scholarly journals A Method to Estimate Fried's Seeing Parameter from a Time Series of Arbitrary Resolved Structures Imaged Through the Atmosphere

1984 ◽  
Vol 79 ◽  
pp. 203-220
Author(s):  
O. von der Lühe
Keyword(s):  
Signal To Noise Ratio ◽  
Imaging Techniques ◽  
Average Power ◽  
Speckle Interferometry ◽  
Reference Object ◽  
Ratio Method ◽  
Modulation Transfer ◽  
Fourier Plane ◽  
First Results ◽  
Average Power Spectrum

AbstractOne of the major fields of application of speckle-interferometric and speckle-imaging techniques is the photometry of astronomical objects exhibiting structure smaller than the seeing limit. The accuracy of the photometry depends critically on the accuracy to which the modulation transfer function (MTF), that describes the atmospheric-telescopic attenuation of the Fourier amplitudes of the object under consideration, is known. The estimation of the effective MTF is especially difficult when no known reference object is within the field of view.A method is presented that allows to estimate the effective MTF from the observation of arbitrary structure with the use of FRIED-KORFF theory. The ratio of the squared modulus of the average Fourier transform and the average power spectrum serves as an estimator for the FRIED parameter r0. To a first approximation, this ratio is independent from the observed object. Additionally, the behaviour of the ratio in regions beyond the seeing limit in the Fourier plane may be analyzed to obtain an estimate of the speckle interferometry signal-to-noise ratio. The basic concept of the ratio method will be described, its accuracy will be discussed. First results on the application of the ratio method to observations of solar granulation will be presented.

Study on Fast Algorithm for SNR and Method for Threshold Confirmation

2013 ◽  
Vol 427-429 ◽  
pp. 1718-1722
Author(s):  
Lin Sun ◽  
Ran Wei ◽  
Fu Ting Bao ◽  
Xian Zhang Tian
Keyword(s):  
Power Spectrum ◽  
Fast Algorithm ◽  
Human Gene ◽  
Signal To Noise Ratio ◽  
Average Power ◽  
Threshold Value ◽  
Computational Experiments ◽  
Rigorous Derivation ◽  
Signal To Noise ◽  
Average Power Spectrum

To reduce the amount of computing resources, a fast algorithm of the average power spectrum and signal-to-noise ratio was presented based on rigorous derivation of the formula. Also, it proved the rule gained from computational experiments. Besides, a method called fitting-optimization to determine the classification threshold value was proposed. It improves the accuracy by about 7% for human gene.

Determination of the Best Emulsion for the Microscopy of Crystals

1981 ◽  
Vol 39 ◽  
pp. 32-33
Author(s):  
David A. Grano ◽  
Kenneth H. Downing
Keyword(s):  
Spatial Frequency ◽  
Information Transfer ◽  
Signal To Noise Ratio ◽  
Experimental Situation ◽  
Photographic Emulsion ◽  
Modulation Transfer ◽  
Signal To Noise ◽  
Frequency Space ◽  
Noise Ratio

The retrieval of high-resolution information from images of biological crystals depends, in part, on the use of the correct photographic emulsion. We have been investigating the information transfer properties of twelve emulsions with a view toward 1) characterizing the emulsions by a few, measurable quantities, and 2) identifying the “best” emulsion of those we have studied for use in any given experimental situation. Because our interests lie in the examination of crystalline specimens, we've chosen to evaluate an emulsion's signal-to-noise ratio (SNR) as a function of spatial frequency and use this as our critereon for determining the best emulsion.The signal-to-noise ratio in frequency space depends on several factors. First, the signal depends on the speed of the emulsion and its modulation transfer function (MTF). By procedures outlined in, MTF's have been found for all the emulsions tested and can be fit by an analytic expression 1/(1+(S/S0)2). Figure 1 shows the experimental data and fitted curve for an emulsion with a better than average MTF. A single parameter, the spatial frequency at which the transfer falls to 50% (S0), characterizes this curve.

scholarly journals 3D super-resolved imaging in live cells using sub-diffractive plasmonic localization of hybrid nanopillar arrays

Nanophotonics ◽  
2020 ◽  
Vol 9 (9) ◽  
pp. 2847-2859
Author(s):  
Soojung Kim ◽  
Hyerin Song ◽  
Heesang Ahn ◽  
Seung Won Jun ◽  
Seungchul Kim ◽  
...  
Keyword(s):  
Signal To Noise Ratio ◽  
Imaging Techniques ◽  
Optical Loss ◽  
Super Resolution ◽  
Living Cells ◽  
Live Cells ◽  
Complex Biological System ◽  
Observation Volume ◽  
Resolution Imaging ◽  
Nanopillar Arrays

AbstractAnalysing dynamics of a single biomolecule using high-resolution imaging techniques has been had significant attentions to understand complex biological system. Among the many approaches, vertical nanopillar arrays in contact with the inside of cells have been reported as a one of useful imaging applications since an observation volume can be confined down to few-tens nanometre theoretically. However, the nanopillars experimentally are not able to obtain super-resolution imaging because their evanescent waves generate a high optical loss and a low signal-to-noise ratio. Also, conventional nanopillars have a limitation to yield 3D information because they do not concern field localization in z-axis. Here, we developed novel hybrid nanopillar arrays (HNPs) that consist of SiO2 nanopillars terminated with gold nanodisks, allowing extreme light localization. The electromagnetic field profiles of HNPs are obtained through simulations and imaging resolution of cell membrane and biomolecules in living cells are tested using one-photon and 3D multiphoton fluorescence microscopy, respectively. Consequently, HNPs present approximately 25 times enhanced intensity compared to controls and obtained an axial and lateral resolution of 110 and 210 nm of the intensities of fluorophores conjugated with biomolecules transported in living cells. These structures can be a great platform to analyse complex intracellular environment.

FIRST RESULTS OF THE OPTICAL SPECKLE INTERFEROMETRY WITH THE 3.5 m TELESCOPE AT CALAR ALTO (SPAIN): MEASUREMENTS AND ORBITS OF VISUAL BINARIES

2008 ◽  
Vol 135 (5) ◽  
pp. 1803-1809 ◽  
Author(s):  
J. A. Docobo ◽  
V. S. Tamazian ◽  
M. Andrade ◽  
J. F. Ling ◽  
Y. Y. Balega ◽  
...  
Keyword(s):  
Speckle Interferometry ◽  
First Results ◽  
Calar Alto ◽  
Visual Binaries

Description and interpretation of the bracts epidermis of Gramineae (Poaceae) with rotated image with maximum average power spectrum (RIMAPS) technique

Micron ◽  
2008 ◽  
Vol 39 (7) ◽  
pp. 985-991 ◽  
Author(s):  
Eduardo A. Favret ◽  
Néstor O. Fuentes ◽  
Ana M. Molina ◽  
Lorena M. Setten
Keyword(s):  
Power Spectrum ◽  
Average Power ◽  
Average Power Spectrum

scholarly journals Speckle Observations of Solar Granulation

1994 ◽  
Vol 158 ◽  
pp. 398-400 ◽  
Author(s):  
C.R. de Boer ◽  
F. Kneer
Keyword(s):  
Transfer Function ◽  
Broad Band ◽  
Active Regions ◽  
Spectral Ratio ◽  
Speckle Interferometry ◽  
Frame Rate ◽  
Small Scale ◽  
Fourier Plane ◽  
Pass Filter ◽  
Low Pass Filter

Image reconstruction by means of speckle interferometry was successfully used to restore the intensity distribution of solar features and to investigate the morphology and dynamics of small-scale structures in active regions of the Sun. The observations were obtained with the Vacuum Tower Telescope (D = 70 cm, f = 46 m) at Observatorio del Teide, Tenerife, on May 17 and 20, 1991, from a plage region close to a sunspot near disc centre. Sequences of bursts consisting of 100 exposures were recorded with a broad-band filter centred at 550 nm (FWHM ≈ 10 nm, diffraction limit 0.2 arcsec). The pickup unit was a video CCD – system with an exposure time of 4 ms and a frame rate of three pictures per second. A description of the observing procedure and of the data handling can be found in de Boer et al. (1992). To obtain the complex Fourier phases speckle masking (Lohmann et al. 1983) was used. The speckle transfer function of the atmosphere was calculated indirectly using Korff's equation (1973). The Fried parameter r0 was estimated with the spectral ratio technique (von der Lühe 1984). This parameter was sometimes as large as 14 cm. With this the theoretical speckle transfer function could be determined for calculating the corrected Fourier amplitudes of the reconstruction. A new low pass filter, based on the reliability of each individual value in the Fourier plane, was applied to the amplitudes to suppress noise at high wavenumbers.

scholarly journals Practical BER-Based Estimation of Residual OFDM CFO by Reducing Noise Margin

2020 ◽  
Vol 2020 ◽  
pp. 1-5
Author(s):  
Ante Mihaljević ◽  
Adriana Lipovac ◽  
Vlatko Lipovac ◽  
Jasmin Musovic
Keyword(s):  
Carrier Frequency Offset ◽  
Signal To Noise Ratio ◽  
Phase Error ◽  
Average Power ◽  
Small Time ◽  
Small Cells ◽  
Test Time ◽  
High Power Amplifier ◽  
Noise Margin ◽  
Long Time

The main OFDM drawbacks are Carrier Frequency Offset (CFO) and large Peak-to-Average Power Ratio (PAPR), which both degrade the Bit Error Rate (BER). Specifically, we consider here clipping or any other PAPR reduction method sufficient to prevent the nonlinear high-power amplifier from generating errors. Moreover, in small cells, the signal-to-noise ratio is large, while the small time dispersion allows the OFDM symbol cyclic prefix to prevent intersymbol interference. This retains the CFO to solely determine the BER and vice versa, enabling indirect estimation of CFO-induced phase distortion by simple BER testing. However, a particular problem is measuring very low BER values (generated by alike residual CFO), which could last a long time in order to acquire statistically enough errors. The test time can be drastically reduced if the noise margin is reduced in a controllable way, by adding the interfering signal to each subcarrier at the receiver. This approach is shown to enable efficient and accurate short-term BER (and so CFO phase error) testing.

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