CN205809286U - The Novel double-channel laser radar improving echo dynamic range receives system - Google Patents

Abstract

This patent discloses a kind of Novel double-channel laser radar improving echo dynamic range and receive system, the coaxial reception unit being made up of beam expanding lens and subsequent optical path is responsible for the reception detection of distance of near field echo-signal, the paraxonic being made up of another large aperture telescope and subsequent optical path receives unit and is responsible for the reception detection of far field distance echo-signal, then the signal curve of two passages is spliced at repeat region, it is thus achieved that complete echo waveform.This patent increases the dynamic range of echo-signal, can effectively strengthen the detectivity of the laser radar system carrying this reception system.

Description

The Novel double-channel laser radar improving echo dynamic range receives system

Technical field

This patent relates to lidar measurement field, and coaxial and paraxonic two ways the Full wave shape laser radar of a kind of employing simultaneously receives system.

Background technology

Laser radar is the radar system launching laser beam to detect target characteristic amount, has the most become one of maximally effective means of atmospheric sounding composition and vertical distribution thereof.Transmitter sends ultrashort laser pulse (5-200ns), constantly interact with the test substance (molecule or molecule) in air during advancing after entering air, its backward Raman scatters, backward Mie scatters, backward Rayleigh scatters, can be received by telescope as echo-signal, photoelectric current is become by photodetector detection, and then it is converted into voltage signal, give modulus switching device (ADC) so that follow-up signal processing works with inverting.

Following formula formula 1 is general laser radar equation:

$P_r\left(R\right)=K\mathrm{\β}\left(R\right)ex\[p-2{\∫}_0^R\mathrm{\α}\left(r\right)dr\]/R^2---\left(1\right)$

P_r(R) being echo signal power, K is the constant of laser system, is decided by emitted energy, telescope effective area, transmissivity of optical system, β (R) backscattering coefficient, α (r) extinction coefficient (attenuation quotient).It can be seen that highly increase (distance is incremented by) along with laser pulse is advanced from formula, signal is decayed therewith, and P_r(R) square being inversely proportional to of height (distance) R is arrived with laser pulse.Therefore, the amplitude difference between echo-signal (by force) and echo-signal (weak) at a distance nearby can be the biggest, in some instances it may even be possible to differs 5-6 the order of magnitude, as shown in Figure 2.If coaxially receiving and dispatching laser radar system, general photodetector is difficult to can also keep good linear output character (voltage is directly proportional to received optical power) under the widest dynamic range, so needing to take some other measures to ensure output.

Receive and dispatch laser radar system for paraxonic, introduce " geometric overlap factor O (R) ", represent that distance enters the ratio of detector for rear orientation light at R, such as Fig. 1.Then radar equation is rewritable is:

$P_r\left(R\right)=KO\left(R\right)\mathrm{\β}\left(R\right)ex\[p-2{\∫}_0^R\mathrm{\α}\left(r\right)dr\]/R^2---\left(2\right)$

Wherein 0.0≤O (R)≤1.0.In order to obtain the good output of detector, the dynamic range needing signal can not be excessive, it is common practice to receiving optical axis, transmitting optical axis is pulled open appropriately distance.Owing to the angle of divergence of laser is smaller with the telescopical angle of visual field, this strong scattering signal allowing near field will not enter field of view of receiver (geometric overlap factor is equal to zero, referred to as blind area)；Along with the increase of distance, two visual fields gradually start to intersect, and the slightly strong signal section near field enters field of view of receiver (geometric overlap factor is between 0～1.0, and is gradually increased)；After certain height, transmitting visual field is completely into field of view of receiver (geometric overlap factor is equal to 1.0), then the echo after this height can be received completely by telescope.So have compressed the dynamic range of echo-signal so that peak signal is unlikely to the biggest with the ratio of weak signal, it is possible to obtain good output, such as Fig. 3.

This way reaches decay near-field signals intensity by increasing the overlap factor of blind area, near field, reduction near field field of view of receiver and transmitting visual field, realizes the dynamic range of compressed signal intensity.It has obvious shortcoming: the existence of blind area sacrifices near-field signals, loses closely the important informations such as (near the ground) information, the following steam of such as atmospheric boundary layer, aerosol.Therefore, this shortcoming, key problem the most to be solved by this invention how are made up.

Summary of the invention

This patent is directed to a kind of Novel double-channel laser radar improving echo dynamic range and receives system, and the purpose of do so is to improve the dynamic range the most not consumption of essence degree of laser radar echo, promotes detectivity and reduces measurement blind area.

Described laser radar receives system and includes coaxially receiving unit and paraxonic reception unit.While inheriting classical paraxonic lidar transmit-receive structure, increase the coaxial transceiver channel of multiplexing beam expander, small-bore transmitting lens barrel as beam expander is become the optics of dual identity, on the one hand continue to take on beam expander, the angle of divergence launching laser is diminished, be on the other hand used as small-bore telescope, receive the atmospheric scattering echo-signal of the distance of near field, owing to this lens barrel bore is less, being appreciated that according to formula 2 also can be less by its atmospheric scattering echo-signal obtained, it is simple to detection；Heavy caliber lens barrel uses paraxonic working method, is only used as telescope, receives the atmospheric scattering echo of far field distance, and its optical axis is parallel and separated by a distance with transmitting optical axis, has one section of blind area on hand, will not receive the echo-signal that near field is too strong.

Described laser radar receives the coaxial unit that receives of system and is made up of beam expander, quarter-wave plate, polarization beam splitter, filter set, coaxial collecting lens, near-field probe.Linearly polarized laser reflects through polarization beam splitter, air is injected through becoming circularly polarized laser after quarter-wave plate, the contrary circularly polarized light of direction of rotation can be become with the echo-signal after test substance effect and return along launching light path, collected by beam expander, the line polarized light vertical with laser emitting laser polarization direction is become through quarter-wave plate, polarization beam splitter can be passed through, through filter set post-concentration on the test surface of near-field probe.The beam expander due to multiplexing, the most coaxial with Laser emission light path, in order to prevent emission pulse laser scurry into reception passage and make near-field probe occur saturated, even burn out, plated film reasonable to polarization beam splitter, simultaneously the running voltage to detector arrange time delay gate.Adjusted Q signal to trigger detector gating circuit by laser instrument and produce a delay pulse, the time of laser firing pulses was placed in this delay pulse time, during this period, the running voltage zero setting of detector or put negative value, high-pressure work power supply (avalanche diode 300-400V voltage source or photomultiplier tube 9000-14000V voltage source) is only just added on detector after delay pulse terminates.

Described laser radar receives the paraxonic of system and receives the mode that unit is taked paraxonic to place by telescope, diaphragm, field lens, paraxonic interferometric filter, paraxonic collecting lens, far field detection device composition, telescope optic axis and transmitting laser beam axis.By formula 1 it will be seen that telescope bore is directly proportional to the echo power received, therefore to receive far-field signal, choose large aperture telescope herein.Far field echo, after telescope receives, is converged on far field detection device test surface by Path of Convergent Rays.

When double optical axises, dual channel mode work, the field of view of receiver of two passages must have overlapping region within a certain height, so that fusion is engaged togather in overlapping region by height (distance) by the echo-signal of two passages i.e. echo vertical distribution curve in Signal Pretreatment, constitute the complete echo strength waveform drawn near.

This patent increases the dynamic range of echo-signal, can effectively strengthen the detectivity of the laser radar system carrying this reception system.

Accompanying drawing explanation

Fig. 1 launch optical axis with receive optical axis parallel and separately receive and dispatch visual field overlapping cases schematic diagram (φ > θ, field of view of receiver always greater than launch visual field).

The laser radar echo power of Fig. 2 simulation is with the curve of scattering object (certain atmospheric product unit of laser road warp) height change.

Fig. 3 echo relative intensity P_r(R) by overlap factor O (R) compression be there is the schematic diagram of blind area in region near the ground to dynamic range.

One detailed description of the invention schematic diagram of Fig. 4 this patent.Label in figure: 1-pulse laser, 2-telescope, 3-beam expander, 4-quarter-wave plate, 5-polarization beam splitter, 6-neutral-density filter, the coaxial interferometric filter of 7-, the coaxial collecting lens of 8-, 9-near-field probe, 10-adjust Q to trigger signal, 11-high voltage power supply, 12-gate time delay, 13-diaphragm, 14-field lens, 15-paraxonic interferometric filter, 16-paraxonic collecting lens, 17-far field detection device, 18-reflecting mirror composition.

Detailed description of the invention

Fig. 4 show described laser radar and receives the system example for laser radar system.Linearly polarized laser pulse launched by pulse laser 1, pulse width is in 1ns-200ns scope, polarization beam splitter 5 disposes with incident light axis angle at 45 °, normal rotatory polarization beam splitting chip around working face, its polarization direction is made to mate with the polarization direction launching laser, launch light beam to be totally reflected by polarization beam splitter 5, rotate quarter-wave plate 4, make the optical axis of wave plate crystal and the angle at 45 °, polarization direction of incident beam, the transmitting light beam of linear polarization becomes circularly polarized light beam after quarter-wave plate 4, circularly polarized light beam passes through beam expander 3, the angle of divergence reduces therewith, beam diameter increases, the angle of divergence of the light beam eventually entering into air is less than the field of view of receiver angle (full-shape) of telescope 2.

Air path in laser process has backscattering echo, and echo is the circularly polarized light that direction of rotation is contrary with incident atmospheric laser.The scatter echo near field returns beam expander 3, when again passing through quarter-wave plate 4, it is reduced into linear polarization, and polarization direction is vertical with the polarization direction of laser instrument 1 shoot laser, therefore it is not polarized beam splitting chip 5 and reflects, but through polarization beam splitter 5, be then passed through the filter set being made up of neutral-density filter 6 and coaxial interferometric filter 7, converged in near-field probe 9 by coaxial collecting lens 8.

Far-field signal is received by large aperture telescope 2, through diaphragm 13, field lens 14, reflecting mirror 18, paraxonic interferometric filter 15, paraxonic collecting lens 16 converges on far field detection device 17.

For the coaxial detection circuit receiving unit, gate time delay 12 is set, delay time is slightly larger than laser pulse width, gate time delay 12 is triggered signal 10 by the tune Q of laser instrument and triggers, in the delay time of gate time delay 12, the high voltage power supply 11 of near-field probe 9 will disconnect with near-field probe 9, and the running voltage in near-field probe 9 is set to zero or negative value；After gate time delay 12 terminates, power supply high pressure 11 recovers to access near-field probe 9.

The foregoing is only this patent a kind of specific embodiments for laser radar system, but the protection domain of this patent is not limited thereto, therefore the protection domain of this patent should be as the criterion with scope of the claims.

Claims (1)

1. the Novel double-channel laser radar improving echo dynamic range receives a system, including coaxially receiving unit and paraxonic reception unit, it is characterised in that:

The described coaxial unit that receives includes beam expander (3), quarter-wave plate (4), polarization beam splitter (5), the filter set being made up of neutral-density filter (6) and coaxial interferometric filter (7), coaxial collecting lens (8), near-field probe (9), described paraxonic receives unit and includes telescope (2), diaphragm (13), field lens (14), reflecting mirror (18), paraxonic interferometric filter (15), paraxonic collecting lens (16), far field detection device (17)；

In coaxial reception unit: the distance of near field echo-signal after circularly polarized laser and test substance effect returns along launching light path, collected by beam expander (3), separating with transmitting light path after polarization beam splitter (5) through quarter-wave plate (4), the filter set and the coaxial collecting lens (8) that constitute via neutral-density filter (6) and coaxial interferometric filter (7) are received by near-field probe (9)；

Paraxonic receives in unit: the far field distance echo-signal after laser and test substance effect is collected by telescope (2), through diaphragm (13), field lens (14), received by far field detection device (17) after reflecting mirror (18), paraxonic interferometric filter (15) and paraxonic collecting lens (16)；

By height or distance, in overlapping region, fusion is engaged togather the echo-signal that the detector of two unit receives i.e. echo vertical distribution curve, constitutes the complete echo strength waveform drawn near.