A cross-calibration method for cross-instrument LIBS spectra
By employing adaptive spectral interpolation and intensity correction, the problem of differences in spectral intensity and characteristic peak positions between different LIBS instruments was solved, enabling accurate cross-calibration of LIBS spectra across instruments and improving the reliability of data analysis.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- TONGJI UNIV
- Filing Date
- 2023-08-15
- Publication Date
- 2026-06-23
AI Technical Summary
When different LIBS instruments detect the same target under different detection environments, the differences in the intensity and peak position of the obtained LIBS spectra lead to inconsistent results in the analysis of material composition, affecting the accuracy and reliability of data analysis. Existing cross-calibration methods across instruments cannot effectively correct for differences in the position and intensity of characteristic peaks.
An adaptive spectral interpolation method is adopted, which uses spline interpolation to interpolate data, calculates spectral intensity unit conversion and performs intensity correction. Combined with an adaptive spectral drift correction method, the position of characteristic peaks is corrected to achieve cross-calibration of LIBS spectra across instruments.
It effectively eliminates differences in spectral intensity and characteristic peak position between different instruments, improves the consistency of spectral data, ensures the consistency of data analysis results between different LIBS loads, and is applicable to various types of LIBS equipment.
Smart Images
Figure CN117129465B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of spectral correction, and in particular to a cross-calibration method for LIBS spectra across instruments. Background Technology
[0002] LIBS (Laser-Induced Breakdown Spectroscopy) continues to play an important role in environmental monitoring, bioarchaeology, metal detection, and mineral composition analysis. LIBS utilizes the interaction of high-power-density lasers with matter to generate transient plasmas, and employs optical systems to collect the emission spectra of atoms and ions in the plasmas. By analyzing the spectral information, qualitative or quantitative analysis of the chemical elements in the matter can be achieved.
[0003] However, due to the influence of instrument parameters and detection environment, the intensity and peak position of LIBS spectra obtained by different LIBS instruments under different detection environments when detecting the same target can vary. This leads to inconsistencies in the results of multiple LIBS spectral observations and analyses of the same target during subsequent material composition analysis, thus affecting the accuracy of the material composition analysis and reducing the reliability of cross-validation of data analysis results between different LIBS payloads. Therefore, a cross-instrument cross-calibration method is needed to correct the differences in intensity and peak position of LIBS spectral data caused by different instrument parameters and detection environment, providing a consistency guarantee and data foundation for cross-validation of data analysis results between different LIBS payloads.
[0004] Existing cross-calibration methods across instruments have the following drawbacks:
[0005] 1) Data interpolation method: Existing methods mainly use a reference spectrum as a benchmark to perform data interpolation on the spectrum to be calibrated. That is, after interpolating the wavelength of the spectrum to be calibrated, only the set of pixels whose wavelength values match those in the reference spectrum are selected from a large number of interpolated data points as the interpolated calibration data. Although this data interpolation method ensures the originality of the reference spectrum, it changes the spectral shape of the spectrum to be calibrated to some extent, especially when the parameters of the two instruments differ significantly, resulting in the loss of some characteristic peak positions.
[0006] 2) Peak Position Correction Methods: Existing methods primarily aim to determine the relationship between pixels and wavelengths. Therefore, polynomial fitting is often used for peak position correction. However, due to the limited resolution of the instrument, a significant wavelength interval still exists between pixels, causing the position of elemental characteristic peaks to typically lie between two pixels. The aforementioned methods only make the wavelengths corresponding to each pixel in the (Charge-coupled Device) CCD more accurate, without correcting the most critical elemental characteristic peak positions.
[0007] Therefore, there is an urgent need to design a cross-instrument LIBS spectral cross-calibration method that can perform characteristic peak position correction and intensity correction. Summary of the Invention
[0008] The purpose of this invention is to overcome the shortcomings of the prior art by providing a cross-instrument LIBS spectral cross-calibration method capable of performing characteristic peak position correction and intensity correction.
[0009] The objective of this invention can be achieved through the following technical solutions:
[0010] A cross-calibration method for LIBS spectra across instruments includes the following steps:
[0011] Step S1: Obtain the LIBS spectrum of the target as a reference spectrum using the first instrument, and obtain the LIBS spectrum of the target as a spectrum to be calibrated using the second instrument. Adaptively extract LIBS spectrum data of the reference spectrum and the spectrum to be calibrated in each same wavelength range. Use each wavelength range as a channel and perform data interpolation on the extracted reference spectrum and the spectrum to be calibrated by channel.
[0012] Step S2: Calculate the conversion relationship between the spectral intensity units of the reference spectrum and the spectral intensity units of the spectrum to be calibrated, and perform unit conversion on the spectrum to be calibrated after data interpolation.
[0013] Step S3: Calculate the intensity ratio of the reference spectrum and the spectrum to be calibrated for the same target using the LIBS spectrum pixel by pixel, and correct the intensity of the spectrum to be calibrated after unit conversion based on the ratio.
[0014] Step S4: Based on the adaptive spectral drift correction method, the characteristic peak positions of the intensity-corrected spectrum to be calibrated are corrected using the reference spectrum after data interpolation as a reference.
[0015] Furthermore, the adaptive extraction method in step S1 is as follows:
[0016] Input the reference spectrum and the spectrum to be calibrated, iterate through the wavelength values of the two spectra, determine the number of segments with the same range in the two spectra based on the total number of discontinuous wavelengths in the two spectra, extract the intersection of the two spectra in each segment, determine the wavelength range of each intersection, and extract the data.
[0017] Furthermore, in step S1, the data interpolation uses spline interpolation to interpolate a specified number of points for each channel.
[0018] Furthermore, the range of the number of points is greater than the number of data points before interpolation.
[0019] Furthermore, in step S2, the calculation expression for unit conversion is:
[0020]
[0021] In the formula, I A I is the intensity unit of the reference spectrum. B λ is the intensity unit of the spectrum to be calibrated, h is Planck's constant, c is the speed of light, and λ is the wavelength corresponding to each pixel of the spectrum to be calibrated.
[0022] Furthermore, in step S3, the intensity ratio is obtained by constructing a numerical matrix from multiple LIBS spectra and averaging each column of the numerical matrix.
[0023] Furthermore, in step S3, the intensity ratio is used to correct the intensity of the spectrum to be calibrated. The specific method is as follows:
[0024] The intensity of each pixel in the spectrum to be calibrated after unit conversion is multiplied by the intensity ratio calculated in step S3.
[0025] Furthermore, the adaptive spectral drift correction method in step S4 is specifically as follows:
[0026] Based on the peak position distribution of the characteristic peaks in the reference spectrum after data interpolation, the reference spectrum is further segmented to obtain the segmentation results. The segmentation results are then applied to the calibrated spectrum after unit conversion. The positions of the characteristic peaks in the same segment of the reference spectrum and the calibrated spectrum are found respectively. After shifting the strongest peak in each segment of the calibrated spectrum to the position of the characteristic peak in the same segment of the reference spectrum, the adaptive spectral drift correction is completed.
[0027] According to a second aspect of the invention, an electronic device is provided, including a memory and a processor, wherein the processor, when executing a program, implements any cross-calibration method for cross-instrument LIBS spectra.
[0028] According to a third aspect of the invention, a computer-readable storage medium is provided having a computer program stored thereon, which, when executed by a processor, implements any cross-calibration method for cross-instrument LIBS spectra.
[0029] Compared with the prior art, the present invention has the following beneficial effects:
[0030] 1) This invention protects the spectral shape of the data to be calibrated by adaptively selecting spectra with wavelengths within the same range for data interpolation, thus avoiding the loss of characteristic peaks. By converting intensity units, the method of this invention can be applied to different types of LIBS equipment. The intensity of the spectrum is corrected according to the ratio to correct the intensity differences caused by instrument parameters and detection environment. An adaptive segmented correction drift correction method is adopted. The spectrum is further segmented according to the position of characteristic peaks, which improves the consistency of the same characteristic peak positions between the reference spectral data and the spectral data to be calibrated before and after cross-calibration, and reduces the impact of differences in instrument parameters and detection environment on the differences in characteristic peak positions.
[0031] 2) This invention can perform cross-calibration between any LIBS spectra of two instruments based on the relevant information of the two instruments, eliminating the differences between the intensity and peak position, and has a wide range of applications. Attached Figure Description
[0032] Figure 1 This is a schematic diagram of the process of the present invention;
[0033] Figure 2 This refers to the intensity of the spectrum to be calibrated used in this embodiment of the invention before and after steps S1, S2 and S3 (i.e. intensity correction related steps) and the intensity of the reference spectrum in the first channel (242-340nm);
[0034] Figure 3 This refers to the intensity of the spectrum to be calibrated used in this embodiment of the invention before and after steps S1, S2 and S3 (i.e. intensity correction related steps) and the intensity of the reference spectrum in the second channel (382-470nm).
[0035] Figure 4 This refers to the intensity of the spectrum to be calibrated used in this embodiment of the invention before and after steps S1, S2 and S3 (i.e. intensity correction related steps) and the reference spectrum in the third channel (474-850nm).
[0036] Figure 5 This describes the peak position correction of the characteristic peak in the first channel (240-340nm) of the spectrum to be calibrated before and after cross-calibration, compared with the reference spectrum in the embodiments of the present invention.
[0037] Figure 6 This is the peak position correction of the characteristic peak in the second channel (382-470nm) of the spectrum to be calibrated used in the embodiments of the present invention before and after cross-calibration, compared with the reference spectrum.
[0038] Figure 7 This describes the peak position correction of the characteristic peak in the third channel (474-850nm) of the spectrum to be calibrated before and after cross-calibration, compared with the reference spectrum, in the embodiments of the present invention. Detailed Implementation
[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.
[0040] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.
[0041] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature.
[0042] Example
[0043] like Figure 1 As shown, this embodiment presents a cross-calibration method for LIBS spectra across instruments, specifically including the following steps:
[0044] Step S1: Obtain the LIBS spectrum of the target as a reference spectrum using the first instrument, and obtain the LIBS spectrum of the target as a spectrum to be calibrated using the second instrument. Adaptively extract LIBS spectrum data of the reference spectrum and the spectrum to be calibrated in each same wavelength range. Use each wavelength range as a channel and perform data interpolation on the extracted reference spectrum and the spectrum to be calibrated by channel.
[0045] Step S2: Calculate the conversion relationship between the spectral intensity units of the reference spectrum and the spectral intensity units of the spectrum to be calibrated, and perform unit conversion on the spectrum to be calibrated after data interpolation.
[0046] Step S3: Calculate the intensity ratio of the reference spectrum and the spectrum to be calibrated for the same target using the LIBS spectrum pixel by pixel, and correct the intensity of the spectrum to be calibrated after unit conversion based on the ratio.
[0047] Step S4: Based on the adaptive spectral drift correction method, the characteristic peak positions of the intensity-corrected spectrum to be calibrated are corrected using the reference spectrum after data interpolation as a reference.
[0048] The specific details of each step in this embodiment are as follows:
[0049] like Figure 1 As shown in the figure, this embodiment presents a cross-calibration method for cross-instrument LIBS data, which specifically includes the following steps:
[0050] Step S1: Obtain the LIBS spectrum of the target as a reference spectrum using the first instrument, and obtain the LIBS spectrum of the target as a calibration spectrum using the second instrument. Input the reference spectrum and the calibration spectrum, iterate through the wavelength values of the two spectra, determine the number of segments with the same range of the two spectra based on the total number of discontinuous wavelengths of the two spectra, extract the intersection of the two spectra in each segment, determine the wavelength range of each intersection, and extract the data.
[0051] In this embodiment, data from the reference spectrum and the spectrum to be calibrated in three wavelength ranges (240-340nm, 382-470nm, and 474-850nm) are extracted for cross-calibration. The data interpolation method used is spline interpolation. Before interpolation, the number of data points in the three wavelength ranges is less than 2000. Since the number of interpolation points should be greater than the number of data points before interpolation, the number of interpolation data points in the three wavelength ranges are 5000, 5000, and 10000, respectively.
[0052] Step S2: Calculate the conversion relationship between the spectral intensity units of the LIBS data acquired by instrument A and instrument B, and convert the intensity units of the spectrum to be calibrated to the intensity units of the reference spectrum.
[0053] The LIBS spectral intensity unit acquired by instrument A is watts, while the LIBS spectral intensity unit acquired by instrument B is photons per second. Therefore, when converting the intensity unit of the spectrum to be calibrated to the reference spectrum, the conversion relationship between the two is as follows:
[0054]
[0055] In the formula, I A I is the intensity unit of the reference spectrum. B λ is the intensity unit of the spectrum to be calibrated, h is Planck's constant, c is the speed of light, and λ is the wavelength corresponding to each pixel of the spectrum to be calibrated.
[0056] Step S3: Calculate the intensity ratio of the LIBS spectrum acquired by instrument A and instrument B for the same target on a pixel-by-pixel basis, and use this ratio to further correct the intensity of the spectrum to be calibrated.
[0057] Using instruments A and B, one and three LIBS spectra were acquired from the same target material, respectively. After processing these four spectra using steps S1 and S2, the intensity ratios of the three LIBS spectra obtained by instrument B and the one LIBS spectrum obtained by instrument A were calculated over 20,000 (5,000 + 5,000 + 10,000) pixels, resulting in a 20,000 × 3 numerical matrix. Finally, by averaging each column, the intensity ratio matrix converted from those obtained by instruments B and A was obtained. The average of each column of this numerical matrix was then used to obtain the intensity ratio per pixel. The intensity of each pixel in the calibrated spectrum was multiplied by the intensity ratio per pixel calculated in step S3 to obtain the intensity-corrected calibrated spectrum.
[0058] like Figure 2-4 As shown, after steps S1-S3, the intensity of the data to be calibrated is significantly closer to the intensity of the standard data, and the difference in intensity between the two is reduced from 10. 10 This order of magnitude drops to 10 0 At this order of magnitude, the difference between the two is significantly reduced. At the same time, after steps S1-S3, the peaks with the strongest intensity in the three channels, especially in the first and second channels, basically achieve the goal of the same intensity, indicating that steps S1-S3 can effectively correct the intensity differences caused by instrument parameters and detection environment.
[0059] Step S4: Based on the adaptive spectral drift correction method, using the reference spectrum as a reference, the peak positions of the spectrum to be calibrated are corrected. The specific process is as follows:
[0060] Based on the peak position distribution of the characteristic peaks in the reference spectrum after data interpolation, the reference spectrum is further segmented to obtain the segmentation results. The segmentation results are then applied to the calibrated spectrum after unit conversion. The positions of the characteristic peaks in the same segment of the reference spectrum and the calibrated spectrum are found respectively. After shifting the strongest peak in each segment of the calibrated spectrum to the position of the characteristic peak in the same segment of the reference spectrum, the adaptive spectral drift correction is completed.
[0061] Table 1. Positions of some characteristic peaks in LIBS spectra before and after calibration (unit: nanometers) (The values in parentheses are the absolute values of the differences in the positions of the same characteristic peaks between the spectrum to be calibrated and the reference spectrum)
[0062]
[0063] Figure 5-7The figure shows the correction of characteristic peaks in the three channels of the spectrum to be calibrated after step S4. It is clear from the figure that the peak positions of the characteristic peaks in the calibrated spectrum after correction are significantly closer to the corresponding characteristic peak positions in the reference spectrum compared to before correction. As shown in Table 1, two prominent characteristic peaks were selected in each of the three channels for peak position statistics before and after correction, with the absolute values of the differences between the peak positions of the calibrated spectrum and the reference spectrum indicated in parentheses. After step S4, i.e., peak position correction of the spectral characteristic peaks, the characteristic peaks in the calibrated spectrum in all three channels are closer to the corresponding characteristic peak positions in the reference spectrum. The average peak position deviations in the three channels decreased from 0.1548 nm, 0.0568 nm, and 0.3300 nm to 0.0307 nm, 0.0046 nm, and 0.1227 nm, respectively, representing reductions of 80.17%, 91.98%, and 62.82%. The above results demonstrate that the method proposed in this invention can effectively perform cross-instrument calibration and correct the intensity and characteristic peak positions between different instruments.
[0064] In summary, through a series of qualitative and quantitative experimental analyses, the results show that the cross-calibration method for LIBS spectra across instruments proposed in this invention has significant advantages in eliminating intensity differences and characteristic peak position differences caused by instrument parameters and detection environment.
[0065] The electronic device of this invention includes a central processing unit (CPU), which can perform various appropriate actions and processes according to computer program instructions stored in read-only memory (ROM) or loaded from a storage unit into random access memory (RAM). The RAM may also store various programs and data required for device operation. The CPU, ROM, and RAM are interconnected via a bus. Input / output (I / O) interfaces are also connected to the bus.
[0066] Multiple components in the device are connected to the I / O interface, including: input units such as keyboards and mice; output units such as various types of displays and speakers; storage units such as disks and optical discs; and communication units such as network interface cards (NICs), modems, and wireless transceivers. The communication unit allows the device to exchange information / data with other devices through computer networks such as the Internet and / or various telecommunications networks.
[0067] The processing unit executes the various methods and processes described above, such as methods S1 to S4. For example, in some embodiments, methods S1 to S4 may be implemented as computer software programs tangibly contained in a machine-readable medium, such as a storage unit. In some embodiments, part or all of the computer program may be loaded and / or installed on the device via ROM and / or a communication unit. When the computer program is loaded into RAM and executed by the CPU, one or more steps of methods S1 to S4 described above may be performed. Alternatively, in other embodiments, the CPU may be configured to execute methods S1 to S4 by any other suitable means (e.g., by means of firmware).
[0068] The functions described above in this document can be performed at least in part by one or more hardware logic components. For example, exemplary types of hardware logic components that can be used, without limitation, include: field programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), application-specific standard products (ASSPs), systems-on-a-chip (SoCs), payload programmable logic devices (CPLDs), and so on.
[0069] The program code used to implement the methods of the present invention can be written in any combination of one or more programming languages. This program code can be provided to a processor or controller of a general-purpose computer, special-purpose computer, or other programmable data processing device, such that when executed by the processor or controller, the program code causes the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The program code can be executed entirely on the machine, partially on the machine, as a standalone software package partially on the machine and partially on a remote machine, or entirely on a remote machine or server.
[0070] In the context of this invention, a machine-readable medium can be a tangible medium that may contain or store a program for use by or in conjunction with an instruction execution system, apparatus, or device. A machine-readable medium can be a machine-readable signal medium or a machine-readable storage medium. Machine-readable media can include, but are not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, apparatus, or devices, or any suitable combination of the foregoing. More specific examples of machine-readable storage media include electrical connections based on one or more wires, portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fibers, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination of the foregoing.
[0071] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.
Claims
1. A cross-calibration method for LIBS spectra across instruments, characterized in that, Includes the following steps: Step S1: Obtain the LIBS spectrum of the target as a reference spectrum using the first instrument, and obtain the LIBS spectrum of the target as a spectrum to be calibrated using the second instrument. Adaptively extract LIBS spectrum data of the reference spectrum and the spectrum to be calibrated in each same wavelength range. Use each wavelength range as a channel and perform data interpolation on the extracted reference spectrum and the spectrum to be calibrated by channel. Step S2: Calculate the conversion relationship between the spectral intensity units of the reference spectrum and the spectral intensity units of the spectrum to be calibrated, and perform unit conversion on the spectrum to be calibrated after data interpolation. Step S3: Calculate the intensity ratio of the reference spectrum and the spectrum to be calibrated for the same target using the LIBS spectrum pixel by pixel, and correct the intensity of the spectrum to be calibrated after unit conversion based on the ratio. Step S4: Based on the adaptive spectral drift correction method, the characteristic peak positions of the intensity-corrected spectrum to be calibrated are corrected using the reference spectrum after data interpolation as a reference. The adaptive spectral drift correction method in step S4 is specifically as follows: Based on the peak position distribution of the characteristic peaks in the interpolated reference spectrum, the interpolated reference spectrum is further segmented to obtain the segmentation results. The segmentation results are then applied to the unit-converted spectrum to be calibrated, and the positions of the characteristic peaks in the same segment of both the interpolated reference spectrum and the unit-converted spectrum to be calibrated are found. After shifting the strongest peak in each segment of the unit-converted spectrum to the position of the characteristic peak in the same segment of the interpolated reference spectrum, the adaptive spectral drift correction is completed.
2. The cross-calibration method for cross-instrument LIBS spectra according to claim 1, characterized in that, The adaptive extraction method in step S1 is as follows: Input the reference spectrum and the spectrum to be calibrated, iterate through the wavelength values of the two spectra, determine the number of segments with the same range in the two spectra based on the total number of discontinuous wavelengths in the two spectra, extract the intersection of the two spectra in each segment, determine the wavelength range of each intersection, and extract the data.
3. The cross-calibration method for cross-instrument LIBS spectra according to claim 1, characterized in that, In step S1, data interpolation uses spline interpolation to interpolate a specified number of points for each channel.
4. The cross-calibration method for cross-instrument LIBS spectra according to claim 3, characterized in that, The range of the number of points is greater than the number of data points before interpolation.
5. The cross-calibration method for cross-instrument LIBS spectra according to claim 1, characterized in that, In step S2, the calculation expression for the unit conversion is: In the formula, I A The unit of intensity is the reference spectrum. I B The intensity unit of the spectrum to be calibrated. h It is Planck's constant. c At the speed of light, The wavelengths corresponding to each pixel in the spectrum to be calibrated.
6. The cross-calibration method for cross-instrument LIBS spectra according to claim 1, characterized in that, In step S3, the intensity ratio is obtained by constructing a numerical matrix from multiple LIBS spectra and averaging each column of the numerical matrix.
7. The cross-calibration method for LIBS spectra across instruments according to claim 1, characterized in that, In step S3, the intensity ratio is used to correct the intensity of the spectrum to be calibrated. The specific method is as follows: The intensity of each pixel in the spectrum to be calibrated after unit conversion is multiplied by the intensity ratio calculated in step S3.
8. An electronic device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the program, it implements a cross-calibration method for cross-instrument LIBS spectra as described in any one of claims 1 to 7.
9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements a cross-calibration method for cross-instrument LIBS spectra as described in any one of claims 1 to 7.