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 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.

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 Common volume coherent and incoherent scatter radar observations of mid-latitude sporadic E-layers and QP echoes

2004 ◽  
Vol 22 (9) ◽  
pp. 3277-3290 ◽  
Author(s):  
D. L. Hysell ◽  
M. F. Larsen ◽  
Q. H. Zhou
Keyword(s):  
Large Scale ◽  
Incoherent Scatter Radar ◽  
Coherent Scatter ◽  
Electrostatic Waves ◽  
Incoherent Scatter ◽  
Scatter Radar ◽  
Dual Beam ◽  
Sporadic E Layers ◽  
E Region ◽  
Sporadic E

Abstract. Common-volume observations of sporadic E-layers made on 14-15 June 2002 with the Arecibo incoherent scatter radar and a 30MHz coherent scatter radar imager located on St. Croix are described. Operating in dual-beam mode, the Arecibo radar detected a slowly descending sporadic E-layer accompanied by a series of dense E-region plasma clouds at a time when the coherent scatter radar was detecting quasi-periodic (QP) echoes. Using coherent radar imaging, we collocate the sources of the coherent scatter with the plasma clouds observed by Arecibo. In addition to patchy, polarized scattering regions drifting through the radar illuminated volume, which have been observed in previous imaging experiments, the 30MHz radar also detected large-scale electrostatic waves in the E-region over Puerto Rico, with a wavelength of about 30km and a period of about 10min, propagating to the southwest. Both the intensity and the Doppler shifts of the coherent echoes were modulated by the wave.

scholarly journals Spatial observations by the CUTLASS coherent scatter radar of ionospheric modification by high power radio waves

1997 ◽  
Vol 15 (11) ◽  
pp. 1412-1421 ◽  
Author(s):  
G. E. Bond ◽  
T. R. Robinson ◽  
P. Eglitis ◽  
D. M. Wright ◽  
A. J. Stocker ◽  
...  
Keyword(s):  
Horizontal Distance ◽  
Radio Waves ◽  
Heated Region ◽  
Coherent Scatter ◽  
Heating Facility ◽  
Incoherent Scatter ◽  
Ionospheric Modification ◽  
Experimental Campaign ◽  
Scatter Radar ◽  
Field Aligned Irregularities

Abstract. Results are presented from an experimental campaign in April 1996, in which the new CUTLASS (Co-operative UK twin-located Auroral Sounding System) coherent scatter radar was employed to observe artificial field aligned irregularities (FAI) generated by the EISCAT (European Incoherent SCATter) heating facility at Tromsø, Norway. The distribution of backscatter intensity from within the heated region has been investigated both in azimuth and range with the Finland component of CUTLASS, and the first observations of artificial irregularities by the Iceland radar are also presented. The heated region has been measured to extend over a horizontal distance of 170±50km, which by comparison with a model of the heater beam pattern corresponds to a threshold electric field for FAI of between 0.1 and 0.01V/m. Differences between field-aligned and vertical propagation heating are also presented.

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