Instrumental Systematic Errors Research Articles

Measurement Biases in Ocean Temperature Profiles from Marine Mammal Dataloggers

Abstract The study focuses on biases in ocean temperature profiles obtained by means of Satellite Relay Data Loggers (SRDL recorders) and time–depth recorder (TDR) attached to marine mammals. Quasi-collocated profiles from Argo floats and from ship-based conductivity–temperature–depth (CTD) profilers are used as reference. SRDL temperature biases depend on the sensor type and vary with depth. For the most numerous group of Valeport 3 (VP3) and conductivity–temperature–fluorescence (CTF) sensors, the bias is negative except for the layer 100–200 m. The vertical bias structure suggests a link to the upper-ocean thermal structure within the upper 200-m layer. Accounting for a time lag which might remain in the postprocessed data reduces the bias variability throughout the water column. Below 200-m depth, the bias remains negative with the overall mean of −0.027° ± 0.07°C. The suggested depth and thermal corrections for biases in SRDL data are within the uncertainty limits declared by the manufacturer. TDR recorders exhibit a different bias pattern, showing the predominantly positive bias of 0.08°–0.14°C below 100 m primarily due to the systematic error in pressure. Significance Statement The purpose of this work is to improve the consistency of the data from the specific instrumentation type used to measure ocean water temperature, namely, the data from miniature temperature sensors attached to marine mammals. As mammals dive during their route to and from their feeding areas, these sensors measure water temperature and dataloggers send the measured temperature data to oceanographic data centers via satellites as soon as the mammals return to the sea surface. We have shown that these data exhibit small systematic instrumental errors and suggested the respective corrections. Taking these corrections into account is important for the assessment of the ocean climate change.

Greenhouse gas retrievals for the CO2M mission using the FOCAL method: first performance estimates

Abstract. The Anthropogenic Carbon Dioxide Monitoring (CO2M) mission is a constellation of satellites currently planned to be launched in 2026. CO2M is planned to be a core component of a Monitoring and Verification Support (MVS) service capacity under development as part of the Copernicus Atmosphere Monitoring Service (CAMS). The CO2M radiance measurements will be used to retrieve column-averaged dry-air mole fractions of atmospheric carbon dioxide (XCO2), methane (XCH4) and total columns of nitrogen dioxide (NO2). Using appropriate inverse modelling, the atmospheric greenhouse gas (GHG) observations will be used to derive United Nations Framework Convention on Climate Change (UNFCCC) COP 21 Paris Agreement relevant information on GHG sources and sinks. This challenging application requires highly accurate XCO2 and XCH4 retrievals. Three different retrieval algorithms to derive XCO2 and XCH4 are currently under development for the operational processing system at EUMETSAT. One of these algorithms uses the heritage of the FOCAL (Fast atmOspheric traCe gAs retrievaL) method, which has already successfully been applied to measurements from other satellites. Here, we show recent results generated using the CO2M version of FOCAL, called FOCAL-CO2M. To assess the quality of the FOCAL-CO2M retrievals, a large set of representative simulated radiance spectra has been generated using the radiative transfer model SCIATRAN. These simulations consider the planned viewing geometry of the CO2 instrument and corresponding geophysical scene data (including different types of aerosols and varying surface properties), which were taken from model data for the year 2015. We consider instrument noise and systematic errors caused by the retrieval method but have not considered additional error sources due to, for example, instrumental issues, spectroscopy or meteorology. On the other hand, we have also not taken advantage in this study of CO2M's MAP (multi-angle polarimeter) instrument, which will provide additional information on aerosols and cirrus clouds. By application of the FOCAL retrieval to these simulated data, confidence is gained that the FOCAL method is able to fulfil the challenging requirements for systematic errors for the CO2M mission (spatio-temporal bias ≤ 0.5 ppm for XCO2 and ≤ 5 ppb for XCH4).

Optimal 1D Ly α forest power spectrum estimation – III. DESI early data

ABSTRACT The 1D power spectrum P1D of the Ly α forest provides important information about cosmological and astrophysical parameters, including constraints on warm dark matter models, the sum of the masses of the three neutrino species, and the thermal state of the intergalactic medium. We present the first measurement of P1D with the quadratic maximum likelihood estimator (QMLE) from the Dark Energy Spectroscopic Instrument (DESI) survey early data sample. This early sample of 54 600 quasars is already comparable in size to the largest previous studies, and we conduct a thorough investigation of numerous instrumental and analysis systematic errors to evaluate their impact on DESI data with QMLE. We demonstrate the excellent performance of the spectroscopic pipeline noise estimation and the impressive accuracy of the spectrograph resolution matrix with 2D image simulations of raw DESI images that we processed with the DESI spectroscopic pipeline. We also study metal line contamination and noise calibration systematics with quasar spectra on the red side of the Ly α emission line. In a companion paper, we present a similar analysis based on the Fast Fourier Transform estimate of the power spectrum. We conclude with a comparison of these two approaches and discuss the key sources of systematic error that we need to address with the upcoming DESI Year 1 analysis.

The Impact of Experimental Conditions on Cell Mechanics as Measured with Nanoindentation.

The evaluation of cell elasticity is becoming increasingly significant, since it is now known that it impacts physiological mechanisms, such as stem cell differentiation and embryogenesis, as well as pathological processes, such as cancer invasiveness and endothelial senescence. However, the results of single-cell mechanical measurements vary considerably, not only due to systematic instrumental errors but also due to the dynamic and non-homogenous nature of the sample. In this work, relying on Chiaro nanoindenter (Optics11Life), we characterized in depth the nanoindentation experimental procedure, in order to highlight whether and how experimental conditions could affect measurements of living cell stiffness. We demonstrated that the procedure can be quite insensitive to technical replicates and that several biological conditions, such as cell confluency, starvation and passage, significantly impact the results. Experiments should be designed to maximally avoid inhomogeneous scenarios to avoid divergences in the measured phenotype.

Mathematical model of instrumental vibration error of angular velocity sensor

The problem of mathematical description of the influence of harmful deterministic and broadband random vibrations of a moving object on the measurement result of the sensor of the angular velocity of rotation of this object installed on it is considered. It is shown that under such conditions a systematic instrumental vibration error arises in the angular velocity sensor. The source of this error is the nonlinearity of the static conversion function of the angular velocity sensor and the asymmetry of its conversion coefficient.
 A mathematical model of this error has been obtained. Formulas for calculating the vibrational error of the angular velocity sensor are obtained depending on the apparent angular velocity of the flight of the aircraft, the vibration parameters of the base on which the sensor is installed and the parameters of the nonlinear sensor conversion function.
 This model makes it possible to calculate the value of the vibration error under specified vibration conditions for a specific angular velocity sensor (direct analysis problem), as well as to select an angular velocity sensor based on the values ​​of its conversion function coefficients, based on ensuring the required accuracy of measuring the angular velocity of a moving object using this angular velocity sensor (inverse synthesis problem).

Probing Galactic variations in the fine-structure constant using solar twin stars: methodology and results

ABSTRACT The rich absorption spectra of Sun-like stars are enticing probes for variations in the fine-structure constant, α, which gauges the strength of electromagnetism. While individual line wavelengths are sensitive to α, they are also sensitive to physical processes in the stellar atmospheres, which has precluded their use so far. Here we demonstrate a new differential approach using solar twins: velocity separations between close pairs of transitions are compared across stars with very similar physical properties, strongly suppressing astrophysical and instrumental systematic errors. We utilize 423 archival exposures of 18 solar twins from the High-Accuracy Radial velocity Planetary Searcher (HARPS), in which calibration errors can be reduced to ≲3 m s−1. For stars with ≈10 high-signal-to-noise ratio spectra (≥200 per pixel), velocity separations between pairs are measured with ≈10 m s−1 statistical precision. A companion paper assesses a range of systematic error sources using 130 stars, with a greater range of stellar parameters, providing accurate corrections for astrophysical effects and a residual, intrinsic star-to-star scatter of 0–13 m s−1. Within these uncertainties, we find no evidence for velocity separation differences in 17 transition pairs between solar twins. In a second companion paper, this is found to limit local (≲50 pc) variations in α to ≈50 parts per billion, ∼2 orders of magnitude less than other Galactic constraints.

Polarized Synchrotron Foreground Assessment for CMB Experiments

Polarized Galactic synchrotron emission is an undesirable foreground for cosmic microwave background experiments observing at frequencies <150 GHz. We perform a combined analysis of observational data at 1.4, 2.3, 23, 30, and 33 GHz to quantify the spatial variation of the polarized synchrotron spectral index, β pol, on ∼3.°5 scales. We compare results from different data combinations to address limitations and inconsistencies present in these public data, and form a composite map of β pol. Data quality masking leaves 44% sky coverage (73% for ∣b∣ > 45°). Generally −3.2 < β pol ≲ −3 in the inner Galactic plane and spurs, but the Fan Region in the outer galaxy has a flatter index. We find a clear spectral index steepening with increasing latitude south of the Galactic plane with Δβ pol = 0.4, and a smaller steepening of 0.25 in the north. Near the south Galactic pole the polarized synchrotron spectral index is β pol ≈ −3.4. Longitudinal spectral index variations of Δβ pol ∼ 0.1 about the latitudinal mean are also detected. Within the BICEP2/Keck survey footprint, we find consistency with a constant value, β pol = −3.25 ± 0.04 (statistical) ±0.02 (systematic). We compute a map of the frequency at which synchrotron and thermal dust emission contribute equally to the total polarized foreground. The limitations and inconsistencies among data sets encountered in this work make clear the value of additional independent surveys at multiple frequencies, especially between 10 and 20 GHz, provided these surveys have sufficient sensitivity and control of instrumental systematic errors.

A Search for the 3.5 keV Line from the Milky Way’s Dark Matter Halo with HaloSat

Abstract Previous detections of an X-ray emission line near 3.5 keV in galaxy clusters and other dark-matter-dominated objects have been interpreted as observational evidence for the decay of sterile neutrino dark matter. Motivated by this, we report on a search for a 3.5 keV emission line from the Milky Way’s galactic dark matter halo with HaloSat. As a single pixel, collimated instrument, HaloSat observations are impervious to potential systematic effects due to grazing incidence reflection and CCD pixelization, and thus may offer a check on possible instrumental systematic errors in previous analyses. We report nondetections of a ∼3.5 keV emission line in four HaloSat observations near the Galactic center. In the context of the sterile neutrino decay interpretation of the putative line feature, we provide 90% confidence level upper limits on the 3.5 keV line flux for a field centered 18.6 degrees from the Galactic center and the corresponding 7.1 keV sterile neutrino mixing angle: F ≤ 0.077 ph cm−2 s−1 sr−1 and sin 2 ( 2 θ ) ≤ 4.25 × 10 − 11 . The HaloSat mixing angle upper limit was calculated using a modern parameterization of the Milky Way’s dark matter distribution, and in order to compare with previous limits, we also report the limit calculated using a common historical model. The HaloSat mixing angle upper limit places constraints on a number of previous mixing angle estimates derived from observations of the Milky Way’s dark matter halo and galaxy clusters, and excludes several previous detections of the line. The upper limits cannot, however, entirely rule out the sterile neutrino decay interpretation of the 3.5 keV line feature.

Simulating Calibration and Beam Systematics for a Future CMB Space Mission with the TOAST Package

Abstract We address in this work the instrumental systematic errors that can potentially affect the forthcoming and future Cosmic Microwave Background experiments aimed at observing its polarized emission. In particular, we focus on the systematics induced by the beam and calibration, which are considered the major sources of leakage from total intensity measurements to polarization. We simulated synthetic data sets with Time-Ordered Astrophysics Scalable Tools, a publicly available simulation and data analysis package. We also propose a mitigation technique aiming at reducing the leakage by means of a template fitting approach. This technique has shown promising results reducing the leakage by 2 orders of magnitude at the power spectrum level when applied to a realistic simulated data set of the LiteBIRD satellite mission.

A new approach to spectroscopic phase curves

We analyse emission spectra of WASP-12b from a partial phase curve observed over three epochs with the Hubble Space Telescope, covering eclipse, quadrature, and transit, respectively. As the 1.1-day period phase curve was only partially covered over three epochs, traditional methods to extract the planet flux and instrument systematic errors cannot recover the thermal emission away from the secondary eclipse. To analyse this partial phase curve, we introduce a new method, which corrects for the wavelength-independent component of the systematic errors. Our new method removes the achromatic instrument and stellar variability, and uses the measured stellar spectrum in eclipse to then retrieve a relative planetary spectrum in wavelength at each phase. We are able to extract the emission spectrum of an exoplanet at quadrature outside of a phase curve for the first time; we recover the quadrature spectrum of WASP-12b up to an additive constant. The dayside emission spectrum is extracted in a similar manner, and in both cases we are able to estimate the brightness temperature, albeit at a greatly reduced precision, because our method removes the absolute level of the spectra, and therefore relies on fitting the slope of the emission spectrum instead of its amplitude. We estimate the brightness temperature from the dayside (Tday = 3186 ± 677 K) and from the quadrature spectrum (Tquad = 2124 ± 417 K) and combine them to constrain the energy budget of the planet. We compare our extracted relative spectra to global circulation models of this planet, which are generally found to be a good match. However, we do see tentative evidence of a steeper spectral slope in the measured dayside spectrum compared to our models. We find that we cannot match this increased slope by increasing optical opacities in our models. We also find that this spectral slope is unlikely to be explained by a non-equilibrium water abundance, as water advected from the nightside is quickly dissociated on the dayside. We present our technique for analysing partial or full phase curves from HST/WFC3 using common mode methods. Importantly, and unlike previous phase curve analyses, this technique does not assume a functional form for the planet’s emission with phase and does not require a full-orbit phase curve. The success of this technique relies upon stable pointing of the telescope between visits, with less than 0.1 pixels drift for example. This technique becomes powerful in the study of new regimes in exoplanetary systems such as for longer period planets, and is ideally suited for future observations with JWST and ARIEL.

Compensation of Geometric Parameter Errors for Terrestrial Laser Scanner by Integrating Intensity Correction

The accuracy of geometric parameters (mainly referred to the incidence angle and measuring distance) in a terrestrial laser scanner (TLS) is not only influenced by the TLS intrinsic systematic instrumental error but also the extrinsic received intensity data. However, the current error compensation methods for geometric parameters mainly focus on the calibration of TLS intrinsic systematic instrumental error and rarely consider the extrinsic intensity data correction. For this reason, this article presents a new method integrating the TLS intrinsic systematic instrumental error calibration and extrinsic intensity data correction to compensate the TLS geometric parameter error. The error compensation procedure is implemented as follows. First, the error compensation mathematical model integrated with TLS intrinsic systematic instrumental error calibration parameters and extrinsic intensity data correction coefficient is established. Second, the hybrid harmonic analysis (HA) and the adaptive wavelet neural network (AWNN) algorithm are proposed to calculate the TLS incidence angle error compensation values. Subsequently, the cubic spline interpolation (CSI) is applied to compute the measuring distance error compensate values. Finally, the TLS (model FARO Focus S150) and the hemispherical angle calibration instrument were used to evaluate the proposed compensation method. The experimental results demonstrate that the geometric parameters are significantly influenced by the intensity data received from TLS, and the proposed method can effectively improve the overall accuracy of the TLS incidence angle and measuring distance.

Calibration of a compact absolute atomic gravimeter**Project supported by the National Key R&D Program of China (Grant No. 2016YFA0301601), the National Natural Science Foundation of China (Grant No. 11674301), Anhui Initiative in Quantum Information Technologies, China (Grant No. AHY120000), and Shanghai Municipal Science and Technology Major Project, China (Grant No. 2019SHZDZX01).

Compact atomic gravimeters are the potential next generation precision instruments for gravity survey from fundamental research to broad field applications. We report the calibration results of our home build compact absolute atomic gravimeter USTC-AG02 at Changping Campus, the National Institute of Metrology (NIM), China in January 2019. The sensitivity of the atomic gravimeter reaches (1 μGal = 1 × 10−8 m/s2) and its long-term stability reaches 0.8 μGal for averaging over 4000 seconds. Considering the statistical uncertainty, the dominant instrumental systematic errors and environmental effects are evaluated and corrected within a total uncertainty (2σ) of 15.3 μGal. After compared with the reference g value given by the corner cube gravimeter NIM-3A, the atomic gravimeter USTC-AG02 reaches the degree of equivalence of 3.7 μGal.

TESS Spots a Compact System of Super-Earths around the Naked-eye Star HR 858

Abstract Transiting Exoplanet Survey Satellite (TESS) observations have revealed a compact multiplanet system around the sixth-magnitude star HR 858 (TIC 178155732, TOI 396), located 32 pc away. Three planets, each about twice the size of Earth, transit this slightly evolved, late F-type star, which is also a member of a visual binary. Two of the planets may be in mean motion resonance. We analyze the TESS observations, using novel methods to model and remove instrumental systematic errors, and combine these data with follow-up observations taken from a suite of ground-based telescopes to characterize the planetary system. The HR 858 planets are enticing targets for precise radial velocity observations, secondary eclipse spectroscopy, and measurements of the Rossiter–McLaughlin effect.

The Hubble Space Telescope PanCET Program: Exospheric Mg ii and Fe ii in the Near-ultraviolet Transmission Spectrum of WASP-121b Using Jitter Decorrelation

Abstract We present Hubble Space Telescope (HST) near-ultraviolet (NUV) transits of the hot Jupiter WASP-121b, acquired as part of the PanCET program. Time-series spectra during two transit events were used to measure the transmission spectra between 2280 and 3070 Å at a resolution of 30,000. Using HST data from 61 Space Telescope Imaging Spectrograph visits, we show that data from HST’s Pointing Control System can be used to decorrelate the instrument systematic errors (jitter decorrelation), which we used to fit the WASP-121b light curves. The NUV spectra show very strong absorption features, with the NUV white light curve found to be larger than the average optical and near-infrared value at 6σ confidence. We identify and spectrally resolve absorption from the Mg ii doublet in the planetary exosphere at a 5.9σ confidence level. The Mg ii doublet is observed to reach altitudes of R pl/R star = 0.284 ± 0.037 for the 2796 Å line and 0.242 ± 0.0431 for the 2804 Å line, which exceeds the Roche lobe size as viewed in transit geometry (R eqRL/R star = 0.158). We also detect and resolve strong features of the Fe ii UV1 and UV2 multiplets, and observe the lines reaching altitudes of R pl/R star ≈ 0.3. At these high altitudes, the atmospheric Mg ii and Fe ii gas is not gravitationally bound to the planet, and these ionized species may be hydrodynamically escaping or could be magnetically confined. Refractory Mg and Fe atoms at high altitudes also indicate that these species are not trapped into condensate clouds at depth, which places constraints on the deep interior temperature.

The PLATO Solar-like Light-curve Simulator

Context. ESA’s PLATO space mission, to be launched by the end of 2026, aims to detect and characterise Earth-like planets in their habitable zone using asteroseismology and the analysis of the transit events. The preparation of science objectives will require the implementation of hare-and-hound exercises relying on the massive generation of representative simulated light-curves. Aims. We developed a light-curve simulator named the PLATO Solar-like Light-curve Simulator (PSLS) in order to generate light-curves representative of typical PLATO targets, that is showing simultaneously solar-like oscillations, stellar granulation, and magnetic activity. At the same time, PSLS also aims at mimicking in a realistic way the random noise and the systematic errors representative of the PLATO multi-telescope concept. Methods. To quantify the instrumental systematic errors, we performed a series of simulations at pixel level that include various relevant sources of perturbations expected for PLATO. From the simulated pixels, we extract the photometry as planned on-board and also simulate the quasi-regular updates of the aperture masks during the observations. The simulated light-curves are then corrected for instrumental effects using the instrument point spread functions reconstructed on the basis of a microscanning technique that will be operated during the in-flight calibration phases of the mission. These corrected and simulated light-curves are then fitted by a parametric model, which we incorporated in PSLS. Simulation of the oscillations and granulation signals rely on current state-of-the-art stellar seismology. Results. We show that the instrumental systematic errors dominate the signal only at frequencies below ∼20 μHz. The systematic errors level is found to mainly depend on stellar magnitude and on the detector charge transfer inefficiency. To illustrate how realistic our simulator is, we compared its predictions with observations made by Kepler on three typical targets and found a good qualitative agreement with the observations. Conclusions. PSLS reproduces the main properties of expected PLATO light-curves. Its speed of execution and its inclusion of relevant stellar signals as well as sources of noises representative of the PLATO cameras make it an indispensable tool for the scientific preparation of the PLATO mission.

Eliminating Non-linear Raman Shift Displacement Between Spectrometers via Moving Window Fast Fourier Transform Cross-Correlation.

Obtaining consistent spectra by using different spectrometers is of critical importance to the fields that rely heavily on Raman spectroscopy. The quality of both qualitative and quantitative analysis depends on the stability of specific Raman peak shifts across instruments. Non-linear drifts in the Raman shifts can, however, introduce additional complexity in model building, potentially even rendering a model impractical. Fortunately, various types of shift correction methods can be applied in data preprocessing in order to address this problem. In this work, a moving window fast Fourier transform cross-correlation is developed to correct non-linear shifts for synchronization of spectra obtained from different Raman instruments. The performance of this method is demonstrated by using a series of Raman spectra of pharmaceuticals as well as comparing with data obtained by using an existing standard Raman shift scattering procedure. The results show that after the removal of shift displacements, the spectral consistency improves significantly, i.e., the spectral correlation coefficient of the two Raman instruments increased from 0.87 to 0.95. The developed standardization method has, to a certain extent, reduced instrumental systematic errors caused by measurement, while enhancing spectral compatibility and consistency through a simple and flexible moving window procedure.

Double-pulse 1.57 μm integrated path differential absorption lidar ground validation for atmospheric carbon dioxide measurement.

A ground-based double-pulse integrated path differential absorption (IPDA) instrument for carbon dioxide (CO2) concentration measurements at 1572nm has been developed. A ground experiment was implemented under different conditions with a known wall located about 1.17km away acting as the scattering hard target. Off-/offline testing of a laser transmitter was conducted to estimate the instrument systematic and random errors. Results showed a differential absorption optical depth (DAOD) offset of 0.0046 existing in the instrument. On-/offline testing was done to achieve the actual DAOD resulting from the CO2 absorption. With 18s pulses average, it demonstrated that a CO2 concentration measurement of 432.71±2.42 ppm with 0.56% uncertainty was achieved. The IPDA ranging led to a measurement uncertainty of 1.5m.

A Low-Cost Environmental Monitoring System: How to Prevent Systematic Errors in the Design Phase through the Combined Use of Additive Manufacturing and Thermographic Techniques

nEMoS (nano Environmental Monitoring System) is a 3D-printed device built following the Do-It-Yourself (DIY) approach. It can be connected to the web and it can be used to assess indoor environmental quality (IEQ). It is built using some low-cost sensors connected to an Arduino microcontroller board. The device is assembled in a small-sized case and both thermohygrometric sensors used to measure the air temperature and relative humidity, and the globe thermometer used to measure the radiant temperature, can be subject to thermal effects due to overheating of some nearby components. A thermographic analysis was made to rule out this possibility. The paper shows how the pervasive technique of additive manufacturing can be combined with the more traditional thermographic techniques to redesign the case and to verify the accuracy of the optimized system in order to prevent instrumental systematic errors in terms of the difference between experimental and actual values of the above-mentioned environmental parameters.

Comparison of Three Timing Systems: Reliability and Best Practice Recommendations in Timing Short-Duration Sprints.

Bond, CW, Willaert, EM, and Noonan, BC. Comparison of three timing systems: reliability and best practice recommendations in timing short-duration sprints. J Strength Cond Res 31(4): 1062-1071, 2017-With the importance placed on athletic speed, it is important to use a valid and reliable timing system, particularly in sprints of short duration. Unfortunately, many of the commonly used timing systems have not been rigorously evaluated. This study aimed to compare results from a single-beam infrared photocell (PC), single-beam laser with a microprocessor (LA), and a previously validated video camera (VC) sacrum-based timing system; and in doing so, determine these systems' reliabilities, and establish best practices for increasing reliability. It was hypothesized that PC and LA times would be different from VC times and show reduced reliability compared with VC. Fifteen athletes performed 5 repetitions of a 60-foot maximal effort sprint with split times recorded for the first and second half. Photocell and LA full-time and first-half split times were significantly slower than VC (p < 0.001), but almost identical for the second half split (p = 0.08). Repeated sprint analysis showed that VC tended to have smaller SD compared with PC and LA for first-half split (0.05 vs. 0.08 vs. 0.09 seconds, respectively) and total time (0.09 vs. 0.10 vs. 0.11 seconds, respectively). Time differences were more dependent on initial forward lean and varying body segments triggering the beam, than on a systematic instrument error. The increased variability of PC and LA systems dampen the ability to determine whether meaningful change has occurred. The VC system allows for very valid and reliable measurements of an athlete's sprint time, especially in distances <30 feet.

Spectral line-shape study by cavity-enhanced complex refractive index spectroscopy

We present a unique experimental setup that enables measurement of high-resolution complex refractive index spectra of gas sample using several cavity-enhanced methods: frequency-stabilized cavity ring-down spectroscopy, cavity mode-width spectroscopy and one-dimensional cavity mode-dispersion spectroscopy. Presented examples of applications cover molecular spectral line-shape investigations, line intensities and unperturbed line center frequency measurements and high-precision detection of systematic instrumental errors of various spectroscopic methods.