CN110231089B - Active light spot energy detector and array of satellite-borne laser altimeter - Google Patents
Active light spot energy detector and array of satellite-borne laser altimeter Download PDFInfo
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Abstract
The invention provides an active light spot energy detector and an array of a satellite-borne laser altimeter, which are used for capturing laser foot spot light spots in an array mode, wherein the energy detector comprises an electric detection module, a communication module, a geometric positioning module, a time synchronization module and a main controller, and the photoelectric detection module is used for capturing the energy of the ground foot spot light spots of the satellite-borne laser altimeter through high-speed stable photoelectric conversion with adjustable amplification factor and analog-to-digital conversion based on high-speed threshold comparison; the communication module is used for realizing data and instruction transmission of the energy detector so as to realize intelligent data networking of the detector array; the time synchronization module is used for taking the pulse per second provided by the GPS as input, combining a high-precision timer and subsequent time compensation and realizing accurate measurement of the capturing moment of the foot spot; the geometric positioning module is used for cooperating the GPS single-point positioning with an external differential station together, and static single-point positioning is realized to reach a sub-meter level in a differential post-processing mode.
Description
Technical Field
The invention belongs to the technical field of satellite-borne laser detection, and relates to an active light spot energy detector and an active light spot energy array of a satellite-borne laser altimeter.
Background
The spot size of the pulse laser emitted by the satellite-borne laser altimeter reaching the ground is large, and the diameter of the spot size is generally between 30m and 100 m. A single detector cannot capture the energy distribution of the entire spot. At present, for the ground light spot detection of a satellite-borne laser altimeter, no substantive products appear in other domestic units, and only the American NASA has designed the ground light spot detector aiming at the GLAS internationally, and the ground light spot detector has only two energy levels and has no intelligent management functions of geometric positioning, time synchronization, wireless communication and the like. In field operation, hundreds of detectors are often needed to capture one light spot, the detector without intelligent management, which is similar to the NASA design and manufacture, has low efficiency, needs to perform positioning, data collection and other work manually, and is easy to cause data error counting, and the working efficiency is very low, thereby causing light spot capture distortion. The simple ground light spot detector designed by NASA has low energy level number, has poor accuracy of positioning the light spot center, and is difficult to meet the current accuracy requirement.
Disclosure of Invention
In order to solve the technical problems in the background art, the invention aims to provide a laser energy detector which is high in sensitivity, low in price, simple in production process and intelligent in design, and captures laser foot spots in an array laying mode so as to determine the positions of the foot spots.
The technical scheme of the invention provides an active light spot energy detector of a satellite-borne laser altimeter, which is used for capturing laser foot spots in an array mode,
the single energy detector comprises an electric detection module, a communication module, a geometric positioning module, a time synchronization module and a main controller, wherein the electric detection module, the communication module, the geometric positioning module and the time synchronization module are respectively connected with the main controller;
the photoelectric detection module is used for realizing the conversion from a laser light signal to an electric signal through high-speed stable photoelectric conversion with adjustable amplification factor and realizing the conversion from an analog signal to a digital signal through analog-to-digital conversion based on high-speed threshold comparison, thereby realizing the energy capture of a ground foot spot of the satellite-borne laser altimeter;
the communication module is used for realizing data and instruction transmission of the energy detector so as to realize intelligent data networking of the detector array;
the time synchronization module is used for taking the pulse per second provided by the GPS as input, combining a high-precision timer and subsequent time compensation and realizing accurate measurement of the capturing moment of the foot spot;
and the geometric positioning module is used for cooperating the GPS single-point positioning with an external differential station together and realizing that the static single-point positioning reaches the sub-meter level in a differential post-processing mode.
The photoelectric detection module comprises a photoelectric conversion circuit, a high-frequency amplification circuit, a high-precision voltage stabilizing circuit, a multi-stage voltage dividing circuit and an analog-to-digital conversion circuit, wherein the analog-to-digital conversion circuit comprises a high-speed threshold comparator, a latch and a level conversion circuit which are sequentially connected, the photoelectric conversion circuit is connected with the high-frequency amplification circuit, the output of the high-frequency amplification circuit is used as the positive end input of the comparator and is connected to the high-speed threshold comparator, the high-precision voltage stabilizing circuit is connected with the multi-stage voltage dividing circuit, the output of the multi-stage voltage dividing circuit is used as the negative end input of the comparator and is connected to the high.
The photoelectric conversion circuit is realized by a PIN photodiode, and a high-frequency amplification circuit amplifies a photo-generated weak current signal generated by the PIN photodiode in a high-frequency operation amplification mode.
Moreover, the anti-interference design is adopted, the narrow-band filter is placed in front of an optical window of the PIN photodiode, stray light of other wave bands is filtered, and it is ensured that pulse laser with the wavelength of 1064nm emitted by the satellite-borne laser altimeter enters a PIN photosensitive surface.
Furthermore, the multistage voltage division circuit employs a 10-stage voltage division circuit.
Moreover, the communication module is realized by adopting an LoRa module.
And the geometric positioning module comprises a GPS chip, longitude and latitude information output by the GPS chip is connected to the main controller, and high-precision longitude and latitude are acquired through back-end differential processing by combining differential station data acquired by a differential station in the field calibration field, so that geometric positioning information is provided for each laser detector.
The time synchronization timing module comprises a high-precision timer and a high-stability active crystal oscillator, wherein the PPS second pulse output and the high-stability active crystal oscillator of the GPS chip in the geometric positioning module are connected to the high-precision timer, the high-precision timer is connected to the main controller, and the GPS chip outputs time information to the main controller to support the realization of synchronization timing work;
the main controller acquires initial GPS time information and combines PPS (pulse per second) pulse to obtain the real-time working time of the current laser detector;
comprehensively determining the time interval between the PPS second pulse and the triggering interruption of the detector according to the crystal oscillator frequency and the counting value of the high-precision timer;
and compensating the measured time interval value by adopting a mode of accumulative error compensation and true value correction, and combining the corrected time interval with the working time information of the current laser detector to obtain the accurate moment of triggering the laser detector by the laser pulse.
The invention also provides an active light spot energy detection array of the satellite-borne laser altimeter, which is arranged in a grid-shaped equal-interval arrangement mode by adopting the active light spot energy detector of the satellite-borne laser altimeter.
Moreover, the arrangement interval is determined according to the energy level of the energy detector, the size of the ground light spot and the required central positioning precision.
The invention solves the problem of capturing the ground foot spot light spots of the satellite-borne laser altimeter, and can realize the capturing of the laser foot spot light spots by adopting a detector array consisting of a plurality of detectors, thereby determining the real position of each laser pulse light spot on the ground and providing basic light spot position data for subsequent data processing. In addition, the invention provides a high-precision and high-stability detector implementation scheme, supports the provision of geometric positioning information of each laser detector in a detector networking array, and provides guarantee for efficiently realizing the ground foot spot light spot energy capture of the satellite-borne laser altimeter.
Drawings
FIG. 1 is a block diagram of an embodiment of the present invention.
Fig. 2 is a schematic diagram of a parameter analysis process of the photodetection module according to the embodiment of the present invention.
Fig. 3 is a schematic diagram of the positioning accuracy of the center of mass of the foot points corresponding to different arrangement pitches of No. GF-7 in the embodiment of the present invention.
Fig. 4 is a block diagram of a photoelectric detection module according to an embodiment of the present invention.
Fig. 5 is a schematic block diagram of a time synchronization timing module according to an embodiment of the present invention.
FIG. 6 is a schematic block diagram of a geometric orientation module according to an embodiment of the present invention.
Fig. 7 is a functional block diagram of a communication module according to an embodiment of the present invention.
Fig. 8 is a schematic diagram of implementing quality control according to an embodiment of the present invention.
Detailed Description
For better understanding of the technical solutions of the present invention, the following detailed description of the present invention is made with reference to the accompanying drawings and examples.
Referring to fig. 1, the active spot energy detector of the satellite-borne laser altimeter according to the embodiment of the present invention is a laser active detector designed for capturing ground spots of the satellite-borne laser altimeter, and includes a photoelectric detection module for detecting spot energy of laser foot points, a communication module, a time synchronization module, a geometric positioning module, and a main controller.
The whole structure of a single detector is a star-shaped structure, the electric detection module, the communication module, the geometric positioning module and the time synchronization module are respectively connected with the main controller, and the photoelectric detection module, the communication module, the geometric positioning module and the time synchronization module cooperatively work under the adjustment of the main controller.
The technical index requirements of the laser detector of the satellite-borne laser altimeter develop a laser detector which has the advantages of cost constraint, low power consumption, high stability, gain adjustment and no interference of background light. The photoelectric detection module is the core of the laser detector and is mainly responsible for effectively detecting the laser energy transmitted to the ground by the satellite laser altimeter under different solar background light and atmospheric environment conditions; the wireless networking functional module transmits and stores laser energy data within an array range formed by a plurality of detector networks through instruction control; the geometric positioning module is responsible for providing geometric positioning information of each laser detector in the detector networking array, and the geometric positioning information comprises longitude and latitude data; and the time synchronization timing module is responsible for providing the time when the laser pulse emitted by the satellite laser altimeter reaches each laser detector.
The photoelectric detection module comprises a photoelectric conversion circuit, a high-frequency amplification circuit and an analog-to-digital conversion circuit, and can convert a pulse laser signal into a digital level signal which can be read by the main controller; the photoelectric detection module in the embodiment realizes the conversion from a laser optical signal to an electric signal by designing a high-speed stable photoelectric conversion circuit with adjustable amplification factor, and then realizes the conversion from an analog signal to a digital signal by an analog-to-digital conversion circuit based on a high-speed threshold comparison circuit, thereby realizing the energy capture of ground foot spots of the satellite-borne laser altimeter.
In an embodiment, the photodetection module mainly includes a photoelectric conversion circuit, a high-frequency amplification circuit, an analog-to-digital conversion circuit, and other key parts, as shown in fig. 4:
the photoelectric detection module comprises a photoelectric conversion circuit, a high-frequency amplification circuit, a high-precision voltage stabilizing circuit, a multi-stage voltage dividing circuit and an analog-digital conversion circuit, wherein the analog-digital conversion circuit comprises a high-speed threshold comparator, a latch and a level conversion circuit which are sequentially connected, the photoelectric conversion circuit is connected with the high-frequency amplification circuit, the output of the high-frequency amplification circuit is used as the positive end input of the comparator and is connected to the high-speed threshold comparator, the high-precision voltage stabilizing circuit is connected with the multi-stage voltage dividing circuit, and the output of the multi-stage voltage dividing circuit is used as the negative end input of. The output of the analog-to-digital conversion circuit is connected with the main controller.
The wavelength of the pulse laser detected by the photoelectric detection module of the embodiment is 1064nm, the pulse width is between 1ns and 100ns, and the photoelectric detection module is realized and described as follows:
1) in consideration of the characteristics of small average energy density, narrow laser pulse width and the like in a laser foot point, a photoelectric conversion device with good performance is required to be adopted to complete the acquisition of laser energy signals, and a PIN photodiode with high sensitivity, high bandwidth and low dark current is selected as a core device of photoelectric conversion in the photoelectric conversion circuit. Meanwhile, because the photo-generated current signal generated by the PIN photodiode is small, the photo-generated current signal can be amplified only by increasing the resistance of the transimpedance, but the bandwidth of the whole detector is reduced, and the working performance of the detector is unstable. Therefore, the high-frequency amplification circuit amplifies the light-induced weak current signal by adopting a high-frequency operation amplification mode.
2) The photoelectric detection module is adjusted and arranged by adopting multiple stages of gears so as to adapt to the variation range of the energy density of the laser foot points. The detection sensitivity ranges of different gears are adjusted by changing the feedback resistors of the high-frequency amplification circuit, and the resistance values of the feedback resistors of different gears are optimally selected according to a certain proportional relation, so that the sensitivity ranges of the gears have certain difference.
3) The analog-to-digital conversion circuit quantifies a voltage signal output by the high-frequency amplifying circuit by using a high-speed threshold comparator, so that laser energy detected by the PIN photodiode is converted into a digital signal. To ensure the accuracy of the digital signal, the threshold voltage of the comparator is required to have better consistency and stability. If the power supply of the photoelectric detection module is directly used for providing the threshold voltage, the threshold voltage is attenuated along with time, the stability of the threshold voltage is affected, and the reference voltage stabilizing chip can provide stable reference voltage output, so that the high-precision reference voltage stabilizing chip is preferably used for generating consistent and stable threshold voltage.
4) In order to meet the requirement of multilevel quantization of the laser detector, a multilevel voltage division circuit is required, and in the embodiment, a resistance grid voltage division mode is adopted. Meanwhile, a high-precision exclusion mode is utilized, and a divider resistor with small difference is selected to ensure the proportional relation of each level of divided voltage, so that stable and reliable reference voltage is provided for subsequent threshold comparison. In the embodiment, the multistage voltage division circuit adopts a 10-stage voltage division circuit.
5) When the high-speed threshold comparator is implemented, a high-sensitivity comparator can be selected, and the output signal can be changed due to millivolt-level input change at a differential input end, so that the requirement on weak signal detection can be met; meanwhile, a comparator with a wide common-mode input voltage value range is selected, and when the input voltage of the comparator is large, the threshold comparison result is guaranteed not to be distorted.
6) When the laser detector captures a laser pulse signal and outputs a low level signal through the high-speed threshold comparator, the duration of the low level is short because the laser pulse is narrow, and in order to stabilize the detection result, the design of the laser detector adopts a latch to hold the output signal of the high-speed threshold comparator. The output level of the high-speed threshold latch is equivalent to the power voltage and is higher than the TTL level required by the main controller, the main controller can be damaged, in order to solve the level matching problem, a level conversion circuit is required to be used as a data buffer to realize stable maintenance of data, the latched data level is reduced to the TTL level, and the data reading of the subsequent main controller is facilitated.
7) When the photoelectric detection module is triggered by laser pulse, the latch with the lowest energy level simultaneously generates a rising edge pulse to be sent to the main controller, and an interrupt event is triggered.
The time synchronization module is based on PPS second pulse provided by GPS, and combines with high-precision timer and follow-up time compensation to realize accurate measurement of the capturing time of the foot spot. The realization mode is that the time information is acquired by the main controller by utilizing the serial port and the GPS chip, and the real-time working time of the detector is provided by combining the PPS second pulse with high precision and high stability provided by the GPS chip; the active crystal oscillator provides stable clock signals for the main controller, the main controller utilizes the high-precision timer to count PPS pulses, when the photoelectric detection module is triggered by laser pulses, the main controller is also triggered to be interrupted, and the accurate time when the laser pulses reach the laser detector, namely the accurate trigger time, can be obtained through modes such as time compensation.
In an embodiment, the time synchronization timing module mainly includes a high-precision timer and a high-stability active crystal oscillator, as shown in fig. 5:
the time synchronization timing module comprises a high-precision timer and a high-stability active crystal oscillator, wherein the PPS second pulse output of the GPS chip and the high-stability active crystal oscillator in the geometric positioning module are connected to the high-precision timer, and the high-precision timer is connected to the main controller. Meanwhile, the GPS chip outputs time information to the main controller to support synchronous timing work.
1) The time synchronization timing module is used for completing work by the cooperation of a time service type GPS chip in the geometric positioning module and a high-precision timer, and the high-precision high-stability PPS second pulse generated by the GPS chip is used as reference time. Each PPS pulse may be considered to be the starting instant of the current time of second.
2) The main controller acquires time information of an initial GPS (global positioning system), and combines PPS (pulse per second) pulse to obtain the real-time working time of the current laser detector, and UTC (universal time control) time information can be adopted in specific implementation, wherein UTC is universal standard time.
3) The time interval t between the PPS second pulse and the trigger interruption of the detector can be comprehensively determined by the crystal oscillator frequency f and the counting value n of the high-precision timer:
the high-stability active crystal oscillator provides a stable clock signal for the timer, thereby ensuring the accuracy of the time required by each counting of the timer. The high accuracy timer starts counting every PPS pulse rising edge. When the laser detector is triggered, a rising edge signal sent by the photoelectric detection module triggers the detector to interrupt response, and the high-precision timer acquires count values of time intervals of a rising edge and an interrupt signal of a PPS pulse, so that a time interval value between the two signals is acquired.
4) Due to the existence of factors such as software running time delay, PPS pulse accumulated counting error and the like, after the laser detector works for a period of time, the time interval measured by the time synchronization timing module is larger than the real time interval, and the deviation amount is increased along with the time. In order to reduce the influence of the error factors, the measured time interval value is compensated in a mode of accumulative error compensation and true value correction, so that a more accurate time interval value is obtained. And combining the corrected time interval with the working time information of the current laser detector to obtain the accurate moment when the laser pulse triggers the laser detector.
The geometric positioning module comprises a GPS chip, and longitude and latitude information output by the GPS chip is connected to the main controller. In specific implementation, considering that the precision of longitude and latitude information output by a single-point GPS chip is low, the invention further combines differential station data acquired by a differential station in an field calibration field, obtains high-precision longitude and latitude through back-end differential processing, provides geometric positioning information for each laser detector, and can set corresponding differential processing software according to an application scene in specific implementation.
In the embodiment, the positioning geometric accuracy of the laser detector provided by the single-point GPS chip is generally greater than 2.5m and does not meet the requirements of corresponding technical indexes, so that a differential station needs to be established in a calibration field, and a high-accuracy geometric positioning result of the laser detector is provided by combining differential data of the differential station and rear-end differential processing software. The geometric positioning work is mainly completed by the cooperation of the GPS chip, the main controller, the differential station and the relevant processing software, as shown in FIG. 6.
1) The main controller is connected with the GPS chip in a serial port mode, and reads geographic position information in the GPS chip. The main controller judges and classifies various GPS information, extracts longitude and latitude and time information meeting the condition of star searching quantity, puts the information into a sending cache, and simultaneously uploads the information to the main control end of the upper computer through the communication module to wait for subsequent processing.
2) The GPS receiver on the differential station can carry out three-dimensional positioning after observing at least 4 satellites, and the coordinates of the differential station can be calculated based on the received data and the processing software. Due to orbit errors, clock errors, SA effects, atmospheric effects, multipath effects and other errors, there are errors between the calculated differential station coordinates and the reference coordinates of the actual differential station layout. The difference station sends the error correction number out by using a data chain, and the error correction number is received by the main control end of the upper computer to correct the geometric positioning coordinates of the subsequent laser detector, so that the positioning precision of the laser detector is improved. Since the above prerequisite is the case where the differential station and the geometric positioning module of the laser detector observe the same set of satellites, the differential station is typically built within 20km of the laser detector array.
3) The upper computer main control end can set back end differential processing software to obtain longitude and latitude data and differential station data of each laser detector, and then pseudo range data after phase smoothing is adopted to carry out multi-point pseudo range baseline calculation to form a baseline network, and networking adjustment is carried out to reduce the influence of various errors such as ephemeris error, ionosphere delay and troposphere delay, and the influence of multipath in the maximum direction is weakened by utilizing the interaction of baselines in different directions, so that the requirement of high-precision single-point positioning is finally met.
The communication module mainly completes data transmission between all laser detectors and the upper computer, and can be realized by adopting an LoRa module in the prior art during specific implementation. LoRa represents Long-distance Radio (Long Range Radio), and the Radio has the greatest characteristic that the Radio is longer in propagation distance than other Radio modes under the same power consumption condition, realizes low power consumption and Long-distance unification, and is 3-5 times longer in distance than traditional Radio frequency communication under the same power consumption condition. In the embodiment, the communication module is based on an LoRa protocol, and an STM32 singlechip is used as a main control chip to realize the transmission function of each data and instruction of the detector, so as to realize the intelligent data networking of the detector array.
The LoRa module is provided with a configuration register, a control chip and a data cache region, and a high-gain antenna and a radio frequency circuit are arranged to establish communication with an upper computer.
The communication module parameters can be configured through the SPI interface of the master controller, and data are sent to the upper computer software through the communication control part by means of the radio frequency circuit and the high-gain antenna. Because the communication mode is set to be the transparent transmission mode, all transmission data are placed in the sending data cache of the main controller, and the communication function with the upper computer software can be realized. When the method is specifically implemented, corresponding upper computer software can be set according to an application scene.
The implementation of the communication module function requires two steps, firstly, parameter configuration is performed on each part of the communication module, and secondly, data transmission is implemented, as shown in fig. 7.
In specific implementation, the communication function is suggested to be implemented as follows:
1) the upper computer is provided with a DTU gateway, and the DTU (data Transfer unit) gateway is a wireless terminal device which is specially used for converting serial port data into IP data or converting the IP data into the serial port data and transmitting the serial port data through a wireless communication network. The upper computer software carries out network parameter configuration on the DTU gateway of the host, and the parameters mainly comprise bit rate, verification mode, data digit and the like so as to establish a basic wireless network.
2) The main controller chip communicates with a control chip CPU in the LoRA module through an SPI interface, and performs parameter configuration on a configuration register in the LoRA module by using the CPU, wherein the parameter configuration mainly comprises bit rate, a verification mode, data digits and the like. All parameters are consistent with the configuration of the DTU gateway in the host, so that all laser detector nodes are added into the wireless network, and all the detector nodes can normally communicate with the host without mutual interference.
3) And aiming at different communication distances, a high-gain antenna and a high-performance radio frequency circuit with proper sizes and materials are selected, so that long-distance data transmission is completed with low power consumption, and network connection is realized. The design of the radio frequency circuit is matched with parameters such as the frequency specification of the antenna, and the radio frequency circuit has the characteristics of high gain, low noise and the like so as to ensure that the radio frequency circuit can amplify signals with a higher signal-to-noise ratio under the state of low power.
4) Under the condition of configuring network parameters, the data transmission format and the verification mode of the corresponding needle head and the corresponding needle tail are specified, so that the completeness and the reliability of data transmission of the detector node are ensured, and the reliable transmission of data and instructions of the laser detector is finally realized.
5) All transmission data place the data buffer in main control unit, and main control unit can be through the mode of serial ports with data transmission to the data buffer in the LoRA module promptly, later utilizes wireless transmission's mode, in the middle of the host computer software is sent to the IP data with serial data conversion through DTU to realize the high-efficient transmission of data. DTU converts the control command (IP data) of host computer into serial port data, is caught by the LoRA module via wireless transmission's mode to deposit in the data cache district, main control unit utilizes serial port communication's mode, reads the instruction data that temporarily exists in LoRA data cache district, and responds to different instructions. And finally, realizing the bidirectional communication between the upper computer terminal and the detector node.
In an embodiment, the communication module is based on a commercial LoRa protocol to ensure a coverage of 500m × 500 m. The time synchronization module adopts a high-performance timer to ensure a time measurement error of 20 mu s, thereby realizing the time synchronization with the emission time of the satellite laser emission system; the geometric positioning module overcomes the problem of insufficient GPS single-point positioning precision in a differential post-processing mode by combining a GPS chip and a post-processing differential algorithm, and cooperates with an external differential station together, thereby realizing the sub-meter-level static positioning precision.
The GPS time information, the high-precision PPS pulse and the longitude and latitude information are provided by a time service type GPS chip, and the MXT902 or MXT906GPS chips of dream core companies can basically meet the requirements. The main control can generally adopt a single chip microcomputer or an FPGA, and the embodiment adopts an STM32f104 single chip microcomputer to meet the functional requirements, so that the transmission function of each data and instruction of the detector is realized, and the intelligent data networking of the detector array is realized. The core device of the photoelectric conversion circuit is a photodiode (pin tube), and the embodiment selects an S5821-01 photodiode (pin tube) of Hamamatsu corporation.
The external differential station is a commercial small-sized movable differential station, and the distance detector is installed at a position less than 30 km.
The invention provides a method for determining technical parameters of each module of a laser detector and the layout parameters of an array of the modules according to the functional module requirements, the detection index requirements and the system parameters of the laser height indicator of the laser detector. For the sake of reference, the laser active detector designed for GF-07 satellite laser altimeter is taken as an example:
and determining technical parameters of each module of the laser detector according to the functional module requirements, the detection index requirements and the system parameters of the laser altimeter of the laser detector. The photoelectric detection module is a key for ensuring whether the laser foot point energy of the GF-7 satellite-borne laser altimeter can be detected, the main technical parameters of the photoelectric detection module comprise the gear, the quantization grade and the sensitivity of a detector, and the main technical parameters are related to factors such as satellite orbit height, laser pulse energy, divergence angle, atmospheric transmittance and the like, and the flow of parameter calculation setting of the photoelectric detection module preferably used in the embodiment is shown in figure 2:
1) calculating to obtain the average laser energy density variation range in the ground laser foot point by taking GF-7 satellite-borne laser altimeter parameters (including laser single pulse energy, laser divergence angle and satellite orbit height) as basic input parameters and assuming atmospheric transmittance fluctuating in a certain range;
2) determining the highest energy value and the lowest energy value within the range of the laser foot points according to the theoretical energy spatial distribution of the laser emitted by the GF-7 spaceborne laser altimeter and the calculation result of the average laser energy density, thereby obtaining the sensitivity setting basis of the laser detector;
3) resolving the variation range of the energy collected by the detector in the range of the laser foot point based on the fluctuation range of the atmosphere and the variation range of the parameters of the emitted laser pulse, and providing reference for setting the gear of the laser detector;
4) and calculating the quantization grade of the laser detector for acquiring the step distribution of the laser foot point energy by considering the difference interval of the highest energy and the lowest energy in the laser foot point range and combining the positioning precision requirement of the laser foot point center. And the final output parameters are the gear setting, the sensitivity setting and the quantization grade setting of the laser detector.
The geometric positioning precision, the synchronous timing precision, the communication distance range and the like of the laser detector can directly refer to corresponding index requirements, and the parameter design of the geometric positioning module, the time synchronous timing module and the wireless communication module takes the index requirements as basic input conditions.
The spot size of the pulse laser emitted by the satellite-borne laser altimeter reaching the ground is large, and the diameter is generally between 30m and 100 m. The single detector cannot capture the energy distribution of the whole light spot, and in order to obtain the energy distribution characteristics of the light spot and extract the central position of the light spot, the invention provides a mode of arranging the detector array.
The detector arrangement array mode adopts a grid-shaped equal-interval arrangement mode. In specific implementation, the layout interval can be determined according to the energy level of the detector, the size of a ground light spot and the required central positioning precision. A preferred way of determining this is to take as input a spot of known spot diameter, energy distribution and centre position, taking into account a certain atmospheric transmittance (generally considered to be 0.7) and atmospheric disturbances, the spot triggering detector arrays of different layout intervals. And simulating the energy distribution of the light spots captured by the detector array by adopting a spline interpolation mode according to the energy level result of the triggered detector. And extracting the central position of the simulated light spot by adopting an energy gravity center algorithm, and comparing the central position with the central position of the input light spot to obtain the central positioning deviation in the simulation experiment. The above process is repeated 1000 times, and the average center positioning deviation obtained by each random spot center position can be regarded as the center positioning accuracy of the detector array under the arrangement interval condition. By traversing different layout intervals, a relation graph of different layout intervals of the detector to the center positioning accuracy can be obtained.
Taking the laser load of the GF-7 satellite as an example, the ground light spot diameter is 17.5m, and assuming that the detector energy level is 8, the relationship between the arrangement interval and the light spot center positioning is shown in fig. 3.
As can be seen from fig. 3, if a spot centering accuracy of 0.8m is desired, the detector array should be spaced apart by 10 m.
For mass laser detectors, it is necessary to ensure good anti-interference capability and consistency in the actual use process. The interference sources of the laser detector are mainly sky background stray light, circuit noise and the like. The uniformity design of the detector focuses on the uniformity design of the detection performance to ensure that the detector response is constant for the same energy of the incident pulsed laser. In order to enable the laser detector to work for a long time in an outdoor environment, the design of low power consumption of each part of the detector is needed. The normal working temperature range of the whole detector is between 0 and 50 ℃. For ease of reference, the implementation of quality control in the embodiments is provided with reference to fig. 8:
1) and (3) anti-interference design: the laser wavelength of the satellite-borne laser altimeter is 1064nm, and the solar background light can be reduced in a narrow-band filter manner to avoid false triggering of the detector. Generally, the spectral response range of the PIN photodiode is long, so that the PIN photodiode can effectively respond to light with different wavelengths, and the PIN photodiode is easily triggered by high-intensity sky background light under the condition of no filtering. The narrow-band filter can be understood as a band-pass filter with a narrow pass band, and the bandwidth is generally 3-4 nm. The main wavelength of the sky background light is visible light, middle and far infrared wave bands, and almost no light with near 1064nm near infrared wave bands exists. The narrow-band filter is placed in front of an optical window of the PIN photodiode in a mode of a narrow-band filter, stray light of other wave bands can be filtered, and light incident to a PIN photosensitive surface is guaranteed to be pulse laser with the wavelength of 1064nm emitted by the satellite-borne laser altimeter; the detector adopts a PIN photodiode as a core comparison device, has certain direct current dark current noise, and can be removed by adopting a direct current blocking capacitor mode. Because the analog-to-digital conversion part of the photoelectric detection module adopts a threshold comparison mode, if a noise signal in a circuit is greater than a comparison threshold, the photoelectric detection module can be triggered by mistake, so that the detection performance of the laser detector is influenced. The circuit noise is mainly caused by the thermal noise of the circuit and the power supply ripple, and for the circuit thermal noise, the scheme reduces the circuit thermal noise in a low-noise circuit mode so as to improve the signal-to-noise ratio of the photoelectric conversion module. The power supply ripple can reduce the amplification performance of the circuit, so that the amplification circuit generates phenomena of self-oscillation and the like, and the amplification circuit loses the accurate amplification capability. The circuit scheme adopts a mode of a power supply filter circuit, and filters high-frequency signals in the power supply by using filter capacitors with different capacitance values so as to ensure the stability of the power supply of each circuit. In the amplifying circuit, since the operational amplifier in the amplifying circuit has a problem of bias voltage, it is easily larger than a comparison threshold of the comparator, and a false trigger is generated. A blocking circuit is added in the high-frequency amplifying circuit, bias voltage in the circuit is filtered, pulse laser pulse width is narrow, a pulse laser light signal can be regarded as a high-frequency signal, and the blocking circuit has no influence on a real laser pulse signal;
2) and (3) consistency design: the consistency is used as a basis for ensuring the authenticity and the effectiveness of the performance indexes of the laser detector, and comprises the step of ensuring the consistency of the partial pressure performance and the amplification performance in order to realize the consistency of the detection performance. Firstly, the model selection and consistency test is carried out on related electronic components in the scheme, and meanwhile, the consistency of the differential gain of the operational amplifier, the voltage stabilization value of the voltage stabilization chip, the differential input voltage of the comparator, the capacitance value of the capacitor and the resistance value of the resistor is guaranteed. The resistance difference between the resistors in the resistor array is generally far smaller than that of a discrete resistor device, and the voltage division value interval of each voltage division gear of the voltage division circuit can be greatly increased by adopting a mode of realizing voltage division array by using the high-precision voltage division resistor, so that the consistency of each voltage division circuit is realized. And (3) low power consumption design: the method comprises a low-power-consumption design in three aspects of circuit, program and networking. On the basis of ensuring the detection performance of the laser detector, a chip with lower power consumption or a low power consumption mode is selected when the chip is selected. In the program control, the detector is in a dormant standby state before being triggered, the laser detector only works normally when data is transmitted and triggered, and the laser detector is in a low power consumption state in the rest time. In the networking scheme, an ad hoc network mode is abandoned, a star-shaped network is adopted, point-to-point communication is carried out, only the detectors in communication work, and the other detectors do not work in communication, so that the power consumption of the whole network is reduced.
The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.
Claims (10)
1. The utility model provides a satellite-borne laser altimeter active facula energy detector which characterized in that: is used for capturing laser foot spots in an array mode,
the single energy detector comprises a photoelectric detection module, a communication module, a geometric positioning module, a time synchronization module and a main controller, wherein the photoelectric detection module, the communication module, the geometric positioning module and the time synchronization module are respectively connected with the main controller;
the photoelectric detection module is used for realizing the conversion from a laser light signal to an electric signal through high-speed stable photoelectric conversion with adjustable amplification factor and realizing the conversion from an analog signal to a digital signal through analog-to-digital conversion based on high-speed threshold comparison, thereby realizing the energy capture of a ground foot spot of the satellite-borne laser altimeter;
the communication module is used for realizing data and instruction transmission of the energy detector so as to realize intelligent data networking of the detector array;
the time synchronization module is used for taking the pulse per second provided by the GPS as input, combining a high-precision timer and subsequent time compensation and realizing accurate measurement of the capturing moment of the foot spot;
and the geometric positioning module is used for cooperating the GPS single-point positioning with an external differential station together and realizing that the static single-point positioning reaches the sub-meter level in a differential post-processing mode.
2. The active spot energy detector of the spaceborne laser altimeter as claimed in claim 1, wherein: the photoelectric detection module comprises a photoelectric conversion circuit, a high-frequency amplification circuit, a high-precision voltage stabilizing circuit, a multi-stage voltage dividing circuit and an analog-to-digital conversion circuit, wherein the analog-to-digital conversion circuit comprises a high-speed threshold comparator, a latch and a level conversion circuit which are sequentially connected, the photoelectric conversion circuit is connected with the high-frequency amplification circuit, the output of the high-frequency amplification circuit is connected to the high-speed threshold comparator as the input of the positive end of the comparator, the high-precision voltage stabilizing circuit is connected with the multi-stage voltage dividing circuit, the output of the multi-stage voltage dividing circuit is connected to the high-speed threshold comparator as the input of the negative.
3. The active spot energy detector of the spaceborne laser altimeter as claimed in claim 2, wherein: the photoelectric conversion circuit is realized by a PIN photodiode, and a high-frequency amplification circuit amplifies a photo-generated weak current signal generated by the PIN photodiode in a high-frequency operation amplification mode.
4. The active spot energy detector of the spaceborne laser altimeter as claimed in claim 3, wherein: the anti-interference design is adopted, the narrow-band filter is placed in front of an optical window of the PIN photodiode, stray light of other wave bands is filtered, and it is guaranteed that pulse laser with the wavelength of 1064nm emitted by the satellite-borne laser altimeter enters the PIN photosensitive surface.
5. The active spot energy detector of the spaceborne laser altimeter as claimed in claim 2, wherein: the multistage voltage division circuit adopts a 10-stage voltage division circuit.
6. The active spot energy detector of the spaceborne laser altimeter according to the claim 1 or 2 or 3 or 4 or 5, characterized in that: the communication module is realized by adopting an LoRa module.
7. The active spot energy detector of the spaceborne laser altimeter according to the claim 1 or 2 or 3 or 4 or 5, characterized in that: the geometric positioning module comprises a GPS chip, longitude and latitude information output by the GPS chip is connected to the main controller, high-precision longitude and latitude are acquired through back-end differential processing by combining differential station data acquired by differential stations in the field calibration field, and geometric positioning information is provided for each energy detector.
8. The active spot energy detector of the spaceborne laser altimeter as claimed in claim 7, wherein: the time synchronization module comprises a high-precision timer and a high-stability active crystal oscillator, the PPS second pulse output of the GPS chip in the geometric positioning module and the high-stability active crystal oscillator are connected to the high-precision timer, the high-precision timer is connected to the main controller, and simultaneously the GPS chip outputs time information to the main controller to support the realization of synchronous timing work, the synchronous timing is realized as follows,
the PPS second pulse with high precision and high stability generated by a GPS chip is used as reference time;
the main controller acquires initial GPS time information and combines PPS (pulse per second) pulse to obtain the real-time working time of the current energy detector;
comprehensively determining the time interval between the PPS second pulse and the triggering interruption of the detector according to the crystal oscillator frequency and the counting value of the high-precision timer;
and compensating the measured time interval value by adopting a mode of accumulative error compensation and true value correction, and combining the corrected time interval with the working time information of the current energy detector to obtain the accurate moment of triggering the energy detector by the laser pulse.
9. The utility model provides a satellite-borne laser altimeter active facula energy detection array which characterized in that: the active light spot energy detectors of the satellite-borne laser altimeter are adopted as claimed in claim 1, 2, 3, 4, 5, 6, 7 or 8 and are arranged in a grid-shaped and equally-spaced mode.
10. The active spot energy detection array of the spaceborne laser altimeter according to claim 9, wherein: the layout interval is determined according to the energy grade of the energy detector, the size of the ground light spot and the required central positioning precision.
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| CN112013874B (en) * | 2020-08-25 | 2022-04-01 | 武汉大学 | Satellite-borne laser altimeter on-orbit calibration method based on laser footprint prior coordinate |
| CN112394339A (en) * | 2020-11-16 | 2021-02-23 | 江苏亮点光电研究有限公司 | Control circuit applied to cloud detection radar |
| CN113093154B (en) * | 2021-03-04 | 2023-08-01 | 武汉大学 | Single photon laser height measurement satellite ground active detector |
| CN113218306B (en) * | 2021-04-28 | 2022-02-15 | 大连理工大学 | FPGA-based light spot position detection system and method |
| CN117784095B (en) * | 2023-12-26 | 2024-07-09 | 自然资源部国土卫星遥感应用中心 | Distributed matrix light spot detection system based on two-stage RS485 bus communication |
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