29 research outputs found
Subtraction of Newtonian Noise Using Optimized Sensor Arrays
Fluctuations in the local Newtonian gravitational field present a limit to
high precision measurements, including searches for gravitational waves using
laser interferometers. In this work, we present a model of this perturbing
gravitational field and evaluate schemes to mitigate the effect by estimating
and subtracting it from the interferometer data stream. Information about the
Newtonian noise is obtained from simulated seismic data. The method is tested
on causal as well as acausal implementations of noise subtraction. In both
cases it is demonstrated that broadband mitigation factors close to 10 can be
achieved removing Newtonian noise as a dominant noise contribution. The
resulting improvement in the detector sensitivity will substantially enhance
the detection rate of gravitational radiation from cosmological sources.Comment: 29 pages, 11 figure
Active noise cancellation in a suspended interferometer
We demonstrate feed-forward vibration isolation on a suspended Fabry-Perot
interferometer using Wiener filtering and a variant of the common Least Mean
Square (LMS) adaptive filter algorithm. We compare the experimental results
with theoretical estimates of the cancellation efficiency. Using data from the
recent LIGO Science Run, we also estimate the impact of this technique on full
scale gravitational wave interferometers. In the future, we expect to use this
technique to also remove acoustic, magnetic, and gravitational noise
perturbations from the LIGO interferometers. This noise cancellation technique
is simple enough to implement in standard laboratory environments and can be
used to improve SNR for a variety of high precision experiments.Comment: PACS numbers: 04.80.Nn, 95.55.Ym, 07.60.Ly, 42.62.E
Multi-color Cavity Metrology
Long baseline laser interferometers used for gravitational wave detection
have proven to be very complicated to control. In order to have sufficient
sensitivity to astrophysical gravitational waves, a set of multiple coupled
optical cavities comprising the interferometer must be brought into resonance
with the laser field. A set of multi-input, multi-output servos then lock these
cavities into place via feedback control. This procedure, known as lock
acquisition, has proven to be a vexing problem and has reduced greatly the
reliability and duty factor of the past generation of laser interferometers. In
this article, we describe a technique for bringing the interferometer from an
uncontrolled state into resonance by using harmonically related external fields
to provide a deterministic hierarchical control. This technique reduces the
effect of the external seismic disturbances by four orders of magnitude and
promises to greatly enhance the stability and reliability of the current
generation of gravitational wave detector. The possibility for using
multi-color techniques to overcome current quantum and thermal noise limits is
also discussed
Global feed-forward vibration isolation in a km scale interferometer
Using a network of seismometers and sets of optimal filters, we implemented a feed-forward control technique to minimize the seismic contribution to multiple interferometric degrees of freedom of the Laser Interferometer Gravitational-wave Observatory interferometers. The filters are constructed by using the Levinson–Durbin recursion relation to approximate the optimal Wiener filter. By reducing the RMS of the interferometer feedback signals below ~10 Hz, we have improved the stability and duty cycle of the joint network of gravitational wave detectors. By suppressing the large control forces and mirror motions, we have dramatically reduced the rate of non-Gaussian transients in the gravitational wave signal stream
Improving the sensitivity of Advanced LIGO using noise subtraction
This paper presents an adaptable, parallelizable method for subtracting linearly coupled noise from Advanced LIGO data. We explain the features developed to ensure that the process is robust enough to handle the variability present in Advanced LIGO data. In this work, we target subtraction of noise due to beam jitter, detector calibration lines, and mains power lines. We demonstrate noise subtraction over the entirety of the second observing run, resulting in increases in sensitivity comparable to those reported in previous targeted efforts. Over the course of the second observing run, we see a 30% increase in Advanced LIGO sensitivity to gravitational waves from a broad range of compact binary systems. We expect the use of this method to result in a higher rate of detected gravitational-wave signals in Advanced LIGO data
Observation of a potential future sensitivity limitation from ground motion at LIGO Hanford
A first detection of terrestrial gravity noise in gravitational-wave detectors is a formidable challenge.With the help of environmental sensors, it can in principle be achieved before the noise becomes dominantby estimating correlations between environmental sensors and the detector. The main complication is todisentangle different coupling mechanisms between the environment and the detector. In this paper, weanalyze the relations between physical couplings and correlations that involve ground motion and LIGOstrain data h(t) recorded during its second science run in 2016 and 2017. We find that all noise correlatedwith ground motion was more than an order of magnitude lower than dominant low-frequency instrumentnoise, and the dominant coupling over part of the spectrum between ground and h(t) was residual couplingthrough the seismic-isolation system. We also present the most accurate gravitational coupling model so farbased on a detailed analysis of data from a seismic array. Despite our best efforts, we were not able tounambiguously identify gravitational coupling in the data, but our improved models confirm previouspredictions that gravitational coupling might already dominate linear ground-to-h(t) coupling over parts ofthe low-frequency, gravitational-wave observation band.M. P. R. and K. V. were supported by funding
from the NSF under Grants No. PHY-1607385,
No. PHY1607391, No. PHY-1912380, and No. PHY1912514. M. W. C., J. D., and S. E. D. are members of
the LIGO Laboratory, supported by funding from the U.S.
National Science Foundation. LIGO was constructed by the
California Institute of Technology and Massachusetts
Institute of Technology with funding from the National
Science Foundation and operates under cooperative agreement PHY0757058. M. W. C. was supported by NSF
Grant No. PHY-1505373 and by the David and Ellen
Lee Postdoctoral Fellowship at the California Institute of
Technology. B. J. J. S. was supported by the ARC Future
Fellowship FT130100329. The authors also gratefully
acknowledge the support of the Australian Research
Council under the ARC Centre of Excellence for
Gravitational Wave Discovery, Grant No. CE170100004
and Linkage Infrastructure, Equipment and Facilities Grant
No. LE13010003
Movement, Behavior, and Habitat Use of a Marine Apex Predator, the Scalloped Hammerhead
Conservation and management efforts of marine apex predators are more reliable when information on movement and habitat use patterns are known. The scalloped hammerhead (Sphyrna lewini) was the first shark species to be protected under the U.S. Endangered Species Act and has life history characteristics that make this species particularly at risk for local depletion. Consequently, the goal of this study was to better understand the movement dynamics of this species in the Gulf of Mexico (GOM) where discards through the longline fishery can be substantial. A total of 33 scalloped hammerheads were tagged with fin mounted satellite tags and tracked for an average of 146 days (ranging from 5 to 479 days) to examine horizontal movements and quantify space use. Scalloped hammerheads showed a wide range of movements throughout the GOM continental shelf with limited long-distance dispersal and females displayed a shelf-edge association relative to more mid-shelf use by males. A generalized additive model was developed to identify habitat suitability for scalloped hammerheads in the GOM, while state-space modeling was used to examine movement behaviors. Model results highlighted the use of continental shelf waters with high occurrence at close proximities to both artificial and hard-bottom habitat combined with low chlorophyll a concentrations (∼0–4 mg m-3) and moderate salinities (33–35.5). Habitat suitability for scalloped hammerheads was predicted to be high on the mid to outer continental shelf inside the 200 m isobath and state-space model results suggest area-restricted behavior was most common relative to transient behavior. Findings from this study provide important information on movement of this species in the GOM and highlight their restricted use of continental shelf habitat and resident behavior that will need to be incorporated in future stock assessments and extinction risk analyses
The James Webb Space Telescope Mission
Twenty-six years ago a small committee report, building on earlier studies,
expounded a compelling and poetic vision for the future of astronomy, calling
for an infrared-optimized space telescope with an aperture of at least .
With the support of their governments in the US, Europe, and Canada, 20,000
people realized that vision as the James Webb Space Telescope. A
generation of astronomers will celebrate their accomplishments for the life of
the mission, potentially as long as 20 years, and beyond. This report and the
scientific discoveries that follow are extended thank-you notes to the 20,000
team members. The telescope is working perfectly, with much better image
quality than expected. In this and accompanying papers, we give a brief
history, describe the observatory, outline its objectives and current observing
program, and discuss the inventions and people who made it possible. We cite
detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space
Telescope Overview, 29 pages, 4 figure