A lidar device for simultaneously detecting vegetation reflectance and fluorescence signals

Abstract

The application discloses a laser radar device structure for synchronously detecting vegetation reflection light and fluorescence signal, which is composed of the following parts: a laser emission unit for emitting monochromatic short-wave high-energy laser pulses to vegetation through a coated full reflection mirror; a return wave receiving unit and a spectrum splitting unit for acquiring and spectrally processing short-wave reflection light signals reflected by the vegetation target and wide-spectrum fluorescence signals generated by the vegetation under excitation; a spectrum data acquisition unit for performing signal conversion and recording on the received reflection light signals and fluorescence signals; a time sequence control unit connected with the laser emission unit and the spectrum data acquisition unit through a data transmission line; and an upper computer connected with the laser emission unit, the spectrum data acquisition unit and the time sequence control unit through connecting lines. The application realizes the integration of vegetation reflection light and fluorescence dual-spectrum signal imaging detection while realizing the acquisition of accurate spatial three-dimensional information of vegetation by laser radar technology, and better serves the vegetation remote sensing monitoring and practical application.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of laser radar remote sensing detection, and relates to a laser radar device for synchronously detecting vegetation reflection light and fluorescence signals. BACKGROUND

[0002] As an active remote sensing detection technology, the laser radar can obtain accurate spatial three-dimensional information of a vegetation target, and is beneficial to the researches of vegetation phenotype detection, three-dimensional reconstruction, identification and classification. However, the traditional laser radar technology only emits single-wavelength laser, and the vegetation remote sensing detection research is carried out by obtaining the spatial three-dimensional information and single-wavelength echo intensity of the vegetation. However, in the application scenarios of vegetation growth state detection, biochemical component inversion, nutrition stress monitoring, pest control and the like, the vegetation fine remote sensing monitoring capability is limited only by the spatial three-dimensional information and single-wavelength echo intensity of the vegetation. Therefore, domestic and foreign researchers have developed various vegetation remote sensing detection technologies and means based on the laser radar technology, such as the active-passive fusion technology, multi / high-spectral laser radar technology, fluorescence laser radar technology and the like, to obtain more and wider range of spectral information and improve the monitoring capability of the vegetation. However, these technical means mostly obtain single-spectral-dimension spectral information, and cannot realize the vegetation remote sensing monitoring of more-dimension spectral information.

[0003] As important spectral characteristics in the vegetation remote sensing detection, the reflection light spectrum and the fluorescence spectrum are closely related to the vegetation growth state, physiological and biochemical components and nutrition stress. At present, domestic and foreign researchers obtain the vegetation reflection light spectrum or fluorescence spectrum by using various types of sensors, analyze the spectral characteristics and changes, and then carry out the vegetation remote sensing monitoring. However, the single-dimension spectral information can only reflect the spectral characteristics of the vegetation in a certain spectral dimension, and cannot completely display the physiological and biochemical information of the vegetation. Therefore, compared with the single-dimension spectral information, the vegetation remote sensing monitoring carried out by combining the vegetation reflection light spectrum and the fluorescence spectrum can achieve the effect of 1+1>2, organically combines the advantages of the two spectral characteristics, and can play an important role in the detection of the physiological and biochemical state of the vegetation, pest control, nutrition stress monitoring and the like.

[0004] However, the existing laser radar technology has not truly realized the synchronous detection and acquisition of the vegetation reflection light spectrum and the fluorescence spectrum information, that is, the vegetation reflection light spectrum and the fluorescence spectrum cannot be integrally and synchronously detected by one device. By means of the laser radar device for synchronously detecting vegetation reflection light and fluorescence signals, the vegetation reflection light spectrum and the fluorescence spectrum can be integrally and synchronously detected, and the single-photon counting technology is adopted to improve the fluorescence signal detection sensitivity considering that the intensity of the stimulated fluorescence signal is weak, so as to realize the integrative remote sensing monitoring of the spatial information, reflection light spectrum information and fluorescence spectrum information of the vegetation target, and has great research potential and commercial value in the fields of intelligent agriculture, forest management and biomass estimation. SUMMARY

[0005] (I) OBJECT OF THE INVENTION

[0006] The object of the present application is to provide a laser radar device for synchronously detecting vegetation reflected light and fluorescence signals, to realize integrated remote sensing monitoring of vegetation target space information, reflected light spectrum information and fluorescence spectrum information, and to comprehensively improve the performance and application range of laser radar vegetation remote sensing detection.

[0007] (II) TECHNICAL SOLUTION

[0008] In order to solve the above technical problems, the present application provides a laser radar device for synchronously detecting vegetation reflected light and fluorescence signals, which comprises a laser emission unit, a return wave receiving unit, a spectral light splitting unit, a spectral data acquisition unit, a time sequence control unit and an upper computer. The monochromatic short-wave high-energy laser pulse emitted by the laser emission unit is irradiated to the vegetation through the coated full reflection mirror. The return wave receiving unit and the spectral light splitting unit acquire and split the short-wave reflected light signal reflected by the vegetation target and the wide-spectrum fluorescence signal generated by the vegetation under excitation. The spectral data acquisition unit converts and records the received reflected light signal and fluorescence signal. The time sequence control unit is connected to the laser emission unit and the spectral data acquisition unit through a data transmission line. The upper computer controls the laser emission unit, the spectral data acquisition unit and the time sequence control unit through a connection line.

[0009] The laser emission unit is connected to the time sequence control unit, and the output of the laser pulse is controlled according to the periodic time sequence signal generated by the time sequence control unit. The frequency and pulse width parameters of the emitted laser are set by the upper computer to meet the needs of different detection targets.

[0010] The laser emission unit comprises a laser module, a water-cooled machine, a modulation module and a full reflection mirror L1. The modulation module makes the laser module emit monochromatic short-wave laser with a set frequency and a set pulse energy, and then the laser beam is reflected to the vegetation surface by the 45° inclined coated full reflection mirror L1. The heat effect caused by the emission of monochromatic short-wave laser by the laser module is cooled by the water-cooled machine to realize stable output of laser energy.

[0011] The echo receiving unit comprises an optical telescope, a focusing lens and a collimating mirror. The echo receiving unit uses the optical telescope and the focusing lens to focus mixed light spectrum formed by single-band reflected light of vegetation and wide-spectrum fluorescent signals, and uses a collimating mirror to collimate the received mixed light spectrum signals, and then transmits the collimated light spectrum signals to the spectrum splitting unit through a spatial light beam or an optical fiber transmission mode. The optical telescope is placed at an angle of 45° with respect to the total reflection mirror L1 in the laser emitting unit. The laser exit light path is reflected by the 45° total reflection mirror placed at the front end of the optical telescope. The laser exit light path, the reflected light signals of the vegetation, the excited fluorescent signals and the central axis of the optical telescope are all on the same axis. After the mixed light spectrum signals are focused at the receiving end of the optical telescope, the focused light beams are collimated by the collimating mirror, so that the light beams enter the spectrum splitting unit in parallel.

[0012] The spectrum splitting unit comprises a dichroic mirror L2, a dichroic mirror L3, a narrow-band filter L4, a narrow-band filter L6, a narrow-band filter L7 and three focusing lenses L5. The narrow-band filter L4 and one focusing lens L5 are arranged in sequence on the light reflecting side of the dichroic mirror L2. The dichroic mirror L3 is arranged on the light transmitting side of the dichroic mirror L2. The narrow-band filter L6 and one focusing lens L5 are arranged in sequence on the light reflecting side of the dichroic mirror L3. The narrow-band filter L7 and one focusing lens L5 are arranged on the light transmitting side of the dichroic mirror L3. The spectrum splitting unit is used to separate the mixed light spectrum signals obtained by the echo receiving unit, to separate single-wavelength reflected light signals and double-wavelength fluorescent band signals, and to transmit the separated light signals to the photoelectric detectors of the spectrum data acquisition unit by using the focusing lenses.

[0013] The center wavelengths of the narrow-band filter L4, the narrow-band filter L6 and the narrow-band filter L7 correspond to the laser exit wavelength, the two vegetation fluorescent characteristic wavelengths 685 nm and 740 nm respectively.

[0014] The spectrum data acquisition unit comprises a photoelectric multiplier PMT1, a photoelectric multiplier PMT2, a photoelectric multiplier PMT3, an ADC and a TDC acquisition board. The photoelectric multipliers PMT1, PMT2 and PMT3 are arranged on the light emitting side of the three focusing lenses L5. The spectrum data acquisition unit detects the separated three light signals by using the photoelectric detectors.

[0015] Wherein, when the three light signals are transmitted to three photomultiplier tubes through focusing lens, the reflected light spectrum signal is received by the first PMT1, the vegetation target distance information and the reflected light intensity information are obtained through the detector ADC conversion and the full waveform recording mode of the acquisition card; the two fluorescence band 685nm and 740nm signals are obtained by the second PMT2 and the third PMT3, the photon quantity is recorded through the detector TDC conversion and the photon number counting mode, the two fluorescence band intensity information of the vegetation target is obtained, and the data is saved to the counter through the data transmission protocol.

[0016] Wherein, the timing control unit includes a digital delay generator, the timing control unit outputs periodic digital pulse signals, synchronously controls the high-energy short-wave laser emission and the optical spectrum detection, and sets multiple repeated observations, effectively accumulates the single-wavelength reflected light intensity and the double-band 685nm and 740nm fluorescence intensity, improves the signal-to-noise ratio of the vegetation target reflected light signal and the double-band fluorescence signal detection, and records the detection distance, the reflected light echo signal intensity and the double-band fluorescence signal intensity in time sequence.

[0017] Wherein, the host computer controls the digital delay generator through the connection line, the digital delay generator is connected with the laser emission module and the ADC and TDC acquisition board card through the control connection line, the digital delay generator controls the laser pulse output and the synchronous detection of the two acquisition board cards through the periodic output of 3TTL amplitude pulse signals, realizes the laser emission, the synchronous detection of three light spectrum signals, and completes the integrated synchronous detection of the vegetation target space information, the reflected light spectrum information and the fluorescence spectrum information.

[0018] (Three) beneficial effects

[0019] The laser radar device for synchronously detecting the reflection light and fluorescence signal of the vegetation provided by the technical scheme can realize integrated remote sensing monitoring of the spatial information, reflection light spectrum information and fluorescence spectrum information of the vegetation target, better monitor the physiological and biochemical state of the vegetation, and achieve better vegetation monitoring effect. The high-energy short-wave laser pulse is emitted to the vegetation surface, interacts with the physiological and biochemical molecules on the surface and inside of the vegetation, and when the reflection light of the same wavelength is reflected, the wide-spectrum fluorescence signal is synchronously excited. The wavelength of the emitted short-wave laser is consistent with the physiological and biochemical sensitive wavelength of the vegetation, so that the reflection light spectrum and the fluorescence spectrum can better serve the vegetation remote sensing monitoring. The dichroic mirror and the narrow-band filter in the step-by-step spectrum splitting module are used to perform step-by-step spectrum separation on the mixed spectrum of the reflection light and the fluorescence obtained by the echo receiving unit. Since the fluorescence signal intensity excited is relatively weak, the linear full waveform sampling method is used by the spectrum data acquisition unit to acquire the reflection light signal, and the single-photon counting method is used to acquire the fluorescence signal, so as to improve the acquisition quality of the two kinds of spectrum information. The time sequence control unit outputs a periodic digital pulse signal to synchronously control the emission of the high-energy short-wave laser and the spectrum detection of the photoelectric detector, so that the reflection light signal and the fluorescence signal of the vegetation target are synchronously and efficiently detected and acquired, and the detection distance, the reflection light echo signal intensity and the dual-band fluorescence signal intensity are recorded in the time sequence. Therefore, the laser radar technology based on the present application can realize integrated imaging and detection of the reflection light and fluorescence dual-spectrum signals of the vegetation while acquiring the accurate spatial three-dimensional information of the vegetation, and better serve the vegetation remote sensing monitoring and practical application. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The structure schematic diagram of the laser radar device for synchronously detecting the reflection light and fluorescence signal of the vegetation provided by the present application.

[0021] Figure 2 The structure schematic diagram of the spectrum splitting and spectrum data acquisition provided by the present application.

[0022] Figure 3 The fluorescence signal intensity diagram of the healthy vegetation leaf excited. DETAILED DESCRIPTION

[0023] In order to make the purpose, content and advantages of the present application clearer, the specific embodiments of the present application are further described in detail below in combination with the drawings and examples.

[0024] The laser radar device for synchronously detecting the reflection light and fluorescence signal of vegetation includes a laser emission unit, a echo receiving unit, a spectral light splitting unit, a spectral data acquisition unit and a timing control unit. The device is similar to the traditional single-wavelength laser radar system, but the device is modified to realize the integrated remote sensing monitoring of the spatial information, reflection light spectrum and fluorescence spectrum of the vegetation target. The laser emission unit uses a monochromatic short-wave high-energy pulse laser, which is used as the excitation light for the wide-spectrum fluorescence signal of the vegetation and the ranging light for distance detection. The distance measurement is mainly based on the time difference of the incident light pulse signal during the air propagation process, and the mixed spectrum is split in the spectral light splitting unit. The spectral light splitting unit mainly relies on different properties of the dichroic mirror and the narrowband filter to stepwise separate the reflection light signal and the dual-wavelength fluorescence band signal, and the distance value, the reflection light intensity value and the fluorescence intensity value are recorded by using the full waveform technology and the single-photon counting technology, respectively. The timing control unit synchronously controls the high-energy short-wave laser emission and the spectral detection of the photoelectric detector, so that the reflection light signal intensity and the fluorescence signal intensity are in the optimal detection state, and the detection quality of the two spectral signals is improved.

[0025] Referring to Figure 1 The laser radar device structure for synchronously detecting the reflection light and fluorescence signal of vegetation in the embodiment includes a laser emission unit, an echo receiving unit, a spectral light splitting unit, a spectral data acquisition unit, a timing control unit and an upper computer. The monochromatic short-wave high-energy laser pulse emitted by the laser emission unit is irradiated to the vegetation through the coated full mirror. The echo receiving unit and the spectral light splitting unit acquire and split the short-wave reflection light signal reflected by the vegetation target and the wide-spectrum fluorescence signal generated by the vegetation. The spectral data acquisition unit converts and records the received reflection light signal and fluorescence signal. The timing control unit is connected to the laser emission unit and the spectral data acquisition unit through a data transmission line. The upper computer controls the laser emission unit, the spectral data acquisition unit and the timing control unit through a connection line.

[0026] The laser emission unit is connected to the timing control unit, and the laser pulse emission is controlled according to the periodic timing signal output by the timing control unit. The frequency and pulse width of the emitted laser are set by the upper computer, so that the device can meet the needs of different detection targets.

[0027] The laser emission unit comprises a laser module, a water cooling machine, a modulation module, and a total reflection mirror L1; the modulation module is used to make the laser module emit monochromatic short-wave laser with a set frequency and a set pulse energy, and the laser beam is reflected to the vegetation surface through the 45° coated total reflection mirror L1. The monochromatic short-wave high-energy pulse laser emitted by the laser emission unit serves as both the excitation light of the vegetation target fluorescence signal and the ranging light of the distance detection. The thermal effect caused by the high-energy laser pulse emitted by the laser module can be recycled and cooled by the water cooling machine, so as to realize stable output of laser energy.

[0028] When the monochromatic short-wave high-energy laser pulse is irradiated to the vegetation surface, the chlorophyll molecules in the vegetation absorb external light radiation energy, and the molecules in an unstable state will transition to a low energy level, and in this process, a wide-spectrum fluorescence signal with a longer wavelength than the incident light wavelength will be generated. The fluorescence signal intensity is extremely linearly related to the laser incident energy, and the laser incident energy needs to be improved as much as possible.

[0029] Moreover, the wavelength of the monochromatic short-wave high-energy pulse laser can be selected to be consistent with the sensitive wavelength of the physiological and biochemical state of the vegetation, for example, 480 nm and 532 nm. In this way, the reflected light signal and the excited fluorescence signal obtained can both have a good correlation with the physiological and biochemical information of the vegetation.

[0030] The echo receiving unit comprises an optical telescope, a focusing lens, and a collimating mirror. The echo receiving unit uses the optical telescope and the focusing lens to perform optical focusing on the mixed light spectrum composed of the vegetation single-band reflected light and the wide-spectrum fluorescence signal, and uses a collimating mirror to collimate the received mixed light spectrum signal, which can be transmitted to the light spectrum splitting unit through a spatial light beam or an optical fiber transmission mode. The type, size, focal length, and other parameters of the optical telescope and the collimating mirror can be adjusted according to the actual detection situation.

[0031] The optical telescope and the total reflection mirror L1 in the laser emission unit are placed at an angle of 45°. The laser emission light path is reflected by the 45° total reflection mirror placed at the front end of the optical telescope, so as to ensure that the laser emission light path, the vegetation reflected light signal and the excited fluorescence signal, and the central axis of the optical telescope are on the same axis. After the mixed light spectrum signal is focused at the receiving end of the optical telescope, a collimating mirror is used to collimate the focused light beam, so that the light beam enters the light spectrum splitting unit in parallel.

[0032] The spectral light splitting unit comprises dichroic mirror L2, dichroic mirror L3, narrow-band filter L4, narrow-band filter L6, narrow-band filter L7, and three focusing lenses L5; the reflecting side of the dichroic mirror L2 is sequentially arranged with the narrow-band filter L4 and one focusing lens L5, the light-transmitting side of the dichroic mirror L2 is arranged with the dichroic mirror L3, the reflecting side of the dichroic mirror L3 is sequentially arranged with the narrow-band filter L6 and one focusing lens L5, and the light-transmitting side of the dichroic mirror L3 is arranged with the narrow-band filter L7 and one focusing lens L5.

[0033] The spectral light splitting unit is used for separating the mixed spectral signal obtained by the echo receiving unit, and the single-wavelength reflected light signal and the two-wavelength fluorescent band signal are separated step by step by using the dichroic mirror, the narrow-band filter and the like, and the separated light signal is transmitted to the photodetector of the spectral data acquisition unit by using the focusing lens.

[0034] The central wavelengths of the three narrow-band filters correspond to the laser exit wavelength, the two vegetation fluorescent characteristic wavelengths 685nm and 740nm respectively, and the full-width-at-half-maximum of the three filters can be adjusted according to the detection application.

[0035] When the spectral light splitting unit works, the reflected light signal and the stimulated wide-spectrum fluorescent signal are separated by the dichroic mirror L2 (low reflection and high transmission, cut-off wavelength 600nm), and the narrow-band filter L4 (central wavelength corresponding to the incident light wavelength) is used for filtering, so that the influence of external light and other factors can be effectively avoided; the wide-spectrum fluorescent signal that transmits through the dichroic mirror L2 is further separated by the dichroic mirror L3 (low reflection and high transmission, cut-off wavelength 710nm), the two fluorescent characteristic wavelengths are filtered by the two narrow-band filters L6 and L7 (central wavelengths are 685nm and 740nm respectively), and the accuracy of the spectral data acquisition of the two fluorescent characteristic wavelengths is ensured. After the three signal light beams are filtered by the narrow-band filters, in order to improve the spectral signal acquisition capability, one focusing lens is added to each, so that the three light signals can be well transmitted to the photodetector receiving end.

[0036] The spectral data acquisition unit comprises photomultiplier tube one (PMT1), photomultiplier tube two (PMT2), photomultiplier tube three (PMT3), and ADC, TDC acquisition board, signal transmission line, and the photomultiplier tube one (PMT1), the photomultiplier tube two (PMT2) and the photomultiplier tube three (PMT3) are arranged on the light-emitting side of the three focusing lenses L5. The spectral data acquisition unit mainly detects the three separated light signals by the photodetector.

[0037] In the embodiment, when the three light signals are transmitted to the three photomultiplier tubes through the focusing lens, the reflected light spectrum signal is received by the first PMT1, the distance information of the vegetation target and the reflected light intensity information are obtained through the detector ADC conversion and the full waveform recording mode of the acquisition card, and the detector end and the acquisition card end are connected through the signal transmission line. The two fluorescence band signals (685 nm and 740 nm) are obtained by the second PMT2 and the third PMT3, the number of photons is recorded through the detector TDC conversion and the photon counting mode, the intensity information of the two fluorescence bands of the vegetation target is obtained, and the data are saved in the counter through the data transmission protocol. Similarly, the two detector ends and the acquisition card end are connected through the signal transmission line.

[0038] The timing control unit includes a digital delay generator, a control connection line. The timing control unit outputs a periodic digital pulse signal, synchronously controls the emission of the high-energy short-wave laser and the spectral detection of the photodetector, sets multiple repeated observations, effectively accumulates the single-wavelength reflected light intensity and the double-band 685 nm and 740 nm fluorescence intensity, improves the signal-to-noise ratio of the reflected light signal and the double-band fluorescence signal of the vegetation target, and records the detection distance, the reflected light echo signal intensity, and the double-band fluorescence signal intensity in the time sequence.

[0039] In the embodiment, the host computer controls the digital delay generator through the connection line, and the digital delay generator is connected to the laser emission module and the ADC and TDC acquisition board card through the control connection line. The third-party digital delay generator mainly controls the laser pulse output and the synchronous detection of the two acquisition board cards through the periodic output of 3 TTL amplitude pulse signals, so as to realize the emission of the laser, the synchronous detection of the three spectral signals, and finally complete the integrated synchronous detection of the spatial information of the vegetation target, the reflected light spectrum information, and the fluorescence spectrum information.

[0040] The recommended model of each component is: the laser includes a laser module, a water cooler, etc., and the preferred model is CNILPS-532-A. The preferred model of the photomultiplier PMT1 is Hamamatsu H10720-20; the preferred model of the photomultiplier PMT2 and PMT3 is PicoQuant PMA 192; the preferred model of the two high-speed acquisition cards is Teledyne SP Devices ADQ7 and PicoQuant HydraHarp 400; the preferred model of the third-party digital delay generator is Stanford Research Systems DG645. The preferred model of the counter is National Instruments PXIe6614.

[0041] It can be seen from the above technical solution that the application breaks through the restriction of traditional single-wavelength laser radar only obtaining the spatial detection capability of a vegetation target, simultaneously obtains the spatial information of the vegetation, and realizes the synchronous acquisition of the reflected light information and the stimulated fluorescence information of the vegetation, finally realizes the integrated remote sensing monitoring of the spatial information, the reflected light spectrum and the fluorescence spectrum of the vegetation target, can effectively monitor the physiological and biochemical state information of the vegetation, breaks through the limitation of the traditional single-wavelength laser radar in the application of spectral information, increases the spectral dimension of the vegetation remote sensing detection, greatly expands the application range of the laser radar technology in the vegetation target monitoring, the biochemical content inversion, the disease and pest control and the like, and makes the detection and monitoring more accurate and efficient.

[0042] The above only describes the preferred embodiments of the application, and it should be noted that, for those skilled in the art, without departing from the technical principles of the application, a number of improvements and modifications can be made, and these improvements and modifications should also be considered as the protection scope of the application.

Claims

1. A structure of a laser radar device for simultaneously detecting a reflection light and a fluorescence signal of vegetation, characterized by comprising: It comprises a laser emission unit, a echo receiving unit, a spectral light splitting unit, a spectral data acquisition unit, a time sequence control unit and a host computer; the monochromatic short-wave high-energy laser pulse emitted by the laser emission unit is irradiated to the vegetation through the coated full reflection mirror; the echo receiving unit and the spectral light splitting unit acquire and split the short-wave reflected light signal reflected by the vegetation target and the wide-spectrum fluorescent signal generated by the vegetation under excitation; the spectral data acquisition unit converts and records the received reflected light signal and fluorescent signal; the time sequence control unit is connected with the laser emission unit and the spectral data acquisition unit through a data transmission line; and the host computer controls the laser emission unit, the spectral data acquisition unit and the time sequence control unit through a connection line. The spectral light splitting unit comprises a dichroic mirror L2, a dichroic mirror L3, a narrow-band filter L4, a narrow-band filter L6, a narrow-band filter L7 and three focusing lenses L5; the narrow-band filter L4 and one focusing lens L5 are arranged on the light reflection side of the dichroic mirror L2 in sequence, the dichroic mirror L3 is arranged on the light transmission side of the dichroic mirror L2, the narrow-band filter L6 and one focusing lens L5 are arranged on the light reflection side of the dichroic mirror L3 in sequence, and the narrow-band filter L7 and one focusing lens L5 are arranged on the light transmission side of the dichroic mirror L3; the spectral light splitting unit is used for separating the mixed spectral signal acquired by the echo receiving unit, separating out the single-wavelength reflected light signal and the double-wavelength fluorescent band signal, and transmitting the separated light signal to the photodetector of the spectral data acquisition unit by using the focusing lens; The central wavelengths of the narrow-band filter L4, the narrow-band filter L6 and the narrow-band filter L7 correspond to the laser emission wavelength, the vegetation fluorescent characteristic wave band 685 nm and the vegetation fluorescent characteristic wave band 740 nm respectively. The laser emission unit is connected with the time sequence control unit, the periodic time sequence signal generated by the time sequence control unit is used for controlling the laser pulse emission, and the frequency and pulse width parameters of the emitted laser are set through the host computer, so that the requirements of different detection targets are met.

2. The structure of a laser radar device for synchronous detection of vegetation reflectance and fluorescence signals according to claim 1, wherein The laser emission unit comprises a laser module, a water cooling machine, a modulation module and a full reflection mirror L1; the modulation module is used for making the laser module emit monochromatic short-wave laser with a set frequency and a set pulse energy, and the laser beam is reflected to the vegetation surface through the 45°-inclined coated full reflection mirror L1; the heat effect caused by the monochromatic short-wave laser emitted by the laser module is cooled in circulation through the water cooling machine, so that the laser energy stability output is realized.

3. The structure of a laser radar device for synchronous detection of vegetation reflectance and fluorescence signals according to claim 2, wherein ​ 4. The structure of a laser radar device for synchronous detection of vegetation reflectance and fluorescence signals according to claim 3, wherein The echo receiving unit comprises an optical telescope, a focusing lens and a collimating mirror, the echo receiving unit uses the optical telescope and the focusing lens to focus mixed light spectrum composed of single-band reflection light of vegetation and wide-spectrum fluorescent signal, and uses a collimating mirror to collimate the received mixed light spectrum signal, and then transmits the collimated signal to a spectrum splitting unit through a spatial light beam or an optical fiber transmission mode; the optical telescope is placed at an angle of 45 degrees with respect to the total reflection mirror L1 in the laser emitting unit, the laser exit light path is reflected by the 45-degree total reflection mirror placed at the front end of the optical telescope, and the central axis of the laser exit light path, the vegetation reflection light signal, the excited fluorescent signal and the optical telescope are ensured to be on the same axis, and after the mixed light spectrum signal is focused at the receiving end of the optical telescope, the focused light beam is collimated by a collimating mirror to make the light beam parallel into the spectrum splitting unit.

5. The structure of a laser radar device for synchronous detection of vegetation reflectance and fluorescence signals according to claim 4, wherein The spectrum data acquisition unit comprises a photomultiplier tube 1 PMT1, a photomultiplier tube 2 PMT2, a photomultiplier tube 3 PMT3, an ADC and a TDC acquisition board, the photomultiplier tube 1 PMT1, the photomultiplier tube 2 PMT2 and the photomultiplier tube 3 PMT3 are arranged on the light exit sides of the three focusing lenses L5 respectively; the spectrum data acquisition unit detects the separated three light signals through a photoelectric detector.

6. The structure of a laser radar device for synchronous detection of vegetation reflectance and fluorescence signals according to claim 5, wherein When the three light signals are transmitted to the three photomultiplier tubes through the focusing lens, the reflected light spectrum signal is received by the first PMT1, the target distance information and the reflected light intensity information of the vegetation are obtained through the detector ADC conversion and the acquisition card full waveform recording mode, the two fluorescent band signals of 685nm and 740nm are obtained by the second PMT2 and the third PMT3, the number of photons is recorded through the detector TDC conversion and the photon number counting mode, the intensity information of the two fluorescent bands of the vegetation target is obtained, and the data is saved in the counter through the data transmission protocol.

7. The structure of a laser radar device for synchronous detection of vegetation reflectance and fluorescence signals according to claim 6, wherein The timing control unit comprises a digital delay generator, the timing control unit outputs periodic digital pulse signals, synchronously controls the laser exit and the spectrum detection of the photoelectric detector, and sets multiple repeated observations, effectively accumulates the single-wavelength reflected light intensity and the double-band fluorescent intensity of 685nm and 740nm, improves the signal-to-noise ratio of the reflected light signal and the double-band fluorescent signal of the vegetation target, and records the detection distance, the reflected light echo signal intensity and the double-band fluorescent signal intensity in time sequence.

8. The structure of a laser radar device for synchronous detection of vegetation reflectance and fluorescence signals according to claim 7, wherein The host computer controls the digital delay generator through a connection line, the digital delay generator is connected with the laser exit module and the ADC and TDC acquisition board through control connection lines, the digital delay generator controls the laser pulse output and the synchronous detection of the two acquisition board cards through the periodic output of 3 TTL amplitude pulse signals, realizes the synchronous detection of the laser exit and the three spectrum signals, and completes the integrated synchronous detection of the spatial information of the vegetation target, the reflected light spectrum information and the fluorescent spectrum information.

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