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

Velocities of Venus clouds derived from VIRTIS observations

Retrograde superrotation is a well known feature of the atmosphere of Venus, with Venus’ cloud tops rotating in only 4.4 days, much faster than the 243-day rotation period of the solid globe. A good characterization of the circulation of the venusian atmosphere is essential in order to understand the mechanisms controlling superrota- tion. VIRTIS, onboard ESA’s Venus Express, is one of the most flexible instruments for such a characterization. The VIRTIS-M imaging spectrometer, operating in the range 0.25 to 5 micrometers, has acquired images of Venus’ clouds from the cloud tops, in visible wavelengths, to the lower cloud layer, close to 40 km, at infrared wavelengths. We present velocity determinations from automated cloud tracking in the night side at 1.74, 2.3 and 5 micrometers, from high to mid latitudes in the south- ern hemisphere. The method is based on a digital correlator which compares two or more consecutive images and identifies patterns by maximizing correlations between image blocks (Luz, Berry and Roos-Serote, 2008, New Ast. 13, 224). Notable features are the variability of the winds and the detection of a clear transition region between 75S and 80S. The meridional component is suggestive of a polar Hadley cell. Wave motions are detected at the transition latitudes with wavenumbers 3 and 8 for the zonal and meridional components. We estimate the contribution from the subsolar to antisolar-point wind component to be higher than 10 m/s

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

South polar dynamics of the Venusian atmosphere from VIRTIS/Venus Express mapping in the thermal range

We report on measurements of Venus cloud velocities from VIRTIS/Venus Express observations of the south polar region of Venus. Cloud tracking has been performed using a method of automated digital correlation. Tracking has been performed on pairs of monochromatic VIRTIS images selected mainly in the 5 μm window, but also at 1.74, 2.3, 3.93 micrometers. Wind measurements from vector retrievals based on automated feature tracking show high variability, indicating the presence of important transient motions. The time-averaged zonal winds indicate different day and night side regimes. On the day side both the zonal wind component (u) and the meridional one (v) are approximately uniform between 84S and 76S, with u ∼ −40 m/s and v ∼ −10 m/s. On the night side the zonal wind decreases poleward, from a maximum at 76S. The meridional wind is smaller than on the day side and appears to change sign from poleward to equatorward at 76S. The cold collar boundary appears to be a transition region not only for the temperature, but for the winds as well. In this region wave motions are also apparent, with amplitudes on the order of 40 m/s for u′ and 10 m/s for v′

A Framework for collaborative writing with recording and post-meeting retrieval capabilities

From a HCI perspective, elucidating and supporting the context in which collaboration takes place is key to implementing successful collaborative systems. Synchronous collaborative writing usually takes place in contexts involving a “meeting” of some sort. Collaborative writing meetings can be face-to-face or, increasingly, remote Internet-based meetings. The latter presents software developers with the possibility of incorporating multimedia recording and information retrieval capabilities into the collaborative environment. The collaborative writing that ensues can be seen as an activity encompassing asynchronous as well as synchronous aspects. In order for revisions, information retrieval and other forms of post-meeting, asynchronous work to be effectively supported, the synchronous collaborative editor must be able to appropriately detect and record meeting metadata. This paper presents a collaborative editor that supports recording of user actions and explicit metadata production. Design and technical implications of introducing such capabilities are discussed with respect to document segmentation, consistency control, and awareness mechanisms

RECOLED: A group-aware collaborative text editor for capturing document history

This paper presents a usability analysis of RECOLED, a shared document editor which supports recording of audio communication in remote collaborative writing sessions, and transparent monitoring of interactions, such as editing, gesturing and scrolling. The editor has been designed so that the collaboration results in the production of a multimedia document history which enriches the final product of the writing activity and can serve as a basis for post-meeting information retrieval. A discussion is presented on how post-meeting processing can highlight the usefulness of such histories in terms of tracking information that would be normally lost in usual collaborative editing settings

Characterization of Atmospheric Waves at the Upper Clouds in the Polar Region of Venus

Non solar-fixed waves at the cloud tops of the southern polar region of Venus are studied in the winds measured with 3.9 and 5.0 μm images taken by the instrument VIRTIS-M onboard Venus Express. Wavenumbers 1, 2 and 3 are detected, with wave amplitudes ranging from 3.6 to 8.0 m/s. The evolution of the phase has been studied in 16 orbits, finding in a subset of orbits wavenumbers 1 and 2 propagating in different directions (zonal wind), and a westward progression with a phase velocity of approximately 5.7 m/s for the wavenumber 1 in the meridional wind. Finally, a new set of analytical solutions to the atmospheric waves is obtained for the planet Venus, and these are used to characterize the found waves in terms of the horizontal wavelength and phase velocity

Titã: Um Mundo por Explorar

Discusão da investigação da atmosfera de Titã

Winds and cloud morphology in the southern polar region of Venus

Spinning on average 60 times faster than the surface, the atmosphere of Venus is superrotational, a state in which the averaged angular momentum is much greater than that corresponding to co-rotation with the solid globe. The rapid mean flow, which is main- tained by momentum transports in the deep atmo- sphere, presents a puzzle to the atmospheric and plan- etary sciences[1]. After previous missions revealed a bright polar feature at the north pole[9, 10], the Venus Express spacecraft discovered a fast-rotating counter- part at the southern polar region[6], which has been identified as a vortex[2]. The southern polar vortex can be observed at 5.0 μm as a bright, highly vari- able structure which is ∼ 15 K warmer than the sur- rounding air[6]. Although the Venus superrotation has been measured by tracking cloud features at UV and infrared wavelengths[7, 4, 8, 5], the winds in the po- lar region remain poorly constrained. Characterizing the zonal and meridional circulation in this region, as well as their variability, is crucial for understanding the mechanisms that maintain superrotation. In partic- ular, mean zonal winds are necessary to understand the nature of the polar vortex, how it is connected with the general circulation of the atmosphere, and to diagnose momentum transports. Winds at 45 and 65 km can be detected from cloud motion monitoring by the VIRTIS-M subsection on- board the Venus Express (VEX) spacecraft. Our ob- jective is to provide direct wind measurements at cloud tops and in the lower cloud level, in order to help in- terpret the VEX observations concerning the meso- spheric wind regime and temperature fields. In par- ticular, we present direct measurements of the zonal and meridional winds at both altitudes. For this work we selected nadir-pointing, high- spatial resolution VIRTIS data cubes obtained from apocenter in order to minimize the geometric distortion of the polar region. On average these contain lat- itudes extending from the pole to 70S. Since the VIR- TIS field of view is rectangular, lower latitudes are also present but cannot be observed over full latitude circles. Cloud tracking has been performed using the method of digital correlation described in a previous article[3]. VEX orbits were selected so as to have in each one at least one pair of images suitable for track- ing, i.e., with a considerable spatial overlap. Tracking has been performed on pairs of monochromatic im- ages at wavelengths of 1.74 μm, 2.3 μm, 3.93 μm and 5 μm. In the data cubes obtained with longer integration times (3s) the long-wavelength range of the spectrum, above 4.3 μm, is saturated. In those cases we se- lected the 3.93 μm radiance map instead of the one at 5 μm. The monochromatic radiance maps are first ex- tracted from data cubes that have undergone the stan- dard VIRTIS calibration procedures. The maps are then projected onto a polar stereographic grid and the wind retrieval procedure is applied. A total of 20 lat- itude bins, separated by 1 degree were used. For the analysis of transient motions the spatial averaging was done in 72 longitude bins at 5 degree intervals. In order to evaluate the variability over the time scale of one orbit, we have computed the orbital aver- ages, i.e., averages of all measurements coming from one given orbit. These orbital averages are only ap- proximations to temporal averages, since they do not cover one full rotation. The differences between same- orbit averages are apparent in both day and night side averages. Some notable features indicating different day and night side regimes are also apparent in the or- bit averages, and the boundary of the cold collar ap- pears to be a transition latitude. Moreover, the vari- ability that can be observed from orbit to orbit and be- tween series of observations from the same orbit indi- cates that departures from this mean flow are large and a persistent feature of the global circulation

The Empirics of the National Minimum Wage and Employment in the U.K.

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