A method and system for calibrating link delay and correcting time stamp of CO2 measurement based on TDLAS

Abstract

The present application relates to the technical field of data processing, in particular to a CO2 measurement link delay calibration and timestamp correction method and system based on TDLAS, which executes TDLAS-CO2 high-frequency measurement through establishing a unified time reference, an open-circuit WMS-TDLAS CO2 measurement module, and continuously outputs CO2 concentration sequence; at the calibration trigger moment, the link delay calibration module injects a CO2 absorption change signal into the measurement link, and determines the actual change starting moment of the CO2 absorption change signal on the optical path; through the delay calculation and timestamp correction module, the output response moment corresponding to the CO2 absorption change signal in the CO2 concentration sequence is identified; through the delay calculation and timestamp correction module, the original output timestamp of each CO2 concentration value is back-pushed and corrected according to the actual change starting moment and the output response moment, so as to reduce the concentration and wind speed fluctuation mismatch risk caused by link processing delay.

Description

Technical Field

[0001] This invention relates to the field of data processing technology, specifically to a method and system for CO2 measurement link delay calibration and timestamp correction based on TDLAS. Background Technology

[0002] Industrial parks typically feature diverse emission sources, fluctuating emission intensity, and complex spatial distribution. CO2 emission monitoring in these parks not only requires stable and reliable average concentration data but is also increasingly evolving towards metrological monitoring with high temporal resolution, traceability, and the ability to perform flux inversion. When conducting CO2 monitoring at park boundaries, key emission units, or open areas, obtaining local emission fluxes often necessitates simultaneous acquisition and joint analysis of CO2 concentration data with meteorological parameters such as wind speed, temperature, humidity, and pressure. Therefore, CO2 concentration data used for flux observation differs from ordinary average concentration monitoring data; it requires not only high response speed and sampling frequency but also accurate correspondence between each concentration value and its actual measurement time.

[0003] Tunable semiconductor laser absorption spectroscopy (TDLAS) is characterized by high selectivity, fast response, and suitability for in-situ or open-circuit measurements, and can be used for the detection of gas concentrations such as CO2, CH4, and CO. In high-precision rapid CO2 measurement, TDLAS systems often employ wavelength modulation spectroscopy (WMS) to extract the absorption signal. This involves superimposing a low-frequency scanning signal and a high-frequency modulation signal onto the laser drive current, causing the laser wavelength to sweep across the target absorption spectrum at the period of the low-frequency scanning signal. Characteristic quantities of high-frequency harmonics such as 1f, 2f, or 2f / 1f are then obtained through demodulation methods and used to invert CO2 concentration.

[0004] Existing CO2 flux observation or industrial park carbon emission monitoring systems typically record CO2 concentration data, three-dimensional wind speed data, and meteorological parameters using a unified data logger, a unified system clock, communication timestamps, or host computer timestamps. This approach reduces data recording errors caused by independent timing by multiple devices and facilitates subsequent interpolation, resampling, and data matching.

[0005] However, the aforementioned synchronization methods primarily address the time consistency of data output from different devices at the acquisition or recording end, and do not directly characterize the link delay between TDLAS-CO2 concentration values ​​and spectral measurement, signal processing, and concentration output. For TDLAS-CO2 high-frequency measurement systems employing WMS, a single concentration value typically requires processing steps such as scanning sampling, harmonic demodulation, filtering, feature extraction, concentration inversion, and communication output. Without a comprehensive time delay calibration method for the entire measurement link, it is difficult to determine the lag of the CO2 concentration sequence relative to the actual spectral measurement time. Summary of the Invention

[0006] The purpose of this invention is to provide a method and system for CO2 measurement link delay calibration and timestamp correction based on TDLAS, which solves the problems in the prior art.

[0007] This invention is achieved through the following technical solution:

[0008] In a first aspect, embodiments of the present invention provide a method for CO2 measurement link delay calibration and timestamp correction based on TDLAS, applied to a TDLAS-CO2 high-frequency measurement system. The system includes an open-circuit WMS-TDLAS CO2 measurement module, a link delay calibration module, and a delay calculation and timestamp correction module. The method includes:

[0009] Establish a unified time reference to synchronize the open-circuit WMS-TDLAS CO2 measurement module, the link delay calibration module, and the delay calculation and timestamp correction module.

[0010] The open-circuit WMS-TDLAS CO2 measurement module performs TDLAS-CO2 high-frequency measurement and continuously outputs a CO2 concentration sequence with the original output timestamp.

[0011] At the calibration trigger time, an identifiable CO2 absorption change signal is injected into the measurement link of the open-circuit WMS-TDLAS CO2 measurement module through the link delay calibration module, and the actual start time of the change of the CO2 absorption change signal on the optical path is determined according to the calibration trigger time.

[0012] The delay calculation and timestamp correction module is used to identify the output response time corresponding to the CO2 absorption change signal in the CO2 concentration sequence.

[0013] The delay calculation and timestamp correction module backtracks and corrects the original output timestamp of each CO2 concentration value based on the actual change start time and the output response time to obtain the corrected timestamp.

[0014] Preferably, the link delay calibration module includes an optically switched dual-absorption cell structure; the optically switched dual-absorption cell structure includes a first absorption branch, a second absorption branch, and an optical switch; the first absorption branch includes a first absorption level cell for providing a first CO2 absorption level; the second absorption branch includes a second absorption level cell for providing a second CO2 absorption level; the step of injecting a identifiable CO2 absorption change signal into the measurement link of the open-circuit WMS-TDLAS CO2 measurement module through the link delay calibration module includes:

[0015] According to the calibrated trigger time, the input optical path is switched from the first absorption branch to the second absorption branch through the optical switch to obtain a CO2 absorption step signal with a clear start time;

[0016] The CO2 absorption step signal is used as a recognizable CO2 absorption change signal injected into the open-circuit WMS-TDLAS CO2 measurement module.

[0017] Preferably, determining the actual start time of the change in the CO2 absorption change signal on the optical path based on the calibration trigger time includes:

[0018] Obtain the self-response time value of the optical switch;

[0019] Based on the calibration trigger time and the self-response time value, the actual start time of the change of the CO2 absorption step signal in the optical path is calculated by adding the calibration trigger time and the self-response time value.

[0020] Preferably, identifying the output response time corresponding to the CO2 absorption change signal in the CO2 concentration sequence includes:

[0021] Based on the CO2 concentration sequence, identify the process of concentration values ​​transitioning from a first stable level to a second stable level;

[0022] Based on the first stable level and the second stable level, calculate the difference between the first stable level and the second stable level to obtain the step amplitude value;

[0023] The concentration determination threshold is calculated based on the step amplitude and the preset step ratio threshold.

[0024] By comparing each concentration value in the CO2 concentration sequence with the concentration determination threshold, the moment corresponding to the concentration value that first reaches or exceeds the concentration determination threshold is determined as the output response moment corresponding to the CO2 absorption change signal.

[0025] Preferably, identifying the output response time corresponding to the CO2 absorption change signal in the CO2 concentration sequence includes:

[0026] Based on the CO2 concentration sequence, a first-order difference operation is performed on the CO2 concentration sequence to obtain a difference sequence;

[0027] Based on the difference sequence, find the maximum value in the difference sequence to obtain the maximum difference value;

[0028] Based on the maximum difference, the time corresponding to the maximum difference on the time axis is obtained, and the time is determined as the output response time corresponding to the CO2 absorption change signal.

[0029] Preferably, the step of back-correcting the original output timestamp of each CO2 concentration value based on the actual change start time and the output response time to obtain the corrected timestamp includes:

[0030] The single link delay value is calculated based on the output response time and the actual change start time during a single calibration process.

[0031] Based on the multiple single link delay values ​​obtained by repeatedly executing the calibration process at multiple calibration trigger times, the link delay calibration value is obtained by taking the median or average value after removing outliers.

[0032] The original output timestamp of each CO2 concentration value is back-corrected based on the link delay calibration value to obtain the corrected timestamp.

[0033] Preferably, the method further includes:

[0034] Synchronization output data is generated based on the link delay calibration value, the original output timestamp, and the corrected timestamp. The synchronization output data includes the CO2 concentration value, the original output timestamp, the corrected timestamp, the link delay calibration value, the calibration status, and the synchronization quality identifier.

[0035] Preferably, the method further includes:

[0036] The corrected timestamp is time-matched with the wind speed sequence output by the external three-dimensional ultrasonic anemometer to obtain a synchronous data sequence for carbon emission flux calculation.

[0037] Secondly, embodiments of the present invention provide a TDLAS-CO2 high-frequency measurement system, comprising:

[0038] An open-circuit WMS-TDLAS CO2 measurement module is used to perform TDLAS-CO2 high-frequency measurements and continuously output CO2 concentration sequences with raw output timestamps;

[0039] The link delay calibration module is used to inject a recognizable CO2 absorption change signal into the measurement link of the open-circuit WMS-TDLAS CO2 measurement module at the calibration trigger time, and determine the actual start time of the change of the CO2 absorption change signal on the optical path according to the calibration trigger time.

[0040] The delay calculation and timestamp correction module is connected to the open-circuit WMS-TDLAS CO2 measurement module and the link delay calibration module, respectively. It is used to receive the CO2 concentration sequence, identify the output response time corresponding to the CO2 absorption change signal in the CO2 concentration sequence, calculate the link delay calibration value based on the actual change start time and the output response time, and back-correct the original output timestamp of each CO2 concentration value based on the link delay calibration value to obtain the corrected timestamp.

[0041] Preferably, the link delay calibration module includes an optical switch-type dual absorption cell structure; the optical switch-type dual absorption cell structure includes a first absorption branch, a second absorption branch, and an optical switch; the first absorption branch includes a first absorption level cell filled with zero or low concentration CO2 gas to provide a first CO2 absorption level; the second absorption branch includes a second absorption level cell filled with high concentration CO2 gas to provide a second CO2 absorption level.

[0042] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0043] By establishing a unified time reference, injecting identifiable CO2 absorption change signals into the TDLAS measurement link at a known trigger time, identifying the corresponding response time in the output concentration sequence, and backtracking and correcting the original output timestamp of each concentration value based on the actual change start time and output response time, a calibration value reflecting the overall link delay from the change in spectral absorption signal to the output of concentration data can be obtained. This calibration value is then used to correct the timestamps of all subsequent concentration data, giving the corrected high-frequency CO2 concentration sequence a unified time reference corresponding to the actual spectral measurement time. This provides a reliable time coordinate for accurate synchronization with the three-dimensional wind speed sequence, reduces the risk of concentration and wind speed pulsation mismatch caused by link processing delay, and improves the reliability of carbon emission flux calculation based on the eddy covariance method. Attached Figure Description

[0044] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings:

[0045] Figure 1 A flowchart illustrating the CO2 measurement link delay calibration and timestamp correction method based on TDLAS provided by this invention;

[0046] Figure 2The timing diagram for link delay calibration provided by this invention;

[0047] Figure 3 Schematic diagram of the TDLAS-CO2 high-frequency measurement system provided by the present invention Figure 1 ;

[0048] Figure 4 Schematic diagram of the TDLAS-CO2 high-frequency measurement system provided by the present invention Figure 2 ;

[0049] Figure 5 This is a schematic diagram of the optical switch-type dual absorption cell calibration module provided by the present invention. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0051] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes said element.

[0052] It should be noted that all actions involving the acquisition of signals, information, or data in this invention are carried out in compliance with the relevant data protection laws and regulations of the locality and with authorization from the owner of the relevant device.

[0053] Example 1

[0054] Please see Figure 1 This invention provides a method for CO2 measurement link delay calibration and timestamp correction based on TDLAS, which is applied to a TDLAS-CO2 high-frequency measurement system. The system includes an open-circuit WMS-TDLAS CO2 measurement module, a link delay calibration module, and a delay calculation and timestamp correction module.

[0055] The open-circuit WMS-TDLAS CO2 measurement module refers to a CO2 concentration measurement unit based on tunable semiconductor laser absorption spectroscopy technology, where laser emission and reception pass directly through open atmospheric space without passing through a closed gas chamber. This module includes at least a laser source, a laser drive and modulation unit, an emitting optical unit, a receiving optical unit, a photodetector, and a signal acquisition unit. The laser drive and modulation unit provides the laser with a drive current superimposed with a low-frequency scanning signal and a high-frequency modulation signal, causing the laser wavelength to periodically sweep across the CO2 target absorption spectrum. After being emitted by the emitting optical unit, the laser passes through the open optical path, is collected by the receiving optical unit, and focused onto the photodetector. The photodetector converts the received light intensity signal into an electrical signal, which is then converted from analog to digital by the signal acquisition unit for subsequent processing. For example, in a measurement system deployed at the boundary of a park, the laser emitted by the laser propagates along an open path tens of meters long. CO2 molecules in the atmosphere absorb the laser at a specific wavelength, and the change in light intensity received by the detector is the CO2 absorption spectrum signal.

[0056] The link delay calibration module is a functional unit used to inject a recognizable absorption change signal into the TDLAS-CO2 measurement link at a known time point. This module includes at least a calibration trigger unit, an optical path switching unit, a calibration absorption unit, and an optical path coupling component. The calibration trigger unit generates a precise trigger signal, the optical path switching unit changes the optical path according to the trigger signal, the calibration absorption unit provides a gas environment with different CO2 absorption levels, and the optical path coupling component connects the calibration optical signal to the existing photodetector. Through this module, the system can actively generate a CO2 absorption change event with a clearly defined start time without changing the normal open optical path measurement state, for subsequent delay calculations. For example, the module can internally set up two absorption cells with different CO2 concentrations, which are rapidly switched via an optical switch, causing the light signal entering the detector to change stepwise between different absorption levels.

[0057] The delay calculation and timestamp correction module receives the concentration output sequence from the open-circuit WMS-TDLAS CO2 measurement module and the trigger time information from the link delay calibration module, and calculates the link delay and corrects the concentration data timestamp accordingly. This module can be implemented using an embedded processor, digital signal processor, or field-programmable gate array (FPGA), and internally includes a timer, comparator, memory unit, and arithmetic logic unit. The module records the calibration trigger time, identifies the response position in the concentration sequence, calculates the difference between the two as the link delay value, and then applies this delay value to the original output timestamp of each subsequent concentration value, obtaining the corrected timestamp through subtraction. This module can also store multiple calibration results and perform statistical processing, outputting a data packet containing the delay calibration value and correction status.

[0058] The method includes:

[0059] S1. Establish a unified time reference to synchronize the open-circuit WMS-TDLAS CO2 measurement module, the link delay calibration module, and the delay calculation and timestamp correction module.

[0060] Specifically, a unified time reference refers to all modules in the system sharing the same reference clock source, enabling the event times recorded by different modules to be compared and calculated under the same time coordinate system. Time synchronization methods include, but are not limited to: all modules jointly receiving high-precision second pulse signals provided by the Global Positioning System or the BeiDou Navigation Satellite System; or the data acquisition controller acting as the master clock, distributing periodic synchronization pulses and absolute time information to each module via a wired connection; or each module's internal real-time clock periodically calibrating via a network time protocol. In this embodiment, the unified time reference ensures that the calibration trigger time recorded by the link delay calibration module, the concentration data timestamp output by the open-circuit WMS-TDLAS CO2 measurement module, and the response time identified by the delay calculation and timestamp correction module are all based on the same time scale. For example, at system startup, the data acquisition controller simultaneously sends a reset pulse to all three modules and writes the current absolute time into the registers of each module. Subsequently, each module increments its time at the same crystal oscillator frequency. Thus, when the calibration trigger signal is generated at time t0, the timestamp t in the subsequent concentration output sequence... raw Alternatively, it can be directly subtracted from t0 without considering clock drift between different devices. After achieving time synchronization, the system has the basic conditions for accurately measuring time differences, avoiding offset errors caused by independent timing of each module.

[0061] S2. Perform TDLAS-CO2 high-frequency measurement through the open-circuit WMS-TDLAS CO2 measurement module, and continuously output CO2 concentration sequence with original output timestamp;

[0062] Specifically, the raw output timestamp refers to the time stamp recorded by the internal timer and attached to each concentration value output by the open-circuit WMS-TDLAS CO2 measurement module. This timestamp typically corresponds to the moment the concentration value is sent from the module's communication interface, or the moment the module completes the concentration inversion algorithm and stores the result in the output buffer. The CO2 concentration sequence is a collection of multiple concentration values ​​and their corresponding timestamps arranged in chronological order, with each concentration value corresponding one-to-one with a raw output timestamp. During TDLAS-CO2 high-frequency measurement, the system repeatedly performs laser scanning, signal sampling, harmonic demodulation, concentration inversion, and data output at a fixed scanning frequency (e.g., 10 or 20 times per second). At the end of each scanning cycle, the module calculates a CO2 concentration value based on the spectral data acquired during that cycle and simultaneously reads the current timer value as the raw output timestamp for that concentration value. This concentration value and the timestamp together form a data point, and multiple consecutive data points constitute a concentration sequence. For example, when the scanning frequency is 20 Hz, the system outputs a concentration value every 50 milliseconds, and the original output timestamps for each concentration value are recorded as 50 milliseconds, 100 milliseconds, 150 milliseconds, etc. These original output timestamps will be used as the objects to be calibrated, and the offset between them and the actual measurement time is the link delay to be calibrated.

[0063] S3. At the calibration trigger time, an identifiable CO2 absorption change signal is injected into the measurement link of the open-circuit WMS-TDLAS CO2 measurement module through the link delay calibration module, and the actual start time of the change of the CO2 absorption change signal on the optical path is determined according to the calibration trigger time.

[0064] Specifically, the calibration trigger time is the specific point in time when the calibration trigger unit within the link delay calibration module generates the trigger signal. This point in time is recorded by the delay calculation and timestamp correction module under a unified time reference. The measurement link refers to the complete signal path from the laser passing through the absorption medium to the photodetector, through signal processing, and finally to the output of the concentration value. This includes optical transmission, photoelectric conversion, analog filtering, analog-to-digital conversion, digital demodulation, harmonic extraction, concentration inversion, data buffering, and communication output. A recognizable CO2 absorption change signal refers to an absorption characteristic change that has a clear starting boundary in the time domain and can be distinguished from the normal output sequence by subsequent signal processing and concentration inversion algorithms. This change can be a step signal where the CO2 absorption intensity jumps from one stable level to another, or a change signal with a specific waveform (such as a square wave, pulse, or ramp). When determining the actual start time of the change, the action delay of the internal components of the link delay calibration module (such as optical switches and electrically controlled mirrors) needs to be considered. The calibration trigger time is the moment the system issues a control command. After the command is executed, the change in the optical path state requires a brief mechanical or electronic response time to complete. Therefore, the actual start time of the change equals the calibration trigger time plus this response time. For example, if it takes 2 milliseconds for the optical switch to completely switch from the first branch to the second branch after receiving the switching command, the system at time t... trig When a switching command is issued, the actual time at which the absorption level in the optical path begins to change is t. trig +2 milliseconds. If the response time of the optical switch is much shorter than the concentration output period of the TDLAS (e.g., less than 1 millisecond), the calibration trigger time can be approximated as the actual change start time. The accuracy of determining the actual change start time directly affects the calculation accuracy of subsequent link delay calibration values.

[0065] In some embodiments, the link delay calibration module includes an optical switch-type dual absorption pool structure; the optical switch-type dual absorption pool structure includes a first absorption branch, a second absorption branch, and an optical switch; the first absorption branch includes a first absorption level pool for providing a first CO2 absorption level; the second absorption branch includes a second absorption level pool for providing a second CO2 absorption level.

[0066] The optically switched dual-absorption cell structure refers to a calibration signal generation device composed of two independent sealed gas chambers and an optical path switching switch. In this structure, the two absorption cells contain gases with different CO2 absorption levels. The optical switch, located at the front end of the optical path, can guide the incident laser to either absorption cell under the control of an external trigger signal. The function of this structure is to generate a clearly defined absorption change event by rapidly switching the optical path, causing the light signal entering the detector to undergo CO2 absorption of different intensities, without altering the laser's output characteristics. For example, the optical switch can be configured as a 1×2 fiber optic switch, with the input fiber connected to the laser and the two output fibers connected to the incident ends of the first and second absorption cells, respectively. The exit ends of the two absorption cells are combined into the same photodetector via a combiner.

[0067] The first absorption branch refers to the complete optical path of the laser beam from the output of the optical switch through the first absorption horizontal cell to the optical coupling component. This path includes an output port of the optical switch, a connecting optical fiber or spatial optical path, the incident window of the first absorption horizontal cell, the gas inside the cell, a reflector or transmission window inside the cell, and a transmission medium leading to the optical coupling component. The first absorption branch is characterized by containing the first absorption horizontal cell, in which the laser beam is absorbed by gas molecules within the cell during transmission. The degree of absorption is determined by the CO2 concentration inside the cell and the effective optical path length.

[0068] The second absorption branch refers to the complete optical path from the output of the optical switch through the second absorption level cell to the optical coupling component. Its structure is similar to that of the first absorption branch, except that the second absorption level cell is filled with a different CO2 concentration than the first absorption level cell. The second absorption branch provides a different CO2 absorption level than the first absorption branch, resulting in a recognizable change in light intensity on the detector when the two branches switch.

[0069] An optical switch is an optical device that routes an input optical signal to different output ports under the control of an electrically triggered signal. Types of optical switches include mechanical optical switches (changing the optical path by moving a mirror or prism), microelectromechanical system (MEMS) optical switches (switching via a micromirror array), and electro-optic or acousto-optic switches (switching by changing the refractive index of a material). Key performance parameters of optical switches include switching time, insertion loss, repeatability, and lifetime. In this scheme, the optical switch's function is to rapidly switch the laser from the first absorption branch to the second absorption branch when the calibrated trigger time arrives, causing a step change in the detected absorption signal. For example, a mechanical optical switch with a switching time of 1 millisecond is selected, completing the optical path switching within 1 millisecond after receiving the trigger signal.

[0070] The first absorption level cell is a closed gas chamber filled with a gas mixture of known CO2 concentration, used to provide a defined intensity of CO2 absorption for laser light passing through it. This chamber typically consists of a cylindrical shell, light-transmitting windows at both ends, an inlet, and an outlet. The shell material can be stainless steel or aluminum alloy, and the window material is chosen from quartz or sapphire, which have high transmittance in the CO2 absorption band. The CO2 concentration in the first absorption level cell can be preset according to calibration needs, for example, by filling it with zero gas (CO2 concentration close to 0 ppm), nitrogen, or a low-concentration CO2 standard gas (e.g., 200 ppm). The effective optical path length within the cell determines the intensity of the absorbed signal and is usually designed to be on the same order of magnitude as the optical path length of the open measurement optical path to ensure that the light intensity received by the detector before and after switching remains within the dynamic range.

[0071] The second absorption level cell has the same structure as the first, except that it is filled with a higher concentration of CO2 gas to provide a second CO2 absorption level distinct from the first. The CO2 concentration in the second absorption level cell can be set to be significantly higher than the ambient background concentration, for example, by filling it with 5000 ppm or 10000 ppm of standard CO2 gas. This ensures a sufficiently large change in light intensity received by the detector after the optical switch is switched, making it easily identifiable in subsequent output sequences. The gas concentration in the cell does not need to be precisely equal to a specific value; it only needs to ensure that the difference in absorption signals generated by the two branches is greater than the system noise level.

[0072] The step of injecting a identifiable CO2 absorption change signal into the measurement link of the open-circuit WMS-TDLAS CO2 measurement module through the link delay calibration module includes:

[0073] According to the calibrated trigger time, the input optical path is switched from the first absorption branch to the second absorption branch through the optical switch to obtain a CO2 absorption step signal with a clear start time;

[0074] Specifically, the delay calculation and timestamp correction module records the calibration trigger time under a unified time reference and sends a switching command to the optical switch. Upon receiving the command, the optical switch, after its inherent response time, changes the transmission path of the input laser from the branch connected to the first absorption level cell to the branch connected to the second absorption level cell. After the path switching is complete, the laser no longer passes through the first absorption level cell but instead passes through the second absorption level cell. Due to the different CO2 concentrations in the two absorption cells, the laser is absorbed to different degrees after passing through, causing the light intensity reaching the photodetector to jump from the value corresponding to the first absorption level to the value corresponding to the second absorption level. This jump in light intensity is represented as an approximately vertical step waveform on the time axis, the starting time of which is determined by the moment the optical switch completes the switching. A specific starting time means that the position of this step on the time coordinate is known and unique, and its error range does not exceed the response time dispersion of the optical switch. For example, as... Figure 2 As shown, the calibration trigger time is t. trig The optical switch response time is τ sw The actual start time of the step signal is t. trig +τ sw The step signal then enters the existing TDLAS measurement link, which includes photoelectric detection, amplification and filtering, analog-to-digital conversion, digital demodulation, and concentration inversion. Through this step, the system injects an event with a known starting point into the link to be calibrated, providing a reference benchmark for the total time delay of subsequent measurement links.

[0075] The CO2 absorption step signal is used as a recognizable CO2 absorption change signal injected into the open-circuit WMS-TDLAS CO2 measurement module.

[0076] Specifically, identifiability means that the signal, after processing through the entire TDLAS measurement link, can be detected and located in the final output CO2 concentration sequence. Because the step signal has a steep leading edge and stable plateaus, even after digital filtering (such as low-pass filtering or moving average), an identifiable transition segment will still be retained in the output sequence, with a fixed time offset between its position and the starting moment of the input step. This offset is the link delay to be calibrated. The advantage of using the step signal as the injection signal is that the step change contains rich frequency components; its low-frequency components can pass through the system's digital filters, while the high-frequency components can be used to verify the system's response bandwidth. The two stable levels provide clear reference values, allowing the response time identification algorithm to be implemented based on simple criteria such as thresholds or slopes. For example, when the concentration output value corresponding to the first absorption level stabilizes around 0 ppm, and the concentration output value corresponding to the second absorption level stabilizes around 5000 ppm, the process of the concentration value in the output sequence rising from 0 ppm to finally reaching 5000 ppm corresponds to the response of the input step signal. The difference between the starting point of the response process on the time axis (such as the moment when the concentration value first exceeds 2500ppm) and the actual starting moment of the input step is the link delay.

[0077] In some embodiments, determining the actual start time of the change in the CO2 absorption change signal on the optical path based on the calibrated trigger time includes:

[0078] Obtain the self-response time value of the optical switch;

[0079] Based on the calibration trigger time and the self-response time value, the actual start time of the change of the CO2 absorption step signal in the optical path is calculated by adding the calibration trigger time and the self-response time value.

[0080] The optical switch's self-response time value refers to the time interval required for the optical switch to complete the optical path switching from receiving the trigger signal. The unit is usually milliseconds or microseconds, which can be obtained from the device datasheet or measured through testing.

[0081] The calibration trigger time refers to the absolute point in time when the delay calculation and timestamp correction module sends a switching command to the optical switch.

[0082] The actual start time of change refers to the instant when the laser path switches from the first absorption branch to the second absorption branch and the light intensity signal begins to change. It is equal to the sum of the calibrated trigger time and the response time of the optical switch itself.

[0083] Specifically, the delay calculation and timestamp correction module records the calibration trigger time t when issuing the switching command. trig Because the optical switch needs its own response time τ to complete the switching process.sw The actual change in the absorbed signal along the optical path does not begin at t. trig Instead, it lags behind τ sw The module will t trig With τ sw Adding them together, we get the actual starting time of the change, t0 = t trig +τ sw The value t0 serves as the starting point for link delay calculation. It is then subtracted from the output response time t1 to obtain a calibration value that reflects only the internal processing delay of the TDLAS measurement link, thus eliminating the influence of optical switch operation delay.

[0084] S4. Using the time delay calculation and timestamp correction module, identify the output response time corresponding to the CO2 absorption change signal in the CO2 concentration sequence;

[0085] Specifically, the output response time refers to the original output timestamp corresponding to the concentration value in the CO2 concentration sequence that first shows the influence of the CO2 absorption change signal. Because the TDLAS measurement link includes digital filtering, averaging, and other processes, the concentration sequence's response to the input absorption change does not appear immediately in the output, but rather after one or more scan cycles. The method for identifying the output response time is based on the detection of changes in the concentration sequence. The delay calculation and timestamp correction module monitors the output CO2 concentration sequence in real time. When the absorption change signal injected by the link delay calibration module occurs, the concentration value will transition from its previous stable level to a new stable level. The module locates the time of change by comparing the change amplitude of adjacent concentration values, calculating the difference in the sequence, or using sliding window template matching. For example, before the absorption step signal is injected, the concentration value is stable around Y0; after injection, the concentration value gradually changes towards Y1. The module can set a threshold; when the concentration value first exceeds Y0 + k*(Y1 - Y0), the original output timestamp corresponding to that concentration value is recorded as the output response time, where k is a preset proportional coefficient (e.g., 0.5). Alternatively, the module performs a first-order difference operation on the concentration sequence; the point with the largest difference value corresponds to the moment of most dramatic change, which is the output response moment. The accuracy of identifying the output response moment depends on the signal-to-noise ratio of the concentration sequence and the clarity of the absorbed change signal. By selecting appropriate identification criteria, the response location can be reliably located in a noisy background.

[0086] In some embodiments, S4, identifying the output response time corresponding to the CO2 absorption change signal in the CO2 concentration sequence, includes:

[0087] Based on the CO2 concentration sequence, identify the process of concentration values ​​transitioning from a first stable level to a second stable level;

[0088] Based on the first stable level and the second stable level, calculate the difference between the first stable level and the second stable level to obtain the step amplitude value;

[0089] The concentration determination threshold is calculated based on the step amplitude and the preset step ratio threshold.

[0090] By comparing each concentration value in the CO2 concentration sequence with the concentration determination threshold, the moment corresponding to the concentration value that first reaches or exceeds the concentration determination threshold is determined as the output response moment corresponding to the CO2 absorption change signal.

[0091] The first stable level refers to the average stable concentration in the concentration sequence before the injection of the absorption change signal.

[0092] The second stability level refers to the average concentration in the concentration sequence after the absorption change signal has been fully injected and the response has stabilized.

[0093] The step amplitude refers to the difference between the second stable level and the first stable level.

[0094] The preset step ratio threshold is a coefficient between 0 and 1, used to determine the position of the output response moment in the transition process.

[0095] The concentration determination threshold is the first stable level plus the product of the step ratio threshold and the step amplitude.

[0096] The output response time refers to the original output timestamp corresponding to the concentration value that first reaches or exceeds the concentration determination threshold in the concentration sequence.

[0097] Specifically, after the absorption step signal is injected, the concentration output rises from the first stable level Y0 to the second stable level Y1. The module presets a proportional threshold k (e.g., 0.5) and calculates the judgment threshold Y. th =Y0+k×(Y1-Y0). During the transition process, the module compares the concentration values ​​one by one. When Y first appears... i ≥Y th When the concentration value is reached, the original timestamp corresponding to it is recorded as the output response time t1. The difference between this time and the actual start time of the optical path change t0 is the link delay calibration value. Using the proportional threshold method can ensure the repeatability of the response time positioning and is not affected by small fluctuations in noise.

[0098] In some other embodiments, S4, identifying the output response time corresponding to the CO2 absorption change signal in the CO2 concentration sequence, includes:

[0099] Based on the CO2 concentration sequence, a first-order difference operation is performed on the CO2 concentration sequence to obtain a difference sequence;

[0100] Based on the difference sequence, find the maximum value in the difference sequence to obtain the maximum difference value;

[0101] Based on the maximum difference, the time corresponding to the maximum difference on the time axis is obtained, and the time is determined as the output response time corresponding to the CO2 absorption change signal.

[0102] Specifically, after the absorption step signal injection, the concentration sequence transitions from a first stable level to a second stable level. During the transition, the rate of change of the concentration value exhibits a characteristic of first increasing and then decreasing, with the moment of maximum rate of change corresponding to the inflection point or steepest position of the response curve. The module calculates the first-order difference of the concentration sequence, and the point where the difference value is maximum is the moment when the concentration rises the fastest. This moment is used as the output response moment and can be used to calculate the link delay calibration value. This method has a certain degree of robustness to noise and does not require pre-determining the specific values ​​of the first and second stable levels.

[0103] S5. Using the delay calculation and timestamp correction module, the original output timestamp of each CO2 concentration value is back-corrected based on the actual change start time and the output response time to obtain the corrected timestamp.

[0104] Specifically, backtracking correction refers to subtracting a fixed duration from the original output timestamp. This duration is equal to the link delay calibration value. The link delay calibration value is equal to the output response time minus the actual change start time, that is, the total time elapsed from the occurrence of CO2 absorption change on the optical path to the inclusion of this change information in the system output concentration value. For example, if the actual change start time is t0 and the output response time is t1, then the link delay calibration value τ = t1 - t0. For each CO2 concentration value output in step two, its original output timestamp is t. raw Corrected timestamp t corr =t raw -τ。 t corrThe meaning of τ is the actual time when the spectral measurement corresponding to the concentration value occurred. Since the processing delay in the TDLAS measurement link is fixed or quasi-fixed (i.e., does not change significantly with time or concentration value), the same τ can be applied to correct all concentration values. The corrected timestamp shifts the concentration value from the device output time coordinate to the actual measurement time coordinate, allowing the concentration value to directly correspond to the 3D wind speed data measured at the same time. For example, if τ = 120 milliseconds, and the original output timestamp of a concentration value is 10:00:01.000, then the corrected timestamp is 10:00:00.880, indicating that the concentration value reflects the CO2 concentration on the optical path at 880 milliseconds. After backtracking correction, the concentration sequence and wind speed sequence can be matched point-by-point under a unified time reference for subsequent flux calculations. The delay calculation and timestamp correction module can perform this operation continuously, calculating and outputting the corrected timestamp immediately each time a new concentration value is obtained.

[0105] In some implementations, S5 involves back-correcting the original output timestamp of each CO2 concentration value based on the actual change start time and the output response time to obtain a corrected timestamp, including:

[0106] The single link delay value is calculated based on the output response time and the actual change start time during a single calibration process.

[0107] Based on the multiple single link delay values ​​obtained by repeatedly executing the calibration process at multiple calibration trigger times, the link delay calibration value is obtained by taking the median or average value after removing outliers.

[0108] The original output timestamp of each CO2 concentration value is back-corrected based on the link delay calibration value to obtain the corrected timestamp.

[0109] Specifically, the link delay value obtained from a single calibration may exhibit occasional fluctuations, such as optical switch jitter, noise interference, or uncertainties in data sampling edges. To improve the reliability of the calibration results, multiple calibrations are performed during system idle periods or periodic maintenance, obtaining a single delay value each time. After collecting multiple single values, the delay calculation module first identifies and removes outliers that significantly deviate from the overall value (e.g., exceeding three standard deviations from the mean). Then, the median or average of the remaining values ​​is taken as the final link delay calibration value τ. This τ represents the fixed or quasi-fixed delay of the TDLAS measurement link. In normal observation mode, for each concentration value, its original output timestamp t is... raw Subtract τ to obtain the corrected timestamp t. corr =t raw -τ. The t corr This is used to directly match the timestamps of 3D wind speed data, eliminating time misalignment caused by link processing delays.

[0110] In some embodiments, the method further includes:

[0111] Synchronization output data is generated based on the link delay calibration value, the original output timestamp, and the corrected timestamp. The synchronization output data includes the CO2 concentration value, the original output timestamp, the corrected timestamp, the link delay calibration value, the calibration status, and the synchronization quality identifier.

[0112] Specifically, during normal observation, the system not only outputs corrected concentration data but also provides auxiliary information to help subsequent data processing software determine the validity of the data. The module outputs both the original and corrected timestamps simultaneously, allowing users to compare the differences before and after correction. Link delay calibration values ​​are output with each data point; even if the calibration values ​​change over long-term operation, downstream software can trace the delay baseline used for each concentration value. Calibration status distinguishes between normal data and transitional data generated during calibration, preventing the latter from participating in throughput calculations. The synchronization quality flag can be set to an integer from 0 to 100; when the most recent calibration time exceeds a preset threshold (e.g., 24 hours), the quality flag decreases, reminding the user to recalibrate. By outputting this information, the system's data traceability and data quality assessment capabilities are enhanced.

[0113] In some embodiments, the method further includes:

[0114] The corrected timestamp is time-matched with the wind speed sequence output by the external three-dimensional ultrasonic anemometer to obtain a synchronous data sequence for carbon emission flux calculation.

[0115] Among them, the external three-dimensional ultrasonic anemometer refers to a wind speed measurement device that is independent of the TDLAS system, and outputs wind speed components (u, v, w) in three orthogonal directions as well as the timestamp corresponding to each wind speed data.

[0116] A wind speed sequence refers to a set of wind speed data points and their timestamps continuously output by a three-dimensional ultrasonic anemometer at a fixed sampling frequency. It usually has a sampling frequency similar to or higher than that of a CO2 concentration sequence.

[0117] Time matching refers to combining the corrected CO2 concentration value with the wind speed value with the closest timestamp into a pair of data points based on a unified time reference, which are then used for subsequent flux calculations.

[0118] Synchronous data sequences refer to data sequences formed after time matching, in which CO2 concentration and three-dimensional wind speed components correspond one-to-one. Each data point includes a concentration value, u component, v component, w component, and a unified timestamp.

[0119] Specifically, after completing the timestamp correction, each CO2 concentration value tcorr This indicates the actual time of the concentration measurement. Three-dimensional ultrasonic anemometers typically output wind speed data based on their own time reference, with their timestamps aligned to the CO2 concentration-corrected timestamp on the same time coordinate system. During matching, for each CO2 concentration value, a search is performed in the wind speed sequence that satisfies |t... wind -t corr The minimum wind speed value, not exceeding half a sampling interval. If the wind speed sampling frequency is 20 Hz and the CO2 sampling frequency is also 20 Hz, the time error after matching will theoretically not exceed 25 milliseconds. Sorting the matched concentration-wind speed data pairs by time yields a synchronized data sequence that can be directly input into eddy covariance calculation software. This sequence eliminates the concentration lag caused by the TDLAS link delay, making the covariance calculation results more accurate and improving the reliability of carbon emission flux estimation.

[0120] Example 2

[0121] Please see Figure 3 This invention provides a TDLAS-CO2 high-frequency measurement system, comprising:

[0122] An open-circuit WMS-TDLAS CO2 measurement module is used to perform TDLAS-CO2 high-frequency measurements and continuously output CO2 concentration sequences with raw output timestamps;

[0123] The link delay calibration module is used to inject a recognizable CO2 absorption change signal into the measurement link of the open-circuit WMS-TDLAS CO2 measurement module at the calibration trigger time, and determine the actual start time of the change of the CO2 absorption change signal on the optical path according to the calibration trigger time.

[0124] The delay calculation and timestamp correction module is connected to the open-circuit WMS-TDLAS CO2 measurement module and the link delay calibration module, respectively. It is used to receive the CO2 concentration sequence, identify the output response time corresponding to the CO2 absorption change signal in the CO2 concentration sequence, calculate the link delay calibration value based on the actual change start time and the output response time, and back-correct the original output timestamp of each CO2 concentration value based on the link delay calibration value to obtain the corrected timestamp.

[0125] In some possible implementations, the system further includes:

[0126] The signal processing and concentration inversion module performs phase-locked demodulation, digital filtering, absorption feature extraction, and concentration inversion on the raw photoelectric signal to generate high-frequency CO2 concentration data. Its output may include CO2 concentration values, raw output timestamps, scan period information, and absorption characteristic quantities used to identify the calibration response.

[0127] The synchronization output module outputs corrected high-frequency CO2 concentration data and related status information. Output may include CO2 concentration values, original timestamp, corrected timestamp, link delay calibration value, calibration status, correction status, and synchronization quality identifier. The corrected high-frequency CO2 concentration sequence can be matched with the three-dimensional wind speed sequence output by the three-dimensional ultrasonic anemometer according to a unified time reference, for use in eddy covariance calculations, local emission flux inversion, and industrial park carbon emission measurement and analysis.

[0128] In some embodiments, the link delay calibration module includes an optical switch-type dual absorption cell structure; the optical switch-type dual absorption cell structure includes a first absorption branch, a second absorption branch, and an optical switch; the first absorption branch includes a first absorption level cell filled with zero or low concentration CO2 gas to provide a first CO2 absorption level; the second absorption branch includes a second absorption level cell filled with high concentration CO2 gas to provide a second CO2 absorption level.

[0129] The following is a specific example to illustrate this embodiment.

[0130] like Figure 4 As shown, the system includes an open-circuit WMS-TDLAS CO2 measurement module, a three-dimensional ultrasonic anemometer, a temperature, humidity and pressure sensor, an acquisition and control module, a link delay calibration module, a link delay calculation module, a synchronization correction module, and a data output module.

[0131] During normal observation, the CO2 open-path WMS-TDLAS CO2 measurement module is deployed at the park boundary, near key emission units, or in open observation areas to acquire high-frequency CO2 concentration sequences on the open optical path; the three-dimensional ultrasonic anemometer synchronously outputs three-dimensional wind speed data; and the temperature, humidity, and pressure sensors output environmental parameters. The acquisition and control module is used to provide or access a unified time reference and record CO2 concentration data, wind speed data, environmental parameters, and the time information of calibration trigger signals.

[0132] The link delay calibration module is used to input a CO2 absorption change signal with a clear start time into the original WMS-TDLAS CO2 measurement link without changing the actual deployment of the outdoor open measurement optical path. For example... Figure 5 As shown, the module includes an optical switch, a first absorption horizontal cell, a second absorption horizontal cell, a first absorption branch, a second absorption branch, and an optical path coupling component.

[0133] The first absorption branch consists of a first absorption level cell and a first calibration optical path formed therein, while the second absorption branch consists of a second absorption level cell and a second calibration optical path formed therein. The first absorption level cell is filled with zero gas, nitrogen, zero air, or a gas with a low CO2 absorption level to form the first CO2 absorption level; the second absorption level cell is filled with a gas with a higher CO2 absorption level to form the second CO2 absorption level. The specific concentration of the gas in the second absorption level cell is not limited, as long as the CO2 absorption signals output from the two absorption branches have a identifiable and repeatable difference.

[0134] To reduce the impact of non-absorption factors on the calibration results, the first and second calibration optical paths are preferably designed to have the same or similar effective optical path length, number of light transmission windows, light transmission aperture, number of optical elements and optical loss, so that the difference between the two calibration signals mainly comes from the difference in CO2 absorption level.

[0135] In calibration mode, the optical switch switches between the first and second absorption branches. The optical path coupling component connects the calibration optical signal, after passing through the corresponding absorption branch, to the original photodetector of the original WMS-TDLAS CO2 measurement module. The calibration signal continues to pass through the existing photodetector, WMS demodulation, digital filtering, feature extraction, concentration inversion, and data output links of the original device, thus reflecting the overall time delay between the change in absorption signal and the output of concentration data in the original TDLAS-CO2 measurement link.

[0136] In normal observation mode, the system switches back to the open measurement optical path. The CO2 open-path WMS-TDLAS CO2 measurement module receives the CO2 absorption signal from the open optical path and outputs high-frequency CO2 concentration data. Switching between calibration mode and normal observation mode can be achieved through an optical path switching component, an optical path coupling component, or an equivalent time-division access method. This allows the original photodetector to receive the corresponding optical signal in different modes and avoids interference from the open measurement optical path signal on the calibration response identification.

[0137] It should be noted that the first and second absorption level cells are mainly used for link delay calibration. Their purpose is not to calibrate the accuracy of outdoor CO2 concentration measurement results, but to input a recognizable absorption level change signal into the original measurement link at a known trigger time to obtain the fixed or quasi-fixed delay of the TDLAS-CO2 measurement link.

[0138] Those skilled in the art will understand that all or part of the steps of the above-described method embodiments can be implemented by hardware related to program instructions. The aforementioned program can be stored in a computer-readable storage medium. When executed, the program performs the steps of the above-described method embodiments; and the aforementioned storage medium includes various media capable of storing program code, such as ROM, RAM, magnetic disks, or optical disks.

[0139] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for calibrating TDLAS-based CO 2 measurement link time delay and correcting time stamp, characterized in that, The method is applied to a TDLAS-CO2 high-frequency measurement system, which includes an open-circuit WMS-TDLAS CO2 measurement module, a link delay calibration module, and a delay calculation and timestamp correction module; the method includes: Establish a unified time reference to synchronize the open-circuit WMS-TDLAS CO2 measurement module, the link delay calibration module, and the delay calculation and timestamp correction module. The open-circuit WMS-TDLAS CO2 measurement module performs TDLAS-CO2 high-frequency measurement and continuously outputs a CO2 concentration sequence with the original output timestamp. At the calibration trigger time, an identifiable CO2 absorption change signal is injected into the measurement link of the open-circuit WMS-TDLAS CO2 measurement module through the link delay calibration module, and the actual start time of the change of the CO2 absorption change signal on the optical path is determined according to the calibration trigger time. The delay calculation and timestamp correction module is used to identify the output response time corresponding to the CO2 absorption change signal in the CO2 concentration sequence. The delay calculation and timestamp correction module backtracks and corrects the original output timestamp of each CO2 concentration value based on the actual change start time and the output response time to obtain the corrected timestamp.

2. The method of claim 1, wherein, The link delay calibration module includes an optically switched dual-absorption cell structure; the optically switched dual-absorption cell structure includes a first absorption branch, a second absorption branch, and an optical switch; the first absorption branch includes a first absorption level cell for providing a first CO2 absorption level; the second absorption branch includes a second absorption level cell for providing a second CO2 absorption level; the injection of a identifiable CO2 absorption change signal into the measurement link of the open-circuit WMS-TDLAS CO2 measurement module through the link delay calibration module includes: According to the calibrated trigger time, the input optical path is switched from the first absorption branch to the second absorption branch through the optical switch to obtain a CO2 absorption step signal with a clear start time; The CO2 absorption step signal is used as a recognizable CO2 absorption change signal injected into the open-circuit WMS-TDLAS CO2 measurement module.

3. The method of claim 2, wherein, Determining the actual start time of the CO2 absorption change signal on the optical path based on the calibrated trigger time includes: Obtain the self-response time value of the optical switch; Based on the calibration trigger time and the self-response time value, the actual start time of the change of the CO2 absorption step signal in the optical path is calculated by adding the calibration trigger time and the self-response time value.

4. The method of claim 1, wherein, The step of identifying the output response time corresponding to the CO2 absorption change signal in the CO2 concentration sequence includes: Based on the CO2 concentration sequence, identify the process of concentration values ​​transitioning from a first stable level to a second stable level; Based on the first stable level and the second stable level, calculate the difference between the first stable level and the second stable level to obtain the step amplitude value; The concentration determination threshold is calculated based on the step amplitude and the preset step ratio threshold. By comparing each concentration value in the CO2 concentration sequence with the concentration determination threshold, the moment corresponding to the concentration value that first reaches or exceeds the concentration determination threshold is determined as the output response moment corresponding to the CO2 absorption change signal.

5. The method of claim 1, wherein, The step of identifying the output response time corresponding to the CO2 absorption change signal in the CO2 concentration sequence includes: Based on the CO2 concentration sequence, a first-order difference operation is performed on the CO2 concentration sequence to obtain a difference sequence; Based on the difference sequence, find the maximum value in the difference sequence to obtain the maximum difference value; Based on the maximum difference, the time corresponding to the maximum difference on the time axis is obtained, and the time is determined as the output response time corresponding to the CO2 absorption change signal.

6. The method of claim 1, wherein, The original output timestamp of each CO2 concentration value is back-corrected based on the actual change start time and the output response time to obtain the corrected timestamp, including: The single link delay value is calculated based on the output response time and the actual change start time during a single calibration process. Based on the multiple single link delay values ​​obtained by repeatedly executing the calibration process at multiple calibration trigger times, the link delay calibration value is obtained by taking the median or average value after removing outliers. The original output timestamp of each CO2 concentration value is back-corrected based on the link delay calibration value to obtain the corrected timestamp.

7. The method of claim 1, wherein, The method further includes: Synchronization output data is generated based on the link delay calibration value, the original output timestamp, and the corrected timestamp. The synchronization output data includes the CO2 concentration value, the original output timestamp, the corrected timestamp, the link delay calibration value, the calibration status, and the synchronization quality identifier.

8. The method of claim 7, wherein, The method further includes: The corrected timestamp is time-matched with the wind speed sequence output by the external three-dimensional ultrasonic anemometer to obtain a synchronous data sequence for carbon emission flux calculation.

9. A TDLAS-CO2 high frequency measurement system, characterized in that, include: An open-circuit WMS-TDLAS CO2 measurement module is used to perform TDLAS-CO2 high-frequency measurements and continuously output CO2 concentration sequences with raw output timestamps; The link delay calibration module is used to inject a recognizable CO2 absorption change signal into the measurement link of the open-circuit WMS-TDLAS CO2 measurement module at the calibration trigger time, and determine the actual start time of the change of the CO2 absorption change signal on the optical path according to the calibration trigger time. The delay calculation and timestamp correction module is connected to the open-circuit WMS-TDLAS CO2 measurement module and the link delay calibration module, respectively. It is used to receive the CO2 concentration sequence, identify the output response time corresponding to the CO2 absorption change signal in the CO2 concentration sequence, calculate the link delay calibration value based on the actual change start time and the output response time, and back-correct the original output timestamp of each CO2 concentration value based on the link delay calibration value to obtain the corrected timestamp.

10. The system of claim 9, wherein, The link delay calibration module includes an optical switch-type dual absorption cell structure; the optical switch-type dual absorption cell structure includes a first absorption branch, a second absorption branch, and an optical switch; the first absorption branch includes a first absorption level cell filled with zero or low concentration CO2 gas to provide a first CO2 absorption level; the second absorption branch includes a second absorption level cell filled with high concentration CO2 gas to provide a second CO2 absorption level.

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