CN111257907A

CN111257907A - Polarization defogging detection device and method based on laser radar

Info

Publication number: CN111257907A
Application number: CN202010204400.XA
Authority: CN
Inventors: 陈凡胜; 孙胜利
Original assignee: Photoelectric Engineering Center Of Shanghai Institute Of Technology And Physics South Taihu Lake Huzhou
Current assignee: Photoelectric Engineering Center Of Shanghai Institute Of Technology And Physics South Taihu Lake Huzhou
Priority date: 2020-03-21
Filing date: 2020-03-21
Publication date: 2020-06-09

Abstract

The invention discloses a polarization defogging detection device and method based on a laser radar, wherein the device comprises: a laser transmitter configured to configure the modulated pulsed laser as an independent laser exit beam; the first polarizer converts the independent laser emergent beam into completely linearly polarized light; a lens array collimating the individual laser exit beams from the first polarizer; a MEMS rotating mirror configured to receive the collimated beam and redirect the collimated beam toward a target scanning area, a second polarizer, convert an echo beam scattered from the background and reflected from the target into linearly polarized light, and direct it to a detector; a detector for detecting at least a portion of the light beam of the second polarizer. The invention can realize more effective detection of low and slow small targets in rainy and foggy weather.

Description

Polarization defogging detection device and method based on laser radar

Technical Field

The invention relates to a polarization defogging detection device and method, in particular to a polarization defogging detection device and method based on a laser radar.

Background

The low-altitude slow-speed small target is called a low-slow small target for short, and is commonly a rotor unmanned aerial vehicle. Due to the complex city background and the confusion of various bird targets, the flying speed of the unmanned aerial vehicle can reach about 20m/s at most, and accurate detection and early warning are difficult to carry out. The unmanned aerial vehicle is light, convenient and easy to control, and the unmanned aerial vehicle is applied more and more due to the characteristics of low cost and the like.

The detection method for the unmanned aerial vehicle comprises methods such as radar, radio frequency and acoustics. However, the radar aims at long-distance detection, and has limited spatial resolution, so that the detection efficiency of the unmanned aerial vehicle is low when the unmanned aerial vehicle hovers or has low speed; the radio frequency detection can intercept signals of the unmanned aerial vehicle, but only plays a role in the type of the unmanned aerial vehicle existing in the communication protocol database; acoustic detection is susceptible to environmental influences and has limited detection range.

Along with the development of the automatic driving industry, the performance of the laser radar is greatly improved, and the laser radar has the advantages of high resolution, small device size and the like. However, like the problem in automatic driving, the lidar has poor performance for detecting low-speed and small targets in severe weather such as rain and fog.

Disclosure of Invention

In view of the above situation, in order to overcome the defects of the prior art, the invention provides a polarization defogging detection device and method based on a laser radar, which can realize more effective detection of low and slow small targets in rainy and foggy weather.

The invention solves the technical problems through the following technical scheme: a polarization defogging detection device based on a laser radar is characterized by comprising:

a laser transmitter configured to configure the modulated pulsed laser as an independent laser exit beam;

the first polarizer converts the independent laser emergent beam into completely linearly polarized light;

a lens array collimating the individual laser exit beams from the first polarizer and focusing the collimated beams onto the MEMS rotating mirror;

a MEMS turning mirror configured to receive the collimated beam and redirect the collimated beam toward a target scanning area;

a second polarizer that converts the echo beam scattered from the background and reflected from the target into linearly polarized light and guides it to a detector;

and the detector detects at least part of the light beam of the second polarizer, obtains the phase and intensity information of the light beam and leads the information to an analyzer for analysis and processing.

Preferably, the laser emitter adopts a laser emitter with the wavelength of 850 nm.

Preferably, the laser transmitter, the first polarizer and the lens array form a transmitting unit, and the detector and the second polarizer form a receiving unit.

Preferably, the laser transmitter is connected with a light source controller, the first polarizer and the second polarizer are both connected with a polarization controller, the MEMS rotating mirror is connected with a rotation controller, and the detector is connected with a detection controller.

Preferably, the second polarizer employs a specific method of scattering removal as follows:

step one, a first polarizer is rotated through a polarization controller until the intensity of an independent laser emergent beam is maximum after passing through the polarizer;

and step two, rotating the second polarizer by a polarization controller until the intensity value obtained by the detector is minimum and is marked as I_min；

And step three, rotating the second polarizer by a polarization controller until the intensity value obtained by the detector is maximum and is recorded as I_max；

Step four, because the intensity value I (x) obtained by the detector_obj) Equal to the object reflection B (x)_obj) Plus background reflection S (x)_obj) And is represented by the following formula:

I(x_obj)＝B(x_obj)+S(x_obj)

step five, in order to remove background scattering, firstly estimating the value of reflection

And the value of scattering

Respectively, are as follows:

step six, including the stepThe value of the required reflection can be known by two formulas of the fifth step

And the value of scattering

The degree of polarization, i.e. P, is determined_scatAnd P_objAn estimated value of (d);

step seven, firstly, estimating the background scattering polarization degree, and detecting the region without the target, wherein the formula is as follows:

step eight, estimating the reflection polarization degree of the target, and detecting under the condition of no background scattering, wherein the formula is as follows:

and step nine, substituting the results of the formula in the step seven and the formula in the step eight into the two formulas in the step five to obtain an estimated value of the background scattering, and removing the background scattering from the intensity information obtained by the detector.

The invention also provides a polarization defogging detection method based on the laser radar, which is characterized in that the polarization defogging detection device based on the laser radar is adopted, and the polarization defogging detection method comprises the following steps:

step eleven, emitting a light beam by a laser emitter to scan the range of the target or the region of interest:

step twelve, converting the light beam emitted by the laser emitter into linearly polarized light through a first polarizer, collimating the linearly polarized light through a lens array and focusing the linearly polarized light on the mirror surface of the MEMS rotating mirror; guiding the light beams emitted by the laser emitter to a target at different angles by adopting an MEMS (micro-electromechanical system) rotating mirror;

step thirteen, converting the light beams reflected from the target and the background into linearly polarized light through a second polarizer, and adjusting the polarization direction through a polarization controller to obtain the polarization angle of the target and the background;

and step fourteen, the phase difference information obtained by the detector comprises phase and intensity information, the obtained phase difference information is converted into distance information by a flight time principle, and the intensity information in different polarization directions is analyzed to obtain the de-scattering information.

The positive progress effects of the invention are as follows:

firstly, the detection of high resolution and wide field of view of a remote unmanned aerial vehicle is realized at low cost by utilizing a Micro-Electro-Mechanical System (MEMS) rotating mirror; two polarizers are used for scattering the background, so that the effective detection of the unmanned aerial vehicle under severe weather conditions such as rain, fog and the like is realized.

Secondly, the invention solves the problem that the prior laser radar has limited detection capability in severe weather in a simpler and more convenient way based on a polarization de-scattering way, and has great application prospect in the civil and military fields.

Drawings

Fig. 1 is a schematic structural diagram of a polarization defogging detection device based on a laser radar.

Fig. 2 is a schematic diagram of scanning according to the present invention.

Fig. 3 is a schematic view of the time-of-flight principle of the present invention.

Detailed Description

The invention determines the distance to the target by using a flight time principle method, improves the contrast between the target and the background by removing background scattering through polarization detection, and realizes the detection of the unmanned aerial vehicle 160 under severe weather conditions such as rain, fog and the like. The size, shape, position, orientation, velocity, etc. of the target within the field of view is determined by analyzing the obtained information, such as intensity and phase. The present invention will be described in more detail below with reference to the accompanying drawings by way of specific embodiments.

As shown in fig. 1, the polarization defogging detection device based on the laser radar of the invention comprises:

a laser transmitter 131 that configures the modulated pulsed laser light into independent laser exit beams;

a first polarizer 132 that converts the independent laser outgoing beam into a completely linearly polarized light;

a lens array 133 that collimates the individual laser exit beams from the first polarizer 132 and focuses the collimated beams on the MEMS turning mirror 140;

a MEMS turning mirror 140 configured to receive the collimated beam and redirect the collimated beam toward a target (drone 160) scanning area;

a second polarizer 151 that converts the echo beam scattered from the background and reflected from the target into linearly polarized light and guides it to the detector 150;

and a detector 150 for detecting at least a part of the light beam of the second polarizer 151, and deriving phase and intensity information of the light beam to an analyzer for analysis. The analyzer may calculate the distance of the target from the detector by time-of-flight principles.

The laser emitter 131 is connected to a light source controller, the first polarizer 132 and the second polarizer 151 are connected to a polarization controller, the MEMS turning mirror 140 is connected to a rotation controller, and the detector 150 is connected to a detection controller, which facilitates control and operation.

The laser transmitter adopts a laser transmitter with the wavelength of 850 nm. Compared with the common laser radar wavelength of 1550nm and 905nm, 850nm has stronger penetrability in rain and fog under the condition of ensuring effective suppression of background clutter or noise in the follow-up process; meanwhile, higher power can be obtained on the premise of ensuring the safety of human eyes, and the detection range is improved.

Although most of coherent light generated by the laser is polarized light, in order to obtain completely linearly polarized light and determine the polarization direction, a first polarizer 132 is added behind the laser emitter 131, the first polarizer 132 converts the laser emergent beam of the laser emitter 131 into completely linearly polarized light, and the obtained linearly polarized light beam is guided to the lens array 133.

The purpose of the lens array 133 is to collimate the received laser beam and, due to the small size of the MEMS scanning mirror, to focus the beam with a lens. On the one hand, the light beams can be focused on the MEMS mirror in full; on the other hand, the possibility of other places inside the laser beam guiding device is reduced, and unnecessary damage is avoided.

The laser emitter 131, the first polarizer 132, and the lens array 133 constitute a transmitting unit, and the detector 150 and the second polarizer 151 constitute a receiving unit, which facilitates transmission and reception.

Referring to fig. 2, the present invention employs a one-dimensional MEMS rotating mirror for scanning. In specific implementation, in order to obtain a vertical field of view, a plurality of laser transmitters can be adopted, at a certain moment, a linear array is obtained through reflection of an MEMS rotating mirror, and an area array is obtained through addition of an angle changing along with time. The volume and the cost of the laser radar device can be reduced by adopting the MEMS rotating mirror, the MEMS rotating mirror is the simplest mode, and the registration difficulty is the minimum. The MEMS turning mirror is used to replace the conventional rotary lidar and direct the received beam at different angles to the target or area of interest.

After obtaining the reflected light beam of the object or region of interest, it is necessary to obtain linearly polarized light of another polarization direction through the second polarizer 151 in order to obtain the effect of de-scattering. The second polarizer 151 adopts a specific method of scattering:

step one, rotating a first polarizer 132 through a polarization controller until the intensity I1 of the independent laser emergent beam passing through the polarizer is maximum;

step two, the second polarizer 151 is rotated by the polarization controller until the intensity value obtained at the detector is minimum and is recorded as I_min；

And step three, rotating the second polarizer 151 by a polarization controller until the intensity value obtained by the detector is maximum and is recorded as I_max；

Step four, because the intensity value I (x) obtained by the detector_obj) Equal to the object reflection B (x)_obj) Plus background reflection S (x)_obj) Expressed as the following formula (1):

I(x_obj)＝B(x_obj)+S(x_obj)..........(1)

And the value of scattering

The following formulas (2) and (3), respectively:

step six, the required reflection value can be known from the formulas (2) and (3)

And the value of scattering

The degree of polarization (DOP), i.e. P, is determined_scatAnd P_objAn estimated value of (d);

step seven, firstly, estimating the background scattering polarization degree, and detecting in a region (void) without a target, wherein the following formula (4) is adopted:

step eight, estimating the reflection polarization degree of the target, and detecting under the condition without background scattering, wherein the detection is as the following formula (5):

and step nine, substituting the results of the formulas (4) and (5) into the formulas (2) and (3), calculating an estimated value of background scattering, and removing the background scattering from the intensity information obtained by the detector.

In the schematic diagram of the time-of-flight principle shown in fig. 3, in order to accurately analyze the phase difference, the pulse generated by the laser emitter 131 is modulated, the echo pulse obtained through the target enters the detector, and the phase difference is analyzed by the analyzer, so that the distance of each pixel point, that is, the depth information can be obtained. The resulting depth information and the intensity information of the background scatter are stored in the one-dimensional tensor of pixels, from which 2D and 3D images of the target/drone can be obtained.

The polarization defogging detection method based on the laser radar adopts the polarization defogging detection device based on the laser radar and comprises the following steps:

step twelve, converting the light beam emitted by the laser emitter into linearly polarized light through a first polarizer, collimating the linearly polarized light through a lens array and focusing the linearly polarized light on the mirror surface of the MEMS rotating mirror; the MEMS rotating mirror is adopted to guide the light beams emitted by the laser emitter to a target at different angles, so that detection of a larger field of view is realized;

Through the device and the method, the unmanned aerial vehicle can be detected under severe weather conditions such as rain and fog, a depth map and an intensity map are obtained, and the detection of the timeliness of the unmanned aerial vehicle has important significance for protecting personal privacy and public safety in view of high resolution and long detection range of the laser radar.

In summary, in order to overcome the defect of the detection capability of the laser radar in severe weather such as rain and fog, the polarization defogging detection device and method based on the laser radar are adopted to detect the unmanned aerial vehicle, remove background scattering, improve contrast, realize the detection of the unmanned aerial vehicle in severe weather such as rain and fog, and protect personal privacy and public safety. The scanning laser radar based on the MEMS abandons the traditional rotary radar part, adopts the MEMS rotary mirror with small size, and saves space and cost. The method of combining polarization and laser radar detection is adopted, the problem that the target of the small unmanned aerial vehicle is difficult to accurately detect under severe weather conditions such as rain, fog and the like in the traditional laser radar detection is solved, and the unmanned aerial vehicle detection method provides help for unmanned aerial vehicle detection under extreme conditions.

While there have been shown and described what are at present considered the fundamental principles and essential features of the invention and its advantages, it will be apparent to those skilled in the art that the invention is not limited to the details of the foregoing exemplary embodiments, but is capable of other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.

Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.

Claims

1. A polarization defogging detection device based on a laser radar is characterized by comprising:

2. The lidar-based polarized defogging detection device according to claim 1 wherein said laser transmitter employs a laser transmitter having a wavelength of 850 nm.

3. The lidar-based polarized defogging detection device of claim 1 wherein said laser transmitter, first polarizer and lens array comprise a transmitting unit and said detector and second polarizer comprise a receiving unit.

4. The lidar-based polarization defogging detection device of claim 1 wherein said laser transmitter is coupled to a light source controller, both said first polarizer and said second polarizer are coupled to a polarization controller, said MEMS rotating mirror is coupled to a rotation controller, and said detector is coupled to a detection controller.

5. The lidar-based polarized defogging detection device according to claim 1 wherein said second polarizer employs the following specific de-scattering method:

I(x_obj)＝B(x_obj)+S(x_obj)

And the value of scattering

Respectively, are as follows:

step six, the required reflection value can be known from the two formulas of the step five

And the value of scattering

6. A lidar based polarization defogging detection method which employs the lidar based polarization defogging detection device according to claim 1, comprising the steps of: