National Space Centre

The effective mirror area of an imaging atmospheric Cherenkov telescope is a crucial key parameter for trigger threshold determination and energy calibration. It is usually calculated by 3D ray-tracing simulation using a simplified telescope model, and the result is used in Monte Carlo simulations. However, simplified telescope and camera models are not adequate for the Schwarzschild-Couder configuration to be used in Small-Sized Telescopes (SSTs) of the Cherenkov Telescope Array. This is because the complex 3D structure of the secondary mirror, telescope masts, and camera body block a significant fraction of Cherenkov and night-sky photons. To evaluate the effective mirror area of an SST and to finalize its camera body design with minimal shadowing, a complex 3D model was built and simulated using the ROBAST ray-tracing library. A camera body size of 570 mm and a window size of 430 mm were selected for the final camera design based on the evaluation of shadowing by simulation. A non-axisymmetric effective area distribution was determined via the modeling of the complex telescope structure, while meeting the SST effective area requirement.

Abstract Denoising is a fundamental challenge in the field of digital image processing and computer vision. Many of the denoising algorithms operate on segments of images in which non-locally distributed similar segments are identified and grouped to form sub-images. The denoising algorithm is applied on these sub-images to recover the actual image. The basis of such denoising algorithm is the existence of non-local self similarity or redundancy of segments within the natural images. But choosing the similarity measures for segment segregation is challenging. An analysis of various sorting measures and its effect on the performance of the denoising algorithms is presented.

The Coastal Zone is very much essential for economic growth as well as for environmental growth. The coastal area of tropical and subtropical region contains major diversity of flora and fauna. Nevertheless, the increasing anthropogenic activities in the coastal region, have hindrance to the natural growth of coastal ecosystem. Consequently, have severe effect on the overall ecosystem. These uncontrolled increasing anthropogenic activities, pressing the requirements for management of coastal zone. Remote sensing and GIS technology is very popular in this area. Those advanced computerized digital plat-forms and technologies promotes the proper management of a coastal zone with the help of satellite platforms like OCEANSAT I (IRS P4) OCM, LAND-SAT, SPOT, IRS LISS II amp; LISS III etc. The scaling methods are very much necessary for a better result. The 1:25,000-scale is generally accepted for the better results for the managing of the coastal zones. The classification of a geographical area is very much required for a better approach for the management strategies, the GIS based software's like ILWIS, JUMP GIS, GRASS GIS, Geosoft, Falcon View etc. The proper classification with the help of those modern and advanced techniques is very much time saving and ac-curate. The information of natural hazards like sedimentation into the delta region, cyclones, sea level rise, draught or excessive flood in coastal zone agricultural area are now easily accessible with the help of these two methods.

Despite the wealth of data produced by previous and current Earth Observation platforms feeding climate models, weather forecasts, disaster monitoring services and countless other applications, the public still lacks the ability to access a live, true colour, global view of our planet, and nudge them towards a realisation of its fragility. The ideas behind commercialization of Earth photography from space has long been dominated by the analytical value of the imagery. What specific knowledge and actionable intelligence can be garnered from these evermore frequent revisits of the planet’s surface? How can I find a market for this analysis? However, what is rarely considered is what is the educational value of the imagery? As students and children become more aware of our several decades of advance in viewing our current planetary state, we should find mechanisms which serve their curiosity, helping to satisfy our children’s simple quest to explore and learn more about what they are seeing. The following study describes the reasons why current GEO and LEO observation platforms are inadequate to provide truly global RGB coverage on an update time-scale of 5-min and proposes an alternative, low-cost, GEO + Molniya 3U CubeSat constellation to perform such an application.

1. Summary DNSC07 is a new global ocean wide satellite altimetry derived gravity field computed at the Danish National Space Center (DTUDenmark) with a spatial resolution of 1 arc-minute by 1 arc-minute covering all marine regions of the world including the Arctic Ocean up to the North Pole. For more than a decade satellite altimetry has been used to determine the marine gravity field. All present satellite based global marine gravity fields are based on the GEOSAT and ERS-1 Geodetic Mission (GM) data combined with other satellite derived datasets. The most urgent outstanding problem with most existing marine gravity fields (i.e. KMS02, Sandwell and Smith V12, NTU 01, GSFC00) was to improve the coverage of the data and the quality of the satellite observations in order to gain higher accuracy of the derived marine gravity field in particularly high latitudes and in coastal regions where many sedimentary basins are found. By using a new double-retracking system for the entire ERS-1 GM mission using a highly advanced expert based system of multiple retrackers and subsequently repacking/retracking we have been able to obtain both higher quality data but also many more data than seen before. Especially in coastal and ice-covered regions the new DNSC07 global marine gravity field is superior to other satellite based global marine gravity fields. We will present the high resolution new global marine gravity field and comparison with existing marine gravity surveys in several regions of the world (Indonesia, Florida Keys and East Greenland) and demonstrate how much accuracy have been gained by retracking the satellite observations compared with existing global marine gravity fields.

In this paper we outline the principles of downward continuation and geoid determination in Mongolia, based on the 2004-5 airborne gravity survey, surface gravimetry from various sources, and detailed digital terrain models from satellite radar interferometry (SRTM). A remove-restore method is used for terrain and global spherical harmonic reference models, with the residual gravity field signal downward continued by least-squares collocation, and the geoid and quasi-geoid computed by spherical Fourier methods. For reference field a GRACE and EGM96 combination field is used, and the geoid assessed using a subset of available GPS-leveling data, indicating that recent GRACE fields still have detectable problems in the harmonic wavelength band 50-100. The gravimetric geoid model computed refers to a global vertical datum; the Kronstadt Baltic Sea level data used in Mongolia shows a difference of more than one meter to the global datum, and therefore it is essential to fit the gravimetric geoid to local height data to obtain an operational geoid model for GPS use.

The origins of HEMT distortion in passive control applications as SPST switch are presented in this paper. Also, this paper describes the change of the AlGaN/GaN HEMT switch distortion properties (second-and third distortion intercept points) over a wide range of temperature. The results indicate that the change in second-and third-order distortion intercept points is smaller (about 2dBm) over a wide range of temperature from −50 to +300°C. A comparison of the GaN-based HEMT switch with InP-and GaAs-HEMT switches shows that the GaN technology generates lower distortion than its InP and GaAs technologies counterpart.

In order to determine the influence of mankind on climate change it is important to understand the natural causes of climate variability. A natural effect that has been hard to understand physically is an apparent link between climate and solar activity. From historical and geological records there are strong indications that the sun has played an important role in the past climate of the Earth, but the physical mechanism is currently unknown. Whatever mechanism caused those earlier changes would most likely also be operating today and may have been active throughout the history of our planet. There have been several attempts to explain the link between solar activity and climate from variations in the sun’s radiative output. These have tended to rely on simulations involving Global Climate Models (GCM), which are limited by our current understanding of the fundamental physics. In the following contribution, an outline of the current candidate mechanisms involving solar activity will be presented together with a description of the ESA funded project to study the Influence of Solar Activity cycles on Earth’s Climate (ISAC)

Described are some applications of conversion electron Mossbauer spectroscopy (CEMS) in geosciences. It is shown how easily this technique can be applied in existing Mossbauer laboratories to investigate natural samples. Some examples demonstrate the kind of information CEMS can give on the weathering history or mechanical properties of samples. The possible application of CEMS on Mars is discussed.

The energy range above 60 keV is important for the study of many open problems in high energy astrophysics such as the role of Inverse Compton with respect to synchrotron or thermal processes in GRBs, non thermal mechanisms in SNR, the study of the high energy cut-offs in AGN spectra, and the detection of nuclear and annihilation lines. Recently the development of high energy Laue lenses with broad energy bandpasses from 60 to 600 keV have been proposed for a Hard X ray focusing Telescope (HAXTEL) in order to study the X-ray continuum of celestial sources. The required focal plane detector should have high detection efficiency over the entire operative range, a spatial resolution of about 1 mm, an energy resolution of a few keV at 500 keV and a sensitivity to linear polarization. We describe a possible configuration of the focal plane detector based on several CdTe/CZT pixelated layers stacked together to achieve the required detection efficiency at high energy. Each layer can operate both as a separate position sensitive detector and polarimeter or work with other layers to increase the overall photopeak efficiency. Each layer has a hexagonal shape in order to minimize the detector surface required to cover the lens field of view. The pixels would have the same geometry so as to provide the best coupling with the lens point spread function and to increase the symmetry for polarimetric studies.