scholarly journals Partially Coherent Backscatter in Radar Observations of Precipitation

2010 ◽  
Vol 67 (6) ◽  
pp. 1928-1946 ◽  
Author(s):  
A. R. Jameson ◽  
A. B. Kostinski
Keyword(s):  
Power Spectrum ◽  
Total Power ◽  
Coherent Scatter ◽  
Incoherent Scatter ◽  
Spectral Peaks ◽  
The Fourier Transform ◽  
Temporal Coherency ◽  
Coherent Backscatter ◽  
Periodic Components ◽  
Lower Frequencies

Abstract Classical radar theory only considers incoherent backscatter from precipitation. Can precipitation generate coherent scatter as well? Until now, the accepted answer has been no, because hydrometeors are distributed sparsely in space (relative to radar wavelength) so that the continuum assumption used to explain coherent scatter in clear air and clouds does not hold. In this work, a theory for a different mechanism is presented. The apparent existence of the proposed mechanism is then illustrated in both rain and snow. A new power spectrum Z( f ), the Fourier transform of the time series of the radar backscattered reflectivities, reveals statistically significant frequencies f of periodic components that cannot be ascribed to incoherent scatter. It is shown that removing those significant fs from Z( f ) at lower frequencies greatly reduces the temporal coherency. These lower frequencies, then, are associated with the increased temporal coherency. It is also shown that these fs are also directly linked to the Doppler spectral peaks through integer multiples of one-half the radar wavelength, characteristic of Bragg scatter. Thus, the enhanced temporal coherency is directly related to the presence of coherent scatter in agreement with theory. Moreover, the normalized backscattered power spectrum Z( f ) permits the estimation of the fractional coherent power contribution to the total power, even for an incoherent radar. Analyses of approximately 26 000 one-second Z( f ) in both rain and snow reveal that the coherent scatter is pervasive in these data. These findings present a challenge to the usual assumption that the scatter of radar waves from precipitation is always incoherent and to interpretations of backscattered power based on this assumption.

scholarly journals On the Enhanced Temporal Coherency of Radar Observations in Precipitation

2010 ◽  
Vol 49 (8) ◽  
pp. 1794-1804 ◽  
Author(s):  
A. R. Jameson ◽  
A. B. Kostinski
Keyword(s):  
Time Series ◽  
Autocorrelation Function ◽  
Doppler Velocity ◽  
Autocorrelation Functions ◽  
Coherent Scatter ◽  
Incoherent Scatter ◽  
The Family ◽  
The Times ◽  
Temporal Coherency ◽  
Coherent Backscatter

Abstract In this work, the authors present observations of enhanced temporal coherency beyond that expected using the observations of the standard deviation of the Doppler velocities and the assumption of a family of exponentially decaying autocorrelation functions. The purpose of this paper is to interpret these observations by developing the complex amplitude autocorrelation function when both incoherent and coherent backscatter are present. Using this expression, it is then shown that when coherent scatter is present, the temporal coherency increases as observed. Data are analyzed in snow and in rain. The results agree with the theoretical expectations, and the authors interpret this agreement as an indication that coherent scatter is the likely explanation for the observed enhanced temporal coherency. This finding does not affect decorrelation times measured using time series. However, when the time series is not available (as in theoretical studies), the times to decorrelation are often computed based upon the assumptions that the autocorrelation function is a member of the family of exponentially decaying autocorrelation functions and that the signal decorrelation is due solely to the Doppler velocity fluctuations associated with incoherent scatter. Such an approach, at times, may significantly underestimate the true required times to decorrelation thus leading to overestimates of statistical reliability of parameters.

scholarly journals On the Temporal Characteristics of Radar Coherent Structures in Snow and Rain

2010 ◽  
Vol 49 (9) ◽  
pp. 1891-1893 ◽  
Author(s):  
A. R. Jameson
Keyword(s):  
Transverse Velocity ◽  
Temporal Structure ◽  
Ice Crystals ◽  
Doppler Velocity ◽  
Coherent Scatter ◽  
Velocity Fluctuations ◽  
Incoherent Scatter ◽  
To Come ◽  
Coherent Backscatter ◽  
Periodic Components

Abstract Previous work showed that the magnitudes of the radar-backscattered amplitudes have statistically significant periodic components of frequencies ( f ) in excess of those arising from the Doppler velocity fluctuations of incoherent scatter. Analyses in both rain and snow in the earlier work revealed what is interpreted as pervasive coherent scatter. This coherency is thought to come from precipitation structures acting like gratings in resonance with the radar wavelength that, when they move with a velocity component transverse to the beam, induce the observed f. The purpose of this article is to characterize briefly the temporal structure of f and, thereby indirectly, the temporal character of the structures producing the radar coherent backscatter. It is found that these structures last considerably longer than the decorrelation times of a few to 10 milliseconds, characteristic of Doppler velocity fluctuations associated with incoherent scatter. For the data analyzed, though, most last no more than a significant fraction of 1 s. Hence, for the observed transverse velocity of 2 ms−1, the dimensions of the gratings producing the radar coherent backscatter are only on the order of tens of centimeters to a few meters. Therefore, the typically large sampling volumes of most radars will contain many of these grids at any given time. Consequently, during 1 s of observations, one can envision the coherent scatter as coming from many individual grids twinkling on and off, much like the transient spectral reflections off ice crystals falling in sunlight.

The on-line use of histogram data for high-speed correction and alignment of electron microscope images

1984 ◽  
Vol 42 ◽  
pp. 556-557
Author(s):  
William Krakow
Keyword(s):  
Power Spectrum ◽  
High Speed ◽  
Direct Memory Access ◽  
Digital Television ◽  
Contrast Transfer Function ◽  
The Past ◽  
High Resolution Tem ◽  
On Line ◽  
Correction Of Astigmatism ◽  
The Fourier Transform

In the past few years on-line digital television frame store devices coupled to computers have been employed to attempt to measure the microscope parameters of defocus and astigmatism. The ultimate goal of such tasks is to fully adjust the operating parameters of the microscope and obtain an optimum image for viewing in terms of its information content. The initial approach to this problem, for high resolution TEM imaging, was to obtain the power spectrum from the Fourier transform of an image, find the contrast transfer function oscillation maxima, and subsequently correct the image. This technique requires a fast computer, a direct memory access device and even an array processor to accomplish these tasks on limited size arrays in a few seconds per image. It is not clear that the power spectrum could be used for more than defocus correction since the correction of astigmatism is a formidable problem of pattern recognition.

Minimum Total Power Spectrum Aware Routing Scheme

2015 ◽  
Vol 3 (2) ◽  
pp. 37-46
Author(s):  
Mehak Mehak ◽  
◽  
G. Poonam ◽  
C. K. Nagpal ◽  
Shailender Gupta ◽  
...  
Keyword(s):  
Power Spectrum ◽  
Total Power ◽  
Routing Scheme

scholarly journals Energetic Efficiency of Vocalization by the Frog Physalaemus Pustulosus

1985 ◽  
Vol 116 (1) ◽  
pp. 47-52 ◽  
Author(s):  
MICHAEL J. RYAN
Keyword(s):  
Lower Limit ◽  
Energy Input ◽  
Acoustic Energy ◽  
Total Power ◽  
Energetic Efficiency ◽  
Physalaemus Pustulosus ◽  
Number Of Components ◽  
Lower Frequencies

1. Male Physalaemus pustulosus consume, on average, 1.2 μl of oxygen in the production of a single call, which is equivalent to an energy input per call of 0.024 J. 2. The total power of complex calls, which can have a varying number of components, ranged from 0.36 to 0.46 mW. The total acoustic energy contained in these complex calls ranged from 0.12 to 0.30mJ. 3. The energetic efficiency of the vocalization ranged from 0.5 to 1.2% which is similar to the range estimated for some other animals. 4. The low energetic efficiency of vocalization by these frogs is due, in part, to the fact that the wavelengths of the call are too long, relative to the size of the frog, to be radiated efficiently. 5. Although shorter wavelengths (higher frequencies) are radiated by the frog at relatively greater intensities, longer wavelengths (lower frequencies) attenuate less rapidly in the environment. It is suggested that selection generated by the acoustics of the environment favours calls with lower frequencies, but the morphology of the animal sets a lower limit to which frequencies can evolve.

scholarly journals INTERRELATION BETWEEN POLYFUNCTIONAL MONITORING DATA IN YOUNG MEN WITH PRE- OR MILD HYPERTENSION WITH DIFFERENT BLOOD PRESSURE DAILY PROFILE

2013 ◽  
Vol 19 (1) ◽  
pp. 44-50 ◽  
Author(s):  
E. N. Kazidaeva ◽  
Yu. L. Venevtseva
Keyword(s):  
Blood Pressure ◽  
Power Spectrum ◽  
Mild Hypertension ◽  
Young Men ◽  
Holter Monitoring ◽  
Left Ventricular ◽  
Total Power ◽  
Night Time ◽  
Arterial Blood ◽  
Functional Features

Objective. To examine the clinical signifi  cance of polyfunctional 24-hour Holter monitoring with simultaneous recording of electrocardiogram, blood pressure (BP) and respiratory efforts by respiratory inductance plethysmography (Incart, Russia) and functional features of young men with prehypertension or mild arterial hypertension with different profi  le of night arterial blood pressure (BP) decline («dippers», «non-dippers», «over-dippers»).Design and methods. We examined 43 adolescents and young men aged 16–26 years (mean age 19,4 ± 0,5 years). All of them underwent echocardiography («Vivid 7», GE); 48,8 % of patients were overweight or obese (body mass index, BMI > 24,9 kg/m2), and BMI was comparable in all groups. Results. Breathing disturbances (apnea/hypopnea episodes) were found in 86 % patients and were positively related with high frequency (HF) spectrum power of heart rate variability (HRV) at night-time and were not related with BMI, BP or type of night BP decline. The analysis of echocardiography revealed that in «non-dippers» (n = 18) left ventricular myocardial mass index (LVMMI) was higher (94,3 ± 16,6 g/m2) than in «over-dippers» (n = 15; 77,8 ± 10,3 g/m2, р < 0,001). In daytime «non-dippers» had lower HRV (total power spectrum and power in all three groups) and power spectrum of VLF and LF spectrum at night. The frequency of repolarization instability (transient T-wave inversion) and early repolarization syndrome was higher in «over-dippers» (66,7 %, р < 0,01). Circadian index of HR was also higher (150 %) in «over-dippers». The number of sleep apnea in «non-dippers» and «dippers» was higher (39,7 ± 29,7 and 37,1 ± 18,1 episodes per hour of sleep) than in «over-dippers» (22,3 ± 12,0 episodes per hour of sleep, р < 0,05), but the last group had more hypopneas.Conclusion. Breathing disturbances were a frequent, and, probably, physiological, fi  nding at polyfunctional 24-hour Holter monitoring in young overweight men with pre- or mild hypertension. There is a relationship between LVMMI and nocturnal BP dipping even in young men. Young «non-dippers» demonstrate the same clinical pattern as the older ones. «Over-dipper» type is characterized predominantly by lower HR at night and ECG repolarization abnormalities. 

Comparing VHF coherent scatter from the radar aurora with incoherent scatter and all-sky auroral imagery

2012 ◽  
Vol 117 (A10) ◽  
pp. n/a-n/a ◽  
Author(s):  
D. Hysell ◽  
R. Miceli ◽  
J. Munk ◽  
D. Hampton ◽  
C. Heinselman ◽  
...  
Keyword(s):  
Coherent Scatter ◽  
Incoherent Scatter

scholarly journals Aspect sensitivity of VHF echoes from field aligned irregularities in meteor trails and thin ionization layers

2004 ◽  
Vol 4 (3) ◽  
pp. 685-692 ◽  
Author(s):  
Q. H. Zhou ◽  
Y. T. Morton ◽  
J. D. Mathews ◽  
D. Janches
Keyword(s):  
Diffusion Rate ◽  
Numerical Models ◽  
Mesopause Region ◽  
Incoherent Scatter ◽  
Vertical Extension ◽  
Spectral Peaks ◽  
Range Spread ◽  
Meteor Trails ◽  
Field Aligned Irregularities ◽  
Aspect Sensitivity

Abstract. The aspect sensitivity of VHF echoes from field aligned irregularities (FAI) within meteor trails and thin ionization layers is studied using numerical models. Although the maximum power is obtained when a radar is pointed perpendicular to the field line (B), substantial power can be obtained off the B direction if the ionization trail/layer is thin. When the FAI length along B is 20 m, the power observed 6° off B is about 10 db below that perpendicular to the B direction. Meteoric FAI echoes can potentially be used to determine the diffusion rate in the mesopause region. Based on the aspect sensitivity analysis, we conclude that the range spread trail echoes far off B observed by powerful VHF radars are likely due to overdense meteors. Our simulation also shows that ionospheric FAI echoes can have an altitude smearing effect of about 4 km if the vertical extension of a FAI-layer is around 100 m, which has often been observed at Arecibo. The altitude smearing effect can account for the fact that the Es-layers observed by the Arecibo incoherent scatter radar are typically much narrower than FAI-layers and the occurrence of double spectral peaks around the Es-layer altitude in FAI echoes.

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