54 results about "Background Correction" patented technology

The invention provides a gas detection method based on galvanometer scanning, and the method comprises the following steps: obtaining a visible light image of a to-be-detected region collected by a visible light imaging module, processing the visible light image based on a pre-trained semantic segmentation model, and obtaining a background category matrix; acquiring gas concentration information of each scanning point obtained by scanning the to-be-detected area by the galvanometer laser telemetering assembly, wherein the galvanometer laser telemetering assembly is registered with the visible light imaging module in advance; and acquiring a background category corresponding to each scanning point according to the background category matrix, and correcting a gas concentration signal of the point based on a background correction coefficient associated with the background category. According to the gas detection method, the problems of false detection and the like caused by factors such as unknown background reflectors and unknown detection object types in the existing galvanometer scanning gas detection are effectively solved, and the accuracy of gas concentration detection is improved.

The invention relates to the technical field of microbe traceability analysis, in particular to a microbe traceability analysis method based on an infrared absorption spectrum and a database, and the method comprises the following steps: acquiring absorbance spectral data: acquiring background spectral data for multiple times, performing background correction, acquiring spectral data of a sample containing a strain, and finally calculating the absorbance spectral data; preprocessing the absorbance spectrum data: smoothing the absorbance spectrum data by adopting an SG smoothing algorithm, and calculating a first-order derivative or a second-order derivative of the smoothed absorbance spectrum data to obtain an absorbance spectrum data set; spectral range selection: presetting different spectral ranges, and selecting different spectral ranges for analysis according to requirements; analyzing the similarity of the strains: analyzing the similarity of the absorbance spectral data set of the strains by adopting an improved hierarchical clustering algorithm; bacterial strain traceability analysis: determining a classification threshold by adopting a threshold determination algorithm, and judging microorganism traceability information; the traceability analysis precision is high, and the reliability, the stability and the practicability are high.

The invention discloses a method for detecting trace chromium element in copper foil based on ICP-OES (Inductively Coupled Plasma-Optical Emission Spectrometer), which comprises the following steps: soaking a lithium battery copper foil in a mixed solution of concentrated nitric acid and hydrofluoric acid for high-temperature digestion, adding a scandium internal standard solution, and fixing the volume to obtain a solution to be detected; preparing a mixed standard solution of chromium element and scandium element with a plurality of concentration gradients, and establishing a standard curve through ICP-OES; and determining the content of the chromium element in the to-be-detected solution according to the standard curve. The lithium battery copper foil is digested through a mixed acid system, concentrated nitric acid provides an acid environment and an oxidation effect, hydrofluoric acid promotes dissolution, it is ensured that the copper foil is completely dissolved, and the digestion efficiency is improved; a scandium internal standard method is introduced, a dynamic background correction mode of ICP-OES is adopted, a scandium internal standard element can correct signal fluctuation in a sample introduction process, dual guarantee is formed by the scandium internal standard element and dynamic background correction, interference of a copper matrix on a Cr spectral line is specifically eliminated, and the trace chromium element detection precision is remarkably improved.

The invention relates to the technical field of metal materials, and discloses a spectral analysis monitoring method for aluminum alloy component detection, and the method comprises the following steps: carrying out standardized surface pretreatment on an aluminum alloy sample; collecting spectral data of the sample by adopting a laser-induced breakdown spectroscopy technology; performing noise filtering and background correction on the spectral data through a wavelet transform algorithm; establishing a spectral feature database for element qualitative identification; carrying out element quantitative analysis by adopting an internal standard method, and calculating the content of each element through a calibration curve; comparing a detection result with a standard mark component range to generate component conformity evaluation; performing deviation analysis and performance prediction on samples which do not meet the standard; and finally, generating a quality grading report based on the multi-dimensional evaluation indexes. According to the method, the accuracy of component qualitative identification is ensured, the detection error is reduced, the repeatability and efficiency of detection are improved, and the effectiveness of risk management and control and the overall reliability of a detection result are improved.

The invention discloses a method for monitoring the heat dissipation performance of a module in a salt mist environment, and belongs to the technical field of material performance monitoring, and the method comprises the steps: carrying out the continuous spectrum data collection of the heat dissipation surface of the module in the salt mist environment, obtaining original multispectral data, carrying out the background correction, generating multispectral imaging data, and recognizing an action region; analyzing the spectral response attribute of the action area, obtaining a characteristic spectral fingerprint, carrying out physical parameter inversion, obtaining heat dissipation related physical parameters, and combining heat flow distribution data during the operation of the synchronous acquisition module to establish a related mapping relationship; and carrying out quantitative evaluation on the influence degree and the degradation trend of the salt mist environment on the heat dissipation performance of the module by combining the related mapping relationship to obtain a performance evaluation report. According to the method, the technical means of combining multispectral imaging analysis and heat flow data modeling is adopted, and quantitative diagnosis and trend prediction of heat dissipation performance degradation can be achieved.

The invention discloses a hierarchical fusion non-uniformity correction method for a multi-channel splicing detector, and belongs to the technical field of photoelectric imaging detection. In an off-line calibration stage, flat field data under multiple groups of different working parameters are collected, and calibration of two sets of correction parameters is executed in parallel after preprocessing: a first path adopts a sequence of first in-channel and second between-channel to calibrate a pixel-level single-channel correction coefficient and an inter-channel global correction coefficient; and the path II adopts a sequence of firstly global and then in the channel to calibrate a global correction coefficient and a pixel-level detail compensation coefficient. And an online correction stage: for the image after background correction, calculating an adaptive weight based on a local signal-to-noise ratio and a spatial gradient feature, performing weighted fusion on the two paths of correction coefficients according to the adaptive weight to obtain equivalent gain and bias coefficients, and finally outputting a corrected image. According to the invention, through double-path complementary correction and an adaptive weight mechanism, image details are effectively protected while uniformity between channels is ensured.

Provided is an X-ray fluorescence spectrometer that achieves a uniform state on a back side of a thin sheet-shaped sample so as to prevent a difference in a measurement condition depending on a measurement position. The X-ray fluorescence spectrometer includes: a sample stage; a background correction cover, which is arranged adjacent to an outer side of the sample stage so that a surface of the background correction cover is substantially flush with a surface of the sample stage; and a moving mechanism. The moving mechanism moves the background correction cover based on movement of the sample stage and, when the sample stage is absent on a back side of the sample at a measurement position, moves the background correction cover so that the background correction cover is located on the back side of the sample at the measurement position.

The invention relates to the technical field of down feather detection, in particular to a method and system for detecting iron in down feather based on spectral analysis. The method comprises the following steps: pretreating to-be-detected down feather to obtain a to-be-detected down feather sample; performing dual-mode spectrum collaborative excitation on the down feather sample to be detected, and performing signal acquisition to obtain detection data of the down feather sample to be detected; performing background correction operation on the detection data of the down feather sample to be detected to obtain correction data of the down feather sample to be detected; obtaining an iron detection result of the down feather sample to be detected according to the correction data of the down feather sample to be detected; therefore, the iron in the down feather can be accurately detected.

The invention discloses a coal composition and gangue rapid identification method in an intelligent coal dressing process, and relates to the technical field of photoelectric detection. The method comprises the following steps: acquiring an original spectral signal and a belt background spectrum, and preprocessing and calibrating the original spectral signal to obtain a current material spectrum; whether belt background interference exists in the current material spectrum or not is judged through spectrum similarity calculation, if the belt background interference exists, a belt signal proportion coefficient alpha is obtained through quantification based on a preset linear spectrum mixing method, and a belt background existence mark is set to be true; the alpha is compared with a preset interference threshold value, when the alpha is higher than the interference threshold value, spectrum background correction is carried out on the current material spectrum, and a corrected material spectrum is obtained; interference of belt reflection on material spectrums can be effectively eliminated, real spectral characteristics of the thin coal seam are completely recovered, and coal resources are prevented from being mistakenly eliminated as gangue.

The invention discloses a polarized light microscopic quantitative method for calcium oxalate crystals in ginseng. The method comprises the following steps: S1, crushing a sample, sieving, precisely weighing, preparing a test sample suspension, vortex and loading; s2, collecting a full-view microscopic image under a polarizing microscope; s3, color separation, background correction, gray level conversion and threshold segmentation processing are carried out on the image, and the full-view calcium oxalate crystal cross-sectional area is calculated; s4, based on a calculation formula of the calcium oxalate crystal cross-sectional area and the dry weight of the sample, calculating to obtain the calcium oxalate crystal cross-sectional area per unit mass; s5, true and false identification of the ginseng and classification evaluation of the ginseng participating in the garden under the forest are achieved through the unit mass calcium oxalate crystal cross-sectional area. The invention belongs to the field of property determination of traditional Chinese medicinal materials, and particularly relates to a polarized light microscopic quantitative method for calcium oxalate crystals in ginseng.

Method (100) of optical spectroscopy for analyzing a sample using an optical spectrometer (10), comprising: Obtaining a sample spectrum (101) of the sample using the optical spectrometer; Obtaining a blank spectrum (102) using the optical spectrometer, wherein the blank spectrum includes structured background radiation that correlates with the sample spectrum; Determining a cross-correlation (103) of the sample spectrum and the blank spectrum; Generating a mapped blind spectrum (105) by mapping the blind spectrum onto the sample spectrum based on cross-correlation; and Subtracting the imaged blank spectrum from the sample spectrum to produce a background-corrected sample spectrum (106).

To provide a radioactive material monitoring device capable of accurately detecting the concentration of radioactive materials in a liquid to be detected. [Solution] A radioactive material monitoring device comprising a flow channel through which a liquid to be detected flows, a counter unit that counts signals based on radiation generated from within the flow channel, and an analysis unit that calculates the concentration of radioactive material in the liquid to be detected based on the radiation count rate obtained from the counter unit, wherein the analysis unit includes a background correction unit that calculates a background value from the count rate based on the volume of the liquid to be detected in the flow channel and the count rate obtained from the counter unit, and a concentration calculation unit that calculates the concentration of radioactive material in the liquid to be detected based on the background value calculated by the background correction unit and the count rate obtained from the counter unit.

The present application relates to the technical field of down detection, and particularly relates to a method and system for detecting iron in down based on spectral analysis; the present application obtains a down sample to be detected by pretreating the down to be detected; performs dual-mode spectral synergistic excitation on the down sample to be detected, collects signals, and obtains detection data of the down sample to be detected; performs background correction on the detection data of the down sample to be detected, and obtains corrected data of the down sample to be detected; obtains an iron detection result of the down sample to be detected according to the corrected data of the down sample to be detected; and thus accurate detection of iron in down is realized.

The invention relates to the technical field of electronic data processing, and discloses a detection data processing method and system for a helium leak detector for a diaphragm compressor, and the method comprises the steps: obtaining an original helium concentration time sequence signal and a periodic frequency parameter of the stroke of the diaphragm compressor; constructing a notch filter bank, and filtering the original helium concentration time sequence signal to obtain a preliminary signal; performing wavelet transform decomposition on the initial signal, performing threshold processing on a wavelet coefficient, and then performing reconstruction to obtain a de-noised signal; iterative fitting is carried out on the de-noised signal, a dynamic background baseline is estimated, and a background correction signal is obtained; calculating a first-order time derivative sequence, a local information entropy sequence and morphological correlation; and when the amplitude of the first-order time derivative sequence is continuously higher than a first threshold value, the local information entropy sequence is lower than a second threshold value, and the morphological correlation degree is higher than a third threshold value, judging that leakage occurs. According to the invention, multi-dimensional and high-confidence identification can be carried out on the leakage event, and the detection sensitivity, the anti-interference capability and the reliability of tiny leakage are improved.

The present application relates to a kind of astronomical image background extraction method and system, mainly for the processing of starry sky background in space small target detection process;Extraction method includes the following steps: S1, according to the gray characteristic of the astronomical image to be processed, the size of the largest star in astronomical image is detected, to set the window length of one-dimensional median filtering;S2, the background of astronomical image is extracted using the method of bidirectional one-dimensional median filtering, to obtain the image after background correction;S3, the background of the image after background correction is extracted using adaptive interframe difference method.The part outside target area is regarded as the background of astronomical image in the present application, and the effect of suppressing complex background interference in star map and filtering background star can be achieved by extracting and subtracting the background of astronomical image, which creates favorable conditions for subsequent detection of space small target.

This invention discloses a multipath error fusion correction method and system based on BeiDou multi-orbit differences. The method includes: collecting BeiDou carrier phase observation data from a reference station and a monitoring station; obtaining double-difference residuals through preprocessing and double-difference calculation, and converting them into single-difference residual sequences; classifying BeiDou satellites into three categories based on their orbital types: geostationary orbit satellites, inclined geosynchronous orbit satellites, and medium Earth orbit satellites; extracting stable background information from the GEO residuals, slowly changing information from the IGSO residuals, and anomalous disturbance information from the MEO residuals by combining satellite azimuth and elevation angle information; constructing a basic hemispherical model based on the stable background information of each satellite, and using the stable background information, slowly changing information, and anomalous disturbance information to constrain and update the basic background correction value, generating the current epoch multipath correction value; and applying the correction value to the corresponding satellite observation value to complete the observation correction and deformation monitoring calculation.

The present invention discloses a polarized light microscopic quantitative method for calcium oxalate crystals in ginseng, comprising the steps of S1. crushing, sieving, accurately weighing, preparing a sample suspension, vortexing, and mounting; S2. collecting a full-field microscopic image under a polarized light microscope; S3. performing color separation, background correction, grayscale conversion, and threshold segmentation on the image to calculate the full-field calcium oxalate crystal cross-sectional area; S4. calculating the unit mass calcium oxalate crystal cross-sectional area based on a calculation formula of the calcium oxalate crystal cross-sectional area and the sample dry weight; S5. realizing the authenticity identification of ginseng and the classification and evaluation of forest ginseng and garden ginseng through the unit mass calcium oxalate crystal cross-sectional area. The present invention belongs to the field of property determination of traditional Chinese medicine, and specifically refers to a polarized light microscopic quantitative method for calcium oxalate crystals in ginseng.

The invention relates to a method and device for measuring the concurrency of vector light beams based on single speckle spatial correlation, and the method comprises the steps: scattering a to-be-measured vector light beam into a spatial incoherent light field, converting the spatial incoherent light field into a partially coherent light field through Fourier transform, collecting an original speckle intensity distribution map in the central region of a Fourier transform plane, and calculating the concurrency of the vector light beam; the method comprises the following steps of: performing background correction and spatial self-correlation operation on the optical concurrency to obtain a normalized spatial correlation distribution diagram, reading a zero displacement point value as a correlation value, calculating the concurrency according to a linear relation between the correlation value and the optical concurrency, and comprising rotary frosted glass, a lens, an image sensor and a calculation module. The concurrency degree can be output in real time only through single-time speckle shooting and single-point correlation reading, the system complexity is remarkably reduced through linear optical device combination, high precision and high robustness are kept in turbulent flow and other complex medium environments, and an efficient measurement scheme is provided for optical communication and other dynamic scenes.

A method of optical spectroscopy for analysing a sample using an optical spectrometer is provided. The method comprises obtaining a sample spectrum of the sample using the optical spectrometer and obtaining a blank spectrum using the optical spectrometer. The blank spectrum comprises structured background radiation which is correlated with the sample spectrum. A cross-correlation of the sample spectrum and the blank spectrum is determined. A mapped blank spectrum is generated by mapping the blank spectrum to the sample spectrum based on the cross-correlation, and the mapped blank spectrum is subtracted from the sample spectrum to generate a background corrected sample spectrum.

The application provides an immune test weak positive sample intelligent interpretation method and system, a weak positive sample image containing a detection line and a quality control line region in an immune chromatography test strip is divided into multiple local region blocks; structural similarities between each group of adjacent local region blocks are determined, candidate line regions and background regions of the detection line are screened from the weak positive sample image based on all the structural similarities; a probability heat map of the detection line is generated according to the gray gradient distribution of the candidate line region, the contribution characteristics of the background region to the weak positive sample image are determined, the background correction characteristic region of the detection line in the weak positive sample image is determined through the contribution characteristics; the contrast index of the signal-to-noise ratio corresponding to the detection line in the immune chromatography test strip is determined by the signal-to-noise ratio of the detection line in the background correction characteristic region, and then a grading report of the weak positive sample is generated. By adopting the scheme, the influence of the continuity of the detection line on the weak positive sample test can be reduced.

The invention provides an adhesive component quantitative detection method and system based on spectral analysis, and relates to the technical field of analysis and detection.According to the method, near infrared spectral data of an adhesive sample are obtained, and environmental background spectral data are synchronously collected for background correction, so that interference is eliminated. And performing signal enhancement processing on the corrected data, extracting spectral features under different scales, and separating overlapped absorption peaks. In the decomposition process, for the possible layering or interfacial effect of the adhesive, an interfacial feature enhancement treatment is introduced to focus on the absorption features of the internal layered structure. A compensation factor of flow-induced spectral distortion is introduced based on the transmission speed of the production line, and characteristics related to the internal structure are corrected. And combining the corrected characteristics into a set, inputting the set into a quantitative prediction model established through supervised learning in advance, and outputting the concentration value of the adhesive component, so that high-precision quantitative detection of the adhesive component can be realized.

The invention discloses a glutathione peroxidase activity determination kit and a determination method thereof, and relates to the technical field of biomedicines.The kit comprises a first reagent unit which is physically separated, freeze-dried reduced glutathione, glutathione reductase, NADPH, a biperoxide substrate, a composite buffer system and a stabilizer; the second reagent unit contains a liquid buffer system, a surfactant, an interference inhibitor and an osmotic pressure regulator; according to the matched determination method, single-step sample adding and 340nm full-time-history dynamic monitoring are adopted, and a background correction algorithm is combined. The invention aims to solve the systematic technical defects of reduced detection accuracy, tedious operation process, insufficient reagent stability, difficulty in adapting to an automatic detection platform and the like caused by sample matrix difference in the prior art, and realizes high sensitivity, high stability, full-automatic detection and inter-batch variation coefficient lt; the method is suitable for high-throughput clinical application.

The application discloses a blood smear white blood cell classification counting method and system based on image analysis, and belongs to the technical field of medical image processing. The method comprises the following steps: after collecting a peripheral blood smear image, performing adaptive background correction and color standardization pretreatment; detecting and segmenting each white blood cell through an instance segmentation network; extracting three-dimensional features of nuclear morphology, cytoplasmic staining and nuclear-cytoplasmic ratio and adaptively fusing; adopting a cascade classifier to perform five-class white blood cell classification and abnormal morphology identification; and counting and labeling suspected abnormal cells for review. The classification coincidence rate of the application reaches more than 95%, can effectively identify abnormal morphologies such as atypical lymphocytes, immature cells and toxic granules, and provides technical support for blood tests at the grassroots level.

The application discloses a method and system for controlling a tunnel lip casting based on infrared positioning, and relates to the technical field of lip casting control. The method for controlling the tunnel lip casting based on infrared positioning projects infrared reference light spots into the inner cavity of the tunnel lip and collects infrared images; through background correction and sub-pixel extraction, actual contour point sets and light spot projection centers are obtained, the center is taken as a reference to generate a positioning eccentricity vector by constraint fitting and to perform positioning adjustment, after the adjustment, infrared time sequence signals of each orientation sprue are collected by sliding, a filling infrared radiation change rate curve is generated by radiation and flow mapping, an asymmetric compensation reference value is generated according to the eccentricity vector, the spatial relative deviation degree is analyzed, the metal liquid pressure injection flow value is generated by composite mapping processing, and the tunnel lip casting control processing is performed. The application realizes the precise control of the lip wall thickness and improves the forming quality of the casting by performing the tunnel lip casting control processing based on the metal liquid pressure injection flow value.

This invention discloses a method and system for identifying and assessing soil heavy metal pollution sources based on machine learning. The method constructs a feature dataset by collecting data on heavy metal element content and spatial environmental attributes of soil in a target area; it decomposes the input matrix using multivariate analysis and k-means clustering to obtain a source spectrum matrix and a source contribution matrix, thus identifying pollution sources and analyzing their contributions; further, it establishes a background contribution model by combining conservative elements and time series information to extract the background contribution value of each pollution source within the target time period; it calculates single-factor and comprehensive risk indices based on pollution source reconstruction and background correction, and generates soil heavy metal pollution risk level information by combining dynamic risk grading thresholds; finally, it generates a soil heavy metal pollution risk distribution map of the target area through spatial interpolation and zoning processing, simultaneously achieving quantitative analysis of pollution sources, background value correction, risk index calculation, and spatial visualization.

The invention discloses a nitrate nitrogen concentration detection method and system based on double interference correction, and the method comprises the steps: obtaining the absorbance data of a water sample to be detected under a plurality of visible light and ultraviolet light wavelengths, constructing a suspended matter interference correction model, and obtaining the absorbance data of the water sample to be detected after suspended matter background correction; constructing a dissolved organic matter interference correction model by using the absorbance data under the ultraviolet wavelength corrected by the suspended matter to obtain the absorbance data of the dissolved organic matter; the method comprises the following steps: removing absorbance data of soluble organic matters from absorbance data of a to-be-detected water sample subjected to suspended matter background correction so as to obtain absorbance data of nitrate nitrogen; calculating the nitrate nitrogen concentration in the to-be-detected water sample based on a pre-calibrated nitrate nitrogen concentration and absorbance relation equation; the method can effectively realize synchronous correction of double interference of suspended matters and soluble organic matters under the condition of no sample pretreatment, so as to obtain high-precision nitrate nitrogen concentration.

Provided is an X-ray fluorescence spectrometer that achieves a uniform state on a back side of a thin sheet-shaped sample so as to prevent a difference in a measurement condition depending on a measurement position. The X-ray fluorescence spectrometer includes: a sample stage a background correction cover, which is arranged adjacent to an outer side of the sample stage so that a surface of the background correction cover is substantially flush with a surface of the sample stage; and a moving mechanism. The moving mechanism moves the background correction cover based on movement of the sample stage and, when the sample stage is absent on a back side of the sample at a measurement position, moves the background correction cover so that the background correction cover is located on the back side of the sample at the measurement position.

An EV71 severe hand-foot-and-mouth disease prevention method based on quantum dot fluorescence sensing belongs to the technical field of disease prevention, and comprises the following steps: selecting a non-functionalized quantum dot solution, a carboxyl ligand solution and a buffer solution to prepare a quantum dot fluorescence probe for specifically recognizing EV71 virus capsid protein; the method comprises the following steps: collecting a biological sample of a subject, and pretreating the biological sample to obtain a sample solution; the quantum dot fluorescent probe is added into a sample solution, fluorescence is excited after incubation, and fluorescence intensity data is collected. And performing background correction on the fluorescence intensity data, and comparing the fluorescence intensity data with a pre-established health and infection threshold library to output a detection result and a risk level corresponding to the detection result. And generating an early warning report according to the detection result and the risk level, and sending the early warning report to the clinical management terminal. According to the invention, early, sensitive and specific detection of the EV71 virus is realized, and early warning is given out before clinical symptoms are not caused by infection, so that intervention measures are started in time.

The application discloses a correction testing device and method for containment penetration sealing detection and evaluation, and belongs to the field of nuclear safety. The device comprises a main simulation module (radiation-resistant acrylic cylinder), a pore simulation module (a plurality of diameter thin wires form a preformed through hole), a pressurized sealing module, a sound insulation anti-interference module and a measurement adaptation module. By establishing a'sound intensity-leakage rate' calibration curve in the laboratory and combining with the field environment background correction, the quantitative evaluation of the leakage rate of BC type penetration under low pressure conditions based on the ultrasonic leak detection method is realized. The method flow is as follows: device sealing verification, flow supplement method for determining standard leakage rate, ultrasonic measurement for recording test sound intensity and background, calculating net sound intensity, establishing a calibration model by cubic polynomial fitting, measuring the field measurement environment background and calculating the linear amplitude correction coefficient, and substituting the calibration model to obtain the field leakage rate. The device takes into account the influence of field noise, is convenient for online rapid detection of nuclear island, reduces detection cost and radiation exposure risk of personnel.

This invention provides a fluorescence X-ray analysis apparatus that, by ensuring that the back surface of a thin plate-shaped sample is uniform, avoids differences in measurement conditions due to measurement positions. The fluorescence X-ray analysis apparatus comprises: an X-ray source that irradiates the surface of a plate-shaped sample with a single X-ray; a detector that measures the intensity of the fluorescence X-rays; a sample stage on which the sample is placed; an analysis unit that performs analysis at multiple measurement positions on the sample surface; a background correction cover having an outer edge portion shaped along a portion of the outer edge of the sample stage, adjacent to the outer side of the sample stage, and having its surface disposed on approximately the same plane as the surface of the sample stage; and a moving mechanism that moves the sample stage to allow single X-ray irradiation at any measurement position on the sample surface, wherein the moving mechanism moves the background correction cover along with the sample stage, and when there is no sample stage on the back surface of the sample at the measurement position, the background correction cover is moved to the back surface of the sample at the measurement position.