1,244 research outputs found
Concurrent-scene/alternate-pattern analysis for robust video-based docking systems
A typical docking target employs a three-point design of retroreflective tape, one at each endpoint of the center-line, and one on the tip of the central post. Scenes, sensed via laser diode illumination, produce pictures with spots corresponding to desired reflection from the retroreflectors and other reflections. Control corrections for each axis of the vehicle can then be properly applied if the desired spots are accurately tracked. However, initial acquisition of these three spots (detection and identification problem) are non-trivial under a severe noise environment. Signal-to-noise enhancement, accomplished by subtracting the non-illuminated scene from the target scene illuminated by laser diodes, can not eliminate every false spot. Hence, minimization of docking failures due to target mistracking would suggest needed inclusion of added processing features pertaining to target locations. In this paper, we present a concurrent processing scheme for a modified docking target scene which could lead to a perfect docking system. Since the non-illuminated target scene is already available, adding another feature to the three-point design by marking two non-reflective lines, one between the two end-points and one from the tip of the central post to the center-line, would allow this line feature to be picked-up only when capturing the background scene (sensor data without laser illumination). Therefore, instead of performing the image subtraction to generate a picture with a high signal-to-noise ratio, a processed line-image based on the robust line detection technique (Hough transform) can be used to fuse with the actively sensed three-point target image to deduce the true locations of the docking target. This dual-channel confirmation scheme is necessary if a fail-safe system is to be realized from both the sensing and processing point-of-views. Detailed algorithms and preliminary results are presented
The properties of extragalactic radio sources selected at 20 GHz
We present some first results on the variability, polarization and general
properties of radio sources selected in a blind survey at 20 GHz, the highest
frequency at which a sensitive radio survey has been carried out over a large
area of sky. Sources with flux densities above 100 mJy in the AT20G Pilot
Survey at declination -60 to -70 were observed at up to three epochs during
2002-4, including near-simultaneous measurements at 5, 8 and 18 GHz in 2003. Of
the 173 sources detected, 65% are candidate QSOs, BL Lac objects or blazars,
20% galaxies and 15% faint (b > 22 mag) optical objects or blank fields.
On a 1-2 year timescale, the general level of variability at 20 GHz appears
to be low. For the 108 sources with good-quality measurements in both 2003 and
2004, the median variability index at 20 GHz was 6.9% and only five sources
varied by more than 30% in flux density.
Most sources in our sample show low levels of linear polarization (typically
1-5%), with a median fractional polarization of 2.3% at 20 GHz. There is a
trend for fainter sources to show higher fractional polarization.
At least 40% of sources selected at 20GHz have strong spectral curvature over
the frequency range 1-20 GHz. We use a radio `two-colour diagram' to
characterize the radio spectra of our sample, and confirm that the radio-source
population at 20 GHz (which is also the foreground point-source population for
CMB anisotropy experiments like WMAP and Planck) cannot be reliably predicted
by extrapolating the results of surveys at lower frequencies. As a result,
direct selection at 20 GHz appears to be a more efficient way of identifying 90
GHz phase calibrators for ALMA than the currently-proposed technique of
extrapolation from all-sky surveys at 1-5 GHz.Comment: 14-page paper plus 5-page data table. Replaced with published versio
Onboard utilization of ground control points for image correction. Volume 1: Executive summary
Operation of a navigation system, centered around image correction, was simulated and the system performance was analyzed. Onboard utilization of ground control points for image correction is summarized. Simulation results, and recommendations for future mission requirements are presented
Adaptive guidance and control for future remote sensing systems
A unique approach to onboard processing was developed that is capable of acquiring high quality image data for users in near real time. The approach is divided into two steps: the development of an onboard cloud detection system; and the development of a landmark tracker. The results of these two developments are outlined and the requirements of an operational guidance and control system capable of providing continuous estimation of the sensor boresight position are summarized
FIRI - a Far-Infrared Interferometer
Half of the energy ever emitted by stars and accreting objects comes to us in
the FIR waveband and has yet to be properly explored. We propose a powerful
Far-InfraRed Interferometer mission, FIRI, to carry out high-resolution imaging
spectroscopy in the FIR. This key observational capability is essential to
reveal how gas and dust evolve into stars and planets, how the first luminous
objects in the Universe ignited, how galaxies formed, and when super-massive
black holes grew. FIRI will disentangle the cosmic histories of star formation
and accretion onto black holes and will trace the assembly and evolution of
quiescent galaxies like our Milky Way. Perhaps most importantly, FIRI will
observe all stages of planetary system formation and recognise Earth-like
planets that may harbour life, via its ability to image the dust structures in
planetary systems. It will thus address directly questions fundamental to our
understanding of how the Universe has developed and evolved - the very
questions posed by ESA's Cosmic Vision.Comment: Proposal developed by a large team of astronomers from Europe, USA
and Canada and submitted to the European Space Agency as part of "Cosmic
Vision 2015-2025
Attitude determination of the spin-stabilized Project Scanner spacecraft
Attitude determination of spin-stabilized spacecraft using star mapping techniqu
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