4,873 research outputs found
A Real-time Faint Space Debris Detector With Learning-based LCM
With the development of aerospace technology, the increasing population of
space debris has posed a great threat to the safety of spacecraft. However, the
low intensity of reflected light and high angular velocity of space debris
impede the extraction. Besides, due to the limitations of the ground
observation methods, small space debris can hardly be detected, making it
necessary to enhance the spacecraft's capacity for space situational awareness
(SSA). Considering that traditional methods have some defects in low-SNR target
detection, such as low effectiveness and large time consumption, this paper
proposes a method for low-SNR streak extraction based on local contrast and
maximum likelihood estimation (MLE), which can detect space objects with SNR
2.0 efficiently. In the proposed algorithm, local contrast will be applied for
crude classifications, which will return connected components as preliminary
results, and then MLE will be performed to reconstruct the connected components
of targets via orientated growth, further improving the precision. The
algorithm has been verified with both simulated streaks and real star tracker
images, and the average centroid error of the proposed algorithm is close to
the state-of-the-art method like ODCC. At the same time, the algorithm in this
paper has significant advantages in efficiency compared with ODCC. In
conclusion, the algorithm in this paper is of high speed and precision, which
guarantees its promising applications in the extraction of high dynamic
targets.Comment: 13 pages, 28 figures, normal articl
Kinect Range Sensing: Structured-Light versus Time-of-Flight Kinect
Recently, the new Kinect One has been issued by Microsoft, providing the next
generation of real-time range sensing devices based on the Time-of-Flight (ToF)
principle. As the first Kinect version was using a structured light approach,
one would expect various differences in the characteristics of the range data
delivered by both devices. This paper presents a detailed and in-depth
comparison between both devices. In order to conduct the comparison, we propose
a framework of seven different experimental setups, which is a generic basis
for evaluating range cameras such as Kinect. The experiments have been designed
with the goal to capture individual effects of the Kinect devices as isolatedly
as possible and in a way, that they can also be adopted, in order to apply them
to any other range sensing device. The overall goal of this paper is to provide
a solid insight into the pros and cons of either device. Thus, scientists that
are interested in using Kinect range sensing cameras in their specific
application scenario can directly assess the expected, specific benefits and
potential problem of either device.Comment: 58 pages, 23 figures. Accepted for publication in Computer Vision and
Image Understanding (CVIU
Modern optical astronomy: technology and impact of interferometry
The present `state of the art' and the path to future progress in high
spatial resolution imaging interferometry is reviewed. The review begins with a
treatment of the fundamentals of stellar optical interferometry, the origin,
properties, optical effects of turbulence in the Earth's atmosphere, the
passive methods that are applied on a single telescope to overcome atmospheric
image degradation such as speckle interferometry, and various other techniques.
These topics include differential speckle interferometry, speckle spectroscopy
and polarimetry, phase diversity, wavefront shearing interferometry,
phase-closure methods, dark speckle imaging, as well as the limitations imposed
by the detectors on the performance of speckle imaging. A brief account is
given of the technological innovation of adaptive-optics (AO) to compensate
such atmospheric effects on the image in real time. A major advancement
involves the transition from single-aperture to the dilute-aperture
interferometry using multiple telescopes. Therefore, the review deals with
recent developments involving ground-based, and space-based optical arrays.
Emphasis is placed on the problems specific to delay-lines, beam recombination,
polarization, dispersion, fringe-tracking, bootstrapping, coherencing and
cophasing, and recovery of the visibility functions. The role of AO in
enhancing visibilities is also discussed. The applications of interferometry,
such as imaging, astrometry, and nulling are described. The mathematical
intricacies of the various `post-detection' image-processing techniques are
examined critically. The review concludes with a discussion of the
astrophysical importance and the perspectives of interferometry.Comment: 65 pages LaTeX file including 23 figures. Reviews of Modern Physics,
2002, to appear in April issu
OAST space research and technology applications: Technology transfer successes
The ultimate measure of success in the Space Research and Technology Program is the incorporation of a technology into an operational mission. Charts are presented that describe technology products which OAST has helped support that (1) have been used in a space mission, (2) have been incorporated into the baseline design of a flight system in the development phase, or (3) have been picked up by a commercial or other non-NASA user. We hope that these examples will demonstrate the value of investment in technology. Pictured on the charts are illustrations of the technology product, the mission or user which has incorporated the technology, and where appropriate, results from the mission itself
Absolute reflectance of a concave mirror used for astro-particle physics experiments
The absolute reflectance of a reflector and its point spread function are the
key parameters of a telescope for measuring light flux. Typically, one is using
low-cost technologies for producing mirrors for the needs of astro-particle
physics experiments. As a rule, these are operating telescopes in open air
conditions at desert or mountainous locations, for cost reasons without
protecting domes. The mirrors on such telescopes are exposed to sand in strong
winds, precipitation and large temperature variations. Due to weathering, their
reflectance is declining within few years. In this report we describe in a
great detail the application of an in-situ method to the MAGIC imaging air
Cherenkov telescopes for regularly monitoring their absolute reflectance and
the point spread function. Compared to similar work that was previously
performed, in this report we focus on important details of light losses due to
scattering. These allowed us to further refine the method and significantly
improve its precision. Also, we report on an in-situ comparison of two mirror
types produced with different technologies.Comment: 24 pages, 13 figures, accepted for publication in Astroparticle
Physics journa
Image Deblurring and Near-real-time Atmospheric Seeing Estimation through the Employment of Convergence of Variance
A new image reconstruction algorithm is presented that will remove the effect of atmospheric turbulence on motion compensated frame average images. The primary focus of this research was to develop a blind deconvolution technique that could be employed in a tactical military environment where both time and computational power are limited. Additionally, this technique can be employed to measure atmospheric seeing conditions. In a blind deconvolution fashion, the algorithm simultaneously computes a high resolution image and an average model for the atmospheric blur parameterized by Fried’s seeing parameter. The difference in this approach is that it does not assume a prior distribution for the seeing parameter, rather it assesses the convergence of the image’s variance as the stopping criteria and identification of the proper seeing parameter from a range of candidate values. Experimental results show that the convergence of variance technique allows for estimation of the seeing parameter accurate to within 0.5 cm and often even better depending on the signal to noise ratio
Multi-conjugated adaptive optics imaging of distant galaxies -- A comparison of Gemini/GSAOI and VLT/HAWK-I data
Multi-conjugated adaptive optics (MCAO) yield nearly diffraction-limited
images at 2m wavelengths. Currently, GeMS/GSAOI at Gemini South is the
only MCAO facility instrument at an 8m telescope. Using real data and for the
first time, we investigate the gain in depth and S/N when MCAO is employed for
-band observations of distant galaxies. Our analysis is based on the
Frontier Fields cluster MACS J0416.1-2403, observed with GeMS/GSAOI (near
diffraction-limited) and compared against VLT/HAWK-I (natural seeing) data.
Using galaxy number counts, we show that the substantially increased thermal
background and lower optical throughput of the MCAO unit are fully compensated
for by the wavefront correction, because the galaxy images can be measured in
smaller apertures with less sky noise. We also performed a direct comparison of
the signal-to-noise ratios (S/N) of sources detected in both data sets. For
objects with intrinsic angular sizes corresponding to half the HAWK-I image
seeing, the gain in S/N is 40 per cent. Even smaller objects experience a boost
in S/N by a up to a factor of 2.5 despite our suboptimal natural guide star
configuration. The depth of the near diffraction limited images is more
difficult to quantify than that of seeing limited images, due to a strong
dependence on the intrinsic source profiles. Our results emphasize the
importance of cooled MCAO systems for -band observations with
future, extremely large telescopes.Comment: 7 pages, 7 figures. Accepted for publication in MNRA
Optical blur disturbs – the influence of optical-blurred images in photogrammtry
Photogrammetric processes such as camera calibration, feature and target detection and referencing are assumed to strongly depend on the quality of the images that are provided for the process. Consequently, motion and optically blurred images are usually excluded from photogrammetric processes to supress their negative influence. To evaluate how much optical blur is acceptable and how large the influence of optical blur is on photogrammetric procedures a variety of test environments were established. These were based upon previous motion blur research and included test fields for the analysis of camera calibration. For the evaluation, a DSLR camera as well as Lytro Illum light field camera were used. The results show that optical blur has a negative influence on photogrammetric procedures, mostly automatic target detection. With the intervention of an experienced operator and the use of semi-automatic tools, acceptable results can be established
The Inertial Stellar Compass: A New Direction in Spacecraft Attitude Determination
The Inertial Stellar Compass (ISC) is a real-time, miniature, low power stellar inertial attitude determination system, composed of a wide field-of-view active pixel star camera and a microelectromechanical system (MEMS) gyro assembly, with associated processing and power electronics. The integrated technologies enable an attitude determination system with an accuracy of 0.1 degree (1 sigma) to be realized at very low power and volume. The attitude knowledge provided by the ISC is applicable to a wide range of space and earth science missions that may include the use of highly maneuverable, stabilized, tumbling, or lost spacecraft. Under the guidance of NASA’s New Millennium ST-6 project, Draper Laboratory is currently developing the Inertial Stellar Compass. Its completion and flight validation will represent a breakthrough in real-time miniature attitude determination sensors. This paper describes system design, development, and validation activities currently underway at Draper
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