, N f is the number of frames of the sampled image, ρ is the density of water, N p is the number of particles in the sampling volume.

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