Spectral Acquisition Rate Research Articles

Integrated fiber-optic Fabry–Perot vibration/acoustic sensing system based on high-speed phase demodulation

A fiber-optic Fabry–Perot (F-P) vibration/acoustic sensing system based on high-speed phase demodulation was developed. The demodulation part is mainly composed of a super luminescent diode (SLD), a miniature high-speed spectral module, and a field programmable gate array (FPGA) based spectral signal acquisition and processing circuit. The spectral acquisition rate is up to 20 kHz. Real-time spectral acquisition, fast Fourier transform (FFT), frequency estimation, phase calculation, and mode hopping suppression are all performed by FPGA to obtain absolute cavity length of a F-P interferometric sensor. As a result, the integrated design significantly improves the speed and stability of the phase demodulation. The performance of the system was verified by a fiber-optic F-P cantilever microphone. Experimental results show that the sensing system can realize highly sensitive detection of acoustic signals with the frequency between 20 Hz and 8 kHz, which basically covers the main range of human voice frequencies. The noise equivalent minimum detection limit of sound pressure reaches 2.8 μPa/Hz1/2 at 1 kHz. The designed fiber-optic acoustic sensing system has the features of resistance to electromagnetic interference, intrinsic safety, remote detection and small size. It can be used for vibration monitoring of transformers and large structures, voice communication in coal mines and nuclear magnetic resonance rooms.

High‐Speed Mid‐Infrared Single‐Photon Upconversion Spectrometer

AbstractSensitive and fast mid‐infrared (MIR) spectroscopy is highly attractive in a variety of applications including astronomical observation, pharmaceutical synthesis, and environmental monitoring. However, the performance of conventional MIR spectrometers has long been hindered by the limited sensitivity of narrow‐bandgap detectors and/or the deficient brightness of broadband light sources. Here, an ultra‐sensitive and broadband MIR upconversion spectrometer, which integrates a supercontinuum source covering 1.5–4.2 m based on a silicon nitride nanophotonic waveguide, is devised and integrated. High‐efficiency and low‐noise nonlinear frequency upconversion is realized based on coincidence pulsed pumping with spectro‐temporal optimization, which enables leverage of silicon detectors for facilitating MIR single‐photon spectroscopy at 0.2 photons/nm/pulse. Furthermore, the upconversion‐based array spectrometer is manifested with high‐speed spectral acquisition rates beyond 200 kHz, which is about tenfold faster than the state‐of‐the‐art scan rates for FTIR‐based spectrometers at a comparable spectral resolution. The achieved features of broadband spectral coverage, single‐photon sensitivity, and sub‐MHz refreshing rate might open up new possibilities for infrared transient spectral measurements in combustion analysis, high‐throughput sorting, and reaction tracking, among others.

High-speed hyperspectral imaging enabled by compressed sensing in time domain

Hyperspectral imaging (HSI) is a powerful tool widely used for various scientific and industrial applications due to its ability to provide rich spatiospectral information. However, in exchange for multiplex spectral information, its image acquisition rate is lower than that of conventional imaging, with up to a few colors. In particular, HSI in the infrared region and using nonlinear optical processes is impractically slow because the three-dimensional (3D) data cube must be scanned in a point-by-point manner. In this study, we demonstrate a framework to improve the spectral image acquisition rate of HSI by integrating time-domain HSI and compressed sensing. Specifically, we simulated broadband coherent Raman imaging at a record high frame rate of 25 frames per second (fps) with 100 pixels × 100 pixels, which is 10 × faster than that of previous work, based on an experimentally feasible sampling scheme utilizing 3D Lissajous scanning.

Ultrafast impulsive Raman spectroscopy across the terahertz–fingerprint region

Broadband Raman spectroscopy (detection bandwidth >1000 cm − 1) is a valuable and widely used tool for understanding samples via label-free measurements of their molecular vibrations. Two important Raman spectral regions are the chemically specific “fingerprint” (200 to 1800 cm − 1) and “low-frequency” or “terahertz” (THz) (<200 cm − 1; <6 THz) regions, which mostly contain intramolecular and intermolecular vibrations, respectively. These two regions are highly complementary; broadband simultaneous measurement of both regions can provide a big picture comprising information about molecular structures and interactions. Although techniques for acquiring broadband Raman spectra covering both regions have been demonstrated, these methods tend to have spectral acquisition rates <10 spectra / s, prohibiting high-speed applications, such as Raman imaging or vibrational detection of transient phenomena. Here, we demonstrate a single-laser method for ultrafast (24,000 spectra / s) broadband Raman spectroscopy covering both THz and fingerprint regions. This is achieved by simultaneous detection of Sagnac-enhanced impulsive stimulated Raman scattering (SE-ISRS; THz-sensitive) and Fourier-transform coherent anti-Stokes Raman scattering (FT-CARS; fingerprint-sensitive). With dual-detection impulsive vibrational spectroscopy, the SE-ISRS signal shows a >500 × enhancement of <6.5 THz sensitivity compared with that of FT-CARS, and the FT-CARS signal shows a >10 × enhancement of fingerprint sensitivity above 1000 cm − 1 compared with that of SE-ISRS.

Delay-Spectral Focusing Dual-Comb Coherent Raman Spectroscopy for Rapid Detection in the High-Wavenumber Region

Rapid multiplex coherent anti-Stokes Raman scattering (CARS) spectroscopy in the high-wavenumber (HW) region shows great advantages in real-time dynamic process visualizations, clinical diagnosis, abundant microplastic assessment, etc. Fourier transform CARS (FT-CARS) improves the acquisition speed of multiplex CARS to the order of tens of kHz, yet typical approaches to utilize the intrinsic coherence of ultrabroadband pulses notably impede the attainable Raman vibrations in the HW region. Here, a novel delay-spectral focusing dual-comb (DC) CARS scheme is proposed for rapid HW Raman detection based on two fiber combs with 100 MHz repetition rates. By combining the particular advantages of DC asynchronous optical sampling and spectral focusing instantaneous single molecular vibration excitation, the Raman spectrum directly maps to DC relative delay, releasing the coherence constraint of excitation sources. Thus, an Er comb and a Yb comb, as pump and Stokes excitation pulses, respectively, flexibly match the Raman vibration in the HW region. Further, a rapid delay focusing method with intracavity electro-optic modulation is applied to actively control the DC relative delay scanning in the Raman shift region of interest. With these efforts, the spectral acquisition rate is improved more than 1000-fold up to 40 000 spectra/s, while keeping spectral resolution (∼10 cm–1) and the signal-to-noise ratio (∼260) stable along with active acquisition rate tuning. Combined with a microfluidic device, high-speed measurement in the HW region of 15 μm microbeads in flow is demonstrated by the system, reaching a high throughput of around 2150 events/s and more than 99% classification consistency. The prospect of rapid acquiring multiplex CARS spectra without the sacrifice of spectral resolution or the need for the coherence of the pulse sources offers huge potential in rapid monitoring circumstances, such as flow cytometry and microspectroscopic imaging in biomedicine.

Imaging and Direct Sampling Capabilities of Nanospray Desorption Electrospray Ionization with Absorption-Mode 21 Tesla Fourier Transform Ion Cyclotron Resonance Mass Spectrometry.

Nanospray desorption electrospray ionization mass spectrometry, a powerful ambient sampling and imaging technique, is herein coupled as an isolated source with 21 Tesla (21T) Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS). Absorption-mode data, enabled by an external data acquisition system, is applied for improved mass resolution, accuracy, and dynamic range without compromising spectral acquisition rates. Isotopic fine structure (IFS) information is obtained from the ambient sampling of living Bacillus and Fusarium species, allowing for high confidence in molecular annotations with a resolution >830 k (at m/z 825). Tandem mass spectrometry experiments for biological samples are shown to retain the IFS in addition to gained fragmentation information, providing a further degree of annotation confidence from ambient analyses. Rat brain was imaged by nanospray desorption electrospray ionization (nano-DESI) 21T FTICR MS in ∼5 h using 768 ms transients, producing over 800 molecular annotations using the METASPACE platform and low-parts-per-billion mass accuracy at a spatial resolution of ∼25 × 180 μm. Finally, nano-DESI 21T FTICR MS imaging is demonstrated to reveal images corresponding to the IFS, as well as hundreds of additional molecular features (including demonstrated differences as low as 8.96 mDa) that are otherwise undetected by a more conventional imaging methodology.

Multiplexable intrinsic Fabry-Pérot interferometers inscribed by femtosecond laser for vibration measurement in high temperature environments

This paper reports fabrication technique and demodulation algorithm developments to use multiplexable intrinsic Fabry-Pérot interferometer (IFPI) fiber sensor array for distributed vibration measurements at high temperatures. Using femtosecond laser direct writing scheme, IFPI array were fabricated through laser-induced Type II scattering points in single mode fiber cores. Reflection spectra of IFPI array were demodulated in real-time using modified Bunemen frequency analysis. The demodulation algorithm, which was implemented using a photodetector-array spectrometer, achieves 64-nε dynamic strain resolution at 1-kHz spectral acquisition rate and 2-kHz maximum vibration bandwidth. Performance and stabilities of IFPI sensor array were characterized from room temperatures to 800 °C. The static strain resolution was 0.6 με and the minimum detectable dynamic strain amplitude was 23 nε/√Hz at 800 °C. The multiplex performance was also tested by measuring dynamic strain in time domain through six IFPI sensor array fabricated in one fiber. This paper presents an integrated and low-cost sensing solution to perform distributed vibration measurements in harsh environments.

Applications and advancements of FT-ICR-MS for interactome studies.

The set of all intra- and intermolecular interactions, collectively known as the interactome, is currently an unmet challenge for any analytical method, but if measured, could provide unparalleled insight on molecular function in living systems. Developments and applications of chemical cross-linking and high-performance mass spectrometry technologies are beginning to reveal details on how proteins interact in cells and how protein conformations and interactions inside cells change with phenotype or during drug treatment or other perturbations. A major contributor to these advances is Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) technology and its implementation with accurate mass measurements on cross-linked peptide-pair precursor and fragment ions to enable improved identification methods. However, these applications place increased demands on mass spectrometer performance in terms of high-resolution spectral acquisition rates for on-line MSn experiments. Moreover, FT-ICR-MS also offers unique opportunities to develop and implement parallel ICR cells for multiplexed signal acquisition and the potential to greatly advance accurate mass acquisition rates for interactome studies. This review highlights our efforts to exploit accurate mass FT-ICR-MS technologies with chemical cross-linking and developments being pursued to realize parallel MS array capabilities that will further advance visualization of the interactome.

Time-stretch infrared spectroscopy

Improving the spectral acquisition rate of broadband mid-infrared spectroscopy promises further advancements of molecular science and technology. Unlike pump-probe spectroscopy, which requires repeated measurements with different pump-probe delays, continuous spectroscopy running at a high spectral acquisition rate enables transient measurements of fast non-repeating phenomena or statistical analysis of a large amount of spectral data. Recently, Fourier-transform infrared spectrometers with rapid delay scan mechanisms including dual-comb spectrometers have significantly improved the measurement rate up to ~1 MSpectra s−1 that is fundamentally limited by the signal-to-noise ratio. Here, we overcome the limit and demonstrate the fastest continuous broadband mid-infrared spectrometer running at 80 MSpectra s−1 by implementing a wavelength-swept time-stretch spectroscopy technique. Our proof-of-concept experiment demonstrates broadband absorption spectroscopy of phenylacetylene from 4.4 to 4.9 μm (2040–2270 cm−1) at a resolution of 15 nm (7.7 cm−1) with a signal-to-noise ratio of 85 without averaging and a shot-to-shot fluctuation of 1.3%.

Multimodal laser-scanning nonlinear optical microscope with a rapid broadband Fourier-transform coherent Raman modality

Nonlinear optical microscopy allows for rapid high-resolution microscopy with image contrast generated from the intrinsic properties of the sample. Established modalities, such as multiphoton excited fluorescence and second/third-harmonic generation, can be combined with other nonlinear techniques, such as coherent Raman spectroscopy, which typically allow chemical imaging of a single resonant vibrational mode of a sample. Here, we utilize a single ultrafast laser source to obtain broadband coherent Raman spectra on a microscope, together with other nonlinear microscopy approaches on the same instrument. We demonstrate that the coherent Raman modality allows broadband measurement (>1000 cm-1), with high spectral resolution (<5 cm-1), with a rapid spectral acquisition rate (3-12 kHz). This enables Raman hyperspectral imaging of kilo-pixel images at >11 frames per second.

Abstract A26: Precise characterization and comparison of KRAS proteoforms by top-down mass spectrometry

Abstract The two KRAS isoforms, 4A and 4B, exhibit high sequence identity, differing mainly in their C-terminal “hypervariable regions”, which bear post-translational modifications (PTMs) governing their association with the plasma membrane and downstream signaling effectors. Moreover, the KRAS gene bears three “mutation hotspot” residues (Gly12, Gly13, and Gln61) represented in a high percentage of human cancers. The similarity between KRAS isoforms, in addition to HRAS and NRAS, renders linking KRAS mutations and PTMs significantly challenging by standard proteomic methods based on digestion of proteins into short peptides. However, intact modified protein forms, or proteoforms, of KRAS4A and KRAS4B can be identified and characterized by “top-down” (TD) proteomic methods, elucidating crosstalk between N-terminal mutations and C-terminal PTMs with precise molecular detail. Previously, we employed the TD approach as part of a novel workflow to precisely characterize KRAS4B proteoforms isolated from colorectal cancer cell lines and primary tumor samples by immunoprecipitation (IP) and subsequent analysis on a benchtop Orbitrap mass spectrometer (1). Here, we modified our IP-TD protocol to include KRAS4A, then applied our workflow to the characterization, quantification, and direct comparison of KRAS4A and KRAS4B proteoforms within the context of multiple cancer cell lines. We hypothesized that we would be able to identify distinct proteoform populations for each KRAS isoform, which could then be compared both within and between different contexts. We have thus far identified nine novel proteoforms of KRAS4A, which not only exhibits differential PTM to KRAS4B, but varies widely in both abundance and PTM profile across all cell lines evaluated. We have also applied IP-TD to the analysis of endogenous KRAS4A and KRAS4B proteoforms using a more powerful 21 Tesla FT-ICR mass spectrometer at the National High Magnetic Field Laboratory. The high mass resolving power, mass measurement accuracy, and spectral acquisition rate achieved at high field combined with use of efficient dissociation methods and an external fragment ion accumulator to improve signal-to-noise ratios of MS/MS spectra produced unparalleled results with respect to degree of KRAS proteoform characterization. We were able to identify up to ten new KRAS proteoforms per context, several of which appear to be mutation- or context-specific. These latest advances have broadened our understanding of KRAS biology and provided new insights into the potential roles of KRAS4A and KRAS4B proteoforms in colorectal and other cancers. Reference 1. Ntai I, Fornelli L, DeHart CJ, Hutton JE, Doubleday PF, LeDuc RD, van Nispen AJ, Fellers RT, Whiteley G, Boja ES, Rodriguez H, Kelleher NL. Precise characterization of KRAS4b proteoforms in human colorectal cells and tumors reveals mutation/modification crosstalk. Proc Natl Acad Sci U S A 2018 Apr 17;115(16):4140-5. Citation Format: Caroline J. DeHart, Lissa C. Anderson, Lauren M. Adams, Luca Fornelli, Christopher L. Hendrickson, Neil L. Kelleher. Precise characterization and comparison of KRAS proteoforms by top-down mass spectrometry [abstract]. In: Proceedings of the AACR Special Conference on Targeting RAS-Driven Cancers; 2018 Dec 9-12; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(5_Suppl):Abstract nr A26.

Continuous-wave cavity ring-down polarimetry.

We present a new cavity-based polarimetric scheme for highly sensitive and time-resolved measurements of birefringence and dichroism, linear and circular, that employs rapidly pulsed single-frequency continuous wave (CW) laser sources and extends current cavity-based spectropolarimetric techniques. We demonstrate how the use of a CW laser source allows for gains in spectral resolution, signal intensity, and data acquisition rate compared to traditional pulsed-based cavity ring-down polarimetry (CRDP). We discuss a particular CW-CRDP modality that is different from intensity-based cavity-enhanced polarimetric schemes as it relies on the determination of the polarization rotation frequency during a ring-down event generated by large intracavity polarization anisotropies. We present the principles of CW-CRDP and validate the applicability of this technique for the measurement of the non-resonant Faraday effect in solid SiO2 and CeF3 and gaseous butane. We give a general analysis of the fundamental sensitivity limits for CRDP techniques and show how the presented frequency-based methodology alleviates the requirement for high finesse cavities to achieve high polarimetric sensitivities and, thus, allows for the extension of cavity-based polarimetric schemes into different spectral regimes, but most importantly renders the CW-CRDP methodology particularly suitable for robust portable polarimetric instrumentations.

Parallel Notched Gas-Phase Enrichment for Improved Proteome Identification and Quantification with Fast Spectral Acquisition Rates.

Gas-phase fractionation enables better quantitative accuracy, improves signal-to-noise ratios, and increases sensitivity in proteomic analyses. However, traditional gas-phase enrichment, which relies upon a large continuous bin, results in suboptimal enrichment, as most chromatographic separations are not 100% orthogonal relative to the first MS dimension (MS1m/z). As such, ions with similar m/z values tend to elute at the same retention time, which prevents the partitioning of narrow precursor m/z distributions into a few large continuous gas-phase enrichment bins. To overcome this issue, we developed and tested the use of notched isolation waveforms, which simultaneously isolate multiple discrete m/z windows in parallel (e.g., 650-700 m/z and 800-850 m/z). By comparison to a canonical gas-phase fractionation method, notched waveforms do not require bin optimization via in silico digestion or wasteful sample injections to isolate multiple precursor windows. Importantly, the collection of all m/z bins simultaneously using the isolation waveform does not suffer from the sensitivity and duty cycle pitfalls inherent to sequential collection of multiple m/z bins. Applying a notched injection waveform provided consistent enrichment of precursor ions, which resulted in improved proteome depth with greater coverage of low-abundance proteins. Finally, using a reductive dimethyl labeling approach, we show that notched isolation waveforms increase the number of quantified peptides with improved accuracy and precision across a wider dynamic range.

Microfluidic mid-infrared spectroscopy via microresonator-based dual-comb source.

Over the past decade, microresonator-based soliton combs based on photonic integration have broadened the scope of applications in sensing, ranging, and imaging. The large comb line spacing on the order of hundreds of gigahertz allows for rapid acquisition of absorption spectra in the condensed matter phase without aliasing via a dual-comb interferometer. We present a proof-of-principle demonstration of high-throughput label-free microresonator-based dual-comb spectroscopy in a microfluidic chip that dynamically probes the linear absorption of liquid acetone in the mid-infrared wavelength regime. We measure the flow dynamics of an acetone droplet with a spectral acquisition rate of 25kHz (40μs per spectrum) covering a spectral range from 2900 to 2990nm. Combining microfluidics and silicon-photonic technology would potentially enable a compact time-resolved spectroscopy system for a wide range of applications such as chemical synthesis, biological cell-sorting, and lab-on-a-chip.

Active Instrument Engagement Combined with a Real-Time Database Search for Improved Performance of Sample Multiplexing Workflows.

Quantitative proteomics employing isobaric reagents has been established as a powerful tool for biological discovery. Current workflows often utilize a dedicated quantitative spectrum to improve quantitative accuracy and precision. A consequence of this approach is a dramatic reduction in the spectral acquisition rate, which necessitates the use of additional instrument time to achieve comprehensive proteomic depth. This work assesses the performance and benefits of online and real-time spectral identification in quantitative multiplexed workflows. A Real-Time Search (RTS) algorithm was implemented to identify fragment spectra within milliseconds as they are acquired using a probabilistic score and to trigger quantitative spectra only upon confident peptide identification. The RTS-MS3 was benchmarked against standard workflows using a complex two-proteome model of interference and a targeted 10-plex comparison of kinase abundance profiles. Applying the RTS-MS3 method provided the comprehensive characterization of a 10-plex proteome in 50% less acquisition time. These data indicate that the RTS-MS3 approach provides dramatic performance improvements for quantitative multiplexed experiments.

Phase-controlled Fourier-transform spectroscopy

Fourier-transform spectroscopy (FTS) has been widely used as a standard analytical technique over the past half-century. FTS is an autocorrelation-based technique that is compatible with both temporally coherent and incoherent light sources, and functions as an active or passive spectrometer. However, it has been mostly used for static measurements due to the low scan rate imposed by technological restrictions. This has impeded its application to continuous rapid measurements, which would be of significant interest for a variety of fields, especially when monitoring of non-repeating or transient complex dynamics is desirable. Here, we demonstrate highly efficient FTS operating at a high spectral acquisition rate with a simple delay line based on a dynamic phase-control technique. The independent adjustability of phase and group delays allows us to achieve the Nyquist-limited spectral acquisition rate over 10,000 spectra per second, while maintaining a large spectral bandwidth and high resolution. We also demonstrate passive spectroscopy with an incoherent light source.

Hadamard-Transform Fluorescence Excitation-Emission-Matrix Spectroscopy.

We present a fluorescence excitation-emission-matrix spectrometer with superior data acquisition rates over previous instruments. Light from a white light emitting diode (LED) source is dispersed onto a digital micromirror array (DMA) and encoded using binary n-size Walsh functions ("barcodes"). The encoded excitation light is used to irradiate the liquid sample and its fluorescence is dispersed and detected using a conventional array spectrometer. After exposure to excitation light encoded in n different ways, the 2-dimensional excitation-emission-matrix (EEM) spectrum is obtained by inverse Hadamard transformation. Using this technique we examined the kinetics of the fluorescence of rhodamine B as a function of temperature and the acid-driven demetalation of chlorophyll-a into pheophytin-a. For these experiments, EEM spectra with 31 excitation channels and 2048 emission channels were recorded every 15 s. In total, data from over 3000 EEM spectra were included in this report. It is shown that the increase in data acquisition rate can be as high as [{n(n + 1)}/2]-fold over conventional EEM spectrometers. Spectral acquisition rates of more than two spectra per second were demonstrated.

Raster-Mode Continuous-Flow Liquid Microjunction Mass Spectrometry Imaging of Proteins in Thin Tissue Sections.

Mass spectrometry imaging by use of continuous-flow liquid microjunction sampling at discrete locations (array mode) has previously been demonstrated. In this Letter, we demonstrate continuous-flow liquid microjunction mass spectrometry imaging of proteins from thin tissue sections in raster mode and discuss advantages (a 10-fold reduction in analysis time) and challenges (suitable solvent systems, data interpretation) of the approach. Visualization of data is nontrivial, requiring correlation of solvent-flow, mass spectral data acquisition rate, data quality, and liquid microjunction sampling area. The latter is particularly important for determining optimum pixel size. The minimum achievable pixel size is related to the scan time of the instrument used. Here we show a minimum achievable pixel size of 50 μm (x-dimension) when using an Orbitrap Elite; however a pixel size of 600 μm is recommended in order to minimize the effects of oversampling on image accuracy.

Identification and Characterization of Human Proteoforms by Top-Down LC-21 Tesla FT-ICR Mass Spectrometry.

Successful high-throughput characterization of intact proteins from complex biological samples by mass spectrometry requires instrumentation capable of high mass resolving power, mass accuracy, sensitivity, and spectral acquisition rate. These limitations often necessitate the performance of hundreds of LC-MS/MS experiments to obtain reasonable coverage of the targeted proteome, which is still typically limited to molecular weights below 30 kDa. The National High Magnetic Field Laboratory (NHMFL) recently installed a 21 T FT-ICR mass spectrometer, which is part of the NHMFL FT-ICR User Facility and available to all qualified users. Here we demonstrate top-down LC-21 T FT-ICR MS/MS of intact proteins derived from human colorectal cancer cell lysate. We identified a combined total of 684 unique protein entries observed as 3238 unique proteoforms at a 1% false discovery rate, based on rapid, data-dependent acquisition of collision-induced and electron-transfer dissociation tandem mass spectra from just 40 LC-MS/MS experiments. Our identifications included 372 proteoforms with molecular weights over 30 kDa detected at isotopic resolution, which substantially extends the accessible mass range for high-throughput top-down LC-MS/MS.

Measurement of dynamic interferometer baseline perturbations by means of wavelength-scanning interferometry

A novel approach for measuring fast oscillations of an absolute value of interferometer optical path difference (OPD) has been developed. The principles of frequency-scanning interferometry are utilized for registration of the interferometer spectral function, from which the OPD is calculated. The proposed approach enables one to capture the absolute baseline variations at frequencies much higher than the spectral acquisition rate. Despite the conventional approaches, associating a single baseline indication to the registered spectrum, in the proposed method a specially developed demodulation procedure is applied to the spectrum. This provides an ability to capture the baseline variations which took place during the spectrum acquisition. An analytical model describing the limitations on the parameters of the possibly registered baseline variations are formulated. The experimental verification of the proposed approach and the developed model has been performed.