Ground detector for single-photon radar laser on-orbit calibration and layout method

Abstract

The invention discloses a ground detector for single-photon radar laser on-orbit calibration and a layout method, and relates to the technical field of satellite laser calibration. The ground detector comprises an optical filter, the optical filter is a narrow-band optical filter, other sunlight and stray light are shielded except for the wavelength of 532 nm + / -delta lambda nm, delta lambda is the bandwidth of the optical filter, and detection laser reaches an avalanche photodiode with precisely controlled bias voltage through the optical filter. A pulse laser detector is developed in a targeted manner, and data support can be provided for on-orbit calibration of the pointing angle of a to-be-emitted Gaofen-7 02 star and other similar single-photon system laser radar beams. The designed detector layout scheme greatly reduces the layout number of the detectors; the detector realizes real-time ground verification of the single photon system laser radar beam pointing angle, the satellite surveying and mapping sampling interval is improved from hectometer level to decimeter level, and the surveying and mapping precision is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of satellite laser calibration, and in particular relates to a ground detector for on-orbit calibration of single-photon radar laser and a deployment method. Background Art

[0002] LiDAR ranging is an active remote sensing technology. The distance between the LiDAR and the Earth's surface, and thus the relative elevation of the Earth's surface, can be obtained by the LiDAR's position, laser pointing, laser emission and return time. A notable application of LiDAR is to monitor the changes in the elevation of polar ice sheets in real time. Studies have shown that the rapid reduction of polar ice sheets can lead to global sea level rise and affect global climate. In order to quantify this impact, long-term data on ice sheet elevation changes are needed.

[0003] In view of this, many countries are developing and launching related laser radar payloads, and the pulsed lasers emitted by related payloads are transitioning from traditional high-energy, low-frequency, wide pulses to low-energy, high-frequency, narrow pulses. The traditional low-frequency pulsed lasers have limited the spatial sampling of samples along the orbit due to their low repetition rate, and the sample interval may be several hundred meters. Theoretically, laser radars working in photon counting mode can improve measurement performance, because the laser pulse frequency they emit is high (kHz), making the sampling along the orbit dense, and can provide centimeter-level ranging resolution. After the laser radar carried by the satellite is launched, the performance of the instrument may change due to the influence of launch vibration and atmospheric turbulence, especially the pointing angle of the laser emitted by the satellite. For this reason, it needs to be recalibrated on orbit. At present, the method with the highest accuracy of laser pointing calibration is the ground detector method, that is, according to the performance of the pulsed laser emitted by the laser radar, the corresponding ground detector is developed, and the pointing angle of the laser is corrected by detecting the centroid coordinates of the ground energy and combining them with the satellite coordinates.

[0004] China is about to launch its first photon-system lidar satellite, GF-7-02, and will continue to launch satellites of similar systems based on the satellite's operation conditions. The core parameters of foreign in-orbit photon-system radars ICESAT-2 and GF-7-02 are shown in the following figure.

[0005] Table 1I Core parameters of CESAT-2 and GF-7-02

[0006]

[0007] At present, traditional ground detectors at home and abroad are mainly used to detect 1nJ / cm 2 Above, the ground laser energy with pulses below 100Hz and pulse widths of 4ns and above cannot detect low energies (energy as low as pJ / cm 2), high frequency (laser pulse frequency is greater than or equal to kHz), and narrow pulse (laser pulse width is as low as 1ns) ground energy. To this end, it is necessary to develop a ground detector that meets the requirements of photon system lidar laser calibration, and the calibration is similar to the laser pointing of the photon system radar of the GF-7 02 star. Summary of the invention

[0008] The purpose of the present invention is to provide a ground detector for on-orbit calibration of a single-photon radar laser and to provide an outdoor deployment solution to solve the problems in the above-mentioned background technology.

[0009] In order to solve the above technical problems, the present invention is achieved through the following technical solutions:

[0010] The present invention is a ground detector for single-photon radar laser on-orbit calibration, comprising:

[0011] The filter is a narrow-band filter capable of shielding sunlight and stray light other than 532nm±Δλnm wavelength, where Δλ is the bandwidth of the filter;

[0012] Avalanche photodiode and bias voltage control module, used to convert the laser light transmitted through the filter into a pulsed electrical signal;

[0013] A three-stage amplification and two-stage peak hold acquisition module, connected to the output end of the avalanche photodiode, for amplifying and acquiring the peak value of the pulse electrical signal;

[0014] The AD conversion module is connected to the output end of the acquisition and amplification module and is used to convert the amplified analog signal into a digital signal;

[0015] The FPGA module is connected to the output end of the AD conversion module and is connected to the MCU through the SPI port, FSMC port, and serial port. It also receives the GPS second pulse through the timing module and records the signal triggering time;

[0016] MCU, connected to the wireless remote transmission control circuit via the UART port;

[0017] A data storage circuit, connected to the MCU, for storing data, wherein the data storage circuit includes at least one of an EEPROM, an SD card, and a FLASH;

[0018] USB data transmission and program interaction serial port, through which the USB data transmission and program interaction serial port are connected to the host computer, to realize human-computer interaction functions such as system parameter configuration and historical data export;

[0019] The charging and discharging circuit provides working power for the MCU, AD conversion module, FPGA module and acquisition and amplification module;

[0020] The protective casing is used to contain and protect the above components.

[0021] As a preferred technical solution of the present invention, the bias voltage control module includes:

[0022] High-speed ADC, used to collect the voltage signal output by the avalanche photodiode;

[0023] Precision DAC to control the output voltage of the boost module;

[0024] The boost module, after the output passes through the power filter, the output voltage noise is reduced to the μV level;

[0025] Power filter, used to reduce the noise of the boost power supply output voltage;

[0026] The TIA amplifier converts the photocurrent output by the avalanche photodiode into a voltage output.

[0027] As a preferred technical solution of the present invention, the acquisition and amplification module includes a two-stage peak preservation circuit. The first stage uses a small capacitor circuit to quickly identify the peak position of the amplified signal, and the second stage uses a large capacitor circuit to increase the peak holding time.

[0028] As a preferred technical solution of the present invention, the acquisition and amplification module is also provided with a filtering function for filtering the response current generated by false triggering of the photodiode response caused by sunlight with a wavelength of 532nm.

[0029] As a preferred technical solution of the present invention, it is characterized in that:

[0030] The timing module comprises:

[0031] Data transmission module, used to receive trigger sequence and time stamp, and transmit to PC, etc.;

[0032] High-precision timing module, used to receive the second pulse of GPS, perform clock training and synchronization, analyze the GPS absolute time mark, and give the time mark of the detector triggering moment;

[0033] The detector circuit trigger detection module is used to operate the input signal to obtain a trigger signal as a timing termination signal of the high-precision timing module.

[0034] As a preferred technical solution of the present invention, the charging and discharging circuit outputs +3.3V as the working power supply of the MCU and AD conversion modules, outputs +1.2V as the working power supply of the FPGA module, and outputs +5V and -5V as the working power supply of the acquisition and amplification module.

[0035] The present invention also provides a method for deploying ground detectors for on-orbit calibration of single-photon radar lasers. The above-mentioned ground detectors for on-orbit calibration of single-photon radar lasers are used. When deployed outdoors, they are arranged in a row side by side to calibrate the laser pointing. The deployment spacing is determined by the diameters of ground laser spots of different satellites.

[0036] The present invention has the following beneficial effects:

[0037] Aiming at the characteristics of single-photon laser radar, namely low energy, high frequency and narrow pulse, the present invention designs a special ground detector, including a narrow-band filter, a precision bias voltage control module, a high-precision timing module, etc., which can realize real-time ground verification of the pointing angle of this type of laser radar light beam, filling the gap in the prior art.

[0038] High precision and high sensitivity: By using avalanche photodiodes and precision bias voltage control modules, the weak light detection limit is greatly improved, allowing the detector to respond as low as pJ / cm 2 At the same time, through the high-precision timing module, the maximum time accuracy of 10ns is achieved, further improving the detection accuracy.

[0039] Optimize outdoor layout: When the ground detectors designed by the present invention are arranged outdoors, only one row is needed to capture lasers and calibrate the direction of lasers, which greatly reduces the number of ground detectors and saves manpower and material resources.

[0040] Wide applicability: The present invention is not only applicable to the Gaofen-7 02 satellite to be launched soon, but also to other similar single-photon lidar satellites, and has broad application prospects.

[0041] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0043] Figure 1 The figure is a schematic diagram of the structure of a ground detector for on-orbit calibration of a single-photon radar laser.

[0044] Figure 2 Schematic diagram of bias voltage control of avalanche photodiode in ground detector.

[0045] Figure 3This is a simplified circuit diagram of a ground detector for on-orbit calibration of a single-photon radar laser.

[0046] In the figure: 1-filter, 2-photodiode, 3-instrument housing, 4-acquisition and amplification module, 5-AD conversion module, 6-FPGA module, 7-charge and discharge circuit, 8-wireless remote transmission control circuit, 9-data storage circuit, 10-USB data transmission and program interaction serial port.

[0047] Figure 4 This paper presents an outdoor calibration layout scheme for ground detectors used for on-orbit calibration of single-photon radar lasers. DETAILED DESCRIPTION

[0048] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0049] See also Figures 1 to 3 A ground detector for single-photon radar laser on-orbit calibration includes a filter 1, an avalanche photodiode 2 and a bias voltage control module, a three-stage amplification and two-stage peak holding acquisition module 4, a timing module, and a protective housing 3. The filter is a narrow-band filter. Except for the wavelength of 532nm±Δλnm (according to Table 1, the satellite laser wavelength is 532nm), other sunlight and stray light are shielded. Δλ is the bandwidth of the filter (to reduce the interference of external stray light on signal light, slow down the attenuation of the performance of optoelectronic devices inside the ground detector, comprehensively consider factors such as cost, and try to choose a narrow-band filter with a small bandwidth, such as a bandwidth of 3nm). After passing through the filter 1, the laser reaches the voltage-biased avalanche photodiode 2, and outputs a pulse electrical signal through the photoelectric conversion of the photodiode 2. The signal peak is amplified and collected by the acquisition and amplification module 4. The output end of the acquisition and amplification module 4 is connected to the input end of the AD conversion module 5. The output end of the AD conversion module 5 is connected to the input end of the FPGA module 6. The FPGA module 6 is connected to the MCU through the SPI port, the FSMC port, and the serial port, and receives the GPS second pulse through the timing module to record the signal trigger time. The MCU is connected to the wireless remote transmission control circuit 8 through the UART port.

[0050] In the specific embodiment: see Figure 1 and Figure 3, the AD conversion module 5 uses the ADC chip to convert the amplified analog signal into a digital quantity. Because the acquisition rate of the single-chip microcomputer is not high, the traditional single-chip microcomputer acquisition is abandoned, and the back-end signal acquisition after the AD analog-to-digital conversion is completed through the FPGA module 6. The acquisition frequency of the FPGA module 6 can reach 200MHz. And the FPGA module 6 can be used to release the collected signal, so that the ground detector can enter the next acquisition process. The present invention adopts a hardware structure method combining an ARM microprocessor and an FPGA to improve the operating performance of the detector and reduce the size. Through the above circuit, the amplification and acquisition of micro signals with a laser pulse width as low as 1ns can be completed.

[0051] The hardware architecture based on ARM technology (Advanced RISC Machines) and FPGA is used to realize signal acquisition and data output. Through the precise control of the signal by FPGA, the pulse peak latch value is released.

[0052] The wireless remote transmission control circuit 8 transmits the signal responded by the ground detector to the server wirelessly through GPRS communication, saving manpower and material resources for on-site inspection, and can control the switch of the detector through remote control instructions.

[0053] Avalanche photodiode 2 can increase the response factor by more than 50 times through precise bias technology, thereby improving the detection limit of weak signals. The bias voltage control diagram is shown in Figure 2 As shown in the figure, it is mainly composed of high-speed ADC, precision DAC, boost module, power filter, TIA amplifier, etc. The output voltage of the boost module is controlled by the output voltage of the precision DAC. After the boost power output passes through the power filter, the output voltage noise is reduced to the μV level, minimizing the coupling of the bias voltage power supply noise to the avalanche photodiode output. The TIA amplifier converts the photocurrent output by the avalanche photodiode into a voltage output. The high-speed ADC collects the voltage and outputs it to the FPGA. The FPGA calculates the root mean square value of the amplifier output voltage signal in real time, and calculates the optimal working bias voltage of the avalanche photodiode in real time.

[0054] The spectral response range of the avalanche photodiode is the visible near-infrared band. According to the photoelectric effect, the photodiode 2 converts the laser signal into a current signal, and the current varies with the light intensity. In addition, the photodiode 2 responds within ±10° from the vertical direction to ensure that the laser radar beam can have a larger deflection angle when calibrating the satellite laser radar outdoors, which improves the applicable scope of the calibration. The avalanche photodiode model can be changed according to the different satellite emission wavelengths. The selection of the detector mainly considers the bandwidth and wavelength of the laser pulse. The present invention is mainly aimed at the 532nm wavelength emitted by the GF-7 02 satellite. If the detection wavelength is in the infrared band, the photodiode 2 must also be temperature controlled to maintain the good operating performance of the detector.

[0055] In this example: See Figure 1 The filter 1 and the photodiode 2 are arranged in the inner cavity of the instrument housing 3.

[0056] The instrument housing 3 provides protection for the filter 1 and the photodiode 2 from sand and the like.

[0057] In this example: See Figure 1 and Figure 3 The acquisition and amplification module 4 includes a two-stage peak preservation circuit. The first stage adopts a small capacitor circuit to quickly identify the peak position of the amplified signal. The second stage adopts a large capacitor circuit to improve the peak holding time. Through these two stages of circuits, the peak of the amplified signal with a pulse width of 1ns is latched and extracted.

[0058] The acquisition and amplification module 4 amplifies the micro-current pulse converted by the photodiode 2. The present invention uses three groups of low-noise transimpedance amplifiers to perform three-stage multi-stage amplification on the electrical signal sensed by the photodiode 2. After the peak value is collected, the AD conversion module 5, i.e., the analog-to-digital conversion circuit, is used to convert the sampled analog signal into a digital quantity.

[0059] In this embodiment: Figure 3 , a high-precision pulse time base system is designed using FPGA to obtain the acquisition time of the avalanche photodiode 2, and to upload and store the processed information. The FPGA-based timing module is mainly composed of a data transmission module, a high-precision timing module, and a detector circuit trigger detection module. The circuit trigger detection module is used to operate the input signal to obtain a trigger signal as the timing termination signal of the high-precision timing module. The high-precision timing module is used to receive the second pulse of the GPS, perform clock training and synchronization, parse the GPS absolute time mark, and give the time mark of the detector trigger moment. The data transmission module is mainly used to receive the trigger sequence and time mark, and transmit them to a PC, etc.

[0060] In this example: See Figure 1 and Figure 3 MCU stores data through data storage circuit 9, which includes EEPROM, SD card, and FLASH.

[0061] The data collected by FPGA is stored in the storage device of the ground detector.

[0062] In this example: See Figure 1 and Figure 3 , MCU is connected to the host computer through USB data transmission and program interactive serial port 10. The data transmission port in USB data transmission and program interactive serial port 10 is the network port W5500, and the program interactive serial port in USB data transmission and program interactive serial port 10 is the CH340USB to serial port.

[0063] Data is transmitted via the local USB data line and can also be used to change instructions in the MCU, such as modifying the acquisition frequency of the FPGA.

[0064] In this example: See Figure 1 and Figure 3 The ground detector for on-orbit calibration of the laser radar also includes a charge and discharge circuit 7, which outputs +3.3V as the working power supply of the MCU and AD conversion module 5, outputs +1.2V as the working power supply of the FPGA module 6, and outputs +5V and -5V as the working power supply of the acquisition and amplification module 4.

[0065] In the present invention, the power source adopts a rechargeable lithium battery. Through the battery power display, the lithium battery is charged by the charge and discharge circuit 7, and the boost and buck operation of the circuit ensures the normal operation of the internal circuit elements of the ground detector. The circuit adopts a low voltage difference regulator for voltage stabilization operation, and the accuracy of voltage regulation is within 1%, so that the ground detector can work under the condition of a smaller output-input voltage difference. A charge and discharge management chip is provided to provide charge and discharge protection.

[0066] In this example: See Figure 1 and Figure 3 The acquisition and amplification module 4 is provided with a filtering function to filter the response current generated by the false triggering of the photodiode 2 caused by the response of the 532nm wavelength sunlight. The theoretical response current caused by sunlight is: I=T×E×S×Δλ×α, where T is the transmittance of the filter 1, E is the spectral irradiance of the 532nm sunlight on the ground, S is the photosensitive area of ​​the avalanche photodiode 2, Δλ is the bandwidth of the filter 1, and α is the responsivity of the photodiode 2.

[0067] Generally, the bandwidth of the filter 1 is about 3nm. By substituting the illumination value simulated by the radiation transmission software and the general value of the photosensitive surface of the photodiode 2 into the formula, it can be known that the current caused by sunlight is at the nA level. The parameters of the filtering device are selected to correspond to the filtering process.

[0068] In this example: See Figure 4 Different from the arrangement of linear ground detectors, the laser frequency emitted by the single-photon satellite is high, as shown in Table 1, the frequency is about 2KHz, and the distance between two adjacent light spots is short, about 3.5m. According to the high repetition rate information of the satellite laser and the timing function of the designed ground detector, the ground detectors for photon radar calibration are arranged in a row to capture the laser and calibrate the laser direction. The timing system of the single-photon ground detector obtains the corresponding time when the ground detector has a response result, and then according to the direction of the satellite orbit, the results at different times are offset to the corresponding position at the same time to obtain the center of mass position at that time. Figure 4 What is shown is that the three ground detectors that responded at time t3 are translated to the corresponding positions at time t1. Similarly, the five ground detectors that responded at time t2 are translated to time t1. Based on the results of these three responses, the centroid position of the light spot at time t1 is obtained, and the satellite laser pointing at time t1 is calibrated.

[0069] The working principle of the present invention is: when the ground detector is placed outdoors to detect pulsed laser, it first passes through the filter 1 and reaches the biased avalanche photodiode 2. After photoelectric conversion, it passes through the acquisition and amplification module 4 to obtain the amplified peak analog signal, and then passes through the AD conversion module 5 to obtain the digital quantity. The digital quantity is collected by the FPGA module 6 and the signal response time is obtained through the timing module. After a group of collection is completed, the FPGA module 6 releases the signal and performs the next collection. The collected digital quantity is stored in its own memory through the data storage circuit 9 through the MCU instruction, or stored in the designated server through the wireless remote transmission control circuit 8. The ground detector system parameter configuration, historical data export and other human-machine interaction functions are realized through USB data transmission and program interactive serial port 10. Since the ground detector has a timing function and the satellite laser has a high repetition rate, the ground detector of the present invention only needs to be arranged in one row when calibrating the laser outdoors. Compared with the calibration of the linear system laser pointing by the traditional ground detector, the number of ground detectors is greatly reduced, which greatly saves manpower and material resources.

[0070] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0071] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A ground detector for single-photon radar laser on-orbit calibration, characterized in that: include: The filter is a narrow-band filter capable of shielding sunlight and stray light other than 532nm±Δλnm wavelength, where Δλ is the bandwidth of the filter; Avalanche photodiode and bias voltage control module, used to convert the laser light transmitted through the filter into a pulsed electrical signal; A three-stage amplification and two-stage peak hold acquisition module, connected to the output end of the avalanche photodiode, for amplifying and acquiring the peak value of the pulse electrical signal; The AD conversion module is connected to the output end of the acquisition and amplification module and is used to convert the amplified analog signal into a digital signal; The FPGA module is connected to the output end of the AD conversion module and is connected to the MCU through the SPI port, FSMC port, and serial port. It also receives the GPS second pulse through the timing module and records the signal triggering time; MCU, connected to the wireless remote transmission control circuit via the UART port; A data storage circuit, connected to the MCU, for storing data, wherein the data storage circuit includes at least one of an EEPROM, an SD card, and a FLASH; USB data transmission and program interaction serial port, through which the USB data transmission and program interaction serial port are connected to the host computer, to realize human-computer interaction functions such as system parameter configuration and historical data export; The charging and discharging circuit provides working power for the MCU, AD conversion module, FPGA module and acquisition and amplification module; The protective casing is used to contain and protect the above components.

2. A ground detector for single-photon radar laser on-orbit calibration according to claim 1, It is characterized in that The bias voltage control module comprises: High-speed ADC, used to collect the voltage signal output by the avalanche photodiode; Precision DAC to control the output voltage of the boost module; The boost module, after the output passes through the power filter, the output voltage noise is reduced to the μV level; Power filter, used to reduce the noise of the boost power supply output voltage; The TIA amplifier converts the photocurrent output by the avalanche photodiode into a voltage output.

3. The ground detector for single-photon radar laser on-orbit calibration according to claim 1 is characterized in that: The acquisition and amplification module includes two levels of peak value preservation circuits. The first level uses a small capacitor circuit to quickly identify the peak position of the amplified signal, and the second level uses a large capacitor circuit to increase the peak holding time.

4. A ground detector for single-photon radar laser on-orbit calibration according to claim 3, characterized in that: The acquisition and amplification module is also provided with a filtering function for filtering the response current generated by false triggering of the photodiode response caused by sunlight with a wavelength of 532nm.

5. The ground detector for single-photon radar laser on-orbit calibration according to claim 1 is characterized in that: The timing module comprises: Data transmission module, used to receive trigger sequence and time stamp, and transmit to PC, etc.; High-precision timing module, used to receive the second pulse of GPS, perform clock training and synchronization, analyze the GPS absolute time mark, and give the time mark of the detector triggering moment; The detector circuit trigger detection module is used to operate the input signal to obtain a trigger signal as a timing termination signal of the high-precision timing module.

6. The ground detector for single-photon radar laser on-orbit calibration according to claim 1 is characterized in that: The charge and discharge circuit outputs +3.3V as the working power supply of the MCU and AD conversion modules, outputs +1.2V as the working power supply of the FPGA module, and outputs +5V and -5V as the working power supply of the acquisition and amplification module.

7. A method for deploying ground detectors for on-orbit calibration of single-photon radar lasers, characterized in that: The ground detector for on-orbit calibration of a single-photon radar laser as described in any one of claims 1 to 6 is characterized in that, when arranged outdoors, it is arranged in a row side by side to calibrate the laser pointing, and the layout spacing is determined by the diameters of the ground laser spots of different satellites.

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