1,298 research outputs found
Null-stream veto for two co-located detectors: Implementation issues
Time-series data from multiple gravitational wave (GW) detectors can be
linearly combined to form a null-stream, in which all GW information will be
cancelled out. This null-stream can be used to distinguish between actual GW
triggers and spurious noise transients in a search for GW bursts using a
network of detectors. The biggest source of error in the null-stream analysis
comes from the fact that the detector data are not perfectly calibrated. In
this paper, we present an implementation of the null-stream veto in the
simplest network of two co-located detectors. The detectors are assumed to have
calibration uncertainties and correlated noise components. We estimate the
effect of calibration uncertainties in the null-stream veto analysis and
propose a new formulation to overcome this. This new formulation is
demonstrated by doing software injections in Gaussian noise.Comment: Minor changes; To appear in Class. Quantum Grav. (Proc. GWDAW10
LISA Sensitivity and SNR Calculations
This Technical Note (LISA reference LISA-LCST-SGS-TN-001) describes the computation of the noise power spectral density, the sensitivity curve and the signal-to-noise ratio for LISA (Laser Interferometer Antenna). It is an applicable document for ESA (European Space Agency) and the reference for the LISA Science Requirement Document
Optimal time-domain combination of the two calibrated output quadratures of GEO 600
GEO 600 is an interferometric gravitational wave detector with a 600 m arm-length and which uses a dual-recycled optical configuration to give enhanced sensitivity over certain frequencies in the detection band. Due to the dual-recycling, GEO 600 has two main output signals, both of which potentially contain gravitational wave signals. These two outputs are calibrated to strain using a time-domain method. In order to simplify the analysis of the GEO 600 data set, it is desirable to combine these two calibrated outputs to form a single strain signal that has optimal signal-to-noise ratio across the detection band. This paper describes a time-domain method for doing this combination. The method presented is similar to one developed for optimally combining the outputs of two colocated gravitational wave detectors. In the scheme presented in this paper, some simplifications are made to allow its implementation using time-domain methods
Robust vetoes for gravitational-wave burst triggers using known instrumental couplings
The search for signatures of transient, unmodelled gravitational-wave (GW)
bursts in the data of ground-based interferometric detectors typically uses
`excess-power' search methods. One of the most challenging problems in the
burst-data-analysis is to distinguish between actual GW bursts and spurious
noise transients that trigger the detection algorithms. In this paper, we
present a unique and robust strategy to `veto' the instrumental glitches. This
method makes use of the phenomenological understanding of the coupling of
different detector sub-systems to the main detector output. The main idea
behind this method is that the noise at the detector output (channel H) can be
projected into two orthogonal directions in the Fourier space -- along, and
orthogonal to, the direction in which the noise in an instrumental channel X
would couple into H. If a noise transient in the detector output originates
from channel X, it leaves the statistics of the noise-component of H orthogonal
to X unchanged, which can be verified by a statistical hypothesis testing. This
strategy is demonstrated by doing software injections in simulated Gaussian
noise. We also formulate a less-rigorous, but computationally inexpensive
alternative to the above method. Here, the parameters of the triggers in
channel X are compared to the parameters of the triggers in channel H to see
whether a trigger in channel H can be `explained' by a trigger in channel X and
the measured transfer function.Comment: 14 Pages, 8 Figures, To appear in Class. Quantum Gra
A closed-loop EKF and multi-failure diagnosis approach for cooperative GNSS positioning
Current cooperative positioning with Global Navigation Satellite System (GNSS) for connected vehicle application mainly uses pseudorange measurements. However the positioning accuracy offered cannot meet the requirements for lane-level positioning, collision avoidance and future automatic driving, which needs real-time positioning accuracy of better than 0.5m. Furthermore, there is an apparent lack of research into the integrity issue for these new applications under emerging driverless vehicle applications. In order to overcome those problems, a new Extended Kalman Filter (EKF) and a multi-failure diagnosis algorithm are developed to process both GNSS pseudorange and carrier phase measurements. We first introduce a new closed-loop EKF with partial ambiguity resolution (PAR) as feedback to address the low accuracy issue. Then a multi-failure diagnosis algorithm is proposed to improve integrity and reliability. The core of this new algorithm includes using Carrier phase based Receiver Autonomous Integrity Monitoring (CRAIM) method for failure detection, and the double extended w-test detectors to identify failure. A cooperative positioning experiment was carried out to validate the proposed method. The results show that the proposed closed-loop EKF can provide highly accurate positioning, and the multi-failure diagnosis method is effective in detecting and identifying failures for both code and carrier phase measurements
A statistical veto method employing an amplitude consistency check
Statistical veto methods are commonly used to reduce the list of candidate gravitational wave (GW) events which are detected as transient (burst) signals in the main output of GW detectors. If a burst event in the GW channel is coincident with an event in a veto channel (where the veto channel does not contain any GW signal), it is possible to veto the event from the GW channel with a low 'false-veto' rate. Unfortunately, many promising veto channels are interferometer channels which can, at some level, contain traces of any detected GW signal. In this case, the application of a 'standard statistical veto' could have a high false-veto rate. We will present an extension to the standard statistical veto method that includes an 'amplitude consistency check'. This method allows the application of statistical vetoes derived from interferometer channels containing GW information with a low false-veto rate. By applying a statistical veto with an amplitude consistency check to data from the GEO 600 detector, veto efficiencies between 5 and 20%, together with a use-percentage of up to 80%, were obtained. The robustness of this veto method was also confirmed by hardware injections. The burst triggers were generated using the mHACR detection algorithm
Calibrating spectral estimation for the LISA Technology Package with multichannel synthetic noise generation
The scientific objectives of the Lisa Technology Package (LTP) experiment, on
board of the LISA Pathfinder mission, demand for an accurate calibration and
validation of the data analysis tools in advance of the mission launch. The
levels of confidence required on the mission outcomes can be reached only with
an intense activity on synthetically generated data. A flexible procedure
allowing the generation of cross-correlated stationary noise time series was
set-up. Multi-channel time series with the desired cross correlation behavior
can be generated once a model for a multichannel cross-spectral matrix is
provided. The core of the procedure is the synthesis of a noise coloring
multichannel filter through a frequency-by-frequency eigendecomposition of the
model cross-spectral matrix and a Z-domain fit. The common problem of initial
transients in noise time series is solved with a proper initialization of the
filter recursive equations. The noise generator performances were tested in a
two dimensional case study of the LTP dynamics along the two principal channels
of the sensing interferometer.Comment: Accepted for publication in Physical Review D (http://prd.aps.org/
The âSystem of Systemsâ receiver: An Australian opportunity?
In the near future, there could be as many as four global navigation satellite systems (GNSS) and three regional navigation satellite systems (RNSS).
This paper examines the visibility of these systems, identifying Australia as a good location to view all of them. The impacts on receiver design are also examined at sub-system level, revealing that a 'system of systems' receiver would be far more sophisticated than a basic GPS L1 receiver
Stabilization of a Fabry-Perot interferometer using a suspension-point interferometer
A suspension-point interferometer (SPI) is an auxiliary interferometer for
active vibration isolation, implemented at the suspension points of the mirrors
of an interferometric gravitational wave detector. We constructed a prototype
Fabry-Perot interferometer equipped with an SPI and observed vibration
isolation in both the spectrum and transfer function. The noise spectrum of the
main interferometer was reduced by 40 dB below 1 Hz. Transfer function
measurements showed that the SPI also produced good vibration suppression above
1 Hz. These results indicate that SPI can improve both the sensitivity and the
stability of the interferometer.Comment: 14 pages, 8 figures; added discussion; to be published in Physics
Letters
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