99,029 research outputs found
Gravitational waves from BH-NS binaries: Effective Fisher matrices and parameter estimation using higher harmonics
Inspiralling black hole-neutron star (BH-NS) binaries emit a complicated
gravitational wave signature, produced by multiple harmonics sourced by their
strong local gravitational field and further modulated by the orbital plane's
precession. Some features of this complex signal are easily accessible to
ground-based interferometers (e.g., the rate of change of frequency); others
less so (e.g., the polarization content); and others unavailable (e.g.,
features of the signal out of band). For this reason, an ambiguity function (a
diagnostic of dissimilarity) between two such signals varies on many parameter
scales and ranges. In this paper, we present a method for computing an
approximate, effective Fisher matrix from variations in the ambiguity function
on physically pertinent scales which depend on the relevant signal to noise
ratio. As a concrete example, we explore how higher harmonics improve parameter
measurement accuracy. As previous studies suggest, for our fiducial BH-NS
binaries and for plausible signal amplitudes, we see that higher harmonics at
best marginally improve our ability to measure parameters. For non-precessing
binaries, these Fisher matrices separate into intrinsic (mass, spin) and
extrinsic (geometrical) parameters; higher harmonics principally improve our
knowledge about the line of sight. For the precessing binaries, the extra
information provided by higher harmonics is distributed across several
parameters. We provide concrete estimates for measurement accuracy, using
coordinates adapted to the precession cone in the detector's sensitive band.Comment: 19 pages, 11 figure
Ambiguity function and accuracy of the hyperbolic chirp: comparison with the linear chirp
In this paper, we derive the Ambiguity Function (AF) of a narrowband and a wideband hyperbolic chirp. We calculate the second derivatives of the squared amplitude of the narrowband Complex Ambiguity Function (CAF) and use them to calculate the Fisher Information Matrix (FIM) of the estimators of the target range and velocity. The FIM is then used to calculate the Cramer-Rao Lower Bounds (CRLB) of the variance of the estimators and to ´ carry out an analysis of estimation performance and a comparison with the case of a liner chirp with a rectangular and a Gaussian amplitude modulation. The analysis and the calculations of the CRLB are also extended to a train of hyperbolic chirps. Results corroborate that at narrowband the hyperbolic chirp is less Doppler tolerant than the linear chirp and show that the hyperbolic chirp provides a comparable measurement accuracy to the linear chirp. Results at wideband corroborate the superior Doppler tolerance of the hyperbolic chirp with respect to that of the linear chirp
The magnetic field configuration of a solar prominence inferred from spectropolarimetric observations in the He I 10830 A triplet
Context: The determination of the magnetic field vector in quiescent solar
prominences is possible by interpreting the Hanle and Zeeman effects in
spectral lines. However, observational measurements are scarce and lack high
spatial resolution. Aims: To determine the magnetic field vector configuration
along a quiescent solar prominence by interpreting spectropolarimetric
measurements in the He I 1083.0 nm triplet obtained with the Tenerife Infrared
Polarimeter installed at the German Vacuum Tower Telescope of the Observatorio
del Teide. Methods. The He I 1083.0 nm triplet Stokes profiles are analyzed
with an inversion code that takes into account the physics responsible of the
polarization signals in this triplet. The results are put into a solar context
with the help of extreme ultraviolet observations taken with the Solar Dynamic
Observatory and the Solar Terrestrial Relations Observatory satellites.
Results: For the most probable magnetic field vector configuration, the
analysis depicts a mean field strength of 7 gauss. We do not find local
variations in the field strength except that the field is, in average, lower in
the prominence body than in the prominence feet, where the field strength
reaches 25 gauss. The averaged magnetic field inclination with respect to the
local vertical is 77 degrees. The acute angle of the magnetic field vector with
the prominence main axis is 24 degrees for the sinistral chirality case and 58
degrees for the dextral chirality. These inferences are in rough agreement with
previous results obtained from the analysis of data acquired with lower spatial
resolutions.Comment: Accepted in A&
Gravitational waves from eccentric compact binaries: Reduction in signal-to-noise ratio due to nonoptimal signal processing
Inspiraling compact binaries have been identified as one of the most
promising sources of gravitational waves for interferometric detectors. Most of
these binaries are expected to have circularized by the time their
gravitational waves enter the instrument's frequency band. However, the
possibility that some of the binaries might still possess a significant
eccentricity is not excluded. We imagine a situation in which eccentric signals
are received by the detector but not explicitly searched for in the data
analysis, which uses exclusively circular waveforms as matched filters. We
ascertain the likelihood that these filters, though not optimal, will
nevertheless be successful at capturing the eccentric signals. We do this by
computing the loss in signal-to-noise ratio incurred when searching for
eccentric signals with those nonoptimal filters. We show that for a binary
system of a given total mass, this loss increases with increasing eccentricity.
We show also that for a given eccentricity, the loss decreases as the total
mass is increased.Comment: 14 pages, 4 figures, ReVTeX; minor changes made after referee's
comment
Detecting Targets above the Earth's Surface Using GNSS-R Delay Doppler Maps: Results from TDS-1
: Global Navigation Satellite System (GNSS) reflected signals can be used to remotely sense
the Earth’s surface, known as GNSS reflectometry (GNSS-R). The GNSS-R technique has been applied
to numerous areas, such as the retrieval of wind speed, and the detection of Earth surface objects.
This work proposes a new application of GNSS-R, namely to detect objects above the Earth’s surface,
such as low Earth orbit (LEO) satellites. To discuss its feasibility, 14 delay Doppler maps (DDMs) are
first presented which contain unusually bright reflected signals as delays shorter than the specular
reflection point over the Earth’s surface. Then, seven possible causes of these anomalies are analysed,
reaching the conclusion that the anomalies are likely due to the signals being reflected from objects
above the Earth’s surface. Next, the positions of the objects are calculated using the delay and
Doppler information, and an appropriate geometry assumption. After that, suspect satellite objects
are searched in the satellite database from Union of Concerned Scientists (UCS). Finally, three objects
have been found to match the delay and Doppler conditions. In the absence of other reasons for these
anomalies, GNSS-R could potentially be used to detect some objects above the Earth’s surface.Peer ReviewedPostprint (published version
Improving the spatial resolution by effective subtraction technique at Irkutsk incoherent scatter radar: the theory and experiment
We describe a sounding technique that allows us to improve spatial resolution
of Irkutsk Incoherent Scatter Radar without loosing spectral resolution. The
technique is based on transmitting of rectangle pulses of different duration in
various sounding runs and subtracting correlation matrixes. Theoretically and
experimentally we have shown, that subtraction of the mean-square parameters of
the scattered signal for different kinds of the sounding signal one from
another allows us to solve the problem within the framework of quasi-static
ionospheric parameters approximation.Comment: 4 pages, 3 figures, to appear at URSI-2011 conferenc
Compressive Matched-Field Processing
Source localization by matched-field processing (MFP) generally involves
solving a number of computationally intensive partial differential equations.
This paper introduces a technique that mitigates this computational workload by
"compressing" these computations. Drawing on key concepts from the recently
developed field of compressed sensing, it shows how a low-dimensional proxy for
the Green's function can be constructed by backpropagating a small set of
random receiver vectors. Then, the source can be located by performing a number
of "short" correlations between this proxy and the projection of the recorded
acoustic data in the compressed space. Numerical experiments in a Pekeris ocean
waveguide are presented which demonstrate that this compressed version of MFP
is as effective as traditional MFP even when the compression is significant.
The results are particularly promising in the broadband regime where using as
few as two random backpropagations per frequency performs almost as well as the
traditional broadband MFP, but with the added benefit of generic applicability.
That is, the computationally intensive backpropagations may be computed offline
independently from the received signals, and may be reused to locate any source
within the search grid area
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