CN118011769A - High-precision time keeping method and system for spaceborne laser radar - Google Patents
High-precision time keeping method and system for spaceborne laser radar Download PDFInfo
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Abstract
The invention provides a high-precision time keeping method and a system for a satellite-borne laser radar, comprising the following steps of S1: setting a register in the laser radar; the register stores a count; step S2: calibrating the laser radar according to the receiving state of the laser radar to finish the self-timekeeping of the laser radar with preset precision; the reception states include reception of a second pulse provided by the satellite platform, reception of a second pulse but reception of a BC broadcast time, and reception of a BC broadcast time. According to the invention, radar time keeping methods are respectively formulated aiming at three conditions of the laser radar, so that the satellite-borne laser radar can still keep high-precision time keeping and safe light emitting on time when a satellite time system is abnormal (such as abnormal pulse per second interval, abnormal broadcasting time and the like), the imaging time of radar echo signals is accurately recorded in remote sensing data, and a foundation is laid for high-precision inversion of laser radar data.
Description
Technical Field
The invention relates to the technical field of satellite population, in particular to a high-precision time keeping method and system for a satellite-borne laser radar.
Background
The traditional satellite passive optical remote sensing technology has serious dependence on solar scattered light, can only perform imaging measurement in an illumination area, but the satellite active detection technology represented by a satellite-borne laser radar is not influenced by illumination, can perform measurement all day time, is not influenced by cloud and aerosol shielding, has obvious advantages, and is widely applied to the field of satellite remote sensing.
The space-borne laser radar actively detects through periodically sending laser pulses, high-precision inversion provides higher requirements on the time precision of the radar, and because the laser energy is strong, if the light-emitting frequency is too high due to poor time keeping scheme, the laser is likely to be damaged, and the safety of the laser radar is affected.
In the Chinese patent document with publication number CN107092183A, a high-precision timing implementation method based on GPS second pulse is disclosed, which comprises the following steps: step one: performing validity check on the received GPS time code by satellite-borne computer software; if the validity detection is passed, the step two is entered; if the validity detection is not passed, entering a step four; step two: the satellite-borne computer software judges whether the received GPS time code is the last period value or not; if the received GPS time code is not the last period value, entering a step III; if the received GPS time code is the last period value, the GPS time code is +1, and then the step three is entered. However, this patent document mainly solves the problem of how to calibrate the satellite count pipe at the time of missing seconds, and does not address the problem of time keeping of the load of simultaneously receiving the second pulse and the digital broadcast.
In chinese patent document CN105890591B, a method for calculating the exposure time of a high-precision star sensor by using a pulse-per-second signal is disclosed, the time t_ AOCC of the pulse-per-second signal sent by a star-borne computer and the number sync_ AOCC of the sent pulse-per-second signal are recorded, the number syncCnt of the pulse-per-second signal corresponding to the four elements and the four elements are read from the star-sensor, the time interval datation of the pulse-per-second signal closest to the star-sensor, the validity of the pulse difference flag Δsync_flag is determined according to the time interval datation, the pulse number difference Δsync is calculated, and the star-borne computer time t_st corresponding to the exposure time of the star-sensor is calculated according to the time t_ AOCC of the pulse-per-second signal, the time interval datation of the pulse-per-second signal and the pulse number difference Δsync. However, the problem of determining satellite attitude by correcting satellite sensitivity with high accuracy using pulse-per-second is essentially different from the problem solved by the present invention.
In the chinese patent document with publication number CN116073935A, a clock synchronization system and method based on IEEE1588 protocol are disclosed, comprising: the time stamp determining module is used for receiving an externally input second pulse signal and determining a time stamp corresponding to the second pulse signal under a local clock time scale; the difference value calculation module is connected with the timestamp determination module and is used for calculating a time difference value containing frequency difference information according to the timestamp; the adjusting module is connected with the difference calculating module and is used for processing the time difference under the action of the local clock and outputting an adjusting value when the maximum frequency of the local clock meets a preset frequency difference threshold value; the step value determining module is connected with the adjusting module and is used for processing a pre-step value according to the adjusting value to obtain a frequency difference ratio step value and adjusting the step value of the time counter corresponding to the local clock according to the frequency difference ratio step value so as to synchronize the frequencies of the local clock and the master clock. The present invention is essentially different from the technology adopted in the patent document in that a time keeping scheme is customized for the on-board lidar in order to cope with the problem that the time interval disagreement caused by various anomalies possibly exists in navigation and digital broadcasting.
In the Chinese patent document with publication number CN115175297A, a satellite load second pulse autonomous recovery synchronization method is disclosed, which specifically comprises the following steps: step S1, second pulse synchronization and initialization reference difference calculation; s2, abnormality judgment and second pulse correction difference measurement; and S3, autonomous compensation and recovery of the second pulse. However, this patent document requires a load to provide a return pulse signal, is complicated to implement, and does not make a time keeping scheme for a state where only a few pipes are broadcast.
In China patent document with publication number CN115047748B, a time service device and method based on satellite navigation signals is disclosed, the device comprises a local reference source, a signal receiving and source difference measuring module, a controllable frequency dividing module, a parameter generating module and a controllable delay module, the signal receiving and source difference measuring module receives satellite navigation signals, and source difference measurement is carried out on the local reference signals to obtain source difference values of the local reference signals; the local reference signal is also input to the controllable frequency dividing module to generate a main clock, the parameter generating module generates an output frequency adjustment value by utilizing the source difference value of the local reference signal, the main clock is divided to generate a second pulse signal, and the second pulse signal is input to the controllable time delay module to obtain controllable second pulse output calibrated relative to satellite time. However, the patent document outputs the second pulse after receiving the navigation second pulse, and is not suitable for the satellite-borne laser radar because the laser radar directly synchronizes the navigation second pulse with potential safety hazards.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a high-precision time keeping method and system for a satellite-borne laser radar.
The invention provides a high-precision time keeping method of a satellite-borne laser radar, which comprises the following steps:
Step S1: setting a register in the laser radar; the register stores a count;
Step S2: calibrating the laser radar according to the receiving state of the laser radar to finish the self-timekeeping of the laser radar with preset precision; the reception states include reception of a second pulse provided by the satellite platform, reception of a second pulse but reception of a BC broadcast time, and reception of a BC broadcast time.
Preferably, the step S1 includes setting a first register and a second register; the first register stores a whole second count i; the second register holds a 0.1ms count j in seconds.
Preferably, the step S2 includes the following substeps:
Step S2.1: when the laser radar is in a second pulse state provided by a receiving satellite platform, calibrating i and j by using second pulses subjected to validity judgment, achieving self-timekeeping of preset precision, transmitting laser pulses, and marking a time stamp i+j in each laser pulse echo signal remote sensing packet;
Step S2.2: when the laser radar is in a state that the laser radar cannot receive the second pulse but receives the BC broadcasting time, calibrating i and j by using the broadcasting time subjected to validity judgment, achieving the self-timekeeping of preset precision and transmitting laser pulses, and marking a time stamp i+j in each laser pulse echo signal remote sensing packet;
Step S2.3: when the laser radar is in a state of being incapable of receiving BC broadcasting time, the laser radar is time-kept according to self-maintained time and transmits laser pulses, and a time stamp i+j is marked in each laser pulse echo signal remote sensing packet.
Preferably, the step S2.1 comprises the following sub-steps:
Step S2.1.1: starting the laser radar, and starting counting for 0.1ms by j;
Step S2.1.2: when the first second pulse is received, assigning the whole second moment of the second pulse to i, and resetting j;
step S2.1.3: when the subsequent second pulse is received, judging the value of j:
if j is less than 9000, not performing timing operation;
If 9000 is less than or equal to j is less than or equal to 11000, assigning the whole second moment of the second pulse to i, and resetting j;
if j is greater than 11000, performing +1 operation on i, and assigning j-10000 to j;
step S2.1.4: if j >11000 occurs in the continuous 5s, it is determined that the pulse per second reception is abnormal, and the time for self-maintenance is calibrated using the BC broadcast data.
Preferably, the step S2.2 comprises the following sub-steps:
step S2.2.1: starting the laser radar, and starting counting for 0.1ms by j, and not performing light emitting operation;
Step S2.2.2: when receiving the first time broadcasting interrupt, assigning the whole second moment to i, and resetting j;
Step S2.2.3: when receiving the broadcast interrupt in the subsequent time, judging the value of j:
If j is less than 8000, not performing timing operation;
if 8000 is less than or equal to j is less than or equal to 12000, assigning the whole second moment of the second pulse to i, and resetting j;
If j >12000, then +1 operation is carried out on i, and j-10000 is assigned to j.
Preferably, the laser radar does not have a time reference before receiving navigation second pulse timing or BC broadcasting time, only does self-watch, and does not perform light emitting operation.
Preferably, the laser radar performs light emitting operation when i+j reaches a corresponding time point according to pulse frequency after receiving navigation second pulse timing or BC broadcasting time, and transmits the i+j time to a data processor, and records the time corresponding to the laser pulse for data inversion.
Preferably, the light emitting time of the laser radar is recorded in real time, and if the time difference between the current calculated light emitting time and the last light emitting time is smaller than a certain threshold value affecting the safety of the laser, no light is emitted at the current time.
Preferably, when the satellite time system fails, the laser radar still keeps the time keeping and running of the preset precision, and the imaging time of the radar echo signal is recorded in the remote sensing data; the fault includes the pulse-per-second interval not reaching a preset value and the broadcast time not reaching a preset value.
The invention provides a high-precision time keeping system of a satellite-borne laser radar, which comprises the following components:
module M1: setting a register in the laser radar; the register stores a count;
Module M2: calibrating the laser radar according to the receiving state of the laser radar to finish the self-timekeeping of the laser radar with preset precision; the reception states include reception of a second pulse provided by the satellite platform, reception of a second pulse but reception of a BC broadcast time, and reception of a BC broadcast time.
Preferably, the module M1 includes a first register and a second register; the first register stores a whole second count i; the second register holds a 0.1ms count j in seconds.
Preferably, the module M2 comprises the following sub-modules:
module M2.1: when the laser radar is in a second pulse state provided by a receiving satellite platform, calibrating i and j by using second pulses subjected to validity judgment, achieving self-timekeeping of preset precision, transmitting laser pulses, and marking a time stamp i+j in each laser pulse echo signal remote sensing packet;
Module M2.2: when the laser radar is in a state that the laser radar cannot receive the second pulse but receives the BC broadcasting time, calibrating i and j by using the broadcasting time subjected to validity judgment, achieving the self-timekeeping of preset precision and transmitting laser pulses, and marking a time stamp i+j in each laser pulse echo signal remote sensing packet;
Module M2.3: when the laser radar is in a state of being incapable of receiving BC broadcasting time, the laser radar is time-kept according to self-maintained time and transmits laser pulses, and a time stamp i+j is marked in each laser pulse echo signal remote sensing packet.
Preferably, the module M2.1 comprises the following sub-modules:
Module M2.1.1: starting the laser radar, and starting counting for 0.1ms by j;
module M2.1.2: when the first second pulse is received, assigning the whole second moment of the second pulse to i, and resetting j;
module M2.1.3: when the subsequent second pulse is received, judging the value of j:
if j is less than 9000, not performing timing operation;
If 9000 is less than or equal to j is less than or equal to 11000, assigning the whole second moment of the second pulse to i, and resetting j;
if j is greater than 11000, performing +1 operation on i, and assigning j-10000 to j;
Module M2.1.4: if j >11000 occurs in the continuous 5s, it is determined that the pulse per second reception is abnormal, and the time for self-maintenance is calibrated using the BC broadcast data.
Preferably, the module M2.2 comprises the following sub-modules:
module M2.2.1: starting the laser radar, and starting counting for 0.1ms by j, and not performing light emitting operation;
module M2.2.2: when receiving the first time broadcasting interrupt, assigning the whole second moment to i, and resetting j;
module M2.2.3: when receiving the broadcast interrupt in the subsequent time, judging the value of j:
If j is less than 8000, not performing timing operation;
if 8000 is less than or equal to j is less than or equal to 12000, assigning the whole second moment of the second pulse to i, and resetting j;
If j >12000, then +1 operation is carried out on i, and j-10000 is assigned to j.
Preferably, the laser radar does not have a time reference before receiving navigation second pulse timing or BC broadcasting time, only does self-watch, and does not perform light emitting operation.
Preferably, the laser radar performs light emitting operation when i+j reaches a corresponding time point according to pulse frequency after receiving navigation second pulse timing or BC broadcasting time, and transmits the i+j time to a data processor, and records the time corresponding to the laser pulse for data inversion.
Preferably, the light emitting time of the laser radar is recorded in real time, and if the time difference between the current calculated light emitting time and the last light emitting time is smaller than a certain threshold value affecting the safety of the laser, no light is emitted at the current time.
Preferably, when the satellite time system fails, the laser radar still keeps the time keeping and running of the preset precision, and the imaging time of the radar echo signal is recorded in the remote sensing data; the fault includes the pulse-per-second interval not reaching a preset value and the broadcast time not reaching a preset value.
Compared with the prior art, the invention has the following beneficial effects:
1. the radar time keeping method is respectively formulated aiming at three conditions that the laser radar can normally receive high-precision second pulses provided by a satellite platform, the second pulses are abnormal in reception, but can normally receive BC broadcasting time and can not normally receive BC broadcasting time, so that the satellite-borne laser radar can still keep high-precision time keeping, time keeping and safe light emitting when a satellite time system is abnormal (such as abnormal second pulse interval and abnormal broadcasting time) and accurately record radar echo signal imaging time in remote sensing data, and a foundation is laid for high-precision inversion of laser radar data.
2. The method is simple to realize, can be widely applied to the fields of laser radar data on-orbit safe work, remote sensing data high-precision inversion and the like, and has good practicability.
Other advantages of the present invention will be set forth in the description of specific technical features and solutions, by which those skilled in the art should understand the advantages that the technical features and solutions bring.
Drawings
Other features, objects and advantages of the present invention will become more apparent upon reading of the detailed description of non-limiting embodiments, given with reference to the accompanying drawings in which:
FIG. 1 is a flow chart of the method of the present invention.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the present invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications could be made by those skilled in the art without departing from the inventive concept. These are all within the scope of the present invention.
Referring to fig. 1, for three time system states (high-precision pulse per second, abnormal pulse per second reception provided by a satellite platform can be normally received, but BC broadcasting time can be normally received, BC broadcasting time can not be normally received) possibly encountered by a satellite-borne laser radar in orbit, the radar time keeping method is respectively formulated, and the satellite-borne laser radar is ensured to still keep high-precision time keeping and normal operation when the satellite time system is abnormal (such as abnormal pulse per second interval, abnormal broadcasting time and the like).
The method comprises the following specific steps:
The lidar is provided with two registers, register a for holding the whole second count i and register B for holding the 0.1ms count j in seconds.
When navigation high-precision second pulse can be normally received, the second pulse subjected to validity judgment is used for calibrating i and j, high-precision self-timekeeping and laser pulse emission are realized, and a time stamp i+j is printed in each laser pulse echo signal remote sensing packet:
Starting the laser radar, and starting counting for 0.1ms by j; when the first second pulse is received, assigning the whole second moment of the second pulse to i, and resetting j;
when the subsequent second pulse is received, judging the value of j:
if j is less than 9000, not performing timing operation;
If 9000 is less than or equal to j is less than or equal to 11000, assigning the whole second moment of the second pulse to i, and resetting j;
if j is greater than 11000, performing +1 operation on i, and assigning j-10000 to j;
if j >11000 occurs in 5 seconds, the pulse per second reception is considered abnormal, and the time maintained by the device is calibrated by using the BC broadcast data.
When navigation high-precision second pulse cannot be normally received, BC broadcast time is received, i and j are calibrated by using the broadcast time subjected to validity judgment, high-precision self-timekeeping and laser pulse emission are realized, and a time stamp i+j is printed in each laser pulse echo signal remote sensing packet:
Starting the laser radar, starting counting for 0.1ms by j, and not performing light emitting operation; when receiving the first time broadcasting interrupt, assigning the whole second moment to i, and resetting j;
When receiving the broadcast interrupt in the subsequent time, judging the value of j:
If j is less than 8000, not performing timing operation;
if 8000 is less than or equal to j is less than or equal to 12000, assigning the whole second moment of the second pulse to i, and resetting j;
If j >12000, then +1 operation is carried out on i, and j-10000 is assigned to j.
When BC broadcasting time cannot be normally received, time keeping and laser pulse emission are carried out according to self-maintained time, and a time stamp i+j is marked in each laser pulse echo signal remote sensing packet.
In the steps, before the navigation second pulse timing or BC broadcasting time is received, the laser radar does not have a time reference, only performs self-time keeping, and does not perform light emitting operation; after receiving navigation second pulse timing or BC broadcasting time, the laser radar performs light emitting operation when i+j reaches a corresponding moment according to pulse frequency, and transmits the moment i+j to the data processor, and records the moment corresponding to the laser pulse for use in data inversion.
The whole process needs to record the last light emitting time of the laser radar, and if the time difference between the current calculated light emitting time and the last light emitting time is smaller than a certain threshold value affecting the safety of the laser, no light is emitted at the current time.
The radar time keeping method is respectively formulated aiming at three conditions that the laser radar can normally receive high-precision second pulses provided by a satellite platform, the second pulses are abnormal in reception, but can normally receive BC broadcasting time and can not normally receive BC broadcasting time, so that the satellite-borne laser radar can still keep high-precision time keeping, time keeping and safe light emitting when a satellite time system is abnormal (such as abnormal second pulse interval and abnormal broadcasting time) and accurately record radar echo signal imaging time in remote sensing data, and a foundation is laid for high-precision inversion of laser radar data.
The foregoing is a basic embodiment of the present invention, and a further description of the technical solution of the present invention is provided below by means of a preferred embodiment.
Example 1
For a satellite with navigation second pulse precision of 1 mu s, the laser emission frequency of the laser radar is 20Hz, and if the frequency precision of the radar crystal oscillator is 50ppm, the accumulated maximum deviation of timing within 1 second is not more than 50 mu s. The time keeping method of the invention is used for:
1) When the laser radar can normally receive the second pulse signal, the maximum error between the time of the radar and the GPS time is not more than 51 mu s, and the time error is within 0.1ms due to the fact that the time resolution of the laser radar is 0.1ms, and the time precision is high;
2) When the laser radar can not normally receive the pulse-per-second signal but can normally receive the BC broadcasting time, the time difference between the actual measurement of the satellite and the GPS is within 0.1ms, so that the maximum time error of the time GPS of the laser radar is not more than 150 mu s, and the time error is within 0.2ms due to the time resolution of the laser radar being 0.1ms, and the time precision is high;
3) The laser radar emits light when the 0.1ms count reaches the integral multiple of 50ms, and the light emitting moment is determined by the radar maintenance time and is not synchronous with navigation second pulse, BC broadcasting moment and the like, so that the on-orbit safe work of the laser radar is ensured;
4) Assuming that the usage characteristics of the laser are that the light-emitting interval is required to be greater than 10ms; and if tj-ti is less than 10ms, the light emitting operation is not performed at this time, and light emitting is performed again at tj+50 ms.
The invention also provides a satellite-borne laser radar high-precision time keeping system, which can be realized by executing the flow steps of the satellite-borne laser radar high-precision time keeping method, namely, a person skilled in the art can understand the satellite-borne laser radar high-precision time keeping method as a preferred implementation mode of the satellite-borne laser radar high-precision time keeping system.
Specifically, a high-precision time keeping system of a satellite-borne laser radar comprises:
module M1: setting a register in the laser radar; the register stores a count;
Module M2: calibrating the laser radar according to the receiving state of the laser radar to finish the self-timekeeping of the laser radar with preset precision; the reception states include reception of a second pulse provided by the satellite platform, reception of a second pulse but reception of a BC broadcast time, and reception of a BC broadcast time.
The module M1 comprises a first register and a second register; the first register stores a whole second count i; the second register holds a 0.1ms count j in seconds.
The module M2 comprises the following sub-modules:
module M2.1: when the laser radar is in a second pulse state provided by a receiving satellite platform, calibrating i and j by using second pulses subjected to validity judgment, achieving self-timekeeping of preset precision, transmitting laser pulses, and marking a time stamp i+j in each laser pulse echo signal remote sensing packet;
Module M2.2: when the laser radar is in a state that the laser radar cannot receive the second pulse but receives the BC broadcasting time, calibrating i and j by using the broadcasting time subjected to validity judgment, achieving the self-timekeeping of preset precision and transmitting laser pulses, and marking a time stamp i+j in each laser pulse echo signal remote sensing packet;
Module M2.3: when the laser radar is in a state of being incapable of receiving BC broadcasting time, the laser radar is time-kept according to self-maintained time and transmits laser pulses, and a time stamp i+j is marked in each laser pulse echo signal remote sensing packet.
The module M2.1 comprises the following sub-modules:
Module M2.1.1: starting the laser radar, and starting counting for 0.1ms by j;
module M2.1.2: when the first second pulse is received, assigning the whole second moment of the second pulse to i, and resetting j;
module M2.1.3: when the subsequent second pulse is received, judging the value of j:
if j is less than 9000, not performing timing operation;
If 9000 is less than or equal to j is less than or equal to 11000, assigning the whole second moment of the second pulse to i, and resetting j;
if j is greater than 11000, performing +1 operation on i, and assigning j-10000 to j;
Module M2.1.4: if j >11000 occurs in the continuous 5s, it is determined that the pulse per second reception is abnormal, and the time for self-maintenance is calibrated using the BC broadcast data.
The module M2.2 comprises the following sub-modules:
module M2.2.1: starting the laser radar, and starting counting for 0.1ms by j, and not performing light emitting operation;
module M2.2.2: when receiving the first time broadcasting interrupt, assigning the whole second moment to i, and resetting j;
module M2.2.3: when receiving the broadcast interrupt in the subsequent time, judging the value of j:
If j is less than 8000, not performing timing operation;
if 8000 is less than or equal to j is less than or equal to 12000, assigning the whole second moment of the second pulse to i, and resetting j;
If j >12000, then +1 operation is carried out on i, and j-10000 is assigned to j.
The laser radar has no time reference before receiving navigation second pulse timing or BC broadcasting time, only performs self-time keeping, and does not perform light emitting operation.
And the laser radar performs light emitting operation when the i+j reaches the corresponding moment according to the pulse frequency after receiving navigation second pulse timing or BC broadcasting time, transmits the i+j moment to a data processor, and records the moment corresponding to the laser pulse for data inversion.
And the light emitting time of the laser radar is recorded in real time, and if the time difference between the current calculated light emitting time and the last light emitting time is smaller than a certain threshold value affecting the safety of the laser, no light is emitted at the current time.
When the satellite time system fails, the laser radar still keeps the time keeping and running of the preset precision, and the imaging time of the radar echo signal is recorded in the remote sensing data; the fault includes the pulse-per-second interval not reaching a preset value and the broadcast time not reaching a preset value.
Those skilled in the art will appreciate that the invention provides a system and its individual devices, modules, units, etc. that can be implemented entirely by logic programming of method steps, in addition to being implemented as pure computer readable program code, in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers, embedded microcontrollers, etc. Therefore, the system and various devices, modules and units thereof provided by the invention can be regarded as a hardware component, and the devices, modules and units for realizing various functions included in the system can also be regarded as structures in the hardware component; means, modules, and units for implementing the various functions may also be considered as either software modules for implementing the methods or structures within hardware components.
The foregoing describes specific embodiments of the present application. It is to be understood that the application is not limited to the particular embodiments described above, and that various changes or modifications may be made by those skilled in the art within the scope of the appended claims without affecting the spirit of the application. The embodiments of the application and the features of the embodiments may be combined with each other arbitrarily without conflict.
Claims (10)
1. The high-precision time keeping method for the satellite-borne laser radar is characterized by comprising the following steps of:
Step S1: setting a register in the laser radar; the register stores a count;
Step S2: calibrating the laser radar according to the receiving state of the laser radar to finish the self-timekeeping of the laser radar with preset precision; the reception states include reception of a second pulse provided by the satellite platform, reception of a second pulse but reception of a BC broadcast time, and reception of a BC broadcast time.
2. The method for high precision time keeping of a satellite-borne lidar according to claim 1, wherein the step S1 comprises setting a first register and a second register; the first register stores a whole second count i; the second register holds a 0.1ms count j in seconds.
3. The method for high precision time keeping of a satellite-borne lidar according to claim 2, wherein the step S2 comprises the following sub-steps:
Step S2.1: when the laser radar is in a second pulse state provided by a receiving satellite platform, calibrating i and j by using second pulses subjected to validity judgment, achieving self-timekeeping of preset precision, transmitting laser pulses, and marking a time stamp i+j in each laser pulse echo signal remote sensing packet;
Step S2.2: when the laser radar is in a state that the laser radar cannot receive the second pulse but receives the BC broadcasting time, calibrating i and j by using the broadcasting time subjected to validity judgment, achieving the self-timekeeping of preset precision and transmitting laser pulses, and marking a time stamp i+j in each laser pulse echo signal remote sensing packet;
Step S2.3: when the laser radar is in a state of being incapable of receiving BC broadcasting time, the laser radar is time-kept according to self-maintained time and transmits laser pulses, and a time stamp i+j is marked in each laser pulse echo signal remote sensing packet.
4. A method of high precision time keeping for a satellite borne lidar according to claim 3, wherein the step S2.1 comprises the sub-steps of:
Step S2.1.1: starting the laser radar, and starting counting for 0.1ms by j;
Step S2.1.2: when the first second pulse is received, assigning the whole second moment of the second pulse to i, and resetting j;
step S2.1.3: when the subsequent second pulse is received, judging the value of j:
if j is less than 9000, not performing timing operation;
If 9000 is less than or equal to j is less than or equal to 11000, assigning the whole second moment of the second pulse to i, and resetting j;
if j is greater than 11000, performing +1 operation on i, and assigning j-10000 to j;
step S2.1.4: if j >11000 occurs in the continuous 5s, it is determined that the pulse per second reception is abnormal, and the time for self-maintenance is calibrated using the BC broadcast data.
5. A method of high precision time keeping for a satellite borne lidar according to claim 3, wherein the step S2.2 comprises the sub-steps of:
step S2.2.1: starting the laser radar, and starting counting for 0.1ms by j, and not performing light emitting operation;
Step S2.2.2: when receiving the first time broadcasting interrupt, assigning the whole second moment to i, and resetting j;
Step S2.2.3: when receiving the broadcast interrupt in the subsequent time, judging the value of j:
If j is less than 8000, not performing timing operation;
if 8000 is less than or equal to j is less than or equal to 12000, assigning the whole second moment of the second pulse to i, and resetting j;
If j >12000, then +1 operation is carried out on i, and j-10000 is assigned to j.
6. A method of high precision time keeping for a satellite borne lidar according to claim 3, wherein the lidar is free of time reference before receiving navigation second pulse timing or BC broadcasting time, is only self-time-keeping, and does not perform light emitting operation.
7. The high-precision time keeping method of the satellite-borne laser radar according to claim 3, wherein the laser radar performs light emitting operation when i+j reaches a corresponding time point according to pulse frequency after receiving navigation second pulse timing or BC broadcasting time, transmits the i+j time to a data processor, and records the time corresponding to the laser pulse for data inversion.
8. The method for high-precision time keeping of a satellite-borne laser radar according to claim 7, wherein the light emitting time of the laser radar is recorded in real time, and if the time difference between the current calculated light emitting time and the last light emitting time is smaller than a certain threshold value affecting the safety of the laser, no light is emitted at the current time.
9. The high-precision time keeping method of the satellite-borne laser radar according to claim 1, wherein when a satellite time system fails, the laser radar still keeps time keeping and running with preset precision, and radar echo signal imaging time is recorded in remote sensing data; the fault includes the pulse-per-second interval not reaching a preset value and the broadcast time not reaching a preset value.
10. The utility model provides a high accuracy time keeping system of spaceborne laser radar which characterized in that includes:
module M1: setting a register in the laser radar; the register stores a count;
Module M2: calibrating the laser radar according to the receiving state of the laser radar to finish the self-timekeeping of the laser radar with preset precision; the reception states include reception of a second pulse provided by the satellite platform, reception of a second pulse but reception of a BC broadcast time, and reception of a BC broadcast time.
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