Transmitting and receiving split type laser ranging system and time delay calibration method

Abstract

The invention discloses a transmitting and receiving split type laser ranging system and a time delay calibration method. The one-way delay and the two-way delay of the system are respectively obtained through three links including a near-earth target, an ultra-near-earth target and a space target. According to the method, the limitation that only system time delay under the same base can be obtained through traditional ground target measurement is broken through, and telescope systems of the bases at different positions are correlated. On the basis of acquiring single system time delay by using a near-earth target, a laser signal is forwarded from a transmitting light path to a receiving light path through an ultra-near-earth target and a space target, and the total time delay of the transmitting-receiving split system is acquired. According to the invention, a multi-means data fusion processing method is combined, the method has the characteristics of high precision and high stability, and the measurement precision and reliability of the ranging system can be effectively improved. In addition, the method also has good adaptability, and ensures that stable and reliable measurement results can be obtained in various complex environments. According to the method, the performance of the laser ranging system can be remarkably improved.

Description

Technical Field

[0001] The invention relates to the technical field of laser ranging, and in particular to a transmitting-receiving split-type laser ranging system and a method for delaying the marking effect. Background Art

[0002] Laser ranging is a high-precision, long-distance space geodetic technology, which is widely used in satellite orbit determination, determination of Earth rotation parameters, laser time comparison and other fields. With the continuous deepening of deep space exploration projects, the laser ranging system has been upgraded from the first generation to the third generation, achieving comprehensive optimization from being bulky, energy-intensive, precision-limited and dependent on manual operation to being miniaturized, high-precision, fully automated and multifunctional. Among them, representative technologies such as Satellite Laser Ranging (SLR), Lunar Laser Ranging (LLR), and Debris Laser Raning (DLR) continue to emerge, providing strong technical support for the development of major national projects such as manned spaceflight and satellite navigation.

[0003] With the continuous extension of the detection distance of the laser ranging system and the increasing number of observed target types, the intensity of the laser ranging echo signal has dropped to the single photon level. According to the laser radar equation, the ground system's ability to receive laser echoes is proportional to the receiving area of ​​the telescope, and a large-aperture receiving telescope system can be used to receive weak echo signals. However, improving the receiving aperture of large-aperture optical telescopes requires high-level optical mirror grinding technology, large-scale support structures, and precision drive devices. These requirements make the development and application of large-aperture telescope systems face many challenges, especially when measuring fast-moving debris targets in low orbits. The complexity and low rapid response capability of large-aperture laser ranging systems further limit practical applications.

[0004] In order to solve the above problems, the laser ranging system with separate transmitter and receiver came into being. Different from the traditional integrated laser ranging system with transmitter and receiver and the remote dual-station and multi-station laser ranging system, the laser ranging system with separate transmitter and receiver is based on the same time reference. Figure 1This is a schematic diagram of laser ranging of space targets with multiple receiving telescopes. Multiple relatively small-aperture telescopes are used to simultaneously receive laser echo signals, which not only achieves the equivalent of a single large-aperture telescope's laser signal receiving capability, but also reduces the difficulty and cost of development. At the same time, since the transmitting telescope and the receiving telescope are on different platforms, when the distance between them is far enough, the stray light in the transmitting optical path can be effectively prevented from entering the receiving optical path, effectively avoiding backscattering and reducing the difficulty of ranging. In addition, the larger-aperture receiving telescope in the system can be used as a general-purpose telescope, which not only does not affect the transmitting system, but also has higher flexibility and reliability. The independent laser signal receiving, detecting and timing system can realize multiple echo detection of a single-shot laser pulse, and process multiple echo signals in parallel, effectively improving the measurement efficiency and anti-interference capability, and making up for the shortcomings of the traditional single large-aperture telescope laser ranging system in terms of rapid tracking, operation and maintenance.

[0005] In order to obtain high-precision laser ranging data, it is particularly important to improve the system's time delay standard accuracy. Figure 2 The laser ranging system is composed of delay distribution. For the laser ranging system, the original data records the time interval between the start pulse generated by the main wave probe and the closing signal obtained by the echo detector. In practical applications, the time on the ground needs to be calculated to the phase center of the telescope (the intersection of the horizontal axis and the vertical axis of the telescope). Since the two detection points do not coincide with the phase center of the instrument, a system path delay is generated, which is specifically manifested as:

[0006]

[0007] Where de1 is the optical path delay from the spectroscope to the phase center of the telescope, de2 is the sum of the optical path delay in the spectroscope and the optical path delay from the spectroscope to the main wave detector; de3 is the internal delay of the main wave detector; de4 is the electrical signal delay from the signal output end of the main wave detector to the event timer end; dr1 is the optical path delay from the phase center of the telescope to the detection surface of the echo detector; dr2 is the internal delay of the echo detector; dr3 is the electrical signal delay from the output end of the echo detector to the event timer end; ε is the link error delay, which mainly refers to the atmospheric transmission error, the error caused by the relativistic effect, and the satellite shape effect error. e =de4+de4+de2-de1 is the transmission delay of the system, δ r=dr1+dr2+dr3 is the receiving delay of the system. In the laser ranging system, the transmission delay and the receiving delay are usually considered as a whole, that is, the system delay. It can be seen that the system delay, as the main factor affecting the stability of the laser ranging data, is related to the optical path delay of the transmitting and receiving systems and the electronic delay caused by the electronic equipment. Among them, the electronic delay is a variable, which is related to the response time of the electronic equipment, the cable length, the cable connector and other factors, and changes with the working state of the electronic equipment. Therefore, in order to improve the accuracy and reliability of the laser ranging system, it is very important to accurately measure the above delays.

[0008] Existing technical solution 1:

[0009] In traditional laser ranging, ground target measurement is usually used to achieve system delay calibration. The so-called "ground target measurement" is to measure the sum of the transmission and reception delays in the system through a ground target with a known distance, and to perform precise calibration of the system delay. According to the distance of the ground target to the laser ranging system, it can be divided into near-ground target and far-ground target. Figure 3 Schematic diagram of near-earth target correction.

[0010] Near-Earth Target is the main method for obtaining system delay in most laser ranging stations. The near-earth target is usually placed in the dome, about 2-3 meters away from the telescope. Two reflectors are used to refract the light, attenuate the emitted laser, and return it to the receiving system. The near-earth target data is obtained by measuring the time difference between the emission and echo signals. The average value of the measured near-earth target data minus L+d / 2 is the system correction value. Figure 3 The figure is a schematic diagram of near-Earth target correction, where O is the telescope phase center reference point, and M1 and M2 are near-Earth target reflectors.

[0011] Disadvantages of prior art 1:

[0012] The laser ranging system with separate transmitters and receivers is equipped with multiple receiving telescopes. The electrical parameters and optical paths of each telescope are not completely consistent, and they are separated from the transmitting system. In the existing technology, the laser passes through the near-ground target and reflects the echo signal to the transmitting system on the same base. Only the system delay of a single telescope can be obtained, which cannot meet the requirements of the multi-telescope ranging system using the same time reference.

[0013] The single photon avalanche diodes (SPADs) used in most SLR systems have a time walk effect. When performing near-Earth target calibration and satellite ranging, their working state is inconsistent with the observation, especially the obvious difference in the number of echo photons received by the SPAD (i.e., echo intensity), which will lead to inaccurate system delay measurement.

[0014] Laser ranging observation is a full-sky observation, and the optical path delay generated by the transmitting and receiving systems is related to the telescope's pointing direction. The near-earth target used in existing technologies is a static target, which cannot accurately reflect the delay changes of the telescope at different pointing directions, limiting its accuracy in practical applications.

[0015] The electronic delay caused by electronic equipment and circuits is closely related to the operating time of the system. When the distance between the near-ground target and the laser ranging system is close and the calibration time is short, the delay has little effect. However, when measuring distant targets, the transmission and observation time of the laser will be extended, which will increase the uncertainty of the system delay and lead to an increase in the error of the measurement result.

[0016] Existing technical solution 2:

[0017] Different from the total delay of traditional near-ground target measurement laser ranging, the one-way delay calibration method of the laser ranging system uses a detector, cable and timer with known delay to form a loop with the transmitting channel and the receiving channel respectively, to achieve accurate measurement of the transmitting delay and receiving delay, and then combine the delays of each part to complete the system delay calibration. Among them, the laser transmitting end and the echo receiving end are two independent parts, and each has its own time system. The principle of one-way laser ranging measurement is as follows Figure 4 shown.

[0018] At the transmitter, each moment is recorded according to its own time system. tran Indicates the time when the signal pulse passes through the transmitting reference point, T st Indicates the signal pulse time recorded by the transmitter time system. The difference between the two is τ1 = T ST -T tran It is called the delay at the transmitting end. ran Flight time, from the transmitting reference point to the receiving reference point. T rec Indicates the time when the signal pulse passes through the receiving reference point, T EN Indicates the signal pulse time recorded by the receiving end time system. The difference between the two is τ2 = T rec -T EN , let △T be the clock error of the one-way laser ranging system, that is:

[0019] T ran =(T rec -△T)-T tran -τ1-τ2-ε;

[0020] Among them, τ1 is the delay of the transmitter, τ2 is the delay of the receiver, and ε is the sum of other errors in the measurement process, including the refraction deviation of the laser in the atmosphere, the deviation of the target center of mass position, random deviation, etc. In the one-way laser ranging delay calibration system, the transmitter and the receiver operate under the same timing, △T = 0, and the above formula is simplified to,

[0021] T rec -T tran -T ran =τ1+τ2+ε,

[0022] Among them, the transmitting end delay τ1 of the laser ranging system is the delay from the event timer A channel to the center of the transmitting axis. According to the principle of one-way laser ranging and the transmission direction of the photoelectric signal of the laser ranging system, the following relationship can be established and obtained after sorting:

[0023] T EN -T ST =τ1+τ L3 +τ L4 +τ DET +τ C3 +ε,

[0024] After sorting, we can get: τ1=T EN -T ST -τ L3 -(τ L4 +τ DET +τ C3 )-ε;

[0025] Among them, T EN -T ST Measure the average of multiple data points for the event timer; τ L3 is the transmission delay of the optical pulse from the reference point to the target, obtained by using a vernier caliper, a ruler, and a laser rangefinder (the speed of light in the calculation is 2.999 8×108 m / s); τ L4 +τ DET +τ C3 is the delay of the standard effect device; τ L4 is the transmission delay of the optical pulse inside the target, which can be obtained by using a ruler; τ DET is the light signal conversion delay of the photodetector, which can be obtained through other types of detectors (such as PIN tube); τ C3 is the cable electrical signal delay between the photodetector and event timer channel B, which can be measured using a high-frequency coaxial cable and a picosecond interval timer. After the equipment is assembled, the delay is fixed, and ε is the error term. Similarly, the system delay at the receiving end can also be obtained using the above method.

[0026] Disadvantages of the second prior art:

[0027] The existing technology is complex to operate and has poor real-time performance, which seriously affects the work efficiency of the system and is not conducive to routine observation.

[0028] The equipment calibration process in the prior art is cumbersome and requires frequent manual intervention, which not only increases the workload of operators but also easily introduces human errors, affecting the accuracy of measurement results.

[0029] Existing technologies are based on measurements under static conditions and lack the ability to respond to dynamic changes in real time, and may not be able to adapt to rapidly changing measurement environments.

[0030] The existing technology uses cables and photoelectric detectors to form a calibration system, which may have system errors, such as nonlinearity of the equipment, inaccurate calibration, etc. These errors reduce the accuracy of the one-way delay calibration.

[0031] Existing technical solution three:

[0032] The optical retroreflective device (ultra-near-ground target) can obtain the system delay value in real time by intercepting a very small part of the emitted light and entering the receiving system. Figure 5 To obtain the delay structure diagram of the laser ranging system using an optical retroreflection device. As can be seen from the figure, unlike the conventional laser ranging system with separate transmission and reception, the telescope system with an optical retroreflection device connects the transmitting telescope and the receiving telescope, and adds a crossbeam. A cone is placed at each end (inside the transmitting telescope barrel and the receiving telescope barrel), and very little light is intercepted from the transmitted light to enter the receiving system. The laser attenuation technology is used to attenuate it, and the receiving system is used to detect the echo of the ground target. After completing the high-repetition-rate calibration of the system delay, the detector is used to detect the echo of the space target. In the single ranging process, the measurement of the system delay is taken into account to realize the real-time, automatic, accurate and effective calibration of the delay value of the laser ranging system.

[0033] Defects of prior art three:

[0034] The receiving part of the independent base-based transmitting and receiving system is composed of multiple sub-telescopes. These sub-telescopes have differences in electrical parameters and optical path configurations, and cannot use optical reverse devices to reflect part of the laser back to their respective receiving systems, thus failing to meet specific application requirements.

[0035] The existing technology connects the transmitting telescope and the receiving telescope, adds a crossbeam, and places a cone at each end (inside the transmitting telescope barrel and the receiving telescope barrel). The telescope will rotate when measuring the ground target, which may cause the position of the cone to change, affecting the accuracy of the measurement system delay.

[0036] The existing technology intercepts part of the laser through the cone, and although the coating is used for attenuation, it is still greater than the echo intensity of the space target, causing new measurement errors, which is not conducive to the stability and measurement accuracy of the system.

[0037] The reflectivity of the cone used in the prior art may fluctuate at different angles, resulting in unstable laser signal intensity and affecting the reliability of the distance measurement results. At the same time, the physical size and installation accuracy of the cone also affect the overall performance of the system. If it is not installed properly, it may cause the laser beam to deviate, further reducing the measurement accuracy. Summary of the invention

[0038] The technical solution of the present invention to solve the above technical problems is to provide a laser ranging system with separate transmitter and receiver, comprising:

[0039] Measurement and positioning module: Determine the position of the telescope reference point and select the transmitting telescope as the reference point in the transmitting and receiving laser ranging system for system delay calibration;

[0040] Launch one-way delay benchmark module: Combined with the "near-earth target", the launch telescope system delay is measured;

[0041] Two-way time delay ground benchmark module: The laser is transmitted to the ground "measurement target" through the transmitting system, and then the echo signal is received by the receiving system to obtain the total delay between the transmitting telescope and the receiving telescope;

[0042] Two-way time-delay space calibration module: The laser is transmitted to the geodynamic satellite through the transmitting system, and then the transmitting system and the receiving system are used to simultaneously receive the echo signal to realize the "target satellite" echo observation, obtain the total time delay of the laser ranging system with separate transmission and reception, and maintain the station coordinates;

[0043] System synthesis benchmark module: synthesizes the acquired system delay values ​​to obtain the delay data of the transmit-receive split laser ranging system.

[0044] In order to solve the above technical problems, the present invention also proposes a method for delay calibration, comprising the following steps:

[0045] The first transmitting telescope (60 cm) transmits laser light to the second receiving telescope (1 m), and the event timer records the transmitting time t1;

[0046] The laser signal is reflected by the reflector (ultra-close-to-ground target) of the second receiving telescope (1m) to the first receiving telescope (60cm). The event timer records the echo time t′1 of the close-to-ground target. The difference between the two times is the observation time interval Δt from the ground target to the measuring station. o =t′1-t1, and make a difference Δt with the distance value c , get the telescope system delay value Δt1;

[0047] The first launch telescope (60 cm) launches laser light to the target satellite, and the event timer records the launch time t2;

[0048] The laser signal is reflected by the target satellite and transmitted to the ground receiving system, and the satellite echo signal is received by the first receiving telescope (60 cm) and the second receiving telescope (1 m); the first receiving telescope (60 cm) records the target satellite echo time t'2, and subtracts it from the distance from the system reference point to the target satellite (considered as a known value) to obtain the first telescope (60 cm) time delay △t'2; the second receiving telescope (1 m) records the target satellite echo time t2'', and subtracts it from the distance from the first transmitting telescope to the target satellite (considered as a known value) to obtain the second telescope (1 m) time delay △t2'', and then obtains the overall time delay value △t2 of the two telescopes.

[0049] Furthermore, the delay calibration method further includes the following steps:

[0050] Read meteorological measurements to obtain local temperature, humidity, and air pressure parameters;

[0051] The outliers are removed by the least square method, and the system delay is processed and synthesized using the average weighted method to obtain the overall delay of the laser ranging system with separate transmitter and receiver.

[0052] Furthermore, the step of the first transmitting telescope (60 cm) transmitting laser light to the second receiving telescope (1 m), and the event timer recording the transmitting time t1 comprises:

[0053] The first transmitting telescope emits laser, generates a range gate (Gate) signal, controls the opening of the single photon detector (C-SPAD), and at the same time, the PIN obtains the main wave emission signal, which is transmitted to the event timer interface by the cable to obtain the precise time t1 of the laser emission.

[0054] Compared with the prior art, this application has the following beneficial effects:

[0055] This patent uses multiple methods such as near-ground targets, ultra-near targets, and space targets to accurately calibrate the system delay of the separate-transmitter-receiver laser ranging. By integrating the measurement data of multiple targets, the error caused by a single target is significantly reduced, and the overall accuracy of the measurement is improved.

[0056] This patent uses a near-ground target to obtain the delay of the launch system, which effectively reduces the error source of obtaining one-way delay by measuring different cable lengths and ensures the accuracy of subsequent measurements.

[0057] This patent adds a reflector to the receiving system and uses an "ultra-close target" to effectively integrate the time difference between the transmitting system and the receiving system, solving the problem of only being able to obtain the time delay of a single telescope system in the prior art, and providing important data support for the overall performance.

[0058] This patent proposes the concept of "space target" and uses a geodynamic satellite with good echo characteristics, high orbit and stability (considered to have a known distance) as a target satellite. It fully considers various error sources such as ground equipment, space environment, target characteristics, etc. in the laser ranging process, ensuring the consistency of the system delay measurement and the space target measurement process, effectively reducing the errors caused by environmental changes in the existing technology, and improving the measurement accuracy and stability of the system delay.

[0059] This patent uses a high-orbit geodynamic satellite as a "space target" to ensure the stability of the echo signal intensity (single photon) of the system's time delay measurement and avoid the detection error caused by multi-photon echoes from near-Earth targets.

[0060] This patent uses a geodynamic satellite with a stable orbit as a dynamic "space target" and realizes accurate calibration of the time delay of the laser ranging system under various measurement environments by performing measurements at different times, different azimuths, and different altitude angles.

[0061] This patent can conveniently and quickly calibrate the system delay through standardized operating procedures, reducing the difficulty of operation.

[0062] This patent automatically realizes system delay measurement by formulating reasonable observation strategies, reducing human intervention and ensuring the accuracy and stability of measurement results.

[0063] This patent conducts statistical analysis on the collected observation data, and can obtain high-precision system delay values ​​by comprehensively analyzing the measurement results of three targets through weighted averaging method and least squares method. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0065] Figure 1 This is a schematic diagram of laser ranging of space targets using multiple receiving telescopes;

[0066] Figure 2 For laser ranging system composition and delay distribution;

[0067] Figure 3 This is a schematic diagram of near-earth target correction;

[0068] Figure 4 This is the principle diagram of the one-way laser ranging delay calibration effect;

[0069] Figure 5This is the structure diagram of the real-time control of laser ranging;

[0070] Figure 6 It is a schematic diagram of the structure of the laser ranging system with separate transmitter and receiver;

[0071] Figure 7 The flowchart of the method for time delay calibration is as follows;

[0072] Figure 8 This is the structure diagram of the near-earth target;

[0073] Fig. 9 It is a schematic diagram of the reference points and position vectors of the two telescopes;

[0074] Fig.10 This is a schematic diagram of the near-Earth target for the launch telescope;

[0075] Fig.11 This is a delay diagram of the ultra-near-earth target measurement system;

[0076] Fig.12 This is the optical path structure diagram of each subsystem of the transceiver split system ((a) 53cm binocular laser ranging receiving / emitting path, 1.2m telescope receiving light path).

[0077] Description of Figure Numbers:

[0078] 1. Measurement and positioning module; 2. Transmission one-way delay benchmark module; 3. Two-way delay ground benchmark module; 4. Two-way delay space benchmark module; 5. System synthesis benchmark module.

[0079] 17-laser, 18-light pulse beam expansion system, 19-main wave sampling circuit, 20-time interval counter, 21-receiving telescope, 22-transmitting telescope, 23-photoelectric detector, 24-clock, M1~M9-folded axis optical path group, M10, M11-optical retroreflection device. DETAILED DESCRIPTION

[0080] The present invention proposes a laser ranging system with separate transmitters and receivers and a method for time delay calibration, aiming to design a laser ranging system with separate transmitters and receivers and a method for time delay calibration, which can solve the problem that the prior art can only obtain the time delay of a single telescope.

[0081] The following will describe the laser ranging system with separate transmitter and receiver according to the present invention in a specific embodiment:

[0082] Embodiment 1:

[0083] A laser ranging system with separate transmitter and receiver, such as Figure 6 As shown, including:

[0084] Measurement and positioning module 1: Determine the position of the telescope reference point and select the transmitting telescope as the reference point in the transmitting and receiving laser ranging system for system delay calibration;

[0085] Launch one-way delay benchmark module 2: Combined with the "near-earth target", the launch telescope system delay is measured;

[0086] Two-way time delay ground benchmark module 3: The laser is transmitted to the ground "measurement target" through the transmitting system, and then the echo signal is received by the receiving system to obtain the total delay between the transmitting telescope and the receiving telescope;

[0087] Two-way time delay spatial calibration module 4: The laser is transmitted to the geodynamic satellite through the transmitting system, and then the transmitting system and the receiving system are used to simultaneously receive the echo signal to realize the echo observation of the "target satellite", obtain the total time delay of the transmitting and receiving laser ranging system, and maintain the station coordinates;

[0088] System synthesis benchmark module 5: synthesizes the acquired system delay values ​​to obtain the delay data of the transmit-receive split laser ranging system.

[0089] The laser ranging system with separate transmitters and receivers uses telescopes placed on different bases (domes) to obtain laser ranging results. Although each telescope uses the same time reference, the electrical parameters and optical paths are not completely consistent. In order to accurately benchmark the delay of the above-mentioned separate transmitter and receiver system, this design constructs a separate transmitter and receiver laser ranging delay benchmarking system by introducing measurement and positioning module 1, transmission one-way delay benchmarking module 2, two-way delay ground benchmarking module 3, two-way delay space benchmarking module 4 and system synthesis benchmarking module 5.

[0090] The transmitting and receiving laser ranging system proposed in this patent takes the transmitting and receiving laser ranging system of Changchun Station as an example. Among them, the first telescope includes a first transmitting telescope and a first receiving telescope, the first telescope is a 60cm SLR system; the second receiving telescope is a 1m laser communication telescope, which are respectively placed in different domes. Fig. 9The following are pictures of different telescopes. The transmitting telescope of the 60cm SLR system receives 0.251m2; the receiving aperture is 60cm; the energy of a single laser pulse is about 1mJ; the transmitting frequency is 1KHz; the laser wavelength is 532nm; the efficiency of the laser transmitting system is 0.6; the laser energy pulse width is 50ps; the divergence angle of the transmitting beam is 11 arc seconds; the receiving efficiency is 0.5; the quantum efficiency of the receiving photoelectric device is 0.2; the receiving field angle is 40 arc seconds; the range gate width is 100ns; the attenuation efficiency is -13dB; the tracking error is 7 arc seconds (1σ); the ratio of the filter transmission band to the response band of the receiving optical system is 1 / 500. The effective aperture of the primary mirror of the receiving telescope of the 1-meter laser communication telescope is 1000±10mm; the secondary mirror aperture is 250mm; the system focal length is 8400mm; the pointing accuracy after the star model correction is ≤5″; the tracking accuracy is ≤5″. The 1-meter laser communication telescope is also equipped with a large-field-of-view guide system. The effective aperture of the guide mirror is 300mm; the field of view is 1°×1°; the main spectrum wavelength is 656.3nm; the achromatic band range is 450–900nm; it can detect stars of magnitude 11; and the angular resolution is 3″RMS.

[0091] In the system experimental benchmark design scheme of this embodiment, each module will be implemented by the following equipment, specifically:

[0092] The measurement and positioning module 1 will be realized by the total station. The specific parameters are: the measuring range can reach 5000m; the accuracy is ±(2+2×10-6·D)mm, D is the measuring distance; the measuring time is accurate to 0.3" and the tracking time is 0.1" seconds.

[0093] The launch one-way delay benchmark module 2 will use a near-ground target to obtain the launch system delay. The near-ground target is placed inside the dome at 3.69m from the telescope. The corner reflector (corner cone) is a right-angle prism, equivalent to one corner of a regular hexahedron, with the bottom surface as the incident surface and the other three surfaces as the reflecting surface. Such a prism has the performance of reflecting the incident light back in the original direction.

[0094] The ultra-close target selection reflector in the two-way time delay ground benchmark module 3 is installed on the receiving telescope (receiving mirror) truss, the reflector is illuminated by the transmitting mirror, the laser pulse is reflected to the receiving optical path, and the overall time delay of the two telescopes is measured.

[0095] The two-way time-delay space calibration module 4 will select the geosynchronous orbit satellite LAGEOS-1 as the space target, and use the 60cm and 1m telescope systems for simultaneous observation to achieve the two-way time-delay space calibration of the system.

[0096] The system synthesis benchmark module 5 will use the least squares method to process the system delay obtained by each module, and then use the average weighted method to synthesize the overall delay of the transmitting and receiving separate laser ranging system.

[0097] Embodiment 2:

[0098] A time-delay calibration method.

[0099] The transmitting and receiving laser ranging system proposed in this patent takes the transmitting and receiving laser ranging system of Changchun Station as an example. Among them, the first telescope includes a first transmitting telescope and a first receiving telescope, the first telescope is a 60cm SLR system; the second receiving telescope is a 1m laser communication telescope, which are respectively placed in different domes. Fig. 9 The following are pictures of different telescopes. The transmitting telescope of the 60cm SLR system receives 0.251m2; the receiving aperture is 60cm; the energy of a single laser pulse is about 1mJ; the transmitting frequency is 1KHz; the laser wavelength is 532nm; the efficiency of the laser transmitting system is 0.6; the laser energy pulse width is 50ps; the divergence angle of the transmitting beam is 11 arc seconds; the receiving efficiency is 0.5; the quantum efficiency of the receiving photoelectric device is 0.2; the receiving field angle is 40 arc seconds; the range gate width is 100ns; the attenuation efficiency is -13dB; the tracking error is 7 arc seconds (1σ); the ratio of the filter transmission band to the response band of the receiving optical system is 1 / 500. The effective aperture of the primary mirror of the receiving telescope of the 1-meter laser communication telescope is 1000±10mm; the secondary mirror aperture is 250mm; the system focal length is 8400mm; the pointing accuracy after the star model correction is ≤5″; the tracking accuracy is ≤5″. The 1-meter laser communication telescope is also equipped with a large-field-of-view guide system. The effective aperture of the guide mirror is 300mm; the field of view is 1°×1°; the main spectrum wavelength is 656.3nm; the achromatic band range is 450–900nm; it can detect stars of magnitude 11; and the angular resolution is 3″RMS.

[0100] like Figure 7 As shown, the specific steps include:

[0101] The first transmitting telescope (60cm) transmits laser to the second receiving telescope (1m), generates a range gate signal, controls the opening of the single photon detector, and at the same time, the PIN obtains the main wave transmission signal, which is transmitted to the event timer interface by the cable, and the event timer records the transmission time t1;

[0102] The laser signal is reflected by the reflector of the second receiving telescope (1m) (installed on the truss, very close to the ground target) to the first receiving telescope (60cm), and the event timer records the near-ground target echo time t′1; the difference between the two times is the observation time interval Δt from the ground target to the measuring station o =t′1-t1, and make a difference Δt with the distance value c , get the telescope system delay value Δt1;

[0103] The first transmitting telescope (60 cm) transmits laser to the target satellite, generates a range gate signal, controls the opening of the single photon detector, and at the same time, the PIN obtains the main wave transmission signal, which is transmitted to the event timer interface by the cable, and the event timer records the transmission time t2;

[0104] The laser signal is reflected by the target satellite and transmitted to the ground receiving system, and the satellite echo signal is received by the first receiving telescope (60 cm) and the second receiving telescope (1 m); the first receiving telescope (60 cm) records the target satellite echo time t'2, and subtracts it from the distance from the system reference point to the target satellite (considered as a known value) to obtain the first telescope (60 cm) time delay △t'2; the second receiving telescope (1 m) records the target satellite echo time t2'', and subtracts it from the distance from the first transmitting telescope to the target satellite (considered as a known value) to obtain the second telescope (1 m) time delay △t2''. The difference between the two times is the observation time interval from the ground target to the measuring station, and is subtracted from the distance value to obtain the overall time delay value △t2 of the two telescopes.

[0105] Read meteorological measurements to obtain local temperature, humidity, and air pressure parameters;

[0106] The outliers are removed by the least square method, and the system delay is processed and synthesized using the average weighted method to obtain the overall delay of the laser ranging system with separate transmitter and receiver.

[0107] Specifically, the reference points of the two telescopes are accurately determined using a total station. Several points are selected in the horizontal direction to determine the position of the vertical axis. Similarly, the position of the horizontal axis is determined. The intersection of the two axes is the reference point. The reference point of the transmitting telescope is selected as the total station coordinate.

[0108] The ground equipment control machine sends out a command signal to guide the telescope to point to the ground target according to the known position, altitude and distance of the ground target, so that the ranging system is in standby state.

[0109] After the telescope is pointed steadily, the first transmitting telescope is controlled to launch, a gate signal is generated, and the single photon detector (C-SPAD) is turned on. At the same time, the PIN obtains the main wave launch signal, which is transmitted to the event timer interface by the cable to obtain the precise time of laser launch (called the main wave launch time).

[0110] The echo signal returned by the ground target is gathered by the 60cm telescope echo receiving system, and reaches the C-SPAD target surface through the field of view aperture and narrow-band filter. After photoelectric conversion, the echo arrival time is recorded by the event timer. The computer terminal pairs and extracts the dual-channel time recorded by the event timer to obtain the original data obtained by the laser ranging system. The difference between the two times is the observation time interval from the ground target to the measuring station, and the difference is made with the distance value to obtain the 60cm telescope system delay value.

[0111] The existing technology can only obtain the time delay value of a laser ranging system with a single telescope (on the same base). Due to the use of pyramidal or flat mirrors, the light transmission and receiving paths of the ground target are parallel, which cannot meet the requirements of a laser ranging system composed of multiple telescopes with separate transmission and reception. Figure 8 This is the structure diagram of the near-earth target used in most measurement stations.

[0112] In this embodiment, the reference points of different telescopes are obtained by a total station, the reference point of the transmitting telescope (transmitting mirror) is selected as the total reference point of the two telescopes, and the vector between the reference points of the two telescopes is accurately measured. Fig. 9 Schematic diagram of the reference points and position vectors of the two telescopes.

[0113] This design calibrates the delay of the split-transmitter laser ranging system through three links: near-earth target, ultra-near-earth target and space target, and realizes the calibration effect of the multi-telescope system delay. Among them, the 60cm SLR system obtains the delay value of the transmitting telescope in the split-transmitter laser ranging system by measuring the near-earth target, which effectively simplifies the complex synchronization process in the one-way delay measurement and significantly improves the efficiency of data processing.

[0114]

[0115] Among them, Δt1 is the measurement result of the fixed distance ground target, τ1 and τ2 are the emission delay and receiving delay of the transmitting mirror respectively, d0 is the distance between the two reflectors on the ground target, d1 is the distance between the reference point of the transmitting mirror and the fixed ground target, and c is the speed of light. Fig.10 Schematic diagram of the near-Earth target for launching the telescope.

[0116] In the figure, l1 is the optical path delay from the reflective surface of the spectrometer to the photosensitizing surface of the photodiode, l2 is the circuit delay from the output of the photodiode to the input of the constant ratio discriminator, and l3 is the circuit delay from the output of the constant ratio discriminator to the event timer channel; l4 is the optical path delay from the spectrometer to the reference point of the telescope, l5 is the optical path delay from the reference point of the telescope to the photosensitizing surface of the single photon avalanche diode, l6 is the circuit delay from the single photon avalanche diode to the input of the constant ratio discriminator, l7 is the circuit delay from the constant ratio discriminator to the event timer channel, and δ1 to δ4 are the internal delays of the single photon avalanche diode, event timer, photodiode, and constant ratio discriminator, respectively.

[0117] In order to solve the problem that the existing technology can only obtain the time delay of a single telescope, this embodiment uses an ultra-close-to-the-ground target and effectively changes the propagation path of the optical signal by installing a reflector on the receiving telescope (receiving mirror) truss. This "one-transmit-one-receive" measurement method enables signals from different telescopes to be processed on the same base, thereby improving the flexibility of the measurement. The overall time delay of the two telescopes is:

[0118]

[0119] Right now

[0120]

[0121] Where Δt2 is the measured value of the pulse flight time, τ3 is the reception delay of the receiving telescope, and d2 is the distance traveled by the light in the link between the reference points of the two telescopes.

[0122] Fig.11 This is a delay diagram of the ultra-near-earth target measurement system. Conventional ground targets and near-earth targets are static targets, while the laser ranging system is a dynamic process. Based on the motion trajectory of the observed target, the laser ranging system tracks the observed target and obtains the laser echo signal. The optical path delay and electronic delay generated are a variable value. For this reason, this embodiment proposes a "space target" to use the observation of the target satellite to ensure that the system can maintain an operating state that is approximately consistent with that during conventional observation (echo photon number intensity). Among them, the target satellite is selected as a geodynamic satellite with a stable orbit, and its distance from the station can be regarded as a known quantity. In addition, since this design uses a "space target", the observation data of the launch telescope can be used to connect the measuring station to the global SLR network to maintain the station coordinates, further ensuring the accuracy of the system reference point and providing technical support for obtaining high-precision system delays.

[0123] Calibration method:

[0124] Observation model:

[0125] The measurement results of SLR are affected by many factors, and the measurement data needs to be corrected, which can be expressed as:

[0126]

[0127] Where ρ is the measured value; ρ up and ρ down are the distances of the laser uplink and downlink respectively; Δρ tide is the correction caused by tides, including solid tide, sea tide and polar tide. The influence of atmospheric tide is small and is not considered in this paper; Δρ trois the tropospheric atmospheric refraction delay correction; Δρ rel is the relativistic time delay correction; Δρ com is the satellite's center of mass correction; ∈ is the station's systematic error. Table 1 shows the models and references used in the above corrections. If in the inertial system, let t be the pulse emission time, then ρ up and ρ down It can be expressed as:

[0128]

[0129] In the formula, and are the coordinates of the station and satellite in the geocentric celestial coordinate system; τ up and τ down are the flight times of the uplink and downlink laser pulses, respectively. They can be interpolated using the 9th-order Lagrange polynomial in the precise ephemeris at the epoch of laser emission as the initial value of the satellite coordinates, and the light travel time can be solved by iteration. The convergence condition is τ up,k+1 -τ up,k <3ps.

[0130]

[0131] Next, the result obtained after iteration is used as the theoretical value and the ranging residual is calculated, which can be expressed as:

[0132]

[0133] Δρ i = ρ c,i - cτ tof,i - Δρ tide - Δρ tro - Δρ rel - Δρ com (4)

[0134] Where i is the index of the observed data in a certain circle; ρ c,i is the theoretical value of the distance between the satellite and the station; Δρ i Represents the ranging residual; τ tof,i Represents the laser pulse flight time. By performing the least squares fitting on the ranging residual of a full circle, the time deviation and distance deviation can be obtained.

[0135]

[0136] Shadow, τ b is the time deviation of this lap, r b It is the distance deviation of this circle.

[0137] Table 1. SLR observation model and reference:

[0138]

[0139]

[0140] The LAGEOS1 satellite is one of the ILRS geodetic satellites with the largest number of observations and the best accuracy [10,11]. Therefore, this paper uses LAGEOS1 as a space target, and according to the SLR observation model, regards the precise ephemeris as an accurate result, calibrates the system delay of the Changchun 60cm laser ranging telescope, and calculates the LAGEOS1 distance deviation into the system delay, which helps to reduce the system errors of other satellites.

[0141] System delay calibration method:

[0142] The LAGEOS1 measurement data τ′ without ground target calibration correction tof Substituting into equation (4) and equation (5), we can get the fitted straight line:

[0143]

[0144] In the formula, Δρ′ i (t) is the two-way residual after fitting, including the receiving delay and the transmitting delay, r' b is the distance deviation including half of the system delay. The average of all fitted residuals in one lap is taken to obtain the system delay τ d :

[0145]

[0146] In the formula, τ d represents the SLR system delay obtained by observing the space target, and n is the number of data points.

[0147] Embodiment 3:

[0148] A time-delay calibration method.

[0149] Take the example of the space debris laser ranging system composed of the 1.56m aperture astronomical telescope and the 60cm aperture laser ranging telescope of the Shanghai Astronomical Observatory, which are 55m apart. The 60cm aperture laser ranging telescope is the transmitting telescope, which receives the echo signal while transmitting the laser signal. The receiving telescope with a 1.56m aperture is the receiving telescope, which is responsible for receiving the echo signal. The specific parameters are as follows:

[0150] Table 1.1.56m telescope system vs. 60cm telescope system:

[0151]

[0152]

[0153] Different from Example 2, in this example, Link 2 (ultra-near-earth target) will no longer use a reflector mounted on the truss of the receiving telescope, but will use optical fiber to change the propagation path of the optical signal, effectively forwarding the laser signal from the transmitting optical path to the receiving optical path, thereby obtaining the overall system delay.

[0154] Embodiment 4:

[0155] A time-delay calibration method.

[0156] Take the Yunnan Observatory's 1.2m aperture 10Hz common optical path laser ranging system and the 53cm binoculars 1kHz SLR astronomical telescope as an example. The two are 55m apart. Among them, the 50cm aperture SLR telescope is the transmitting telescope, which receives the echo signal while emitting the laser signal. The receiving aperture 1.2m telescope is the receiving telescope, which is responsible for receiving the echo signal. Fig.12 Diagram of the optical path of the telescope.

[0157] Different from the second embodiment, in this example, the link 3 (target satellite) will select the geosynchronous satellite LAGEOS-2, and LAGEOS-2 will be used to obtain the overall system delay.

[0158] The ultra-near-earth target used in the present invention may be a corner cone, a rotating mirror, an optical fiber, etc., and the structure of the near-earth target is not unique.

[0159] The target satellite used in the present invention may be LAGEOS-1, LAGEOS-2, etc., and the geosynchronous orbit satellite is not unique.

[0160] The data processing method adopted by the present invention can adopt the average weight method and the least square method, and the data processing method is not unique.

[0161] The observation strategy of the present invention can adopt manual identification and automatic processing, and the system delay task selection method is not unique.

[0162] The optical telescope system in the laser ranging system with separate transmitter and receiver used in the present invention can be a separate transmitter and receiver system or a coaxial transmitter and receiver system, and the selection of the telescope system is not unique.

[0163] The laser ranging system with separate transmitter and receiver to which the present invention is applicable may be a satellite laser ranging system, a space debris laser ranging system, and a lunar laser ranging system, and the system functions are not unique.

[0164] The laser ranging system with separate transmitter and receiver used in the present invention can be a dual-telescope laser ranging system or a triple-telescope laser ranging system, and the telescopes are arranged uniquely.

[0165] The optical telescope system in the laser ranging system with separate transmitters and receivers to which the present invention is applicable can be a separate transmitter-receiver system or a coaxial transmitter-receiver system, and the selection of the telescope system is not unique.

[0166] The laser source in the transmitting and receiving split laser ranging system applicable to the present invention can be selected from 532nm, 1064nm,

[0167] 1550nm, etc. The applicable wavelength is not unique.

[0168] The laser repetition rate used in the laser distance measurement system with separate transmission and reception for the present invention is 1KHz.

[0169] 2KHz, 100KHz, etc. The laser repetition rate is not unique.

[0170] The aperture of the optical telescope system in the transmitting-receiving split laser ranging system applicable to the present invention can be 60 cm, 120 cm, or 250 cm, and the telescope aperture is not unique.

[0171] The receiving detector in the transmitting-receiving split laser ranging system applicable to the present invention can be APD, PMT, SNSPD, etc., and the detector selection is not unique.

[0172] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A laser ranging system with separate transmitter and receiver, characterized in that: include: Measurement and positioning module: Determine the position of the telescope reference point and select the transmitting telescope as the reference point in the transmitting and receiving laser ranging system for system delay calibration; Launch one-way delay benchmark module: Combined with the near-earth target, the launch telescope system delay is measured; Two-way time delay ground benchmark module: The laser is transmitted to the ground measurement target through the transmitting system, and then the echo signal is received by the receiving system to obtain the total delay between the transmitting telescope and the receiving telescope; Two-way time-delay space calibration module: The laser is transmitted to the space target through the transmitting system, and then the transmitting system and the receiving system are used to simultaneously receive the echo signal to realize the target satellite echo observation, obtain the total time delay of the transmitting and receiving laser ranging system, and maintain the station coordinates; System synthesis benchmark module: synthesizes the acquired system delay values ​​to obtain the delay data of the transmit-receive split laser ranging system.

2. A method for delay calibration, characterized in that: The following steps are involved: The first transmitting telescope transmits laser light to the second receiving telescope, and the event timer records the transmitting time t1; The laser signal is reflected by the reflector of the second receiving telescope to the first receiving telescope, and the event timer records the near-ground target echo time t′1; the difference between the two times is the observation time interval Δt from the ground target to the measuring station o =t′1-t1, and make a difference Δt with the distance value c , get the telescope system delay value Δt1; The first launch telescope launches laser light to the target satellite, and the event timer records the launch time t2; The laser signal is reflected by the target satellite and transmitted to the ground receiving system, and the satellite echo signal is received by the first receiving telescope and the second receiving telescope. The first receiving telescope records the target satellite echo time t'2, and subtracts it from the distance from the system reference point to the target satellite to obtain the first telescope delay △t'2; the second receiving telescope records the target satellite echo time t''2, and subtracts it from the distance from the first transmitting telescope to the target satellite to obtain the second telescope delay △t''2, and then obtains the overall time delay value △t2 of the two telescopes.

3. The method for delay calibration according to claim 2, characterized in that: The following steps are also included: Read meteorological measurements to obtain local temperature, humidity, and air pressure parameters; The outliers are removed by the least square method, and the system delay is processed and synthesized using the average weighted method to obtain the overall delay of the laser ranging system with separate transmitter and receiver.

4. The method for delay calibration according to claim 2, characterized in that: The step of the first transmitting telescope transmitting laser to the second receiving telescope and the event timer recording the transmitting time t1 comprises: The first transmitting telescope emits laser, generates a range gate signal, controls the opening of the single photon detector, and at the same time, the PIN obtains the main wave emission signal, which is transmitted to the event timer interface by the cable to obtain the precise time t1 of the laser emission.

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