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Cellino A.,National institute for astrophysics | Muinonen K.,University of Helsinki | Muinonen K.,Finnish Geospatial Research Institute | Hestroffer D.,IMCCE | Carbognani A.,Osservatorio Astronomico della Valle dAosta
Planetary and Space Science | Year: 2015

The inversion of sparse photometric data of asteroids to derive from them information about the spin and shape properties of the objects is a hot topic in the era of the Gaia space mission. We have used a rigorous analytical treatment of the Lommel-Seeliger light-scattering law computed for the particular case of bodies having the shapes of ideal triaxial ellipsoids, and we have implemented this in the software developed for the treatment of Gaia photometric data for asteroids. In a set of numerical simulations, the performances of the photometry inversion code improve significantly with respect to the case in which purely geometric scattering is taken into account. When applied to real photometric data of asteroids obtained in the past by the Hipparcos satellite, however, we do not see any relevant improvement of the performances, due to the poor accuracy of these measurements. These results suggest that the role played by the light-scattering properties of asteroid surfaces is indeed relevant. On the other hand, any refined treatment of light-scattering effects cannot improve the reliability of photometric inversion when the quantity and quality of available data are much worse than what we expect to obtain from Gaia. © 2015 Elsevier Ltd. Source

Wang X.,Chinese Academy of Sciences | Muinonen K.,University of Helsinki | Muinonen K.,Finnish Geospatial Research Institute | Wang Y.,Chinese Academy of Sciences | Wang Y.,University of Chinese Academy of Sciences
Planetary and Space Science | Year: 2015

The physical properties of asteroids, such as their spin and shape, are very important for understanding the formation and evolution of the entire asteroid belt, as well as the individual asteroid itself. However, only a small part of asteroids had been determined accurately for their spin parameters and shapes due to lack of data or narrow aspect angle distribution of dataset. In the present paper, the spin parameters and convex shapes of two C-type main-belt asteroids (362) Havnia and (506) Marion are analyzed using the convex inversion method and the virtual-photometry Monte Carlo method. A pair of poles are found for (362) Havnia at (96°.2-2.0+3.0,+38°.8-2.4+6.8) and (273°.0-6.5+1.3,+40°.0-9.9+1.2) in ecliptic coordinates, the spin period values corresponding to the two poles are 16.918773-6.4(-6)+2.8(-5) h (here +2.8(-5) represents +2.8×10-5) and 16.918935-4.3(-5)+1.2(-5) h, respectively. Similarly, two candidate poles are found for (506) Marion at (88°.0-0.3+1.3,+22°.3-1.5+1.3) and (264°.5-0.03+1.2,-7°.5-0.92+1.1). The spin periods for the two poles are 13.549826-9.8(-6)+1.2(-5) h and 13.549751-5.9(-6)+1.3(-5) h. The shapes of Havnia for the pair of poles approximate to Maclaurin spheroids. Whereas the convex shapes of Marion for the two poles are prolate shapes, and it rotates around the longest axis. The significant divergence of weight coefficients c for Havina and Marion implies different materials on the two asteroids' surface. © 2015 Elsevier Ltd. Source

Bilker-Koivula M.,Finnish Geospatial Research Institute | Bilker-Koivula M.,Aalto University
International Association of Geodesy Symposia | Year: 2014

The two high-resolution global gravity field models, EGM2008 and EIGEN-6C, are compared with ground truth in Finland and surrounding areas. Thereafter, the models are used as background models in the calculation of a quasi-geoid model for Finland. The differences between height anomalies calculated from the globalmodels and from two GPSlevelling datasets for Finland show standard deviations between 5 and 7 cm. Comparisons with free-air anomalies show small and homogeneously distributed differences over most of the area. In both comparisons the largest discrepancies are found close to the Russian border east of the 29° longitude line. This is most probably due to lower resolution Russian data used in the global models. When the global models are used as background models in the calculation of a quasi-geoid model for Finland, the problems around the 29° longitude line disappear. Comparison between the final quasi-geoid models and GPS-levelling data show an improvement over earlier models for Finland. © Springer International Publishing Switzerland 2014. Source

Sainio J.,Abo Akademi University | Westerholm J.,Abo Akademi University | Oksanen J.,Finnish Geospatial Research Institute
ISPRS International Journal of Geo-Information | Year: 2015

The breakthrough of GPS-equipped smartphones has enabled the collection of track data from human mobility on massive scales that can be used in route recommendation, urban planning and traffic management. In this work we present a fast map server that can generate and visualize heat maps of popular routes online from massive sports track data based on client preferences, e.g., running routes lasting less than an hour. The heat maps shown respect user privacy by not showing routes with less than a predefined number of different users, for instance five. The results are represented to the client using a dynamic tile layer. The current implementation uses data collected by the Sports Tracker mobile application with over 800,000 different tracks and 2.8 billion GPS data points. Stress tests indicate that the server can handle hundreds of simultaneous client requests in a single server configuration. © 2015 by the authors; licensee MDPI, Basel, Switzerland. Source

Fedorets G.,University of Helsinki | Granvik M.,University of Helsinki | Granvik M.,Finnish Geospatial Research Institute
Planetary and Space Science | Year: 2015

We obtained observations and performed rotation period, pole orientation and convex shape model analysis for the slowly rotating Hungaria asteroid (39420) Elizabethgaskell as a follow-up to the Thousand Asteroid Light Curve Survey (TALCS, Masiero et al., 2009). The TALCS observations combined with our follow-up observations did not allow for an unambiguous spin and shape solution. To reject the possibility of a methodological failure in the analysis, we simulated a lightcurve of an elongated object by generating synthetic detections with the same cadence as in the real observations and added random noise. The same period, pole and shape analysis was then successfully performed for a simulated object. Thus, we conclude that (39420) Elizabethgaskell is either a binary or, more likely, a non-principal-axis rotator. Being one of only two Hungarias observed in an untargeted survey, the properties of (39420) Elizabethgaskell suggest that binaries and/or non-principal-axis rotators are common in the Hungaria population. © 2015 Elsevier Ltd. Source

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