An Automated Method for Tracking Clouds in Planetary Atmospheres

We present an automated method for cloud tracking which can be applied to planetary images. The method is based on a digital correlator which compares two or more consecutive images and identifies patterns by maximizing correlations between image blocks. This approach bypasses the problem of feature detection. Four variations of the algorithm are tested on real cloud images of Jupiter’s white ovals from the Galileo mission, previously analyzed in Vasavada et al. [Vasavada, A.R., Ingersoll, A.P., Banfield, D., Bell, M., Gierasch, P.J., Belton, M.J.S., Orton, G.S., Klaasen, K.P., Dejong, E., Breneman, H.H., Jones, T.J., Kaufman, J.M., Magee, K.P., Senske, D.A. 1998. Galileo imaging of Jupiter’s atmosphere: the great red spot, equatorial region, and white ovals. Icarus, 135, 265, doi:10.1006/icar.1998.5984]. Direct correlation, using the sum of squared differences between image radiances as a distance estimator (baseline case), yields displacement vectors very similar to this previous analysis. Combining this distance estimator with the method of order ranks results in a technique which is more robust in the presence of outliers and noise and of better quality. Finally, we introduce a distance metric which, combined with order ranks, provides results of similar quality to the baseline case and is faster. The new approach can be applied to data from a number of space-based imaging instruments with a non-negligible gain in computing time

A Cloud Tracking Tool for Planetary Orbiter Images

During their operations phase, planetary missions continuously produce a wealth of data that tend to overwhelm research teams. Spectral imagers, in particular, produce data cubes in which the wavelength dimension adds to the two spatial dimensions. Tracking of atmospheric features in order to derive winds and the construction of global maps from such large data volumes becomes particularly time-consuming if done manually. This highlights the importance of automated procedures capable of analysing sequences of data cubes with minimal user interaction. A tool for cloud tracking for such a purpose is currently under development in our group. In its present state it is based on synthetic images and uses a simple method of multiple matrix comparison to derive wind components. Deriving winds from data from the Venus Express - Visible and InfraRed Thermal Imaging Spectrometer (VIRTIS) instrument will be a possible application. We shall present an overview of the method, its benchmarking and the current status and future development of the project

Viagens e Viajantes Portugueses na Ásia Central (séculos XVI-XVII)

A história das viagens terrestres portuguesas pela Ásia Central era, e continua a ser, esparsa, quer como elemento no processo da Expansão Portuguesa, quer como objeto específico de análise historiográfica. Para os indivíduos do Estado da Índia, a posição longínqua e interior da Ásia Central tornava-a incompatível com a natureza predominantemente marítima da Ásia portuguesa, fazendo da perspetiva de uma atividade ativa e duradoura uma impossibilidade geoestratégica. Consequentemente, houve um impacto diminuto da presença portuguesa naquela região, constituindo as viagens terrestres pelo interior asiático um episódio que recebe pouco mais que uma breve menção por parte da maioria dos historiadores. Contudo, a história das viagens portuguesas pelas Rotas da Seda terrestres e a historiografia que tem vindo a relatar e analisar tais iniciativas, revelam um rico potencial de informações interessantes para compreendermos inúmeros aspetos relativos à Ásia Central na época moderna e à Expansão Portuguesa. Por isso, a viagem terrestre transformou-se num nicho em ambos os tempos, passado e presente. Na época moderna, indivíduos oriundos da Ásia portuguesa demonstraram interesses e investiram esforços em espaços como a Pérsia Safávida, a Transoxiana e o Tibete. Tais interesses manifestaram-se sob a forma de viagens de procura de caminhos alternativos e de lendas com origem na medievalidade, bem como no estabelecimento de missões católicas na Pérsia e no Tibete. Desde a década de 1990, que se tem vindo a desenvolver uma historiografia sobre os viajantes, as viagens e as suas dinâmicas. O maior obstáculo para o desenvolvimento da área é a sua falta de visibilidade na academia, exacerbada pela ausência de uma história geral que aglomere diferentes tempos, espaços, viagens e viajantes, contrariando a tendência em especificar um só viajante ou grupo de viajantes que percorreram os mesmos caminhos. Este trabalho faz uma análise global da história da presença e atuação portuguesa na Ásia Central, incidindo sobre viagens realizadas pela Pérsia Safávida até o Reino de Portugal, sobre as viagens pelo Tibete e seus arredores, numa tentativa de busca pelo Cataio, e sobre as viagens dos jesuítas portugueses, inseridos na corte Qing, à Tartária.The history of Portuguese overland travel in Central Asia was, and to some extent still is, sparse, both as an element in the process of Portuguese Expansion and as a specific object of historiographical analysis. For the individuals from the State of India, the distant and inland position of Central Asia made it incompatible with the predominantly maritime nature of Portuguese Asia, turning the prospect of active and sustained activity into a geostrategic impossibility. Consequently, there was little impact on the Portuguese presence in that region, and overland voyages through the Asian interior are an episode that receives little more than brief mention by most historians. However, the history of Portuguese voyages along the terrestrial Silk Roads and the historiography that has been reporting and analyzing such initiatives, reveal a rich potential of interesting information to understand many aspects of Central Asia in modern times and the Portuguese Expansion. Therefore, overland travel has become a niche in both past and present times. In modern times, individuals from Portuguese Asia showed interest and invested efforts in spaces such as Safavid Persia, Transoxiana and Tibet. These interests manifested themselves in the form of journeys in search of alternative routes and legends originating in the Middle Ages, as well as in the establishment of Catholic missions in Persia and Tibet. Since the 1990s, a historiography on travelers, journeys and their dynamics has been developing. The biggest obstacle to the advancement of the area is its lack of visibility in academia, exacerbated by the absence of a general history that brings together different times, spaces, journeys and travelers, contrary to the tendency to specify a single traveler or group of travelers who journeyed through the same paths. This work makes a global analysis of the history of the Portuguese presence and action in Central Asia, focusing on the voyages made from Safavid Persia to the Kingdom of Portugal, on the voyages through Tibet and its surroundings, in an attempt to search for Cathay, and on the voyages of the Portuguese Jesuits, in the Qing court, to Tartary

Reply to comment by Fries on â Cometary origin of atmospheric methane variations on Mars unlikelyâ

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137383/1/jgre20652_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137383/2/jgre20652.pd

Empirical modeling of the stellar spectrum of galaxies

An empirical method of modeling the stellar spectrum of galaxies is proposed, based on two successive applications of Principal Component Analysis (PCA). PCA is first applied to the newly available stellar library STELIB, supplemented by the J, H and K$_{s}$ magnitudes taken mainly from the 2 Micron All Sky Survey (2MASS). Next the resultant eigen-spectra are used to fit the observed spectra of a sample of 1016 galaxies selected from the Sloan Digital Sky Survey Data Release One (SDSS DR1). PCA is again applied, to the fitted spectra to construct the eigen-spectra of galaxies with zero velocity dispersion. The first 9 galactic eigen-spectra so obtained are then used to model the stellar spectrum of the galaxies in SDSS DR1, and synchronously to estimate the stellar velocity dispersion, the spectral type, the near-infrared SED, and the average reddening. Extensive tests show that the spectra of different type galaxies can be modeled quite accurately using these eigen-spectra. The method can yield stellar velocity dispersion with accuracies better than 10%, for the spectra of typical S/N ratios in SDSS DR1.Comment: 34 pages with 18 figures, submitted to A

Constraining the solutions of an inverse method of stellar population synthesis

In three previous papers (Pelat 1997, 1998 and Moultaka & Pelat 2000), we set out an inverse stellar population synthesis method which uses a database of stellar spectra. Unlike other methods, this one provides a full knowledge of all possible solutions as well as a good estimation of their stability; moreover, it provides the unique approximate solution, when the problem is overdetermined, using a rigorous minimization procedure. In Boisson et al. (2000), this method has been applied to 10 active and 2 normal galaxies. In this paper we analyse the results of the method after constraining the solutions. Adding {\it a priori} physical conditions on the solutions constitutes a good way to regularize the synthesis problem. As an illustration we introduce physical constraints on the relative number of stars taking into account our present knowledge of the initial mass function in galaxies. In order to avoid biases on the solutions due to such constraints, we use constraints involving only inequalities between the number of stars, after dividing the H-R diagram into various groups of stellar masses. We discuss the results for a well-known globular cluster of the galaxy M31 and discuss some of the galaxies studied in Boisson et al. (2000). We find that, given the spectral resolution and the spectral domain, the method is very stable according to such constraints (i.e. the constrained solutions are almost the same as the unconstrained one). However, an additional information can be derived about the evolutionary stage of the last burst of star formation, but the precise age of this particular burst seems to be questionable.Comment: Accepted in A&A. 15 pages, 5 figures and 6 table