CN108169763A - Underwater remote imaging system based on compressed sensing theory - Google Patents

Abstract

The invention belongs to the technical field of underwater imaging, and in particular relates to an underwater long-distance imaging system based on compressed sensing theory. The system includes a compressive sensing imaging system arranged in a watertight pressure-resistant shell, a pulse laser and a microcomputer, and the microcomputer is connected with the compressive sensing imaging system; the compressive sensing imaging system includes a digital micromirror device, an imaging unit, a sampling unit and extinction unit, the sampling unit and extinction unit are symmetrically distributed on both sides of the imaging unit; the digital micromirror device performs compressive sensing measurement on the imaging target image signal, then reflects the signal light into the sampling unit, and reflects the stray light into the extinction unit unit. The present invention can subdivide the echo signals at different distances in time series, and selectively extract the data according to the corresponding time for image reconstruction. Therefore, the imaging of targets at different distances can be realized through one imaging process, and the operation Simple, not easy to lose the target.

Description

Underwater Long-distance Imaging System Based on Compressed Sensing Theory

technical field

The invention belongs to the technical field of underwater imaging, and in particular relates to an underwater long-distance imaging system based on compressed sensing theory.

Background technique

Underwater optical imaging technology has the advantages of high imaging resolution, large information content, good confidentiality, and intuitive imaging, which are not available in other underwater detection technologies. Therefore, there is an extensive and urgent demand for long-distance and high-resolution underwater optical imaging technology in many fields such as marine resource investigation, underwater scientific investigation, underwater robot, underwater security, underwater military target detection, and underwater engineering. Because the water body and its contained substances have a strong attenuation effect on the imaging beam, it makes long-distance imaging very difficult.

At present, the main method for underwater optical imaging distance is underwater optical range gating technology, which uses the range gating shutter of a typical ICCD (enhanced charge coupled) camera, and controls the opening and closing of the shutter to achieve The non-imaging stray light at a non-selected distance is blocked from the ICCD camera, while the imaging beam at a selected distance is transmitted to the ICCD camera for imaging. The essence of this technology is to eliminate the stray light from the time sequence through the hardware according to the time difference between most of the stray light such as back scattering and the imaging beam reaching the imaging system, and improve the imaging quality.

The underwater range-gated camera uses an ICCD camera as an imaging element, and images a target at a specific distance from the camera by setting the shutter width of the ICCD camera. However, this technology can only obtain targets at a preset distance in a single imaging. If you want to obtain images of the target at different positions before and after the target, you need to reset the camera shutter, which is a complicated operation and may easily cause the target to be lost.

Contents of the invention

The purpose of the present invention is to provide an underwater long-distance imaging system based on compressed sensing theory, which solves the technical problem that the existing underwater optical imaging technology cannot acquire target images at different distances in a single imaging.

The technical solution of the present invention is: an underwater long-distance imaging system based on compressed sensing theory, which is special in that it includes a compressed sensing imaging system, a pulse laser and a microcomputer arranged in a watertight pressure-resistant shell, and the The microcomputer is connected with the compressed sensing imaging system;

The compressed sensing imaging system includes a digital micromirror device, an imaging unit, a sampling unit and an extinction unit, and the sampling unit and the extinction unit are symmetrically distributed on both sides of the imaging unit;

The digital micromirror device performs compressed sensing measurement on the imaging target image signal, then reflects the signal light into the sampling unit, and reflects the stray light into the extinction unit.

Further, the imaging unit includes an incoming light source shielding cylinder, an optical imaging lens cylinder, a first imaging objective lens, a diaphragm, a second imaging objective lens, a spacer and a third imaging objective lens arranged in sequence along the propagation direction of the imaging light beam.

Further, the sampling unit includes a first optical condenser lens, a first electromagnetic shielding cylinder and a photomultiplier tube sequentially arranged along the propagation direction of the signal light reflected by the digital micromirror device;

The extinction unit includes a second optical condenser lens, a second electromagnetic shielding tube and a darkroom which are sequentially arranged along the propagating direction of the stray light reflected by the digital micromirror device.

Preferably, the above-mentioned watertight pressure-resistant shell is a cylindrical shell structure, and the two ends of the shell are sealed statically by end face sealing rings or axial sealing rings.

Further, the above-mentioned watertight pressure-resistant casing is provided with an axial partition, and the axial partition divides the interior of the watertight pressure-resistant casing into an upper chamber and a lower chamber; the compressive sensing imaging system and the microcomputer Located in the upper chamber, the pulsed laser is located in the lower chamber.

Further, the compressive sensing imaging system and the microcomputer are fixed on the upper surface of the axial partition, and the pulse laser is fixed on the lower surface of the axial partition.

Further, the above-mentioned digital micromirror device is provided with an array of mirrors, and the mirrors can be flipped around a fixed axis at an included angle of ±12°.

Further, the above-mentioned digital micromirror device is fixed on the multi-degree-of-freedom fine-tuning mount.

Further, the output port of the pulsed laser is provided with an optical lens.

Further, an optical path light splitting seat is arranged on the optical path of the digital micromirror device.

The beneficial effects of the present invention are:

(1) The present invention applies compressed sensing imaging technology to the field of underwater imaging, and combines the advantages of distance gating technology to eliminate stray light interference to imaging and the characteristics that underwater laser lighting can effectively increase the energy of imaging beams, and designs a pulsed laser underwater Compressed sensing single-phase pixel camera system; for the first time, the algorithm-controlled range gating technology is applied to the system sampling, using the unique structure of the underwater compressed sensing imaging system and the characteristics of ultra-high frequency sampling (0.2 nanoseconds/time) of the photomultiplier tube, it can The echo signals at different distances are subdivided in time series, and the data is selectively extracted according to the corresponding time for image reconstruction. Therefore, the imaging of targets at different distances can be realized through one imaging process, and the operation is simple and the target is not easy to be lost.

(2) The present invention adopts the algorithmic distance gating technology for the first time, and by performing selective sampling and image reconstruction to position target signals at any distance, the time consumed in the sampling process is reduced, and the non-imaging distance is greatly reduced. The effect of stray light produced.

Description of drawings

Figure 1 is an isometric side view of the underwater remote imaging system of the present invention.

Fig. 2 is an internal assembly view of the underwater long-distance imaging system of the present invention.

FIG. 3 is a schematic exploded view of the structure of the compressed sensing imaging system of the present invention.

Wherein, reference signs are: 1-compressed sensing imaging system, 2-axial partition, 3-microcomputer, 4-pulse laser, 5-watertight pressure-resistant housing, 6-digital micromirror device, 7-imaging Unit, 8-sampling unit, 9-extinction unit, 61-light path beam splitter, 71-incoming light source shielding cylinder, 72-optical imaging lens barrel, 73-first imaging objective lens, 74-diaphragm, 75-second imaging objective lens , 76-spacer, 77-third imaging objective lens, 81-first optical condenser, 82-first electromagnetic shielding tube, 83-photomultiplier tube, 91-second optical condenser, 92-second electromagnetic shielding tube, 93 -darkroom.

Detailed ways

The design principle of the present invention is: by using short-pulse (nanosecond) laser active illumination, utilizing the characteristics of high energy density and good directionality of short-pulse laser to enhance the energy of the echo target, digital micromirror device (DMD) and The photomultiplier tube constitutes the compressed sensing sampling system, which performs high-frequency sampling and image reconstruction through the algorithm integrated in the computer. Due to the influence of the water medium, the relatively static time of the target object and the imaging system is longer than that of the land, and the sampling time of the system is also longer, which is beneficial for the compressed sensing sampling system to "reduce the underwater weak echo signal". High-frequency sampling with multiple values, thus effectively improving the image resolution and having a high signal-to-noise ratio, realizing underwater long-distance high-quality imaging. The specific implementation plan is as follows:

Referring to Fig. 1 and Fig. 2, this embodiment is an underwater long-distance imaging system based on compressive sensing theory, and its structure includes a compressive sensing imaging system 1 arranged in a watertight pressure-resistant housing 5, a pulse laser 4 and a micro The computer 3 and the microcomputer 3 are connected with the compressed sensing imaging system 1 .

The compressed sensing imaging system 1 is the core part of the present invention. It can extract the sampling signal at the same distance from the target position by using the algorithm to control the distance gating, and obtain a high-quality image at the distance through the reconstruction algorithm.

Microcomputer 3 integrates algorithms based on compressed sensing theory, and is the brain of range gating control and image reconstruction.

The pulse laser 4 is used as the light source of the active lighting system, and the use of the short pulse laser can increase the absolute value of the energy of the imaging beam reaching the imaging surface to realize long-distance imaging, and the present invention can set an optical lens in front of the short pulse laser so as to effectively increase the laser pulse expansion. The angle of the beam makes the illumination area coincide with the maximum range of the imaging range and improves the utilization rate of energy;

The water-tight pressure-resistant housing 5 plays the role of outer layer protection for all components in the system. Since it is used underwater, the water-tight pressure-resistant housing 5 should have certain compressive strength and stability, easy to install, and waterproof and sealed. Good performance and strong corrosion resistance. More preferably, the watertight pressure-resistant shell 5 is a cylindrical shell structure, and the two ends of the shell are sealed statically by end face seal rings or axial seal rings. An axial partition 2 can be arranged in the watertight pressure-resistant housing 5 as a flat plate on which all components are installed and fixed, and it can be disassembled from the water-tight pressure-resistant housing 5 to facilitate the installation and removal of components. In addition, the axial partition 2 also serves as a support for the front and rear end covers of the watertight pressure-resistant casing 5 , increasing the rigidity of the watertight pressure-resistant casing 5 .

The axial partition 2 divides the inside of the watertight pressure-resistant shell 5 into an upper chamber and a lower chamber. The compressed sensing imaging system 1 and the microcomputer 3 are located in the upper chamber, and the pulse laser 4 is located in the lower chamber. The axial partition 2 can effectively play the role of electromagnetic shielding. The compressive sensing imaging system 1 and the microcomputer are fixed on the upper surface of the axial partition, and the pulse laser is fixed on the lower surface of the axial partition. The arrangement of the structure can make the distance between the illuminating light beam and the imaging light beam reach a minimum of 79mm, which minimizes the imaging blind area.

Referring to Fig. 3, the compressed sensing imaging system 1 comprises a digital micromirror device 6, an imaging unit 7, a sampling unit 8 and an extinction unit 9, and the sampling unit 8 and the extinction unit 9 are symmetrically distributed on both sides of the imaging unit 7;

The imaging unit 7 includes an incoming light source shielding cylinder 71, an optical imaging lens barrel 72, a first imaging objective lens 73, a diaphragm 74, a second imaging objective lens 75, a spacer ring 76 and a third imaging objective lens 77 arranged in sequence along the propagation direction of the imaging light beam. . Considering the underwater use, the wavelength band light to be passed can be selected by coating to increase the energy of the imaging beam.

The digital micromirror device 6 performs compressive sensing measurement on the imaging target image signal, then reflects the selected signal light into the sampling unit 8 , and reflects the stray light into the extinction unit 9 . In order to improve the optical path isolation effect, the digital micromirror device 6 can be provided with an optical path beam splitter 61 on the optical path.

Sampling unit 8 is used for realizing compressed sampling, comprises first optical condenser 81, the first electromagnetic shielding cylinder 82 and photomultiplier tube 83 that are arranged successively along the signal light propagating direction that digital micromirror device 6 reflects, and first optical condenser 81 will select A certain imaging light beam is converged to the photomultiplier tube 83 for sampling and imaging. The photomultiplier tube 83 is the sampling receiving device of the compressed sensing imaging system 1. It has the characteristics of high-frequency sampling, and can be controlled by the algorithm integrated in the microcomputer 3 to subdivide and sample the echo signals at a selected distance in time sequence. , and convert the sampled optical signal into an electrical signal value, and then reconstruct the image in the microcomputer 3 . Because the photomultiplier tube 83 is relatively sensitive to external photoelectricity, the present invention designs the first electromagnetic shielding tube 82 and the optical path beam splitter 61 to effectively isolate the electromagnetic and optical paths to achieve the best imaging effect.

The extinction unit 9 is used to eliminate stray light, including a second optical condenser 91, a second electromagnetic shielding tube 92 and a darkroom 93 arranged in sequence along the stray light propagation direction reflected by the digital micromirror device 6, the extinction unit 9, and the second optical condenser 91 Unnecessary stray light is gathered into the dark room 93 for absorption.

The digital micromirror device (DMD) is the key component to achieve compressed sampling. It performs compressed sensing measurement on the target image signal on the imaging surface, and reflects the selected part of the signal to the photomultiplier tube through the optical condenser to form a sample. The DMD is composed of a group of tiny mirrors arranged in an array. The mirrors can be flipped around a fixed axis at an angle of ±12°. Therefore, the photomultiplier tube and the imaging beam irradiated on the DMD are distributed on both sides of ±12°. This property of the DMD reflects the desired beam signal in one direction and the unwanted signal (ie stray light signal) in the other direction.

Because DMD has higher requirements on the alignment of imaging beams, and there are machining and installation errors in the optical path beam splitter 61 and imaging unit 7, in view of these problems, the present invention designs a multi-degree-of-freedom fine-tuning mounting seat for the DMD device, which not only ensures the DMD The reliable installation of the DMD ensures the fine adjustment of the centering of the DMD relative to the imaging beam.

Underwater imaging technology based on compressed sensing theory uses the non-simultaneity of stray light and echo signal light to eliminate the influence of stray light on imaging. However, the present invention does not set hardware such as a range gate shutter, but uses an underwater compressed sensing single-pixel camera system with a sampling frequency above 10 ¹⁰ Hz as an imaging receiver to receive the echo signal after the laser illumination pulse is emitted throughout. What the receiver receives is a time series echo signal, and the echo signals at different distances are received in time order. To image a target at a certain distance, the data corresponding to the time in each sampling sequence is extracted to form a vector of compressed sensing sampling values. Substituting this vector into the reconstruction algorithm can calculate the image of the corresponding distance. Therefore, the imaging of targets at different distances can be realized through one imaging process, and the operation is simple and the target is not easy to be lost.

Compared with the underwater range-gated imaging method (i.e. the ICCD camera range-gated imaging method), the imaging distance of the present invention can be increased by 1 time; compared with the underwater laser scanning imaging technology, the sampling quantity of the present invention is 60%～ 90%, greatly reducing the cost and difficulty of system hardware, and has many advantages such as flexible imaging, simple system, low cost and small system error.

Claims (10)

1. a kind of underwater remote imaging system based on compressive sensing theory, it is characterised in that：It is resistance to including being arranged on watertightness Compressed sensing imaging system, pulse laser and microcomputer in pressure shell body, the microcomputer and compressed sensing into As system is connected；

The compressed sensing imaging system includes Digital Micromirror Device, imaging unit, sampling unit and delustring unit, sampling unit It is symmetrical in the both sides of imaging unit with delustring unit；

Imageable target picture signal is carried out compressed sensing measurement by the Digital Micromirror Device, is then reflected into flashlight and is adopted Stray light is reflected into delustring unit by sample unit.

2. the underwater remote imaging system according to claim 1 based on compressive sensing theory, it is characterised in that：It is described Imaging unit includes being imaged into light source shielding cylinder, optical imagery lens barrel, first along what the direction of propagation of imaging beam was set gradually Object lens, diaphragm, the second image-forming objective lens, spacer ring and third image-forming objective lens.

3. the underwater remote imaging system according to claim 2 based on compressive sensing theory, it is characterised in that：It is described Sampling unit includes the first optical concentration mirror that the signal optical propagation direction that reflect along Digital Micromirror Device sets gradually, first electric Magnetic shielding cylinder and photomultiplier；

The delustring unit includes the second optical concentration set gradually along the spuious optical propagation direction that Digital Micromirror Device reflects Mirror, the second electromagnetic shielding cylinder and darkroom.

4. according to the underwater remote imaging system based on compressive sensing theory any in claim 1-3, feature It is：The watertightness pressure hull is cylinder shell structure, housing both ends using end-face seal ring or axial sealing ring into Row hydrostatic seal.

5. the underwater remote imaging system according to claim 4 based on compressive sensing theory, it is characterised in that：It is described Be provided with axial partition board in watertightness pressure hull, the axial direction partition board will be divided into inside watertightness pressure hull upper chamber and Lower chambers；The compressed sensing imaging system and microcomputer are located in upper chamber, and the pulse laser is located at lower chambers It is interior.

6. the underwater remote imaging system according to claim 5 based on compressive sensing theory, it is characterised in that：It is described Compressed sensing imaging system and microcomputer are fixed on the upper surface of axial partition board, the pulse laser be fixed on it is axial every The lower surface of plate.

7. the underwater remote imaging system according to claim 6 based on compressive sensing theory, it is characterised in that：It is described Reflection mirror array is provided in Digital Micromirror Device, speculum can carry out the overturning of ± 12 ° of angles around fixing axle.

8. the underwater remote imaging system according to claim 7 based on compressive sensing theory, it is characterised in that：It is described Digital Micromirror Device is fixed in multiple free degree micro regulation mounting base.

9. the underwater remote imaging system according to claim 8 based on compressive sensing theory, it is characterised in that：It is described The output port setting optical lens of pulse laser.

10. the underwater remote imaging system according to claim 9 based on compressive sensing theory, it is characterised in that：Institute It states and light path light splitting seat is provided in the light path of Digital Micromirror Device.