15,740 research outputs found
Twinsat earth gravity field mapping
Results of a sensitivity study on the proposed Lo-Lo (Twinsat) satellite-to-satellite tracking mission are described. The relative range-rate signal due to a local gravitational anomaly is investigated as a function of height and satellite separation. It is shown that the signal strength is weak and that an optimal combination of signal strength and resolution is achieved when the satellites are separated by 3 deg along-track. The signal does not resolve point masses closer than 5 deg apart when the satellites are at 300 km altitude. The influence of other factors on the system is evaluated, including the low frequency gravitation field effect on the orbit and the dependence of the noise of the data type on (electronic) integration time
Earth's gravity field mapping requirements and concept
A future sensor is considered for mapping the Earth's gravity field to meet future scientific and practical requirements for earth and oceanic dynamics. These are approximately + or - 0.1 to 10 mgal over a block size of about 50 km and over land and an ocean geoid to 1 to 2 cm over a distance of about 50 km. To achieve these values requires a gravity gradiometer with a sensitivity of approximately 10 to the -4 power EU in a circular polar orbiting spacecraft with an orbital altitude ranging 160 km to 180 km
Informative Path Planning for Active Field Mapping under Localization Uncertainty
Information gathering algorithms play a key role in unlocking the potential
of robots for efficient data collection in a wide range of applications.
However, most existing strategies neglect the fundamental problem of the robot
pose uncertainty, which is an implicit requirement for creating robust,
high-quality maps. To address this issue, we introduce an informative planning
framework for active mapping that explicitly accounts for the pose uncertainty
in both the mapping and planning tasks. Our strategy exploits a Gaussian
Process (GP) model to capture a target environmental field given the
uncertainty on its inputs. For planning, we formulate a new utility function
that couples the localization and field mapping objectives in GP-based mapping
scenarios in a principled way, without relying on any manually tuned
parameters. Extensive simulations show that our approach outperforms existing
strategies, with reductions in mean pose uncertainty and map error. We also
present a proof of concept in an indoor temperature mapping scenario.Comment: 8 pages, 7 figures, submission (revised) to Robotics & Automation
Letters (and IEEE International Conference on Robotics and Automation
Resolved Magnetic Field Mapping of a Molecular Cloud Using GPIPS
We present the first resolved map of plane-of-sky magnetic field strength for
a quiescent molecular cloud. GRSMC 45.60+0.30 subtends 40 x 10 pc at a distance
of 1.88 kpc, masses 16,000 M_sun, and exhibits no star formation. Near-infrared
background starlight polarizations were obtained for the Galactic Plane
Infrared Polarization Survey using the 1.8 m Perkins telescope and the Mimir
instrument. The cloud area of 0.78 deg2 contains 2684 significant starlight
polarizations for Two Micron All Sky Survey matched stars brighter than 12.5
mag in the H band. Polarizations are generally aligned with the cloud's major
axis, showing an average position angle dispersion of 15 \pm 2{\deg} and
polarization of 1.8 \pm 0.6%. The polarizations were combined with Galactic
Ring Survey 13CO spectroscopy and the Chandrasekhar-Fermi method to estimate
plane-of-sky magnetic field strengths, with an angular resolution of 100
arcsec. The average plane-of-sky magnetic field strength across the cloud is
5.40 \pm 0.04 {\mu}G. The magnetic field strength map exhibits seven
enhancements or "magnetic cores." These cores show an average magnetic field
strength of 8.3 \pm 0.9 {\mu}G, radius of 1.2 \pm 0.2 pc, intercore spacing of
5.7 \pm 0.9 pc, and exclusively subcritical mass-to-flux ratios, implying their
magnetic fields continue to suppress star formation. The magnetic field
strength shows a power-law dependence on gas volume density, with slope 0.75
\pm 0.02 for n_{H_2} >=10 cm-3. This power-law index is identical to those in
studies at higher densities, but disagrees with predictions for the densities
probed here.Comment: 11 pages, 15 figures, published in ApJ (2012, 755, 130
Development and testing of an image tube camera and spectrograph Quarterly progress report, period ending 31 Mar. 1969
Electron beam field mapping with aid of image tube cameras and spectrometer
Nanoscale magnetic field mapping with a single spin scanning probe magnetometer
We demonstrate quantitative magnetic field mapping with nanoscale resolution,
by applying a lock-in technique on the electron spin resonance frequency of a
single nitrogen-vacancy defect placed at the apex of an atomic force microscope
tip. In addition, we report an all-optical magnetic imaging technique which is
sensitive to large off-axis magnetic fields, thus extending the operation range
of diamond-based magnetometry. Both techniques are illustrated by using a
magnetic hard disk as a test sample. Owing to the non-perturbing and
quantitative nature of the magnetic probe, this work should open up numerous
perspectives in nanomagnetism and spintronics
Far-field mapping of the longitudinal magnetic and electric optical fields
In this letter, we demonstrate the experimental mapping of the longitudinal
magnetic and electric optical fields with a standard scanning microscope that
involves a high numerical aperture far-field objective. The imaging concept
relies upon the insertion of an azimuthal or a radial polarizer within the
detection path of the microscope which acts as an optical electromagnetic
filter aimed at transmitting selectively to the detector the signal from the
magnetic or electric longitudinal fields present in the detection volume,
respectively. The resulting system is thus versatile, non invasive, of high
resolution, and shows high detection efficiencies. Magnetic optical properties
of physical and biological micro and nano-structures may thus be revealed with
a far-field microscope
Investigation of an Optimum Detection Scheme for a Star-Field Mapping System
An investigation was made to determine the optimum detection scheme for a star-field mapping system that uses coded detection resulting from starlight shining through specially arranged multiple slits of a reticle. The computer solution of equations derived from a theoretical model showed that the greatest probability of detection for a given star and background intensity occurred with the use of a single transparent slit. However, use of multiple slits improved the system's ability to reject the detection of undesirable lower intensity stars, but only by decreasing the probability of detection for lower intensity stars to be mapped. Also, it was found that the coding arrangement affected the root-mean-square star-position error and that detection is possible with error in the system's detected spin rate, though at a reduced probability
A room temperature 19-channel magnetic field mapping device for cardiac signals
We present a multichannel cardiac magnetic field imaging system built in
Fribourg from optical double-resonance Cs vapor magnetometers. It consists of
25 individual sensors designed to record magnetic field maps of the beating
human heart by simultaneous measurements on a grid of 19 points over the chest.
The system is operated as an array of second order gradiometers using
sophisticated digitally controlled feedback loops.Comment: 3 pages, 3 figures, submitted to Applied Physics Letter
Satellite-to-satellite tracking experiment for global gravity field mapping
The satellite-to-satellite (STS) tracking concept for estimating gravitational parameters offers an attractive means to improve on regional and global gravity models in areas where data availability is limited. The extent to which the STS tracking measurements can be effectively utilized in global field models depends primarily on the satellite's altitude, number of satellites, and their orbit constellation. The estimation accuracy of the gravity field recovery also depends on the measurement accuracy of the sensors employed in the STS tracking concept. A comparison of the obtainable accuracies in the gravity field recovery using various STS tracking concepts was presented by Jekeli. The results of a feasibility study for a specific realization of the STS high-low tracking concept are summarized. In this realization, the high altitude satellites are the GPS satellites, and the low orbit satellite is the space shuttle. The GPS satellite constellation consists of 18 satellites in 6 orbital planes inclined at 55 deg. The shuttle orbit is at approximately 300 km, with an inclination of 30 deg. This specific configuration of high-low satellites for measuring perturbation in the gravity field is named the Air Foce STAGE (Shuttle GPS Tracking for Anomalous Gravitation Estimation) mission. The STAGE mission objective is to estimate the perturbations in gravity vector at the shuttle altitude to an accuracy of 1 mgal or better. Recent simulation studies have confirmed that the 1 mgal accuracy objective is near optimum for the STAGE mission
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