Discovery of high-quality daytime seeing windows at the Antarctic Taishan station

2020 ◽  
Vol 493 (4) ◽  
pp. 5648-5652 ◽  
Author(s):  
Qiguo Tian ◽  
Peng Jiang ◽  
Xinmiao Jin ◽  
Jialu Li ◽  
Chong Pei ◽  
...  
Keyword(s):  
Structure Constant ◽  
Temperature Gradients ◽  
Cumulative Distribution ◽  
Image Motion ◽  
Index Structure ◽  
Temporal Association ◽  
High Quality ◽  
Solar Observations ◽  
The Antarctic ◽  
Temporal Windows

ABSTRACT We report on the initial results of seeing measurements at the Antarctic Taishan Station (ATS) using a differential image motion monitor observed in the visible at a height of 2.5 m above the snow surface, during the site-testing experiments carried out on 2014 January 13 and 15. The median seeing was found to be 0.73 arcsec and the 25th and 75th percentiles of the seeing cumulative distribution were 0.59 and 0.87 arcsec, respectively, with a minimum of ∼0.5 arcsec at ∼16:00–19:00 local time (UTC + 5). Such a seeing minimum has a good temporal association with the refractive index structure constant ($C_n^2$) minimum simultaneously observed at ATS. Interestingly, both temporal windows of $C_n^2$ and seeing minimum coincide with those of minimum temperature gradients ($\rm \sim 0\,^{\circ }C\,m^{-1}$), we had more than one month of continuous measurements of Cn2 and temperature gradients between 2013 December 30 and 2014 February 10. This suggests that high-quality seeing windows might be opened at ATS with the potential for astronomical activities, especially for solar observations.

scholarly journals Re-Visiting Acoustic Sounding to Advance the Measurement of Optical Turbulence

2021 ◽  
Vol 11 (16) ◽  
pp. 7658
Author(s):  
Steven Fiorino ◽  
Santasri Bose-Pillai ◽  
Kevin Keefer
Keyword(s):  
Large Scale ◽  
Velocity Structure ◽  
Sonic Anemometer ◽  
Structure Constant ◽  
Vertical Wind Shear ◽  
Index Of Refraction ◽  
Image Motion ◽  
Index Structure ◽  
Temperature Structure ◽  
Optical Turbulence

Optical turbulence, as determined by the widely accepted practice of profiling the temperature structure constant, CT2, via the measurement of ambient atmospheric temperature gradients, can be found to differ quite significantly when characterizing such gradients via thermal-couple differential temperature sensors as compared to doing so with acoustic probes such as those commonly used in sonic anemometry. Similar inconsistencies are observed when comparing optical turbulence strength derived via CT2 as compared to those through direct optical or imaging measurements of small fluctuations of the index of refraction of air (i.e., scintillation). These irregularities are especially apparent in stable atmospheric layers and during diurnal quiescent periods. Our research demonstrates that when care is taken to properly remove large-scale index of refraction gradients, the sonic anemometer-derived velocity structure constant, Cv2, coupled with the similarly derived turbulence-driven index of refraction and vertical wind shear gradients, provides a refractive index structure constant, Cn2, that can more closely match the optical turbulence strengths inferred by more direct means such as scintillometers or differential image motion techniques. The research also illustrates the utility and robustness of quantifying Cn2 from CT2 at a point using a single sonic anemometer and establishes a clear set of equations to calculate volumetric Cn2 data using instrumentation that measures wind velocities with more spatial/temporal fidelity than temperature.

scholarly journals Method for Measuring the Second-Order Moment of Atmospheric Turbulence

Atmosphere ◽  
2021 ◽  
Vol 12 (5) ◽  
pp. 564
Author(s):  
Hong Shen ◽  
Longkun Yu ◽  
Xu Jing ◽  
Fengfu Tan
Keyword(s):  
Atmospheric Turbulence ◽  
Weighting Function ◽  
Structure Constant ◽  
Turbulence Models ◽  
Second Order ◽  
Index Structure ◽  
Order Moment ◽  
Site Testing ◽  
Optical Effects ◽  
Novel Method

The turbulence moment of order m (μm) is defined as the refractive index structure constant Cn2 integrated over the whole path z with path-weighting function zm. Optical effects of atmospheric turbulence are directly related to turbulence moments. To evaluate the optical effects of atmospheric turbulence, it is necessary to measure the turbulence moment. It is well known that zero-order moments of turbulence (μ0) and five-thirds-order moments of turbulence (μ5/3), which correspond to the seeing and the isoplanatic angles, respectively, have been monitored as routine parameters in astronomical site testing. However, the direct measurement of second-order moments of turbulence (μ2) of the whole layer atmosphere has not been reported. Using a star as the light source, it has been found that μ2 can be measured through the covariance of the irradiance in two receiver apertures with suitable aperture size and aperture separation. Numerical results show that the theoretical error of this novel method is negligible in all the typical turbulence models. This method enabled us to monitor μ2 as a routine parameter in astronomical site testing, which is helpful to understand the characteristics of atmospheric turbulence better combined with μ0 and μ5/3.

scholarly journals Strong uniform consistency rates of conditional quantile estimation in the single functional index model under random censorship

2018 ◽  
Vol 6 (1) ◽  
pp. 197-227 ◽  
Author(s):  
Nadia Kadiri ◽  
Abbes Rabhi ◽  
Amina Angelika Bouchentouf
Keyword(s):  
Cumulative Distribution Function ◽  
Complete Convergence ◽  
Asymptotic Properties ◽  
Cumulative Distribution ◽  
Index Structure ◽  
Functional Index ◽  
Conditional Quantile ◽  
Index Model ◽  
Strong Uniform Consistency ◽  
Mixing Sequence

AbstractThe main objective of this paper is to non-parametrically estimate the quantiles of a conditional distribution in the censorship model when the sample is considered as an -mixing sequence. First of all, a kernel type estimator for the conditional cumulative distribution function (cond-cdf) is introduced. Afterwards, we estimate the quantiles by inverting this estimated cond-cdf and state the asymptotic properties when the observations are linked with a single-index structure. The pointwise almost complete convergence and the uniform almost complete convergence (with rate) of the kernel estimate of this model are established. This approach can be applied in time series analysis.

scholarly journals Spray Drying of a Subcritical Extract Using Marrubium vulgare as a Method of Choice for Obtaining High Quality Powder

Pharmaceutics ◽  
2019 ◽  
Vol 11 (10) ◽  
pp. 523 ◽  
Author(s):  
Aleksandra Gavarić ◽  
Jelena Vladić ◽  
Rita Ambrus ◽  
Stela Jokić ◽  
Piroska Szabó-Révész ◽  
...  
Keyword(s):  
Spray Drying ◽  
Subcritical Water ◽  
Structure Constant ◽  
Amorphous Structure ◽  
Perennial Herb ◽  
Subcritical Water Extraction ◽  
Extraction Technology ◽  
High Quality ◽  
Marrubium Vulgare ◽  
Ancient Times

White horehound (Marrubium vulgare L.), is a grey-leaved perennial herb, belonging to Lamiaceae family, distributed in Eurasia and northern Africa. Despite the fact that M. vulgare has been used since ancient times in treating diverse diseases, it is only in the last decade or so that scientists have been able to lay the foundation for its potential pharmacological actions from the results observed through the prism of ethnopharmacological use of this species. The novelty of this study was that subcritical water extraction, acknowledged as a powerful extraction technology to recover phenolic compounds, was coupled with spray drying. The subcritical horehound extract, obtained using optimal process parameters, was used as a liquid feed in spray drying. Maltodextrin was used as a carrier in a concentration of 10%. Thus, two M. vulgare powders, carrier-free and 10% MD, were produced. Comprehensive powders characterization was conducted in order to evaluate their quality. Results confirmed that spray drying can be used as a method of choice for obtaining high quality horehound powders which kept the amorphous structure constant after 6 months.

Estimating refractive index structure constant and extinction coefficient under misalignment

Optik ◽  
2020 ◽  
Vol 206 ◽  
pp. 164182
Author(s):  
Dagang Jiang ◽  
Ting Lyu ◽  
Xin Liu ◽  
Yishuai Yuan ◽  
Bin Zhu
Keyword(s):  
Refractive Index ◽  
Extinction Coefficient ◽  
Structure Constant ◽  
Index Structure

scholarly journals Ten years from the Antarctic Sub-millimeter Telescope and Remote Observatory

2006 ◽  
Vol 2 (14) ◽  
pp. 686-688
Author(s):  
Christopher L. Martin
Keyword(s):  
Atmospheric Stability ◽  
Winter Season ◽  
South Pole ◽  
High Quality ◽  
Low Humidity ◽  
The Antarctic

Beginning with the winter season of 1995 and for the next ten years, the Antarctic Sub-mm Telescope and Remote Observatory (AST/RO, Stark et al. 1997; Stark et al. 2001; <http://www.cfa.harvard.edu/ASTRO/>), a 1.7m diameter, offset Gregorian telescope located at an altitude of 2847m at the Amundsen-Scott South Pole Station collected sub-mm and Terahertz data in the 1.3mm to 200μm wavelength bands. From its location just a few hundred meters away from the geophysical South Pole, AST/RO was the first sub-mm telescope to over-winter on the polar plateau, a location uniquely suited to high quality sub-mm observations due its very low humidity, high atmospheric stability and thin troposphere (Chamberlin et al. 1997).

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