Refractive Variation Research Articles

Performance Analysis of Tropospheric Radio Refractivity along with Refractivity Gradient and Effective Earth Radius in the Coastal Zone of Nigeria

Study’s Excerpt Analysis of the variability in tropospheric radio refractivity in Ogoja and Warri, Nigeria, was carried out by examining a 42-year dataset (1981-2022) of meteorological factors obtained from NASA. The contributions of dry and wet terms to radio refractivity variations were identified and key parameters such as refractivity gradients and the effective earth radius (k-factor) for both locations were evaluated. The radio wave propagation in the region is lowest during the dry season. Full Abstract Radio refractivity is the ratio of the velocity of radio waves in a specific medium to that in free space. Radio waves propagate according to variations in tropospheric radio refractive index. This study used the refractive index and other pertinent meteorological factors to calculate the radio refractivity of the seasonal troposphere and analyse its variability with monthly temperature, relative humidity, and atmospheric pressure measurements that were collected from the National Aeronautic and Space Administration (NASA) for Ogoja and Warri over a forty-two-year period (1981 to 2022). We looked at the proportion contributions of the dry and wet term radio refractivity, the refractivity gradient, and the effective earth radius. The outcome signified that in the two locations, radio refractivity values were lowest for the dry season and highest during the rainy season. For Ogoja and Warri, the highest and lowest average radio refractivity values recorded in the wet and dry seasons are, respectively, 382.9085 N-units in May, 346.4311 N-units in January, and 390.9042 N-units in April, 370.3009 N-units in January. For Ogoja and Warri, the wet term (Nwet) provides 31.5210 % and 30.1793%, respectively, to the primary variation in radio refractivity's overall value, whereas the dry term (Ndry) adds up to 69.8207 % and 68.4790 %. Mean refractivity gradients of -43.8326 and -44.5326 N-units/km were found in the subject areas under examination. Furthermore, it was discovered that the mean effective earth radius (k-factor) for Warri and Ogoja were 1.3959 and 1.3873, respectively. The values provided represent the propagation conditions of superrefraction.

Relative intensity noise management and thermal/shot noise control for high speed ultra high bandwidth fiber reach transmission performance

Abstract This work has clarified the relative intensity noise management and thermal/shot noise control for high speed ultra high bandwidth fiber reach transmission performance. Total link losses variations are clarified against ambient temperature and relative refractive index difference variations at 1,550 nm wavelength, 20 km fiber link length, and 45 % fluoride dopant ratio inside the fiber material cable. Besides the total link losses variations are demonstrated versus fiber link length and relative refractive index difference variations at 1,550 nm wavelength, room temperature, and 45 % fluoride dopant ratio inside the fiber material cable. Required optical signal per noise ratio (OSNR), electronic signal to noise ratio (SNR), and optimum gain variations are measured and analyzed versus the fiber link length and relative refractive index difference variations at 1,550 nm wavelength, room temperature, and 45 % fluoride dopant ratio inside the fiber material cable.

A model of radio scintillations in the deep Venus atmosphere: Application to the DAVINCI probe

Power fluctuations have been noted on radio signals propagating through the Venus atmosphere since the very first descent probe there (Venera 4) and have been observed as a routine feature in radio occultations, where the grazing ray geometry amplifies the effect of refractive scattering structures. Motivated by DAVINCI and other missions currently in development, a physical model of refraction variations in the Venus atmosphere is developed using the VEGA-2 high-resolution temperature profile down to the surface and other data, which suggest several distinct layers of more intense scattering. The resultant modeled radio scintillations are compared with observed scintillations and assessed for the DAVINCI relay link. High-time-resolution radio signal power measurements on the DAVINCI radio link promise to be an interesting probe of the Venus atmosphere.

The Investigation of Surface Radio Refractivity Over Lokoja, Kogi State Nigeria

This research investigated the variation of Surface Radio Refractivity and its propagation effects on radio signals over Lokoja, Kogi State, Nigeria. The study used six years (2015-2020) of satellite data on temperature, pressure, relative humidity and rainfall at the surface (12 km) above ground level. The data retrieved were used to determine the monthly, seasonal, and annual Surface Radio Refractivity value for Lokoja Kogi State. Results show that high Surface Radio Refractivity values were recorded generally during the wet season months compared to the dry season months in all Six years (2015-2020). The average values of Surface Radio Refractivity 307.7407 (N-units) and 323.4674 (N-units) were obtained during the dry and wet season, respectively. The minimum surface radio refractivity values of 280.7245, 284.6583, 308.0021, 285.2304, 304.2521 and 285.9139 (N-units) were recorded for the years 2015, 2016, 2017, 2018, 2019, and 2020 respectively. On the other hand, the highest values of 330.8153, 331.8133, 330.3580, 330.9278, 332.4704, and 331.1316 (N-units) were recorded for the years 2015, 2016, 2017, 2018, 2019 and 2020, respectively. Higher values of Surface Radio Refractivity were recorded generally during the wet season compared to the dry season months in all years (2015-2020) in Lokoja, Kogi State. This implies higher radio signal attenuation due to Ns during the wet season compared to the dry season. The correlation coefficients between Surface Radio Refractivity Ns and temperature are -0.41, -0.51, -0.49, -0.48, -0.46, -0.50, pressure 0.07, -0.15, -0.28, -0.08, -0.11, -0.26, relative humidity 0.89, 0.84, 0.75, 0.84, 0.77, 0.83, and the amount of rainfall 0.76, 0.64, 0.73, 0.58, 0.51, 0.65 respectively in the year 2015, 2016, 2017, 2018, 2019, 2020. The overall findings of the work will be useful to radio engineers for properly planning a reliable power budget for terrestrial radio communication over Lokoja, Kogi State.

A Non-Destructive Study of Optical, Geometric and Luminescent Parameters of Active Optical Fibers Preforms

This work is devoted to the scientific and technical aspects of individual stages of active optical fibers preforms’ optical-geometric parameters metrological control. The concept of a system presented makes it possible to carry out a study of a rare earth element distribution in the preform of an active optical fiber and to monitor geometric parameters, and also to study the evolution of the refractive index profile along the length of the sample at a qualitative level. As far as it is known, it is the first description of the preform optical, geometric, and luminescent properties measurement within a single automated laboratory bench. Also, the novelty of the approach lies in the fact that the study of the refractive index profile variation along the length of the preform is, for the first time, conducted using the “dry” method, that is, without immersing the sample in synthetic oil, which makes the process less labor-intensive and safer.

Refractivity corrected distance measurement using the intermode beats derived from a supercontinuum.

Simultaneous distance measurements on two or more optical wavelengths enable dispersion-based correction of deviations that result from insufficient knowledge of the refractive index along the signal propagation path. We demonstrate a supercontinuum-based approach for highly accurate distance measurements suitable for such an inline refractivity compensation. The distance is estimated from the phase delay observations on the intermode beats. We use a supercontinuum (SC) coherently broadened from a 780 nm frequency comb and spanning the spectral range of 570-970 nm. Experiments are performed on the 590 and 890 nm wavelength bands filtered from the SC spectrum. Results show distance measurements with standard deviations of around 0.01 mm at 50 m, and a distance-dependent component below 0.2 ppm on the individual spectral bands. Distance residuals compared to a reference interferometer are on the order of 0.1 ppm for displacements up to 50 m. Controlled pressure-induced refractivity variations are created over a length of 15 m, resulting in an optical path length change of 0.4 mm. Using the two-color method, we demonstrate refractivity-corrected distance measurement with a standard deviation of around 0.08 mm for a 60 s averaging window. The current experimental configuration can be easily extended to distance measurements on more than two wavelengths. The results highlight its potential for practical long-distance measurements through inline refractivity compensation.

High-performance biosensors based on angular plasmonic of a multilayer design: new materials for enhancing sensitivity of one-dimensional designs.

In this study, a theoretical examination is conducted to investigate the biosensing capabilities of different surface plasmon resonance (SPR) based hybrid multilayer structures, which are composed of two-dimensional (2D) materials. The transfer matrix formulation is implemented to calibrate the results of this study. A He-Ne laser of wavelength = 632.8 nm is used to simulate the results. Many permutations and combinations of layers of silver (Ag), aluminum oxynitride (AlON), and 2D materials were utilized to obtain the optimized structure. Ten dielectrics and twelve 2D materials were tested for a highly sensitive multilayer hybrid sensing design, which is composed of the prism (Ohara S-FPL53)/Ag/AlON/WS2/AlON/sensing medium. The optimized biosensing design is capable of sensing and detecting analytes whose refractive variation is limited between 1.33 and 1.34. The maximum sensitivity, which is achieved by using the proposed design is 488.2° per RIU. Additionally, the quality factor, figure of merit, detection limit, and qualification limit values of the optimized design were also calculated to obtain a true picture of the sensing capabilities. The designing approach based on the multilayer hybrid SPR biosensors has the potential to develop various plasmonic biosensors that are related to food, chemical, and biomedical engineering fields.

Miniature fiber-optic near-surface gap-coupled cladding waveguide Mach-Zehnder interferometric refractive index sensor inscribed by femtosecond laser

A miniature fiber-optic gap-coupled cladding waveguide Mach-Zehnder interferometer (MZI) is proposed and demonstrated for high-sensitive refractive index measurement. Two straight cladding waveguides respectively coupled with the fiber core are inscribed by a femtosecond laser (fs) to form the MZI structure. At their far ends, the two cladding waveguides are very close to the cladding surface, and a short separation was intentionally designed for the coupling of light between them and generating light field with evanescent wave expanded outside the cladding surface, which makes the MZI structure very sensitive to ambient refractive variations. In a refractive index range of 1.34–1.42, a high sensitivity of −59.90238 nm/RIU is achieved simultaneously with good linearity. The sensing structure also shows good characteristic of temperature insensitivity, which may find practical applications in chemical or biological sensing.

Multimode parabolic index fiber integrated with spatiotemporal vertical cavity surface emitting laser sources for optical fiber system improvement

Abstract This study has demonstrated the multimode parabolic index fibers integrated with spatiotemporal VCSEL sources for the optical fiber system improvement. Average radial intensity is clarified against fiber radius variations with 0.1 % refractive difference index step. The Max base band Q factor form is demonstrated against the fiber refractive index step variations. The Max base band Q factor form variations are demonstrated against VCSEL diode bias current variations. The Max base band Q factor form variations are clarified against the fiber core radius variations. The Max base band Q factor form is simulated against the fiber cladding thickness variations. Multimode fiber calculation report at the wavelength 1550 nm for the light source (Pol. X = VCSEL LP [0,1]) is reported. The Max lighted base optical band form power is clarified versus time after parabolic index multimode fiber with 0.1 % refractive difference index step. The Max optical lighted base band power form is demonstrated against wavelength after parabolic index multimode fiber with 0.1 % refractive difference index step. The Max base Q band form factor is simulated after spatial APD photodetector receiver with 0.1 % refractive difference index step. The fiber base band mode form intensity in x and d directions is demonstrated within the fiber with 0.1 % refractive difference index step. The fiber base band encircled flux form is studied and simulated versus fiber radius variations with 0.1 % refractive difference index step.

Variation of Nonlinear Refraction and Three-Photon Absorption of Indium-Tin Oxide Quantum Dot Thin Films and Solutions in Near Infrared Range.

We characterize the nonlinear optical properties of indium-tin oxide (ITO) quantum dots (QDs) in the IR range using the Z-scan method. We present results of three-photon absorption (3PA), third harmonic generation (3HG), and Kerr-effect-induced nonlinear refraction in ITO QDs. Z-scan measurements were carried out for the QDs solution, while 3HG was demonstrated using QD thin films. The Kerr-induced nonlinear refractive index was analyzed along the 800-950 nm range showing an increase in this parameter from -6.7 × 10-18 to -1.5 × 10-17 m2 W-1. At longer wavelengths (1000-1100 nm), the higher-order effects started to contribute to a nonlinear refractive index. The 3PA coefficient at 950 nm was measured to be 1.42 × 10-25 m3/W2. We discuss the peculiarities in the wavelength-dependent variation of the coefficient of nonlinear absorption responsible for 3PA in the range of 800-1150 nm. Third harmonic generation was analyzed in the 1200-1550 nm spectral range. The absolute value of 3HG conversion efficiency in the 150 nm thick film at the wavelength of laser radiation (1350 nm) was estimated to be ~10-5.

Physical and optical traits of tellurite glass: effect of bimetallic TiO2/Au nanoparticles

The dependence of TiO2/Au concentrations on the physical and optical properties of glass was investigated thoroughly. Variations in density, molar volume, molar refraction, refractive index, and polarizability with varying TiO2/Au contents were affected by the formation of non-bridging oxygen. The formation of big islands in the atomic force microscopy image signifies the growth of nanoparticles. The decrement in band gap manifests alteration in the glass network mainly the local field around the Er3+ ions. The rise in Urbach energy illustrates disorder in the glass. The beneficial features of the current glass composition may be useful for photonic devices.

Comparative Analysis of Surface Refractivity Variations in the Sahel and Coastal Zones of Nigeria

Comparative Analysis of Surface Refractivity Variations in the Sahel and Coastal Zones of Nigeria

Diurnal Variation of Visual Acuity and Refraction in Fuchs Endothelial Corneal Dystrophy.

Patients with advanced Fuchs endothelial corneal dystrophy frequently report poor vision in the morning, which improves as the day progresses. This study quantified the amount of variation in near and distance visual acuity and refraction over the course of a day. This was a prospective cohort study. Best-corrected distance visual acuity and near visual acuity were tested in participants with clinically advanced Fuchs dystrophy and in controls with healthy corneas. Subjective refraction and autorefraction were conducted in a presumed steady state in the afternoon. Measurements were repeated directly after eye opening in the hospital the next morning. In a subgroup, measurements were repeated every 30 minutes for up to 2 hours. In Fuchs dystrophy, the mean distance visual acuity was worse by -3 letters (95% confidence interval, -4 to -1) directly after eye opening in the morning compared with late afternoon. No such difference was seen in healthy corneas. In Fuchs dystrophy, visual acuity improved over the course of the study. Visual acuity in the morning could be improved with fine tuning of refraction, and refractive changes were exclusive to Fuchs dystrophy (0.5-1.0 D in spherical equivalent in 30%, >1.0 D in 2% of eyes). Distance and near visual acuity and refraction changes over the course of the day in patients with advanced Fuchs dystrophy. Although small changes in refraction may not usually require a second set of glasses for the first hours of the day, diurnal variation should be considered when determining disease severity in routine practice and in clinical trials.

A Simplified Method to Minimize Systematic Bias of Single-Optimized Intraocular Lens Power Calculation Formulas

To provide a simplified method to optimize lens constants to zero the mean prediction error (ME) of an intraocularlens (IOL) calculation formula, without the need to program the formula itself, by exploring the influence of IOL and corneal power on the refractive impact of variations in effective lens position. Theoretical development of an optimized formula and retrospective clinical evaluation on documented datasets. Retrospective data from 8878 patients with cataracts with pre- and postoperative measurements available using 4 IOL models and 6 IOL power calculation formulas were examined. A schematic eye model was used to study the impact of small variations in effective lens position (ELP) on the postoperative spherical equivalent (SE) refraction. The impact of keratometry (K) and IOL power (P) on SE was investigated. A theoretical thick lens model was used to devise a formula to zero the average prediction error of an IOL power calculation formula. This was achieved by incrementing the predicted ELP, which could then be translated into an increment in the IOL constant. This method was tested on documented real-life postoperative datasets, using different IOL models and single-constant optimized IOL calculation formulas. For small variations in ELP, there was an exponential relationship between IOL power and the resultant postoperative refractive variation. The ELP adjustment necessary to zero the ME equated to a ratio between the ME and the mean of the following expression: 0.0006*(P2+2K*P) on the considered datasets. The accuracy of the values obtained using this formula was confirmed on documented postoperative datasets, and on published and nonpublished formulas. The proposed method allows surgeons without special expertise to optimize an IOL constant to nullify the ME on a documented dataset without coding the different formulas. The influence of individual eyes is proportional to the squared power of the implanted IOL.

Ultra-compact In<sub>2</sub>Se<sub>3</sub> tunable power splitter based on direct binary search algorithm

Power splitter with multi-mode interference coupler structure has many advantages, such as large bandwidth and better manufacturing robustness, and has received much attention for a long time. Conventional power beam splitters usually use algorithms or numerical simulation to achieve a single beam splitting ratio; if the circuit has the requirement for power, the structural parameters of the device need changing and recalculating. In order to improve the utilization rate of power splitter in photonic integrated circuit and meet various demands for different optical paths, an ultra-compact tunable power splitter based on phase change material In<sub>2</sub>Se<sub>3</sub> with a 1×2 multimode interference coupler structure is proposed in this paper. The device consists of an input waveguide, a coupling region, and two output waveguides with a coupling region of only 2.4 μm× 3.6 μm in size, which contains several circular holes of the same size and is filled with SiO<sub>2</sub>. The number and location of circular holes in the coupling region are optimized by direct binary search algorithm, making the device achieve different power splitting ratios by using only the high refractive index contrast variation between the two crystalline states (<i>α</i> and <i>β</i>) of In<sub>2</sub>Se<sub>3</sub> without changing any other structural parameter. In a wavelength range of 1540–1560 nm, three splitting ratios of 1∶1, 1∶1.5 and 1∶2 are achieved by this device, and the insertion losses of these three beam splitting ratios are less than 0.27, 0.13 and 0.17 dB, respectively. In addition, the robustness and balance of the device are analyzed and discussed, and compared with those of the power splitter of the same size designed by SOI platform and several power beam splitters reported in recent years, demonstrating the compact structure and simple regulation of this power splitter based on the phase change material In<sub>2</sub>Se<sub>3</sub>, its good robustness, and its possibility of application on photonic integrated circuits.

Tropical Cyclone Planetary Boundary Layer Heights Derived from GPS Radio Occultation over the Western Pacific Ocean

According to GPS radio occultation data from previous studies, the height of the planetary boundary layer (PBLH) is defined as the altitude at which the vertical gradient of refractivity N is at its local minimum, called the gradient approach. As with its density, the atmosphere’s refractivity falls broadly exponentially with height. The spherically symmetric refractivity Nss(r) was established to account for the standard deviation of atmospheric refractivity with altitude. Ni is the residual from the fundamental vertical variations of refractivity, defined as Ni(r) = N(r) − Nss(r). In this study, the vertical gradient of N is replaced by the vertical gradient of Ni to optimize the gradient approach, called the local gradient approach. Using the US radiosonde and Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) radio occultations (ROs) data from 2007–2011, these two PBLH-determining approaches are evaluated. The PBLHs estimated by the gradient approach and the local gradient approach have RMSE values of 0.73 km and 0.65 km, respectively. The PBLH obtained by the local gradient approach is closer to the radiosonde-derived value. In this paper, the COSMIC-2 ROs data and the western Pacific typhoon best track data are collocated in time and space during 2020–2021, and the axisymmetric composite structural characteristics of the tropical cyclone (TC) PBLs are analyzed. The lowest vertical gradients of N and Ni of TCs correspond closely with the average PBLHs. We find that the mean PBLHs of tropical depressions (TD), tropical storms (TS), and typhoons (TY) all have their local maxima at a radial distance of 125 km with heights of 1.03 km, 1.12 km, and 1.36 km, respectively. After 375 km, 575 km, and 935 km of TD, TS, and TY radial distances, the mean PBLHs become stable and cease to vary. The mean PBLH undulations increase significantly with the increase in tropical cyclone intensity. Niwet is the residual from the fundamental vertical variations of wet refractivity, defined as Niwet(r) = Nwet(r) − Nsswet(r). Local minima of Niwet and Ni vertical gradients of TD, TS, and TY have comparable distributions and are concentrated between 0.5 km and 1 km.

Seasonal and latitudinal variations of surface radio refractivity over Nigeria

Refractivity is a significant challenge of radio signal propagation. As it often distorts or leads to loss of signals. The seasonal and latitudinal variations of surface refractivity at three Nigerian tropospheric Observatory stations in Nigeria, namely Port-Harcourt, Lagos, and Makurdi, are presented in this paper. Values of monthly averages of pressure, temperature, relative humidity, and water vapour from the stations were used to compute surface refractivity at each station. The results show that the values of surface refractivity increase from the arid region in the north to the coastal area in the south. There was an increase in the values of surface radio refractivity from the minimum value of about 332.83 N-units at Makurdi station to a maximum value of 386.69 N-units at Lagos station. Seasonal variations are seen to be caused by weather conditions. The values of the surface refractivity increased significantly in the wet season and reduced in the dry season. It also shows that the values of surface radio refractivity are affected by the meteorological components mentioned above. The result of this study is needed for effective planning of good signal reception in these stations.

Impact of Viewing Conditions and Vision Anomalies on Accuracy and Dynamics of Noncycloplegic Autorefraction.

This study was conducted to analyze the influence of binocular vision and accommodation anomalies on refraction dynamics. Our results may help to design more accurate autorefractors and to better understand the difficulties in prescribing an optical correction or adaptation to a correction. This study aimed to verify whether viewing conditions (open- or closed-field) or vision anomalies, such as ocular surface diseases, accommodative dysfunctions, and binocular vision anomalies, influence (1) the differences between subjective refraction and autorefraction and (2) the characteristics of the short-term refractive state variation. The subjective refraction of 64 subjects aged 23 to 60 years was measured during a comprehensive optometric examination, and the Ocular Surface Disease Index questionnaire was collected. Twenty successive measurements of automated refraction of each eye were obtained using a conventional autorefractor Nidek ARK-510A and an open-field autorefractor Shin-Nippon NVision-K 5001. Conventional notation of refractive error (sphere, cylinder, axis) was transformed to h-vectors, presented in scatterplots, and analyzed statistically. The three-way analysis of variance tests showed that there is no influence of accommodation dysfunctions (P = .22 for ARK-510A), binocular vision anomalies (P = .97 for ARK-510A), and ocular surface diseases (P = .20 for ARK-510A) on differences between autorefraction and subjective refraction. The binocular vision anomalies affected the results from open-field autorefractor, whereas the accommodation impacted closed-field refraction measurements. Changes in short-term refractive state variation occurred in sphere power, indicating accommodative state changes; however, 30 subjects demonstrated at least one outlier and/or polymodality of refractive state distributions. The study showed that the presence of accommodative dysfunctions or binocular vision anomalies might increase the range of short-term refractive state variation. The impact of vision anomalies differs between viewing conditions. The polymodal distribution of refractive state variation and the presence of outliers imply that automatic modes used typically in autorefractors with three to five readings may not accurately represent the refractive state of the eye.

Understanding Evaporation Duct Variabilities on Turbulent Eddy Scales

AbstractEvaporative Ducts (ED) are common refractive features that exist due to the persistent/strong vertical moisture gradient inherent to the lowest 10s of meters of the marine atmospheric surface layer (MASL). The ED plays a large role in the propagation of signals from the surface‐ or ship‐based radar/communications systems due to the ducting of electromagnetic (EM) waves. Previous studies have characterized ED structure using mesoscale and surface layer models which are based on the Monin‐Obukhov similarity theory. As a result, only the spatially/temporally averaged mean ED structure has been examined. Conversely, this study focuses on ED variability occurring over turbulent energy‐containing eddy scales by utilizing large‐eddy simulations (LES) of the MASL. This innovative approach reveals that the LES‐resolved refractivity perturbations are directly linked to MASL large eddy dynamic and thermodynamic processes. In the thermally unstable MASL, significant turbulent ED variability is noted, with regions of increased ED heights associated with convective updrafts and positive moisture perturbations. In contrast, the thermally stable MASL is shown to exhibit significantly less ED variability over the LES domain. Since current surface layer models have difficulties in calculating ED properties in the thermally stable MASL, utilization of LES is helpful to gain an understanding of the ED in these conditions. A conceptual model of turbulent ED variation is proposed to describe the relationship between MASL dynamics/thermodynamic processes, state variable perturbations, and refractive variations.

Dependencies of GPS Scintillation Indices on the Ionospheric Plasma Drift and Rate of Change of TEC Around the Dawn Sector of the Polar Ionosphere

AbstractThe dependencies of global positioning system (GPS) scintillation indices on ionospheric plasma flow and the rate of change of total electron content (TEC) around the dawn sector for the first time of the polar ionosphere are investigated. The phase scintillation index (σφ) derived from GPS measurements of the Canadian High Arctic Ionospheric Network (CHAIN) shows linear dependencies on both the plasma drift speed measured by the SuperDARN radar and on the rate of change of TEC estimated from the GPS receivers of CHAIN. However, the amplitude scintillation index (S4) does not show any dependence on the plasma flow or the rate of change of TEC. These results further support Wang et al. (2018), https://doi.org/10.1002/2017JA024805 at the noon sector. The dependence of the phase scintillation index on the plasma flow further evidences that the standard phase scintillation index is dominated by refractive variations due to the use of a fixed cut‐off frequency of 0.1 Hz while detrending the phase observable. The dependence of the phase scintillation index on the rate of change of TEC consolidates the dominance of refractive variations inside.