Non-expert interpretations of hurricane forecast uncertainty visualizations

Uncertainty represented in visualizations is often ignored or misunderstood by the non-expert user. The National Hurricane Center displays hurricane forecasts using a track forecast cone, depicting the expected track of the storm and the uncertainty in the forecast. Our goal was to test whether different graphical displays of a hurricane forecast containing uncertainty would influence a decision about storm characteristics. Participants viewed one of five different visualization types. Three varied the currently used forecast cone, one presented a track with no uncertainty, and one presented an ensemble of multiple possible hurricane tracks. Results show that individuals make different decisions using uncertainty visualizations with different visual properties, demonstrating that basic visual properties must be considered in visualization design and communication.     

X-ray timing and spectral observations of active galactic nuclei

Conclusions X-ray variability is seen in all types of AGN but large amplitude ( factor 2) outbursts on short timescales (days) occur rarely, perhaps once every 100 days. There is no strong dependence of variability on luminosity, but radio-powerful AGN, particularly BL Lacs and 0VV QS0s, do vary most. Sensitive detectors, such as the EXOSAT ME, have been able to detect variability of smaller amplitude (20%) and on shorter timescales (1 hour) than previous experiments, but this too is not common. There is very little evidence of spectral variability during changes in intensity and so it is very likely that such changes are total power variations and not artefacts of variable obscuration. The variability timescales imply that most Seyfert galaxies are emitting well below the Eddington limit. On efficiency considerations only two observations of X-ray variability, those of the QS01525+227 and the BL Lac H0322+022, require exotic black hole models, relativistic beaming, or a change in the assumed value of H₀. The most dramatic observation of variability so far reported, that of repeated variations on a timescale of 4000 seconds in NGC4051 is probably related to a hydrodynamical timescale in the accretion disc and encourages us to believe that, with future observations, our understanding of AGN may approach that of galactic X-ray sources.Many Seyferts do have a canonical =0.7 spectral index, but it is becoming increasingly clear that a wide variety of spectral indices exist, both in Seyfert galaxies and in other classes of AGN. Both thermal and non-thermal emission mechanisms are tenable explanations for most of these spectra as, in general, the very high energy observations which could distinguish between the two are not available.Timing observations rarely require relativistic beaming, however, the (low) observed X-ray fluxes of BL Lacs and 0VV QS0s generally do. reacceleration of particles on short timescales is necessary to explain the continuous infrared to X-ray spectra of BL Lacs.The status of soft excesses in the low energy spectra of Seyfert galaxies which have canonical medium energy spectra is not clear. A separate soft component has been detected in EXOSAT observations of NGC4151 but this need not be associated with the nuclear continuum source. No SSS or EXOSAT observations definitely require such excesses. EXOSAT is, in principle, very sensitive to soft excesses but the uncertainty in the Boron filter calibration and in the value of the galactic absorption at present limit precise determinations.The absorbing column in the direction of many AGN is, in many cases, entirely accountable for purely by absorption in our own galaxy. In cases where a substantial absorbing column is detected, variations in the column are occasionally seen but it is not yet clear whether these variations are due to bulk movements of obscuring material or increased photoionisation (warm absorbers). All observations of iron lines are consistent with fluorescence in a cold gas which probably surrounds the X-ray emitting region in a sphere or shell-type geometry, though (by Gauss' law) this need not necessarily lie immediately next to the central black hole.Detailed observations of the time-variability of the complete X-ray to radio spectrum offer the best hope of further progress in this complex but interesting field.     

Project Icarus: A review of local interstellar medium properties of relevance for space missions to the nearest stars

I review those properties of the interstellar medium within 15 light-years of the Sun, which will be relevant for the planning of future rapid (v≥0.1c) interstellar space missions to the nearest stars. As the detailed properties of the local interstellar medium (LISM) may only become apparent after interstellar probes have been able to make in situ measurements, the first such probes will have to be designed conservatively with respect to what can be learned about the LISM from the immediate environment of the Solar System. It follows that studies of interstellar vehicles should assume the lowest plausible density when considering braking devices, which rely on transferring momentum from the vehicle to the surrounding medium, but the highest plausible densities when considering possible damage caused by the impact of the vehicle with interstellar material. Some suggestions for working values of these parameters are provided. This paper is a submission of the Project Icarus Study Group.     

Implementing international co-operation in space exploration

This article discusses the outcomes of an April 2005 workshop held at ISU in Strasbourg. Experts sought to tailor an international co-ordination mechanism that would achieve the classical benefits of international co-operation for the unique venture of space exploration. The mechanism they developed provides a permanent forum for those with vested interests in exploration (currently space agencies in key spacefaring nations) to exchange information about national plans and activities so as to build confidence in one another's programs and, to the extent they choose, to develop beneficial interdependencies. The product of this co-ordination effort would be a consolidated international exploration roadmap that would both inform and reflect national program decisions. The co-ordination mechanism would simultaneously involve, but in less central roles, other important interested parties (industry, the science community, other countries without current exploration programs), whose advice is important to the development of a consolidated roadmap. Recognizing that the stakeholders in exploration will almost certainly evolve over time, the mechanism also presents the flexibility to accommodate new players (e.g. companies and countries not yet with investments in exploration) in more central roles as they become stakeholders with vested interests in exploration.     

The Cassini Ultraviolet Imaging Spectrograph Investigation

The Cassini Ultraviolet Imaging Spectrograph (UVIS) is part of the remote sensing payload of the Cassini orbiter spacecraft. UVIS has two spectrographic channels that provide images and spectra covering the ranges from 56 to 118 nm and 110 to 190 nm. A third optical path with a solar blind CsI photocathode is used for high signal-to-noise-ratio stellar occultations by rings and atmospheres. A separate Hydrogen Deuterium Absorption Cell measures the relative abundance of deuterium and hydrogen from their Lyman-α emission. The UVIS science objectives include investigation of the chemistry, aerosols, clouds, and energy balance of the Titan and Saturn atmospheres; neutrals in the Saturn magnetosphere; the deuterium-to-hydrogen (D/H) ratio for Titan and Saturn; icy satellite surface properties; and the structure and evolution of Saturn’s rings.This revised version was published online in July 2005 with a corrected cover date.     

Potential of laser-induced ablation for future space applications

This paper surveys recent and current advancements of laser-induced ablation technology for space-based applications and discusses ways of bringing such applications to fruition. Laser ablation is achieved by illuminating a given material with a laser light source. The high surface power densities provided by the laser enable the illuminated material to sublimate and ablate. Possible applications include the deflection of Near Earth Objects – asteroids and comets – from an Earth-impacting event, the vaporisation of space structures and debris, the mineral and material extraction of asteroids and/or as an energy source for future propulsion systems. This paper will discuss each application and the technological advancements that are required to make laser-induced ablation a practical process for use within the space arena. Particular improvements include the efficiency of high power lasers, the collimation of the laser beam (including beam quality) and the power conversion process. These key technological improvements are seen as strategic and merit greater political and commercial support.     

Michelson Interferometer for Global High-Resolution Thermospheric Imaging (MIGHTI): Monolithic Interferometer Design and Test

The design and laboratory tests of the interferometers for the Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) instrument which measures thermospheric wind and temperature for the NASA-sponsored Ionospheric Connection (ICON) Explorer mission are described. The monolithic interferometers use the Doppler Asymmetric Spatial Heterodyne (DASH) Spectroscopy technique for wind measurements and a multi-element photometer approach to measure thermospheric temperatures. The DASH technique and overall optical design of the MIGHTI instrument are described in an overview followed by details on the design, element fabrication, assembly, laboratory tests and thermal control of the interferometers that are the heart of MIGHTI.     

Michelson Interferometer for Global High-Resolution Thermospheric Imaging (MIGHTI): Instrument Design and Calibration

The Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) instrument was built for launch and operation on the NASA Ionospheric Connection Explorer (ICON) mission. The instrument was designed to measure thermospheric horizontal wind velocity profiles and thermospheric temperature in altitude regions between 90 km and 300 km, during day and night. For the wind measurements it uses two perpendicular fields of view pointed at the Earth’s limb, observing the Doppler shift of the atomic oxygen red and green lines at 630.0 nm and 557.7 nm wavelength. The wavelength shift is measured using field-widened, temperature compensated Doppler Asymmetric Spatial Heterodyne (DASH) spectrometers, employing low order échelle gratings operating at two different orders for the different atmospheric lines. The temperature measurement is accomplished by a multichannel photometric measurement of the spectral shape of the molecular oxygen A-band around 762 nm wavelength. For each field of view, the signals of the two oxygen lines and the A-band are detected on different regions of a single, cooled, frame transfer charge coupled device (CCD) detector. On-board calibration sources are used to periodically quantify thermal drifts, simultaneously with observing the atmosphere. The MIGHTI requirements, the resulting instrument design and the calibration are described.     

The integrated applications promotion: A new field of action for the European Space Agency

Since ESA's establishment the context in which it operates has evolved greatly, from one of development of technologies and general competence to one of responding to the needs of an increasingly wide range of users, many of whose requirements straddle several applications categories. The IAP programme is ESA's response to this challenge, aimed at fostering the growth of a downstream industry, creating a market for the space industry and serving economic growth overall. The programme's structure and the platforms themselves are described and the programme's achievements and prospects presented. Its success testifies to ESA's continuing ability to adapt to changing environments and operate effectively in new sectors.