An adaptive range-gated ocean lidar

Abstract

The present invention discloses an adaptive distance-gated ocean laser radar, which belongs to the field of underwater laser imaging technology. Based on the traditional distance-gated underwater laser imaging radar, the system adds the functions of automatic switching of the receiving channel optical path and active ranging. The target distance information obtained by the ranging channel is actively fed back to the imaging camera, and the imaging camera is accurately controlled to work only within the time when the target echo returns. At the same time, the receiving optical path has an automatic switching function, which replaces the optical path splitting method, so that all laser energy is used for ranging or imaging to ensure the detection effect. The addition of the active ranging function allows the system to adaptively control the gating time, which solves the shortcoming of the traditional distance-gated underwater imaging radar that requires continuous slicing, and greatly improves the measurement speed of the system.

Description

Technical Field

[0001] The invention relates to the technical field of underwater laser imaging, and in particular to an adaptive range-gated ocean laser radar. Background Art

[0002] Underwater laser range gating technology is one of the underwater optoelectronic imaging technologies that is being developed and effectively applied at home and abroad. It has important application value in the fields of seabed topography detection, seabed engineering construction, marine environment monitoring, underwater rescue, underwater archaeology, etc. Underwater target imaging is different from that on land. When the laser is transmitted in water, it will be affected by the absorption and scattering of the water medium, which makes the underwater image seriously degraded. Among them, the absorption of the water body will cause the attenuation of the laser energy and reduce the detection distance of the system; and the scattering effect is mainly divided into forward scattering and backward scattering. The forward scattering effect causes the laser to deviate from the original propagation direction, thereby reducing the resolution of the image, and the backward scattering will transmit the light scattered by particles in the water to the ICCD, causing a "curtain effect", which ultimately causes a decrease in image contrast. Underwater laser range gating technology is one of the technologies currently widely used to solve the influence of backscattering in water.

[0003] Traditional underwater laser range gating technology requires knowing the distance of the target in advance or adjusting the ICCD gate opening time continuously by stepping or slicing. The former has a poor effect when imaging targets with unknown distances and has certain limitations, while the latter requires continuous adjustment of the ICCD gate opening time until the ICCD gate opening time accurately matches the target distance to achieve a better imaging effect. This adjustment process takes a certain amount of time and the imaging speed is slow. In addition, a proportional beam splitter is currently usually used to divide the laser energy of the receiving channel into two beams, which enter the ranging and imaging channels respectively. In this case, both channels cannot respond to all echo signals, and the capacity is not fully utilized, which is not conducive to high-performance detection of long-distance targets. Summary of the invention

[0004] In order to solve the problem that the traditional underwater laser range gating technology needs to know the target distance in advance or the imaging speed is slow through the slice imaging method, the present invention proposes an adaptive range gating active and passive ocean laser radar for the first time. This invention not only effectively solves the above limitations of the traditional method, but also uses the automatic switching technology of the receiving optical path to improve the energy utilization rate and further improve the system's ranging and imaging performance.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] An adaptive distance-gated ocean laser radar comprises a pulse laser, a proportional beam splitter, a transmitting optical system, a photodetector, a receiving optical system, a plane reflector, a PMT detector, an enhanced electric coupling device (ICCD) and a signal acquisition processing and control module; the pulse laser periodically emits high-power pulse laser and transmits it to the proportional beam splitter, and the proportional beam splitter distributes the high-power laser emitted by the pulse laser to the photodetector and the transmitting optical system; the photodetector transmits the signal to the signal acquisition processing and control module to record the start time of the pulse emission; the receiving optical system collects the echo signal scattered by the underwater target, and transmits it to the ranging channel according to the position state of the plane reflector, and the PMT detector responds to complete the target ranging; or transmits it to the imaging channel, and the enhanced electric coupling device (ICCD) responds to complete the target imaging; the signal acquisition processing and control module completes the signal acquisition and processing.

[0007] Preferably, the plane reflector is mounted on a reflector electric mounting bracket, and the movement of the reflector electric mounting bracket is controlled to place the plane reflector in the receiving light path to determine the distance of the target; the plane reflector is moved out of the receiving channel, and the received laser echo signal is not reflected by the plane reflector, but directly enters the imaging channel to complete clear imaging of the target.

[0008] Preferably, the rule for switching the position of the electric mounting bracket is as follows: in the initial state of the system, the plane reflector is placed in the receiving light path, and m consecutively emitted pulse periods are regarded as one group. When at least two identical flight times are detected in one group, the target distance measurement is determined to be completed; that is, assuming that the flight time corresponding to one pulse period is recorded as ,when When , the ranging is considered to be completed, where is an indicative function, when When the value is 1, the distance measurement is completed; the signal acquisition processing and control module drives the electric mounting frame to remove the plane reflector from the receiving light path to prepare for the target imaging; with the next pulse emission, the laser returned by the target directly enters the enhanced electric coupling device ICCD without being reflected by the reflector, and the gate opening time of the enhanced electric coupling device ICCD is determined according to the pulse flight time determined by the ranging process to complete the imaging of the target. At this time, a complete distance gating imaging process is completed through the steps of ranging-imaging. After the imaging process is completed, the signal acquisition processing and control module drives the electric mounting frame to move to position 1 again, waiting for the completion of the target ranging, and starting the next cycle of distance gating imaging process.

[0009] Preferably, the pulse laser periodically emits 532nm narrow pulse laser, and the proportional beam splitter distributes the laser pulses emitted by the 532nm pulse laser to the photodetector and the emission optical system in a ratio of 1:99.

[0010] Preferably, the enhanced electric coupling device ICCD receives the gate information sent by the signal acquisition processing and control module, accurately controls the time when the enhanced electric coupling device ICCD starts to respond to the echo signal, and controls the gate opening time of the enhanced electric coupling device ICCD, that is, the duration of the response echo signal to the pulse width. The purpose is to make the enhanced electric coupling device ICCD detect only the target echo signal, filter out the backscatter noise as much as possible, and improve the contrast and clarity of the enhanced electric coupling device ICCD imaging.

[0011] Preferably, the photoelectric detector records the pulse emission time t0. When the echo photon reaches the ranging channel, the PMT detector is excited to generate a pulse response and the signal acquisition, processing and control module records the pulse response time of the PMT detector as a timing stop signal, recorded as t1. The signal acquisition and processing module obtains the distance r of the underwater target:

[0012] ;

[0013] Among them, c is the speed of light, and r is the target distance measured by the ranging channel.

[0014] Preferably, after determining the target distance, the signal acquisition processing and control module controls the movement of the reflector electric mounting frame to move the plane reflector out of the receiving optical path, and the enhanced inductively coupled device ICCD imaging channel will officially start high-definition imaging of the target in the next pulse emission cycle; the laser emission time t0 and the moment t1 when the laser irradiates the target and returns are obtained, and the gated opening moment of the enhanced inductively coupled device ICCD is accurately calculated. Considering the time delay t2 of the system circuit transmission and the time delay t3 of the enhanced inductively coupled device ICCD, the moment t4 when the signal acquisition processing and control module transmits the gated opening control instruction to the enhanced inductively coupled device ICCD can be determined:

[0015] t4=(t1-t0)-(t2+t3);

[0016] Therefore, the target distance is first determined by emitting a pulsed laser, and the gate opening time of the enhanced electrically coupled device (ICCD) is determined after considering the system delay; then in the next pulse emission cycle, the enhanced electrically coupled device (ICCD) imaging channel will officially start high-definition imaging of the target.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The adaptive distance-gated active and passive ocean laser radar uses a combination of a plane reflector and a reflector electric mounting bracket to enable the receiving optical path to have an automatic switching function, replacing the optical path splitting method. It can use all the laser energy for ranging or imaging to ensure the detection effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the structure of the present invention (the plane reflector is located in the receiving light path).

[0020] Figure 2 This is a schematic diagram of the structure of the present invention (the plane reflector removes the receiving light path).

[0021] In the figure, 1- pulse laser, 2- proportional beam splitter, 3- transmitting optical system, 4- photoelectric detector, 5- receiving optical system, 6- plane reflector, 7- reflector electric mounting bracket, 8- enhanced electrically coupled device ICCD, 9- PMT detector, 10- signal acquisition processing and control module. DETAILED DESCRIPTION

[0022] In order to make the purpose of the present invention: the scheme and advantages of the adaptive distance-gated active and passive ocean laser radar more clearly explained, the present invention is further described in detail below in combination with specific implementation methods and with reference to the accompanying drawings.

[0023] like Figure 1 As shown, the adaptive distance-gated active-passive marine laser radar proposed by the present invention comprises a 532nm pulse laser 1, a proportional beam splitter 2, a transmitting optical system 3, a photodetector 4, a receiving optical system 5, a plane reflector 6, a reflector electric mounting bracket 7, a PMT detector 9, an enhanced electric coupling device ICCD 8, and a signal acquisition processing and control module 10. The pulse laser periodically emits high-power pulse laser and transmits it to the proportional beam splitter, which distributes the high-power laser emitted by the pulse laser to the photodetector and the transmitting optical system; the photodetector transmits the signal to the signal acquisition processing and control module to record the start time of the pulse emission; the receiving optical system collects the echo signal scattered by the underwater target, and transmits it to the ranging channel according to the position state of the plane reflector, and the PMT detector responds to complete the target ranging; or transmits it to the imaging channel, and the enhanced electric coupling device ICCD responds to complete the target imaging; the signal acquisition processing and control module completes the signal acquisition and processing.

[0024] The 532nm pulse laser periodically emits high-power pulse laser and transmits it to the proportional beam splitter, which is a 1:99 power beam splitter. The high-power laser generated by the 532nm pulse laser is distributed to the photodetector and the emission optical system at a ratio of 1:99. The photodetector, as the light trigger detector of the system, responds to 1% of the pulse laser power and records the moment t0 of the pulse laser emission as the timing start moment of the system. The emission optical system directly irradiates 99% of the pulse laser energy distributed by the proportional beam splitter on the target to illuminate the underwater target.

[0025] The receiving optical system collects the echo signal scattered by the underwater target, and transmits it to the ranging channel according to the position state of the plane reflector, and the PMT detector responds to complete the target ranging; or transmits it to the imaging channel, and the enhanced electric coupling device ICCD responds to complete the target imaging. When the echo photon reaches the ranging channel, the PMT detector is excited to generate a pulse response, and the signal acquisition processing and control module records the pulse response time of the PMT detector as a timing stop signal, recorded as t1. The signal acquisition and processing module obtains the distance r of the underwater target:

[0026] ;

[0027] Among them, c is the speed of light, and r is the target distance measured by the ranging channel.

[0028] After the system determines the target distance, the signal acquisition processing and control module drives the electric mounting frame to remove the plane reflector from the receiving optical path, and the enhanced inductive coupling device ICCD imaging channel will officially start high-definition imaging of the target in the next pulse emission cycle. The laser emission time t0 and the moment t1 when the laser irradiates the target and returns are obtained, and the gated opening moment of the enhanced inductive coupling device ICCD is accurately calculated. Considering the time delay t2 of the system circuit transmission and the time delay t3 of the enhanced inductive coupling device ICCD, the time t4 when the signal acquisition processing and control module transmits the gated opening control instruction to the enhanced inductive coupling device ICCD can be determined:

[0029] t4=(t1-t0)-(t2+t3);

[0030] Therefore, through this pulse emission, the distance of the target is first determined, and the gate opening time of the enhanced electrically coupled device (ICCD) is further determined; then in the next pulse emission cycle, the enhanced electrically coupled device (ICCD) imaging channel will officially start high-definition imaging of the target.

[0031] In the initial state of the system, the plane reflector is located in the receiving light path, the purpose is to complete the detection of the target distance first. In order to improve the accuracy of the target distance detection, at least two identical flight times are detected within m consecutive pulse cycles before the target distance measurement is determined to be completed. That is, the flight time corresponding to one pulse cycle is recorded as ,when When , the ranging is considered to be completed, where is an indicative function, when When the value is 1, the ranging is completed; the signal acquisition processing and control module drives the electric mounting frame to remove the plane reflector from the receiving optical path to prepare for target imaging. With the emission of the next pulse, the laser returned by the target directly enters the enhanced electrically coupled device ICCD without being reflected by the reflector. According to the pulse flight time determined by the ranging process, the gate opening time of the enhanced electrically coupled device ICCD is determined to complete the imaging of the target. At this time, a complete distance-gated imaging process is completed through the ranging-imaging steps. After the imaging process is completed, the signal acquisition processing and control module drives the electric mounting frame again to move the plane reflector to the receiving optical path, waits for the target ranging to be completed, and starts the next cycle of distance-gated imaging process.

[0032] In short, the core idea of ​​the present invention is to first quickly and accurately determine the target distance through the ranging channel, and according to the preset rules, after the target distance is known, move the plane reflector out of the receiving light path, and determine the time for the enhanced inductive coupling device ICCD to be gated on according to the target flight time obtained during the ranging process, so that the enhanced inductive coupling device ICCD starts working only when the target echo returns, so that the backscattering noise can be suppressed to the maximum extent and the laser energy can be fully utilized, and finally the purpose of fast and high-definition imaging of underwater targets can be achieved.

Claims

1. An adaptive range-gated ocean laser radar, characterized in that: It includes a pulse laser, a proportional beam splitter, a transmitting optical system, a photoelectric detector, a receiving optical system, a plane reflector, a PMT detector, an enhanced electrically coupled device ICCD and a signal acquisition processing and control module; the pulse laser periodically emits high-power pulse laser and transmits it to the proportional beam splitter, and the proportional beam splitter distributes the high-power laser emitted by the pulse laser to the photoelectric detector and the transmitting optical system; The photoelectric detector transmits the signal to the signal acquisition processing and control module to record the start time of the pulse emission; the receiving optical system collects the echo signal scattered by the underwater target and transmits it to the ranging channel according to the position state of the plane reflector, and the PMT detector responds to complete the target ranging; Or transmitted to the imaging channel, the enhanced electric coupling device ICCD responds to complete the target imaging; the signal acquisition processing and control module completes the signal acquisition and processing; In the initial state of the system, a plane reflector is placed in the receiving light path, and m consecutively emitted pulse periods are considered as one group. When at least two identical flight times are detected in one group, the target distance measurement is considered to be completed; that is, assuming that the flight time corresponding to one pulse period is recorded as t n ,when When , the ranging is considered to be completed, where is an indicative function, when When the value is 1, the ranging is completed; the signal acquisition processing and control module drives the electric mounting bracket to remove the plane reflector from the receiving light path to prepare for target imaging; with the next pulse emission, the laser returned by the target directly enters the enhanced electrically coupled device ICCD without being reflected by the reflector, and the gate opening time of the enhanced electrically coupled device ICCD is determined according to the pulse flight time determined during the ranging process to complete the imaging of the target.

2. The adaptive range-gated ocean laser radar according to claim 1, characterized in that: The plane reflector is installed on the reflector electric mounting bracket. The movement of the reflector electric mounting bracket is controlled to place the plane reflector in the receiving light path to determine the distance of the target; the plane reflector is moved out of the receiving channel, and the received laser echo signal is not reflected by the plane reflector and directly enters the imaging channel to complete clear imaging of the target.

3. The adaptive range-gated ocean laser radar according to claim 1, characterized in that: The pulse laser periodically emits 532nm narrow pulse laser, and the proportional beam splitter distributes the laser pulses emitted by the 532nm pulse laser to the photoelectric detector and the emission optical system in a ratio of 1:

99.

4. The adaptive range-gated ocean laser radar according to claim 1, characterized in that: The enhanced electrically coupled device ICCD receives the gating information sent by the signal acquisition processing and control module, accurately controls the time when the ICCD starts to respond to the echo signal, and controls the gate opening duration of the ICCD, that is, the duration of the response echo signal is the width of the pulse.

5. The adaptive range-gated ocean laser radar according to claim 1, characterized in that: The photoelectric detector records the pulse emission time t0. When the echo photon reaches the ranging channel, the PMT detector is excited to generate a pulse response and the signal acquisition, processing and control module records the pulse response time of the PMT detector as a timing stop signal, recorded as the pulse return time t1. The signal acquisition and processing module obtains the distance r of the underwater target: Among them, c is the speed of light, and r is the target distance measured by the ranging channel.

6. The adaptive range-gated ocean laser radar according to claim 1, characterized in that: After determining the target distance, the signal acquisition processing and control module controls the movement of the reflector electric mounting frame to move the plane reflector out of the receiving optical path. In the next pulse emission cycle, the enhanced inductive coupling device ICCD imaging channel will officially start high-definition imaging of the target. The pulse emission time t0 and the pulse return time t1 are obtained, and the gate opening time of the enhanced inductive coupling device ICCD is accurately calculated. Considering the time delay t2 of the system circuit transmission and the time delay t3 of the enhanced inductive coupling device ICCD, the time t4 when the signal acquisition processing and control module transmits the gate opening control instruction to the enhanced inductive coupling device ICCD can be determined: t4=(t1-t0)-(t2+t3) Therefore, the target distance is first determined by emitting a pulsed laser, and the gate opening time of the enhanced electrically coupled device (ICCD) is determined after considering the system delay; then in the next pulse emission cycle, the enhanced electrically coupled device (ICCD) imaging channel will officially start high-definition imaging of the target.

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