Accurate and automatic NOAA-AVHRR image navigation using a global contour matching approach

The problem of precise and automatic AVHRR image navigation is tractable in theory, but has proved to be somewhat difficult in practice. The authors' work has been motivated by the need for a fully automatic and operational navigation system capable of geo-referencing NOAA-AVHRR images with high accuracy and without operator supervision. The proposed method is based on the simultaneous use of an orbital model and a contour matching approach. This last process, relying on an affine transformation model, is used to correct the errors caused by inaccuracies in orbit modeling, nonzero value for the spacecraft's roll, pitch and yaw, errors due to inaccuracies in the satellite positioning and failures in the satellite internal clock. The automatic global contour matching process is summarized as follows: i) Estimation of the gradient energy map (edges) in the sensed image and detection of the cloudless (reliable) areas in this map. ii) Initialization of the affine model parameters by minimizing the Euclidean distance between the reference and sensed images objects. iii) Simultaneous optimization of all reference image contours on the sensed image by energy minimization in the domain of the global transformation parameters. The process is iterated in a hierarchical way, reducing the parameter searching space at each iteration. The proposed image navigation algorithm has proved to be capable of geo-referencing a satellite image within 1 pixel.Peer ReviewedPostprint (published version

Pair separation of magnetic elements in the quiet Sun

The dynamic properties of the quiet Sun photosphere can be investigated by analyzing the pair dispersion of small-scale magnetic fields (i.e., magnetic elements). By using $25$ hr-long Hinode magnetograms at high spatial resolution ($0".3$), we tracked $68,490$ magnetic element pairs within a supergranular cell near the disk center. The computed pair separation spectrum, calculated on the whole set of particle pairs independently of their initial separation, points out what is known as a super-diffusive regime with spectral index $\gamma=1.55\pm0.05$, in agreement with the most recent literature, but extended to unprecedented spatial and temporal scales (from granular to supergranular). Furthermore, for the first time, we investigated here the spectrum of the mean square displacement of pairs of magnetic elements, depending on their initial separation $r_0$. We found that there is a typical initial distance above (below) which the pair separation is faster (slower) than the average. A possible physical interpretation of such a typical spatial scale is also provided

Consumo de plantas pioneras por murciélagos frugívoros en una localidad de la orinoquía colombiana

English: Feeding behavior plays a major role as a resource partitioning strategy within assemblages of fruit bats. Although Colombia is one of the most diverse countries in terms of bat diversity, the influence of phenology of consumed resources on bat diets in local ensembles is still poorly known. In this study, we analyze trophic structure of a fruit bat assemblage in a locality of Colombian Orinoco, and we evaluate its relationship with fruiting patterns of four tree species (Cecropia peltata, C. sciadophylla, Ficus schultesii, and F. gomelleira) and two shrub species (Piper arboreum and P. obliquum), all of them representing focal dietary resources of Neotropical fruit bats. The analysis of 191 dietary records of 20 species shows that vertical stratification constitutes the main mechanism for resource partitioning among the studied bat ensemble. This mechanism is independent of the fructification patterns of the evaluated plants. Bats fed mainly on plants with continuous fructification patterns and spatially homogenous distributions. Therefore, categories based on the preference of plants with different fructification strategies do not explain the consumption patterns of the studied ensemble. Spanish: El comportamiento alimentario cumple un papel principal en la estrategia de partición de recursos dentro de los ensambles de murciélagos frugívoros. A pesar de que Colombia es uno de los países con mayor riqueza de este grupo de fauna, la influencia de la fenología de los recursos consumidos sobre las dietas de las especies en los ensambles locales aún está pobremente estudiada. En este trabajo analizamos la estructura trófica de un ensamble de murciélagos frugívoros en una localidad de la Orinoquía colombiana y evaluamos su relación con los patrones de fructificación de cuatro especies de árboles (Cecropia peltata, C. sciadophylla, Ficus schultesii y F. gomelleira) y dos especies de arbustos (Piper arboreum y P. obliquum), los cuales constituyen elementos dietarios focales en la dieta de murciélagos frugívoros neotropicales. El análisis de 191 registros dietarios de 20 especies muestra que la estratificación vertical constituye el principal mecanismo en la estrategia de partición de recursos del ensamble de murciélagos frugívoros estudiado. Este mecanismo es independiente de los patrones de fructificación de las plantas evaluadas. Los murciélagos centraron su dieta en plantas con patrones de fructificación continuos y distribuciones espacialmente homogéneas. Por lo tanto, el uso de categorías de forrajeo basadas en la preferencia de plantas con diferentes estrategias de fructificación no explica los patrones de consumo encontrados en el ensamble estudiado

A search for water maser emission toward obscured post-AGB star and planetary nebula candidates

Water maser emission at 22 GHz is a useful probe to study the transition between the nearly spherical mass-loss in the AGB to a collimated one in the post-AGB phase. In their turn, collimated jets in the post-AGB phase could determine the shape of planetary nebulae (PNe) once photoionization starts. We intend to find new cases of post-AGB stars and PNe with water maser emission, including water fountains or water-maser-emitting PNe. We observed water maser emission in a sample of 133 objects, with a significant fraction being post-AGB and young PN candidate sources with strong obscuration. We detected this emission in 15 of them, of which seven are reported here for the first time. We identified three water fountain candidates: IRAS 17291-2147, with a total velocity spread of ~96 km/s in its water maser components and two sources (IRAS 17021-3109 and IRAS 17348-2906) that show water maser emission outside the velocity range covered by OH masers. We have also identified IRAS 17393-2727 as a possible new water-maser-emitting PN. The detection rate is higher in obscured objects (14%) than in those with optical counterparts (7%), consistent with previous results. Water maser emission seems to be common in objects that are bipolar in the near-IR (43% detection rate). The water maser spectra of water fountain candidates like IRAS 17291-2147 show significantly less maser components than others (e.g., IRAS 18113-2503). We speculate that most post-AGBs may show water maser emission with wide enough velocity spread (> 100 km/s) when observed with enough sensitivity and/or for long enough periods of time. Therefore, it may be necessary to single out a special group of "water fountains", probably defined by their high maser luminosities. We also suggest that the presence of both water and OH masers in a PN is a better tracer of its youth, rather than the presence of just one of these species.Comment: To be published in Astronomy & Astrophysics. 16 pages, 1 figure (spanning 5 pages). This version includes some minor language corrections and fixes some errors in Table

Alimentacao do tucunare Cichla sp. (Pisces, cichlidae) um peixe introduzido no Pantanal, Brasil.

Com o objetivo de estudar a alimentacao do tucunare (Cichla sp.) no Pantanal, foram realizadas cinco coletas entre novembro/1992 e junho/1994. Foram capturados 425 especimes, destes 207 apresentaram conteudo estomacal. Foram analisadas a Frequencia de Ocorrencia (FO), Volume Relativo (Vr) e "Indice Alimentar" (IA). Os peixes foram o principal item alimentar (FO=97,10%, Vr=96,45, IAi=99,81%), seguido de "restos vegetais", (FO=6,28%, Vr=2,49, IAi=16%) e camaroes (FO=1,93%, Vr=1,04, IAi=2%). Foram identificadas 21 especies de peixes no conteudo estomacal do "tucunare". Curimatella dorsalis foi a presa predominante em numero de individuos (18,75%) e em biomassa (28,81%). A familia mais representativa em biomassa foi Curimatidae (27,36%) e Cichlidae (26,93%); em numero de individuos, Sternopygidae foi mais representada (26,66%), seguida de Cichlidae e Curimatidae, com 15,55%. Os resultados permitem caracterizar o tucunare como piscivoro generalista.bitstream/item/37429/1/BP23.pd

Spectra of Harmonium in a magnetic field using an initial value representation of the semiclassical propagator

For two Coulombically interacting electrons in a quantum dot with harmonic confinement and a constant magnetic field, we show that time-dependent semiclassical calculations using the Herman-Kluk initial value representation of the propagator lead to eigenvalues of the same accuracy as WKB calculations with Langer correction. The latter are restricted to integrable systems, however, whereas the time-dependent initial value approach allows for applications to high-dimensional, possibly chaotic dynamics and is extendable to arbitrary shapes of the potential.Comment: 11 pages, 1 figur