CN101788667A - Light amplification type three-dimensional imaging method and system - Google Patents

Abstract

The invention discloses an optical amplification type three-dimensional imaging method and system. One output of the timing signal control module controls the pulsed laser to emit pulsed light through the beam expander system and irradiates the object under test. The returned signal light enters the optical amplifier module through the imaging system for amplification. It is received by the first camera, and the other part is received by the second camera. The other three channels of the timing signal control module respectively control the optical amplification module, the gain modulation receiver and the image processing module. The images acquired by the two cameras are processed by the image processing module to calculate the distance of each pixel in the image corresponding to the target and obtain the three-dimensional image of the target. The present invention reduces the impact of random shot noise on signal light and improves distance measurement accuracy without changing the power of the light source and the gate gate time.

Description

A kind of light amplification type three-dimensional imaging method and system

Technical field

The present invention relates to the method and system of three-dimensional imaging, especially relate to a kind of light amplification type three-dimensional imaging method and system.

Background technology

Along with the development need of human scientific-technical progress with society, high speed aircraft navigations such as aircraft, the round-the-clock target recognition and tracking of over the horizon, application such as geographical relief high precision exploration have all proposed high requirement to long-range target acquisition.The fast development of three-dimensional imaging laser radar solves problems such as long-range detection new research direction is provided for people.But traditional three-dimensional imaging laser radar system capture to such an extent that the light signal signal to noise ratio (S/N ratio) is lower, thereby the performance at aspects such as resolution of ranging is difficult to that breakthrough raising is arranged when surveying target far away.So study high performance three-dimensional imaging technology and be one of focus that people pay close attention to.

Avalanche photodide (AvalanchePhoto Diode, APD) the three-dimensional ranging technology of range finding single-point module construction of Geiger (Geiger) pattern adopted in the Lincoln laboratory of the U.S..This method is subject to technological level, and pixel count is low, and it is serious to crosstalk between pixel.People such as Denmark Andersen have invented the door gate type three-dimensional laser radar technology based on time slice (TimeSlicing).The limitation of this method need to be tens of width of cloth intensity maps could pass through to calculate and to obtain a width of cloth 3-D view.People such as the graduate Martin Laurenzis in moral method St. Louis utilize light pulse of high-quality rectangle and door gating, can obtain trapezoidal distance-The Relationship of Light intensity.Two width of cloth images can obtain 3-D view.The limitation of this method need to be the modulation quality of strict control light pulse and receptacle.

The applicant had once proposed no scanning pulsed modulation formula three-D imaging method and system's (patent No. 20051004946.3), the measuring accuracy of this system is irrelevant with the shape of emission laser pulse, but in actual conditions, it is far away to be subjected to detection of a target distance, light source power can not be excessive, the receiving optics bore can not be excessive etc. the influence of factor, make light signal that detector obtains a little less than, cause signal to noise ratio (S/N ratio) to descend, measuring accuracy reduces.

Summary of the invention

The object of the present invention is to provide a kind of light amplification type three-dimensional imaging method and system, improve three-dimensional imaging laser radar range performance.

The technical solution used in the present invention is as follows:

One, a kind of light amplification type three-dimensional imaging method:

Laser instrument produces light pulse, shining testee returns, adopt the light amplification module, the pulsed optical signals that collects is amplified, pass through beam splitting system then, with the light signal separated into two parts after amplifying, a part is received by video camera by the gain modulation receiver, and another part is directly received by another video camera, with image processing module the image that receives is handled, calculate the distance of the corresponding target of each picture element in the image, generate 3-D view.

Two, a kind of light amplification type three-dimensional imaging system:

Comprise the clock signal control module, pulsed laser, beam-expanding system, imaging system, gain modulation receiver, two video cameras and image processing module; The first via output control pulse laser instrument of clock signal control module sends pulsed light by beam-expanding system, is radiated on the testee.The light that fires back enters the light amplification module through imaging system, be divided into two-way after the light signal process beam splitting system beam split that is exaggerated, lead up to the gain modulation receiver, received by first video camera, another road is received by second video camera, the image that two video cameras obtain outputs to image processing module respectively, and second, third of clock signal control module, the four tunnel is connected with image processing module with light amplification module, gain modulation receiver respectively.

Described pulsed laser is the laser instrument of optical pulse width greater than tens nanoseconds; Described light amplification module is the video screen fluorescence lifetime image intensifier shorter than the light pulse duration, or is made up of many optical fiber with enlarging function; Described gain modulation receiver is an image intensifier; Described image processing module is personal computer, DSP digital information processing system or flush bonding processor.

The beneficial effect that the present invention has is:

The present invention amplifies flashlight by the light amplification module under the condition that does not change light source power and door gating time, reduces at random shot noise to the influence of flashlight, thereby has improved distance accuracy.

Description of drawings

Accompanying drawing is a structural principle synoptic diagram of the present invention.

Among the figure: 1, clock signal control module, 2, pulsed laser, 3, beam-expanding system, 4, imaging system, 5, the light amplification module, 6, beam splitting system, 7, the gain modulation receiver, 8, first video cameras, 9, second video cameras, 10, image processing module.

Embodiment

Below in conjunction with drawings and Examples method and system of the present invention is described further.

The principle that the present invention improves detection accuracy is:

By laser radar equation, the laser power that the single pixel-by-pixel basis of detection system is received can be expressed as:

$P_R=\frac{P_T\mathrm{\π}{D}^2\mathrm{\β}}{4\mathrm{\πi}{R}^2}{e}^{2\mathrm{\γR}}---\left(1\right)$

P in the formula _RBe the laser power that single pixel-by-pixel basis is received, P _TBe the emission laser power, D is a receiving aperture, and β is the reflectivity of target, and γ is the proportion of goods damageds of transmitting in medium, and R is the laser radar range-to-go, and i is the pixel count of detector.

In order to suppress bias light and rear orientation light enters system, need before receiving system, add narrow band filter slice

And adopt the mode of door gating to survey.Suitable door gating time is set, guarantees the return signal of the laser pulse of reception that the gating process is complete each time.Then the receiving plane pixel receives the expectation E (N) that light pulse comprises photon number N and is:

$E\left(N\right)=\frac{\mathrm{m\η}{P}_R}{\mathrm{h\υ}}---\left(2\right)$

M is the emitting times of light pulse in once surveying in the formula, and η is the quantum efficiency of receiver, and h is a Planck constant, and υ is the incident light frequency.

There is the randomness that arrives room and time at spatial transmission in light signal to receiving plane, this process is a Poisson stochastic process.Obtaining standard deviation by Poisson distribution is $\mathrm{\σ}=\sqrt{N},$ σ represents the fluctuating of light signal, is referred to as shot noise.Owing to require during three-dimensional imaging the signal to noise ratio (S/N ratio) of image higher relatively, the photon number that light signal comprises is generally greater than 1000, so the error that causes of shot noise is much larger than the influence of other factors.The signal to noise ratio snr of tested light signal ₁Can be expressed as:

${\mathrm{SNR}}_1=\frac{N}{\sqrt{N}}=\sqrt{N}=\sqrt{\frac{\mathrm{m\η}{P}_R}{\mathrm{h\υ}}}---\left(3\right)$

By (3) formula as can be known, the signal to noise ratio (S/N ratio) of measured signal is directly proportional with the square root of received optical power.The power that is to say receiving optical signals is big more, and signal to noise ratio (S/N ratio) is high more.

1. when not adding the light amplification module:

Flashlight is received by video camera by the gain modulation receiver through a part after the beam splitting system without amplification module, and another part is directly received by video camera.

If the light pulse after the beam split is respectively in the photon number that a certain pixel comprised: N ₁+ σ ₁And N ₁+ σ ₂, σ wherein ₁, σ ₂Represent the shot noise that this pixel light signal is additional respectively.Shot noise meets Poisson distribution, therefore has $E\left({\mathrm{\σ}}_1\right)=E\left({\mathrm{\σ}}_2\right)=\sqrt{N_1}.$

If the gain modulation function of gain modulation receiver is f (t), f (t) is at [t ₁, t ₂] be dull, t ₁And t ₂Represent the time that the door gating begins and finishes respectively.T represent light from light source through scene reflectivity to detector institute elapsed time, it and scene have following relation to detector apart from x:

$x=\frac{1}{2}{V}_{C}t---\left(4\right)$

V in the formula _cThe velocity of propagation of light in medium for this kind wavelength.After the gain modulation receiver was advanced in a part of light pulse after the beam split, the photon number M that receives of this pixel on the video camera ₁For:

M ₁＝f(t)(N ₁+σ ₁) (5)

Another part light pulse after the beam split directly enters video camera, the photon number M that receives of this pixel on the video camera ₂For:

M ₂＝N ₁+σ ₂ (6)

(5) (6) are divided by and are obtained:

$\frac{M_1}{M_2}=\frac{f\left(t\right)(N_1+{\mathrm{\σ}}_1)}{N_1+{\mathrm{\σ}}_2}\≈f\left(t\right)[1+\frac{{\mathrm{\σ}}_1+{\mathrm{\σ}}_2}{N_1}]---\left(7\right)$

The uncertain factor that introduce this moment is: $E\left(\frac{{\mathrm{\σ}}_1+{\mathrm{\σ}}_2}{N_1}\right)=\frac{2\sqrt{N_1}}{N_1}=\frac{2}{\sqrt{N_1}}---\left(8\right)$

2. when adding the light amplification module:

Flashlight is received by video camera by the gain modulation receiver through a part after the beam splitting system through behind the amplification module, and another part is directly received by video camera.

Light pulse in the photon number that a certain pixel comprised is before amplifying: N ₃+ σ ₃, σ wherein ₃The additional shot noise of expression light signal, $E\left({\mathrm{\σ}}_3\right)=\sqrt{N_3}.$

If the enlargement factor of light amplification module is k, behind the flashlight process amplification module, the photon number M that light pulse comprised of this pixel outgoing ₃For:

M ₃＝k(N ₃+σ ₃)+σ ₄ (9)

σ in the formula ₄Be the noise of introducing in the amplification process.Amplify because photon is received the back by photocathode, photoelectronic outgoing also is a typical Poisson process.So $E\left({\mathrm{\σ}}_4\right)=\sqrt{k(N_3+{\mathrm{\σ}}_3)}.$ By (3) formula as can be known: after the light amplification module, it is big that optical signal power becomes, and signal to noise ratio (S/N ratio) improves.The light signal signal to noise ratio snr of this pixel ₂Can be expressed as:

${\mathrm{SNR}}_2=\sqrt{M_3}=\sqrt{k(N_3+{\mathrm{\σ}}_3)+{\mathrm{\σ}}_4}---\left(10\right)$

When k was big, signal to noise ratio (S/N ratio) was higher, the noise σ that introduces in the amplification process ₄Relative signal can be ignored.So the photon number that light pulse comprised of this pixel outgoing can be reduced to M after amplifying ₄:

M ₄＝k(N ₃+σ ₃) (11)

After the light signal process 1:1 beam split after the amplification, the photon number that the corresponding pixel points light pulse is comprised is respectively: With σ wherein ₅, σ ₆Be respectively light beam after the amplification additional shot noise in transmission course.Shot noise meets Poisson distribution, therefore has $E\left({\mathrm{\σ}}_5\right)=E\left({\mathrm{\σ}}_6\right)=\sqrt{\frac{M_4}{2}}.$

If the gain modulation function of gain modulation receiver is g (t), g (t) is at [t ₁, t ₂] be dull, t ₁And t ₂Represent the time that the door gating begins and finishes respectively.The photon number M that receives of this pixel on the video camera ₅, M ₆Be respectively:

$M_5=g\left(t\right)[\frac{M_4}{2}+{\mathrm{\σ}}_5]---\left(12\right)$

$M_6=\frac{M_4}{2}+{\mathrm{\σ}}_6---\left(13\right)$

(12) (13) are divided by and are obtained:

$\frac{M_5}{M_6}=\frac{g\left(t\right)[\frac{M_4}{2}+{\mathrm{\σ}}_5]}{\frac{M_4}{2}+{\mathrm{\σ}}_6}=g\left(t\right)(1+\frac{{\mathrm{\σ}}_5+{\mathrm{\σ}}_6}{\frac{M_4}{2}})---\left(14\right)$

The uncertain factor of bringing thus is: $E\left(\frac{{\mathrm{\σ}}_5+{\mathrm{\σ}}_6}{\frac{M_4}{2}}\right)=\frac{2\sqrt{\frac{M_4}{2}}}{\frac{M_4}{2}}\≈\frac{2}{\sqrt{\frac{{\mathrm{kN}}_3}{2}}}.$

When k →+during ∞, $\frac{2}{\sqrt{\frac{{\mathrm{kN}}_3}{2}}}\→0.$ Therefore, when the gain of light amplification module was big, the uncertain factor leveled off to 0.

Below specific embodiments of the present invention is elaborated: as shown in Figure 1, system of the present invention comprises: clock signal control module 1, pulsed laser 2, beam-expanding system 3, imaging system 4, light amplification module 5, beam splitting system 6, gain modulation receiver 7, two video cameras 8,9 and image processing module 10; The first via output control pulse laser instrument 2 of clock signal control module 1 sends pulsed light by beam-expanding system 3, is radiated on the testee.The light that fires back enters light amplification module 5 through imaging system 4, be divided into two-way after light signal process beam splitting system 6 beam split that are exaggerated, lead up to gain modulation receiver 7, received by first video camera 8, another road is received by second video camera 9, the image that two video cameras 8,9 obtain outputs to image processing module 10 respectively, and second, third of clock signal control module 1, the four tunnel is connected with light amplification module 5, gain modulation receiver 7 and image processing module 10 respectively.

Described pulsed laser 2 is the laser instrument of optical pulse width greater than tens nanoseconds; Described light amplification module 5 is video screen fluorescence lifetime image intensifiers shorter than the light pulse duration, or is made up of many optical fiber with enlarging function; Described gain modulation receiver 7 is image intensifiers; Described image processing module 10 is personal computer, DSP digital information processing system or flush bonding processor.

The output intensity of image intensifier is directly proportional with input light intensity and gain product.In light amplification module 5, set suitable image intensifier gain coefficient, the light signal that will contain scene information amplifies.The gain modulation function of setting image intensifier in the gain modulation receiver 7 is monotonic quantity in the door gating time.During intensity image by once or several times exposures obtain.After obtaining intensity image, can calculate range image.Generate 3-D view thus.

1, pulsed laser 2 sends pulsed light through beam-expanding system 3, the tested scene of throwing light on.The light intensity I that pixel receives when entering imaging system 4 ₁Can be expressed as:

I ₁＝Kn(P _S+P _N) (16)

K is a scale-up factor in the formula, and the transformational relation between expression light intensity and the luminous energy, n are the number of times of door gating in once surveying, P _SBe the luminous power of back light signal, P _NBe in the flashlight communication process because the time and space uncertainty that arrives causes the luminous power of shot noise correspondence.

2, flashlight enters light amplification module 5 by imaging system 4.Because by after the light amplification module, it is big that optical signal power becomes, signal to noise ratio (S/N ratio) improves, and the noise relative signal of introducing in the amplification process can be ignored.The image intensifier gain of setting light amplification module 5 is under the situation of constant, the light intensity I that this picture element receives on the video screen of light amplification module 5 ₂Can be expressed as:

I ₂＝AI ₁ (17)

A is the gain of image intensifier in the formula.

3, after process beam splitting system 6 was pressed the 1:1 beam split, part signal light was received by video camera 8 by gain modulation receiver 7.The light intensity I that this pixel receives on the video camera 8 ₃Can be expressed as

$I_3=\frac{I_2}{2}h\left(t\right)---\left(18\right)$

H in the formula (t) is the gain modulation function of gain modulation device image intensifier.H (t) is at [t ₁, t ₂] be dull, t ₁And t ₂Represent the time that the door gating begins and finishes respectively.

4, after process beam splitting system 6 was pressed the 1:1 beam split, another part flashlight directly entered video camera 9.The light intensity I that this pixel receives on the video camera 9 ₄Can be expressed as follows:

$I_4=\frac{I_2}{2}---\left(19\right)$

5, two video cameras 8,9 are demarcated by experiment, determine the corresponding relation of same pixel gray scale and position after, can obtain the ratio of the light intensity of same pixel point:

$\frac{I_3}{I_4}=h\left(t\right)---\left(20\right)$

6, by formula (4) (20), and h (t) is at [t ₁, t ₂] be dull, so h ^-1(t) exist.Can obtain relative position x, can be expressed as in the corresponding target of interior this pixel of gating distance:

$x=\frac{1}{2}{V}_C{h}^{-1}\left(\frac{I_3}{I_4}\right)---\left(21\right)$

V in the formula _CRepresent the velocity of propagation of this kind wavelength in medium.

Claims (3)

1. An optical amplification type three-dimensional imaging method is characterized in that: the laser generates optical pulses, irradiates the object to be measured and returns, adopts an optical amplification module to amplify the pulsed optical signals collected, and then passes through the spectroscopic system to amplify the amplified The optical signal is divided into two parts, one part is received by the camera through the gain modulation receiver, and the other part is directly received by another camera, and the received image is processed by the image processing module to calculate the distance of each pixel in the image corresponding to the target. Generate a 3D image. 2. a kind of optical amplification type three-dimensional imaging system that implements the described method of claim 1, comprises timing signal control module (1), pulsed laser (2), beam expander system (3), imaging system (4), gain A modulation receiver (7), two cameras (8, 9) and an image processing module (10); the first output of the timing signal control module (1) controls the pulsed laser (2) to emit pulsed light through the beam expander system (3 ), irradiating on the measured object; it is characterized in that: the light emitted back enters the optical amplification module (5) through the imaging system (4), and the amplified optical signal is divided into two paths after being split by the spectroscopic system (6), one path Through the gain modulation receiver (7), it is received by the first camera (8), and the other is received by the second camera (9), and the images acquired by the two cameras (8, 9) are respectively output to the image processing module (10 ), the second, third and fourth paths of the timing signal control module (1) are respectively connected to the optical amplification module (5), the gain modulation receiver (7) and the image processing module (10). 3. A kind of optical amplification type three-dimensional imaging system according to claim 2, is characterized in that: described pulsed laser (2) is the laser with light pulse width greater than tens of nanoseconds; Described optical amplification module ( 5) It is an image intensifier whose fluorescence lifetime of the fluorescent screen is shorter than the duration of the light pulse, or is composed of a plurality of optical fibers with amplifying functions; the gain modulation receiver (7) is an image intensifier; the image processing The module (10) is a personal computer, a DSP digital signal processing system or an embedded processor.

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