1,721,519 research outputs found
The 1999 Quadrantids and the lunar Na atmosphere
Full text linkEnhancements of the Na emission and temperature from the lunar atmosphere were reported during the Leonid meteor showers of 1995, 1997 and 1998. Here we report a search for similar enhancement during the 1999 Quadrantids, which have the highest mass flux of any of the major streams. No enhancements were detected. We suggest that different chemical-physical properties of the Leonid and Quadrantid streams may be responsible for the difference
Topographic correction of HiRISE and CaSSIS images: Validation and application to color observations of Martian albedo features
No full textThe topographic correction of satellite images has to be applied to both disentangle albedo features from illumination effects induced by local topography and performspectrophotometric analyses of planetary surfaces. This work focuses on the modeling and removal of surface brightness variations induced by topography, referred astopographic shading, from high resolution images of Mars. Topographic shading can be modeled through functions of the surface illumination and observation anglescalled disk functions. We consider four disk functions that are widely used in planetary photometry: the Lambert, Lommel-Seeliger, Akimov and Minnaert diskfunctions. We test and evaluate their performances in removing topographic shading from High Resolution Imaging Science Experiment (HiRISE) and Colour andSurface Science Imaging System (CaSSIS) images. We here validate our method, moreover, we report scientific applications to single or multi-band datasets byanalyzing topographically corrected HiRISE colour observations of Martian recurring slope lineae and dust devil tracks, as well as CaSSIS panchromatic observations
Using process simulators for steady-state and dynamic plant analysis - An industrial case study
No full textProcess simulation tools are widely adopted for the design and optimization of chemical
processes. However, for quite a long time their use has been confined within research
centres and highly specialized technical groups. This is especially true for dynamic
simulation software, long regarded as a very specific tool requiring considerable expertise. In
this work we intend to demonstrate the benefits that process engineers working on the plant
may receive from an appropriate use of commercial software currently available for steady-state
and dynamic simulation. A case-study concerning the purification section of an industrial plant
for vinyl chloride monomer production will be considered. First of all, a steady-state simulation
will be considered. Primarily, the simulation will allow a better judgement of the plant
operating conditions; then it will be illustrated that sensitivity studies may produce great
benefits in the general economy and productivity of the plant. Secondly, it will be shown how a
dynamic model suitable for practical needs can be derived from the steady-state model. This
model can be used as a powerful tool to assess the performance of the control system in
handling standard operational disturbances as well as abnormal events. Simple improvements
of the control system design will be also simulated and commented on
Evaluation of an area-based matching algorithm with advanced shape models
No full textNowadays, the scientific institutions involved in planetary mapping are working on new strategies to produce accurate high resolution DTMs from space images at planetary scale, usually dealing with extremely large data volumes. From a methodological point of view, despite the introduction of a series of new algorithms for image matching (e.g. the Semi Global Matching) that yield superior results (especially because they produce usually smooth and continuous surfaces) with lower processing times, the preference in this field still goes to well established area-based matching techniques. Many efforts are consequently directed to improve each phase of the photogrammetric process, from image pre-processing to DTM interpolation. In this context, the Dense Matcher software (DM) developed at the University of Parma has been recently optimized to cope with very high resolution images provided by the most recent missions (LROC NAC and HiRISE) focusing the efforts mainly to the improvement of the correlation phase and the process automation. Important changes have been made to the correlation algorithm, still maintaining its high performance in terms of precision and accuracy, by implementing an advanced version of the Least Squares Matching (LSM) algorithm. In particular, an iterative algorithm has been developed to adapt the geometric transformation in image resampling using different shape functions as originally proposed by other authors in different applications
Optical performance evaluation of the high spatial resolution imaging camera of BepiColombo space mission
No full textThermo-elastic analyses of the High spatial Resolution Imaging Camera (HRIC), which is mounted on Mercury Planetary Orbiter BepiColombo Integrated Observatory SYStem suit (SIMBIO-SYS) of BepiColombo space mission, are carried out in order to evaluate the effect of thermo-elastic deformations on the optical performance experienced by the camera at the worst thermal scenario of Mercury space environment. In particular, the optical performance is evaluated in terms of the pointing error of the camera and the potential presence of optical aberrations
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