Comparisons between high-resolution profiles of squared refractive index gradient &lt;i&gt;M&lt;/i&gt;&lt;sup&gt;2&lt;/sup&gt; measured by the Middle and Upper  Atmosphere Radar and unmanned aerial vehicles (UAVs) during the Shigaraki UAV-Radar Experiment 2015 campaign

Abstract. New comparisons between the square of the generalized potential refractive index gradient M2, estimated from the very high-frequency (VHF) Middle and Upper Atmosphere (MU) Radar, located at Shigaraki, Japan, and unmanned aerial vehicle (UAV) measurements are presented. These comparisons were performed at unprecedented temporal and range resolutions (1–4 min and ∼  20 m, respectively) in the altitude range ∼  1.27–4.5 km from simultaneous and nearly collocated measurements made during the ShUREX (Shigaraki UAV-Radar Experiment) 2015 campaign. Seven consecutive UAV flights made during daytime on 7 June 2015 were used for this purpose. The MU Radar was operated in range imaging mode for improving the range resolution at vertical incidence (typically a few tens of meters). The proportionality of the radar echo power to M2 is reported for the first time at such high time and range resolutions for stratified conditions for which Fresnel scatter or a reflection mechanism is expected. In more complex features obtained for a range of turbulent layers generated by shear instabilities or associated with convective cloud cells, M2 estimated from UAV data does not reproduce observed radar echo power profiles. Proposed interpretations of this discrepancy are presented.

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Comparisons of refractive index gradient and stability profiles measured by balloons and the MU radar at a high vertical resolution in the lower stratosphere

Annales Geophysicae ◽

10.5194/angeo-25-47-2007 ◽

2007 ◽

Vol 25 (1) ◽

pp. 47-57 ◽

Cited By ~ 26

Author(s):

H. Luce ◽

G. Hassenpflug ◽

M. Yamamoto ◽

S. Fukao

Keyword(s):

Lower Stratosphere ◽

Imaging Technique ◽

Refractive Index Gradient ◽

Vertical Resolution ◽

Range Imaging ◽

Range Resolution ◽

Mu Radar ◽

Resolution Improvement ◽

Radar Echo ◽

Index Gradient

Abstract. Many experimental studies have demonstrated that VHF Stratosphere-Troposphere (ST) radar echo power is proportional to the generalized refractive index gradient squared M2 when using a vertically oriented beam. Because humidity is generally negligible above the tropopause, VHF ST radars can thus provide information on the static stability (quantified by the squared Brunt-Väisälä frequency N2) at stratospheric heights and this capability is useful for many scientific applications. Most studies have been performed until now at a vertical resolution of 150 m or more. In the present paper, results of comparisons between radar- and (balloon borne) radiosonde-derived M2 and N2 are shown at a better vertical resolution of 50 m with the MU radar (34.85° N, 136.15° E; Japan) by benefiting from the range resolution improvement provided by the multi-frequency range imaging technique, using the Capon processing method. Owing to favorable winds in the troposphere, the radiosondes did not drift horizontally more than about 30 km from the MU radar site by the time they reached an altitude of 20 km. The measurements were thus simultaneous and almost collocated. Very good agreements have been obtained between both high resolution profiles of M2, as well as profiles of N2. It is also shown that this agreement can still be improved by taking into account a frozen-in advection of the air parcels by a horizontally uniform wind. Therefore, it can be concluded that 1) the range imaging technique with the Capon method really provides substantial range resolution improvement, despite the relatively weak Signal-to-Noise Ratios (SNR) over the analyzed region of the lower stratosphere, 2) the proportionality of the radar echo power to M2 at a vertical scale down to 50 m in the lower stratosphere is experimentally demonstrated, 3) the MU radar can provide stability profiles with a vertical resolution of 50 m at heights where humidity is negligible, 4) stable stratospheric layers as thin as 50 m or less have at least a horizontal extent of a few km to several tens of kilometers and can be considered as frozenly advected over scales of a few tens of minutes.

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Radar-Echo Enhancement at Frontal Boundaries by Refractive Index Inhomogeneities

Bulletin of the American Meteorological Society ◽

10.1175/1520-0477-40.6.295 ◽

1959 ◽

Vol 40 (6) ◽

pp. 295-300 ◽

Cited By ~ 1

Author(s):

John Schuetz

Keyword(s):

Refractive Index ◽

Radar Data ◽

Refractive Index Gradient ◽

Radar Echo ◽

Index Gradient

Observations associated with some unusual radar echo lines are presented. Analysis of raingage and radar data indicates that echo enhancement due to a steep refractive index gradient is occurring. Acceleration of the front may play an important role in forming this echo. Synoptic application of observations of these unusual echo lines is discussed.

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A Refractive INdex Gradient (RING) diagnostic for transient discharges or expansions of vapor or plasmas

IEEE Transactions on Plasma Science ◽

10.1109/27.108417 ◽

1991 ◽

Vol 19 (5) ◽

pp. 800-813 ◽

Cited By ~ 19

Author(s):

M.E. Cuneo ◽

T.R. Lockner ◽

G.C. Tisone

Keyword(s):

Refractive Index ◽

Refractive Index Gradient ◽

Index Gradient

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The Reflection of Waves at a Discontinuity in Refractive Index Gradient

Journal of Mathematics and Physics ◽

10.1002/sapm1966451162 ◽

1966 ◽

Vol 45 (1-4) ◽

pp. 162-168 ◽

Cited By ~ 2

Author(s):

R. Burman

Keyword(s):

Refractive Index ◽

Refractive Index Gradient ◽

Index Gradient ◽

Reflection Of Waves

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Label-Free Digital Holo-tomographic Microscopy Reveals Virus-Induced Cytopathic Effects in Live Cells

mSphere ◽

10.1128/mspheredirect.00599-18 ◽

2018 ◽

Vol 3 (6) ◽

Cited By ~ 5

Author(s):

Artur Yakimovich ◽

Robert Witte ◽

Vardan Andriasyan ◽

Fanny Georgi ◽

Urs F. Greber

Keyword(s):

Refractive Index ◽

Vaccinia Virus ◽

Virus Type ◽

Live Cells ◽

Refractive Index Gradient ◽

Label Free ◽

Virus Infections ◽

Cytopathic Effects ◽

Infected Cells ◽

Index Gradient

ABSTRACTCytopathic effects (CPEs) are a hallmark of infections. CPEs are difficult to observe due to phototoxicity from classical light microscopy. We report distinct patterns of virus infections in live cells using digital holo-tomographic microscopy (DHTM). DHTM is label-free and records the phase shift of low-energy light passing through the specimen on a transparent surface with minimal perturbation. DHTM measures the refractive index (RI) and computes the refractive index gradient (RIG), unveiling optical heterogeneity in cells. We find that vaccinia virus (VACV), herpes simplex virus (HSV), and rhinovirus (RV) infections progressively and distinctly increased RIG. VACV infection, but not HSV and RV infections, induced oscillations of cell volume, while all three viruses altered cytoplasmic membrane dynamics and induced apoptotic features akin to those caused by the chemical compound staurosporine. In sum, we introduce DHTM for quantitative label-free microscopy in infection research and uncover virus type-specific changes and CPE in living cells with minimal interference.IMPORTANCEThis study introduces label-free digital holo-tomographic microscopy (DHTM) and refractive index gradient (RIG) measurements of live, virus-infected cells. We use DHTM to describe virus type-specific cytopathic effects, including cyclic volume changes of vaccinia virus infections, and cytoplasmic condensations in herpesvirus and rhinovirus infections, distinct from apoptotic cells. This work shows for the first time that DHTM is suitable to observe virus-infected cells and distinguishes virus type-specific signatures under noninvasive conditions. It provides a basis for future studies, where correlative fluorescence microscopy of cell and virus structures annotate distinct RIG values derived from DHTM.

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