| 1. |
- Ghaemi, Hirad, 1980, et al.
(författare)
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CLEAN technique in strip-map SAR for high-quality imaging
- 2009
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Ingår i: IEEE Aerospace Conference Proceedings. - 1095-323X. - 9781424426225 ; , s. Art. no. 4839474-
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Konferensbidrag (refereegranskat)abstract
- The maximum obtainable resolution of a strip-map synthetic aperture radar (SAR) system can be retained by simply avoiding weighting, or tapering, data samples in the along-track compression process. However, this will lead to hazardous artifacts caused by strong sidelobes of the corresponding adjacent scatterers whose interference might severely weaken the desired targets or even introduce false targets. On the other hand, some residual artifacts, even after tapering process, may still deteriorate the quality (contrast) of the SAR image. These issues can be remedied by applying the so-called CLEAN technique, which can mitigate these ill-effects in strip-map SAR imagery while maintaining the maximum resolution. This, indeed, is carried out as a post processing step, i.e., after the azimuth compression is accomplished, in the SAR system. The objective of this paper is to extend the CLEAN technique to strip-map SAR system to produce high-quality images with a very good along-track resolution. The algorithm is then applied to data from a ground-based circular SAR (CSAR) system to verify its implementation as well as this new application of the CLEAN technique.
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| 2. |
- Ota, S., et al.
(författare)
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Neutron Production in the Lunar Subsurface from Galactic Cosmic Rays
- 2009
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Ingår i: IEEE Aerospace Conference Proceedings. - 1095-323X. - 9781424438877
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Konferensbidrag (refereegranskat)abstract
- The neutron production from galactic cosmic ray (GCR) protons and alpha particles in the lunar subsurface was estimated using the three-dimensional Monte Carlo simulation code PHITS. The PHITS simulations of equilibrium neutron density profiles in the lunar subsurface were compared with experimental data by the Apollo 17 Lunar Neutron Probe Experiment. By use of the latest GCR spectra based on BESS measurements and well-benchmarked nuclear interaction models, our calculations well reproduced the data within the experimental error of 15% (measurement) + 30% (systematic) at the region shallower than 300 g/cm2. However, our calculation showed 10-20% higher values in the deeper region.
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| 3. |
- Sihver, Lembit, 1962, et al.
(författare)
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Simulations of th MTR-R and MTR Experiments at ISS, and Shielding Properties using PHITS
- 2009
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Ingår i: IEEE Aerospace Conference Proceedings. - 1095-323X. - 9781424426218
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Konferensbidrag (refereegranskat)abstract
- Concerns about the biological effects of space radiation are increasing rapidly due to the perspective of long-duration manned missions, both in relation to the International Space Station (ISS) and to manned interplanetary missions to the Moon and Mars in the future. As a preparation for these long duration space missions it is important to ensure an excellent capability to evaluate the impact of space radiation on human health in order to secure the safety of the astronauts/cosmonauts and minimize their risks. It is therefore necessary to measure the radiation load on the personnel both inside and outside the space vehicles and certify that organ and tissue equivalent doses can be simulated as accurate as possible. In this paper we will present preliminary results from simulations, using the three-dimensional Monte Carlo Particle and Heavy Ions Transport code System (PHITS), of long term dose distribution measurements performed with the joint ESA-FSA experiment MATROSHKA-R (MTR-R) led by the Russian Federation Institute of Biomedical Problems (IMBP). MTR-R is a spherical phantom located inside the crew cabin of ISS. We also show some results from PHITS simulations of the ESA supported experiment MATROSHKA (MTR), which consists of an anthropomorphic phantom containing over 6000 radiation detectors, mimicking a human head and torso. The MTR experiment, led by the German Aerospace Center (DLR), was launched in January 2004 and has measured the absorbed dose from space radiation both inside and outside the ISS. In this paper preliminary comparisons of measurements outside the ISS will be presented. For the purpose of examining the applicability of PHITS to the shielding design, the absorbed doses and dose equivalents in a cylindrical phantom with tissue equivalent material inside an imaginary space vessel on a geostationary orbit at solar minimum has also been estimated for different shielding materials of different thicknesses. All the results indicate that PHITS is - a suitable tool when estimating radiation risks for humans on manned space missions and when performing shielding design studies of spacecraft.
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