Laser radar echo signal optical detection system for detecting marine particulate organic carbon

Abstract

The invention belongs to the technical field of photoelectric signal conversion and processing, and particularly discloses a laser radar echo signal optical detection system for ocean particulate organic carbon detection, which consists of a high-speed photoelectric detector driving circuit, a high-speed photoelectric detector, a trans-impedance amplifier, a voltage amplifier and an FPGA (Field Programmable Gate Array) module. Echo signal light of the ocean laser radar can be detected and processed, firstly, an echo light signal is converted into a current signal through a high-speed photoelectric detector, then current-voltage conversion is carried out through a trans-impedance amplifier, the signal is amplified through a voltage amplifier, and finally signal acquisition and processing are completed through an FPGA module. The system can meet the detection of echo signal light of different ocean profile depths, and is simple and reliable in structure and easy to adjust.

Description

Technical Field

[0001] The present invention relates to the technical field of optoelectronic signal conversion and processing, and particularly relates to a lidar echo signal optical detection system for detecting marine particulate organic carbon, which is used to achieve large dynamic range and high-sensitivity detection of lidar echo optical signals in the ocean. Background Art

[0002] In nature, the carbon in the atmosphere is "collected" mainly through the carbon pools formed by terrestrial and marine ecosystems. In the global natural ecosystem, more than half of the carbon captured through photosynthesis is captured by marine organisms. Therefore, the ocean is an important link in the global carbon cycle. In the ocean, an important form of carbon existence is particulate organic carbon (POC). The output of POC from the euphotic zone to the deep layer and its burial in sediments reflect the carbon sink effect of the ocean. To evaluate the carbon sink capacity of the ocean, it is very necessary to detect the content of POC in the ocean.

[0003] Traditional marine remote sensing detection technologies are difficult to obtain the quantity and coverage of ocean buoys related to the vertical distribution of POC in the ocean, and cannot achieve reliable large-scale detection of ocean POC. In contrast, lidar in the blue-green band is a currently known technical means that is expected to achieve vertical stratification remote sensing detection of the ocean. By means of the blue-green optical window of seawater, a certain depth of seawater penetration can be achieved, and then the three-dimensional distribution characteristics of ocean POC can be obtained.

[0004] Lidar uses laser as the detection medium, and the characteristics of the detected target are retrieved by analyzing characteristic parameters such as the phase, frequency, amplitude, and polarization state of the echo signal light. Its optoelectronic detection system usually uses a photomultiplier tube to realize the conversion of optoelectronic signals, and subsequent processing is carried out by using the analog detection method and the photon counting method according to the intensity and pulse characteristics of the echo optical signal. When the echo signal light reaching the photomultiplier tube is strong, the output pulse signal intervals of the photomultiplier tube are narrow and then overlap with each other to form an analog signal waveform; when the echo optical signal is weak, the photon counting method is used for detection. At this time, the photomultiplier tube outputs discrete pulse signals, and the number of pulses can be counted and statistically analyzed in binary form. Therefore, analog detection takes the signal amplitude as the processing object, while photon counting takes the number of pulses as the processing object. Since photon counting can separate signals and noise by reasonably setting the pulse discrimination threshold voltage, photon counting is more suitable for application fields with weak signal detection and strict system signal-to-noise ratio requirements.

[0005] It should be noted that the information disclosed in the above background art section is only used to strengthen the understanding of the background of the present invention, and therefore may include information that does not constitute the prior art known to those of ordinary skill in the art. Summary of the Invention

[0006] The object of the present invention is to solve the technical problems existing in the background art. For this purpose, a lidar echo signal optical detection system for marine particulate organic carbon detection is provided. Through the collaborative design of analog circuits and digital circuits, combined with the composite detection modes of analog detection and photon counting, it meets the detection and processing of lidar echo signal light at different marine profile depths, achieving a detection sensitivity of single photon level, a large dynamic range of 50 dB, and a response bandwidth requirement of 200 MHz.

[0007] In order to achieve the above object, the technical solutions adopted by the present invention are as follows:

[0008] A lidar echo signal optical detection system for marine particulate organic carbon detection, comprising a high-speed photodetector driving circuit, a high-speed photodetector, a transimpedance amplifier, a voltage amplifier, and an FPGA module;

[0009] The high-speed photodetector driving circuit is used to provide the working voltage required for the conversion of photoelectric signals to the high-speed photodetector;

[0010] The high-speed photodetector is used to receive the echo signal light and convert the echo signal light into a current signal;

[0011] The transimpedance amplifier is used to receive the current signal of the high-speed photodetector and convert the current signal into a voltage signal;

[0012] The voltage amplifier is used to receive the voltage signal of the transimpedance amplifier and amplify the voltage signal;

[0013] The FPGA module is used to receive the voltage amplification signal of the voltage amplifier, perform digital processing on the voltage amplification signal, convert it into a digital signal, and process the signal using a digital filtering algorithm, and then input it into the analog detection channel and the photon counting channel respectively.

[0014] The following is a further limited technical solution of the present invention. The high-speed photodetector driving circuit includes a reverse bias voltage source, a photocathode voltage source, and a monitoring module;

[0015] The reverse bias voltage source is used to provide a reverse bias voltage for the high-speed photodetector;

[0016] The photocathode voltage source is used to provide a photocathode voltage for the high-speed photodetector;

[0017] The monitoring module is used to display the output voltage of the reverse bias voltage source, the output voltage of the photocathode voltage source, and the output current situation in real time to ensure the normal working state of the high-speed photodetector.

[0018] The following is a further limited technical solution of the present invention. The output voltage range of the reverse bias voltage source is 0 to 500 V.

[0019] The following is a further limited technical solution of the present invention. The output voltage range of the photocathode voltage source is 0 to -10,000V.

[0020] The following is a further limited technical solution of the present invention. The FPGA module includes an analog-to-digital conversion module, an algorithm module, a digital-to-analog conversion module, a signal discrimination module, a single-photon counting module, and a particulate organic carbon concentration extraction module;

[0021] The analog-to-digital conversion module is used to receive the voltage amplification signal of the voltage amplifier and perform analog-to-digital conversion on the voltage amplification signal, thereby converting the analog signal into a digital signal;

[0022] The algorithm module is used to receive the digital signal output by the analog-to-digital conversion module and process the digital signal using the autocorrelation algorithm and the median average filtering algorithm to suppress noise. One path of the output of the algorithm module is input to the analog detection channel, and the other path of the output of the algorithm module is input to the photon counting channel;

[0023] The analog detection channel includes a digital-to-analog conversion module;

[0024] The digital-to-analog conversion module receives one path of the signal processed and output by the algorithm module and is used to monitor the state change of the ocean echo signal light in real time;

[0025] The photon counting channel includes a signal discrimination module, a single-photon counting module, and a particulate organic carbon concentration extraction module;

[0026] The signal discrimination module receives the other path of the signal processed and output by the algorithm module and performs signal discrimination processing;

[0027] The single-photon counting module receives the signal output by the signal discrimination module and performs single-photon counting;

[0028] The particulate organic carbon concentration extraction module receives the signal output by the single-photon counting module and performs particulate organic carbon concentration extraction.

[0029] The following is a further limited technical solution of the present invention. The autocorrelation algorithm is used to eliminate the real-time jitter of the echo pulse signal; the median average filtering algorithm samples the input signal to obtain a set of values, then sorts the data, removes the maximum and minimum values, and calculates the average value, and then uses the obtained average value as the filtered signal output.

[0030] The following is a further limited technical solution of the present invention. The transimpedance amplifier performs current-voltage conversion on the current signal output by the high-speed photodetector and outputs a pulse voltage signal.

[0031] The following is a further defined technical solution of the present invention. The voltage amplifier amplifies the pulsed voltage signal output by the transimpedance amplifier, dynamically adjusts the gain multiple according to the amplitude of the input signal, and realizes the linear amplification of signals with a large dynamic range.

[0032] Compared with the prior art, the present invention has the following technical effects:

[0033] 1) The high-speed photodetector has a fast response speed and high gain, can effectively suppress afterpulses, and avoid the interference of stray light on the real ocean echo signal light;

[0034] 2) The reverse bias voltage and photocathode voltage provided by the driving circuit of the high-speed photodetector can be continuously adjusted in real time between 0 to 500V and 0 to -10000V respectively, and accurately control the photoelectric gain of the high-speed photodetector;

[0035] 3) It can simultaneously meet the detection and processing of strong echo signal light and weak echo signal light. Analog detection is suitable for the reception of continuous echo signal light on the water surface and near the water surface, and photon counting is suitable for the reception of discrete photon signals in deep water bodies. The dynamic range of the detected signal can reach 50dB;

[0036] 4) The voltage amplifier can automatically and quickly adjust its voltage gain, and can ensure that the output signal intensity meets the processing requirements of the system in the case of changes in the amplitude of the input voltage signal. It is suitable for application scenarios where the echo signal intensity of marine lidar is variable and the dynamic range is large.

[0037] 5) The FPGA module is used for the digital processing of the pulsed voltage signal output by the voltage amplifier, including analog-to-digital conversion, noise suppression, digital-to-analog conversion, signal discrimination, single-photon counting, and extraction of particulate organic carbon concentration, etc. Compared with analog circuits, the digital signal processing based on FPGA has powerful data processing capabilities. By designing processing algorithms such as digital filtering, it can effectively separate noise from effective signals and significantly improve the accuracy of photon counting and extraction of POC concentration distribution information.

[0038] The present invention will be further described below in conjunction with the drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the embodiments or the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0040] Figure 1 It is a schematic diagram of the system structure of the present invention.

[0041] Reference numerals: 1, high-speed photodetector drive circuit; 2, reverse bias voltage source; 3, photocathode voltage source; 4, monitoring module; 5, high-speed photodetector; 6, transimpedance amplifier; 7, voltage amplifier; 8, FPGA module; 9, analog-to-digital conversion module; 10, algorithm module; 11, digital-to-analog conversion module; 12, signal discrimination module; 13, single-photon counting module; 14, particulate organic carbon concentration extraction module. Detailed implementation manners

[0042] In order to make the above objects, features, and advantages of the present invention more obvious and understandable, the following will describe the detailed implementation manners of the present invention in conjunction with the accompanying drawings. Many specific details are set forth in the following description in order to fully understand the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0043] As Figure 1 shown, this embodiment provides a lidar echo signal optical detection system for marine particulate organic carbon detection, which is a circuit for detecting and processing the lidar echo signal light when the lidar system obtains the POC profile concentration information of the marine water body. It mainly consists of a high-speed photodetector drive circuit 1, a high-speed photodetector 5, a high-speed high-gain transimpedance amplifier 6, a voltage amplifier 7, an FPGA module 8, etc. Through the collaborative design of analog circuits and digital circuits, combined with the analog detection and photon counting composite detection modes, the efficient processing of the POC echo signal light detected by the marine lidar is realized.

[0044] The high-speed photodetector drive circuit 1 provides a reverse bias voltage and a photocathode voltage for the high-speed photodetector 5. The high-speed photodetector 5 receives the echo signal light and converts it into a current signal. After this current signal is converted into a voltage signal by the high-speed high-gain transimpedance amplifier 6, it is input to the voltage amplifier 7 for signal amplification. The amplified signal is transmitted to the FPGA module 8. First, the analog signal is converted into a digital signal through analog-to-digital conversion (ADC), and then the autocorrelation algorithm and the median average filtering algorithm are used to process the digital signal to effectively suppress noise interference. The processed signal is divided into two paths: one is the analog detection channel, which is not only used for the detection and processing of the echo signal light on the ocean surface, but also monitors the state change of the ocean echo signal light in real time through digital-to-analog conversion (DAC); the other is the photon counting channel, and through operations such as signal discrimination, single-photon counting, and particulate organic carbon concentration extraction, the target information is finally obtained.

[0045] The high-speed photodetector drive circuit 1 consists of a reverse bias voltage source 2, a photocathode voltage source 3, a monitoring module 4, etc. The reverse bias voltage source 2 provides a reverse bias voltage for the high-speed photodetector 5; the photocathode voltage source 3 provides a photocathode voltage for the high-speed photodetector 5; the monitoring module 4 is used to display the output voltage of the reverse bias voltage source 2, the output voltage of the photocathode voltage source 3, and the output current in real time to ensure the normal working state of the high-speed photodetector 5. Therefore, by adjusting the magnitudes of the reverse bias voltage and the photocathode voltage, precise control of the photoelectric gain of the high-speed photodetector 5 can be achieved. The reverse bias voltage source 2 can output a reverse bias voltage with a voltage range of 0 to 500V, and the photocathode voltage source 3 can output a photocathode voltage with a voltage range of 0 to -10000V.

[0046] The high-speed and high-gain transimpedance amplifier 6 is used to perform current-voltage conversion on the current signal output by the high-speed photodetector 5 and output a pulsed voltage signal, facilitating subsequent signal amplification, filtering, and digital processing. The high-speed and high-gain transimpedance amplifier 6 takes into account requirements such as gain, bandwidth, input current noise, and input voltage noise, and can effectively prevent problems such as unstable circuit working states caused by oscillation and drift.

[0047] The voltage amplifier 7 is used to amplify the pulsed voltage signal output by the high-speed and high-gain transimpedance amplifier 6, and can dynamically adjust the signal gain according to the amplitude of the input signal and the amplitude requirements of the output signal, realizing linear amplification of signals with a large dynamic range, and can also take into account requirements such as signal bandwidth and response time.

[0048] The FPGA module 8 consists of an analog-to-digital conversion module 9, an algorithm module 10, a digital-to-analog conversion module 11, a signal discrimination module 12, a single-photon counting module 13, a particulate organic carbon concentration extraction module 14, etc. The FPGA module 8 is used to perform digital processing on the pulsed voltage signal output by the voltage amplifier 7, including analog-to-digital conversion, noise suppression, digital-to-analog conversion, signal discrimination, single-photon counting, and particulate organic carbon concentration extraction, etc. Compared with analog circuits, digital signal processing based on FPGA has powerful data processing capabilities. By designing processing algorithms such as digital filtering, the noise and effective signals can be effectively separated, significantly improving the accuracy of photon counting and the extraction of POC concentration distribution information.

[0049] The analog-to-digital conversion module 9 is used to receive the voltage amplification signal of the voltage amplifier 7 and perform analog-to-digital conversion on the voltage amplification signal, thereby converting the analog signal into a digital signal.

[0050] The algorithm module 10 is used to receive the digital signal output by the analog-to-digital conversion module 9 and process the digital signal using an autocorrelation algorithm and a median average filtering algorithm to suppress noise. One output of the algorithm module 10 is input to the analog detection channel, and the other output of the algorithm module 10 is input to the photon counting channel.

[0051] The analog detection channel includes an analog-to-digital conversion module 11.

[0052] The analog-to-digital conversion module 11 receives one path of the signal output after being processed by the algorithm module 10, and is used to monitor the state change of the ocean echo signal light in real time.

[0053] The photon counting channel includes a signal discrimination module 12, a single photon counting module 13, and a particulate organic carbon concentration extraction module 14.

[0054] The signal discrimination module 12 receives the other path of the signal output after being processed by the algorithm module 10 and performs signal discrimination processing.

[0055] The single photon counting module 13 receives the signal output by the signal discrimination module 12 and performs single photon counting.

[0056] The particulate organic carbon concentration extraction module 14 receives the signal output by the single photon counting module 13 and performs particulate organic carbon concentration extraction.

[0057] The high-speed photodetector 5 is composed of a photocathode surface and an avalanche diode. When the echo signal light is incident on the photocathode surface of the high-speed photodetector 5, the photocathode releases electrons corresponding to the incident light flux. Then, the negative high voltage applied to the photocathode surface accelerates the electrons and makes them incident on the avalanche diode. Under the action of the reverse bias voltage, the avalanche diode generates electron-hole pairs corresponding to the energy of the incident photo electrons, realizing electron bombardment gain. Therefore, the gain of the high-speed photodetector 5 is jointly determined by the photocathode voltage and the reverse bias voltage of the avalanche diode. By adjusting these two voltage parameters, precise control of the detector gain can be achieved.

[0058] The FPGA module 8 is used to digitally process the noise of the signal. In the marine lidar detection system, the noise mainly comes from the detector, the detection circuit, and the electromagnetic environment. These noises will significantly affect the detection performance of the system. Especially in the case of detecting weak echo signal light below the water surface, the noise will significantly reduce the signal-to-noise ratio and the minimum detectable ability of the system, interfere with the accuracy and reliability of the signal, and cause signal distortion. Therefore, relying on the powerful data processing ability of the FPGA module 8, in the FPGA module 8, first, a processing algorithm is written based on the autocorrelation of the signal to eliminate the real-time jitter of the echo pulse signal and improve the detection accuracy and reliability of the system; second, the median average filtering algorithm is used to effectively separate the noise from the effective signal, thereby improving the accuracy of photon counting and POC extraction. The median average filtering algorithm samples the input signal to obtain a set of values, then sorts the data, removes the maximum and minimum values, calculates the average value, and then outputs the obtained average value as the filtered signal.

[0059] The analog detection channel is not only used for detecting and processing the echo signal light on the ocean surface and near the surface. With the digital-to-analog conversion (DAC) in the FPGA module 8, it can also monitor the state change of the ocean echo signal light in real time. Since the intensity of the echo light signal is relatively high, the pulse current signal output by the high-speed photodetector 5 is relatively large and the noise interference is relatively small. This signal is converted from current to voltage through the high-speed high-gain transimpedance amplifier 6, and then amplified by the voltage amplifier 7 and transmitted to the FPGA module 8 for analog-to-digital conversion (ADC) and digital filtering processing to further reduce the influence of noise.

[0060] The photon counting channel is suitable for detecting and processing the echo signal light with the intensity of the signal light in deep water being as weak as the single-photon level. Since the intensity of the echo signal light in deep water is extremely weak, its signal presents a discrete pulse state. In order to overcome the influence of the sampling rate and noise of the sampling system and obtain a higher signal-to-noise ratio, after high-gain photoelectric conversion of the echo signal light, the signal is amplified by the voltage amplifier 7, and the amplified signal is converted into a digital signal through the analog-to-digital conversion processing of the FPGA module 8. Then, the digital autocorrelation algorithm and the median average filtering algorithm are used to effectively separate the pulse signal and the noise. Finally, photon counting statistics are carried out, and the POC information at different depths underwater is extracted.

[0061] Since the signal bandwidth of the processing circuit corresponding to the lidar echo signal light detection system is 200 MHz, and the weakest echo signal light can reach the single-photon level, the design and layout of the printed circuit board directly affect the performance of signal processing. When designing the printed circuit board of the ocean lidar echo signal light detection system, a four-layer board structure is adopted, and the middle power layer and ground layer are used as shielding layers to reduce interference such as parasitic capacitance and parasitic inductance; secondly, the connection length between each component is shortened to reduce the distributed parameters of the connection and the cross-interference between signals.

[0062] Through the collaborative design of analog circuits and digital circuits and the combination of analog detection and photon counting composite detection modes, the present invention realizes the detection and processing of the ocean lidar echo signal light, with a response bandwidth of up to 200 MHz, a signal detection dynamic range of 50 dB, and a detection sensitivity of up to the single-photon level, which can meet the detection requirements of the POC concentration at different ocean profile depths, and has a simple and reliable structure and is easy to adjust.

[0063] The above are only the preferred embodiments of the present invention and do not impose any form of limitation on the present invention. Any person skilled in the art can make many possible changes and modifications to the technical solution of the present invention or modify it into an equivalent embodiment with equivalent changes without departing from the scope of the technical solution of the present invention. Therefore, all equivalent changes made according to the shape, structure and principle of the present invention without departing from the content of the technical solution of the present invention shall be covered by the protection scope of the present invention.

Claims

1. A lidar echo signal optical detection system for detecting marine particulate organic carbon, characterized in that It includes a high-speed photodetector drive circuit, a high-speed photodetector, a transimpedance amplifier, a voltage amplifier, and an FPGA module; The high-speed photodetector drive circuit is used to provide the working voltage required for the conversion of the photoelectric signal to the high-speed photodetector; The high-speed photodetector is used to receive the echo signal light and convert the echo signal light into a current signal; The transimpedance amplifier is used to receive the current signal of the high-speed photodetector and convert the current signal into a voltage signal; The voltage amplifier is used to receive the voltage signal of the transimpedance amplifier and amplify the voltage signal; The FPGA module is used to receive the voltage amplified signal of the voltage amplifier, perform digital processing on the voltage amplified signal, convert it into a digital signal, and process the signal using a digital filtering algorithm, and then input it into the analog detection channel and the photon counting channel respectively.

2. The lidar echo signal optical detection system for marine particulate organic carbon detection according to claim 1, characterized in that, The high-speed photodetector drive circuit includes a reverse bias voltage source, a photocathode voltage source, and a monitoring module; The reverse bias voltage source is used to provide a reverse bias voltage for the high-speed photodetector; The photocathode voltage source is used to provide a photocathode voltage for the high-speed photodetector; The monitoring module is used to display the output voltage of the reverse bias voltage source, the output voltage of the photocathode voltage source, and the output current situation in real time to ensure the normal working state of the high-speed photodetector.

3. The lidar echo signal optical detection system for marine particulate organic carbon detection according to claim 2, characterized in that, The output voltage range of the reverse bias voltage source is 0 to 500V.

4. The lidar echo signal optical detection system for marine particulate organic carbon detection according to claim 2, characterized in that, The output voltage range of the photocathode voltage source is 0 to -10000V.

5. The lidar echo signal optical detection system for marine particulate organic carbon detection according to claim 1, wherein, The FPGA module includes an analog-to-digital conversion module, an algorithm module, a digital-to-analog conversion module, a signal discrimination module, a single photon counting module, and a particulate organic carbon concentration extraction module; The analog-to-digital conversion module is used to receive the voltage amplified signal of the voltage amplifier and perform analog-to-digital conversion on the voltage amplified signal, so as to convert the analog signal into a digital signal; The algorithm module is used to receive the digital signal output by the analog-to-digital conversion module and process the digital signal using an autocorrelation algorithm and a median average filtering algorithm to suppress noise. One path output by the algorithm module is input to the analog detection channel, and the other path output by the algorithm module is input to the photon counting channel; The analog detection channel includes a digital-to-analog conversion module; The digital-to-analog conversion module receives one path of the signal processed and output by the algorithm module and is used to monitor the state change of the ocean echo signal light in real time; The photon counting channel includes a signal discrimination module, a single photon counting module, and a particulate organic carbon concentration extraction module; The signal discrimination module receives the other path of the signal processed and output by the algorithm module and performs signal discrimination processing; The single photon counting module receives the signal output by the signal discrimination module and performs single photon counting; The particulate organic carbon concentration extraction module receives the signal output by the single photon counting module and extracts the particulate organic carbon concentration.

6. The lidar echo signal optical detection system for marine particulate organic carbon detection according to claim 5, characterized in that, The autocorrelation algorithm is used to eliminate the real-time jitter of the echo pulse signal; the median average filtering algorithm samples the input signal to obtain a set of values, then sorts the data, removes the maximum and minimum values, and then calculates the average value, and then outputs the obtained average value as the filtered signal.

7. The lidar echo signal optical detection system for marine particulate organic carbon detection according to claim 1, characterized in that, The transimpedance amplifier performs current-voltage conversion on the current signal output by the high-speed photodetector and outputs a pulse voltage signal.

8. The lidar echo signal optical detection system for marine particulate organic carbon detection according to claim 1, characterized in that The voltage amplifier amplifies the pulsed voltage signal output by the transimpedance amplifier, dynamically adjusts the gain multiple according to the amplitude of the input signal, and realizes the linear amplification of signals with a large dynamic range.

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