Millstone Hill ISR Measurements of Small Aspect Angle Spectra

Abstract. Data collected by the CUTLASS Finland HF radar are used to illustrate the significant difference between the cosine component of the plasma convection in the F-region and the Doppler velocity of the E-region coherent echoes observed at large flow angles. We show that the E-region velocity is ~5 times smaller in magnitude and rotated by ~30° clockwise with respect to convection in the F-region. Also, measurements at flow angles larger than 90° exhibit a completely new feature: Doppler velocity increase with the expected aspect angle and spatial anticorrelation with the backscatter power. By considering DMSP drift-meter measurements we argue that the difference between F- and E-region velocities cannot be interpreted in terms of the convection change with latitude. The observed features in the velocity of the E-region echoes can be explained by taking into account the ion drift contribution to the irregularity phase velocity as predicted by the linear fluid theory. Key words. Ionosphere (auroral ionosphere; ionospheric irregularities; plasma convection)

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Oblique Pulsator Model for the Blazhko Effect of RR Lyrae Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100036757 ◽

1995 ◽

Vol 155 ◽

pp. 42-43

Author(s):

Hiromoto Shibahashi ◽

Masao Takata

Keyword(s):

Rotation Axis ◽

Oscillation Mode ◽

Stellar Rotation ◽

Rr Lyrae Stars ◽

Aspect Angle ◽

Rr Lyrae ◽

Quadrupole Component ◽

Blazhko Effect ◽

Apparent Variation ◽

Lyrae Stars

AbstractBy assuming that the RR Lyrae stars have fairly strong dipole magnetic fields with the symmetry axis oblique to the rotation axis of the star, we show that the oscillation mode which would be a pure radial oscillation in absence of the magnetic field has a quadrupole component, which is axisymmetric with respect to the magnetic axis. The aspect angle of the quadrupole component changes due to the stellar rotation, and this apparent variation is interpreted as the Blazhko effect in RR Lyrae stars.

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Rotating Parabolic-Reflector Antenna Target in SAR Data: Model, Characteristics, and Parameter Estimation

International Journal of Antennas and Propagation ◽

10.1155/2013/583865 ◽

2013 ◽

Vol 2013 ◽

pp. 1-13 ◽

Cited By ~ 2

Author(s):

Bin Deng ◽

Hong-Qiang Wang ◽

Yu-Liang Qin ◽

Sha Zhu ◽

Xiang Li

Keyword(s):

Parameter Estimation ◽

Data Model ◽

Target Recognition ◽

Image Interpretation ◽

Likelihood Estimator ◽

Parabolic Reflector ◽

Time Frequency ◽

Aspect Angle ◽

Multiple Parameters ◽

Scattering Center

Parabolic-reflector antennas (PRAs), usually possessing rotation, are a particular type of targets of potential interest to the synthetic aperture radar (SAR) community. This paper is aimed to investigate PRA’s scattering characteristics and then to extract PRA’s parameters from SAR returns, for supporting image interpretation and target recognition. We at first obtain both closed-form and numeric solutions to PRA’s backscattering by geometrical optics (GO), physical optics, and graphical electromagnetic computation, respectively. Based on the GO solution, a migratory scattering center model is at first presented for representing the movement of the specular point with aspect angle, and then a hybrid model, named the migratory/micromotion scattering center (MMSC) model, is proposed for characterizing a rotating PRA in the SAR geometry, which incorporates PRA’s rotation into its migratory scattering center model. Additionally, we in detail analyze PRA’s radar characteristics on radar cross-section, high-resolution range profiles, time-frequency distribution, and 2D images, which also confirm the models proposed. A maximal likelihood estimator is developed for jointly solving the MMSC model for PRA’s multiple parameters by optimization. By exploiting the aforementioned characteristics, the coarse parameter estimation guarantees convergency upon global minima. The signatures recovered can be favorably utilized for SAR image interpretation and target recognition.

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