4,457 research outputs found
Deterministic-statistical model coupling in a DSS for river-basin management
This paper presents a method for appropriate coupling of deterministic and statistical models. In the decision-support system for the Elbe river, a conceptual rainfall-runoff model is used to obtain the discharge statistics and corresponding average number of flood days, which is a key input variable for a rule-based model for floodplain vegetation. The required quality of the discharge time series cannot be determined by a sensitivity analysis because a deterministic model is linked to a statistical model. To solve the problem, artificial discharge time series are generated that mimic the hypothetical output of rainfall-runoff models of different accuracy. The results indicate that a feasible calibration of the rainfall-runoff model is sufficient to obtain consistency with the vegetation model in view of its sensitivity to changes in the number of flood days in the floodplains
The influence of forward-scattered light in transmission measurements of (exo)planetary atmospheres
[Abridged] The transmission of light through a planetary atmosphere can be
studied as a function of altitude and wavelength using stellar or solar
occultations, giving often unique constraints on the atmospheric composition.
For exoplanets, a transit yields a limb-integrated, wavelength-dependent
transmission spectrum of an atmosphere. When scattering haze and/or cloud
particles are present in the planetary atmosphere, the amount of transmitted
flux not only depends on the total optical thickness of the slant light path
that is probed, but also on the amount of forward-scattering by the scattering
particles. Here, we present results of calculations with a three-dimensional
Monte Carlo code that simulates the transmitted flux during occultations or
transits. For isotropically scattering particles, like gas molecules, the
transmitted flux appears to be well-described by the total atmospheric optical
thickness. Strongly forward-scattering particles, however, such as commonly
found in atmospheres of Solar System planets, can increase the transmitted flux
significantly. For exoplanets, such added flux can decrease the apparent radius
of the planet by several scale heights, which is comparable to predicted and
measured features in exoplanet transit spectra. We performed detailed
calculations for Titan's atmosphere between 2.0 and 2.8 micron and show that
haze and gas abundances will be underestimated by about 8% if
forward-scattering is ignored in the retrievals. At shorter wavelengths, errors
in the gas and haze abundances and in the spectral slope of the haze particles
can be several tens of percent, also for other Solar System planetary
atmospheres. We also find that the contribution of forward-scattering can be
fairly well described by modelling the atmosphere as a plane-parallel slab.Comment: Icarus, accepted for publicatio
Information gap for classical and quantum communication in a Schwarzschild spacetime
Communication between a free-falling observer and an observer hovering above
the Schwarzschild horizon of a black hole suffers from Unruh-Hawking noise,
which degrades communication channels. Ignoring time dilation, which affects
all channels equally, we show that for bosonic communication using single and
dual rail encoding the classical channel capacity reaches a finite value and
the quantum coherent information tends to zero. We conclude that classical
correlations still exist at infinite acceleration, whereas the quantum
coherence is fully removed.Comment: 5 pages, 4 figure
The orbital motion, absolute mass, and high-altitude winds of exoplanet HD209458b
For extrasolar planets discovered using the radial velocity method, the
spectral characterization of the host star leads to a mass-estimate of the star
and subsequently of the orbiting planet. In contrast, if also the orbital
velocity of the planet would be known, the masses of both star and planet could
be determined directly using Newton's law of gravity, just as in the case of
stellar double-line eclipsing binaries. Here we report on the detection of the
orbital velocity of extrasolar planet HD209458b. High dispersion ground-based
spectroscopy during a transit of this planet reveals absorption lines from
carbon monoxide produced in the planet atmosphere, which shift significantly in
wavelength due to the change in the radial component of the planet orbital
velocity. These observations result in a mass determination of the star and
planet of 1.00+-0.22 Msun and 0.64+-0.09 Mjup respectively. A ~2 km/sec
blueshift of the carbon monoxide signal with respect to the systemic velocity
of the host star suggests the presence of a strong wind flowing from the
irradiated dayside to the non-irradiated nightside of the planet within the
0.01-0.1 mbar atmospheric pressure range probed by these observations. The
strength of the carbon monoxide signal suggests a CO mixing ratio of 1-3x10-3
in this planet's upper atmosphere.Comment: 11 Pages main article and 6 pages suppl. information: A final, edited
version appears in the 24 May 2010 issue of Natur
Search for water in a super-Earth atmosphere: High-resolution optical spectroscopy of 55 Cancri e
We present the analysis of high-resolution optical spectra of four transits
of 55Cnc e, a low-density, super-Earth that orbits a nearby Sun-like star in
under 18 hours. The inferred bulk density of the planet implies a substantial
envelope, which, according to mass-radius relationships, could be either a
low-mass extended or a high-mass compact atmosphere. Our observations
investigate the latter scenario, with water as the dominant species. We take
advantage of the Doppler cross-correlation technique, high-spectral resolution
and the large wavelength coverage of our observations to search for the
signature of thousands of optical water absorption lines. Using our
observations with HDS on the Subaru telescope and ESPaDOnS on the
Canada-France-Hawaii Telescope, we are able to place a 3-sigma lower limit of
10 g/mol on the mean-molecular weight of 55Cnc e's water-rich (volume mixing
ratio >10%), optically-thin atmosphere, which corresponds to an atmospheric
scale-height of ~80 km. Our study marks the first high-spectral resolution
search for water in a super-Earth atmosphere and demonstrates that it is
possible to recover known water-vapour absorption signals, in a nearby
super-Earth atmosphere, using high-resolution transit spectroscopy with current
ground-based instruments.Comment: Accepted for publication in ApJ 12 pages, 9 figures. Email:
[email protected]; [email protected]; [email protected];
[email protected]; [email protected]
Integrating Earth observation with field data and model simulations the ISECA project
The cross-border cooperation ISECA (Information System on the Eutrophication of our CoAstal Seas) is a demonstration project to improve the exchange of data and scientific insights related to the eutrophication of coastal waters in the English Channel and the Southern North Sea. The Web-based Application Server (WAS) demonstrates the added value of combining earth observation and in-situ data on marine eutrophication with the outcomes of model simulations. The WAS allows visualization of Earth Observation data hosted by partner institutes and provides access to map layers showing different model scenarios, as well as functionalities for up- and downloading of in-situ data, including trend analysis. The envisaged en-users include the scientific community, marine managers, and general public
Appropriate Accuracy of Models for Decision-Support Systems: Case Example for the Elbe River Basin
Given the growing complexity of water-resources management there will be an increasing need\ud
for integrated tools to support policy analysis, communication, and research. A key aspect of the design is the\ud
combination of process models from different scientific disciplines in an integrated system. In general these\ud
models differ in sensitivity and accuracy, while non-linear and qualitative models can be present. The current\ud
practice is that the preferences of the designers of a decision-support system, and practical considerations\ud
such as data availability guide the selection of models and data. Due to a lack of clear scientific guidelines the\ud
design becomes an ad-hoc process, depending on the case study at hand, while selected models can be overly\ud
complex or too coarse for their purpose. Ideally, the design should allow for the ranking of selected\ud
management measures according to the objectives set by end users, without being more complex than\ud
necessary. De Kok and Wind [2003] refer to this approach as appropriate modeling. A good case example is\ud
the ongoing pilot project aiming at the design of a decision-support system for the Elbe river basin. Four\ud
functions are accounted for: navigability, floodplain ecology, flooding safety, and water quality. This paper\ud
concerns the response of floodplain biotope types to river engineering works and changes in the flooding\ud
frequency of the floodplains. The HBV-D conceptual rainfall-runoff model is used to simulate the impact of\ud
climate and land use change on the discharge statistics. The question was raised how well this rainfall-runoff\ud
model should be calibrated as compared to the observed discharge data. Sensitivity analyses indicate that a\ud
value of R2 = 0.87 should be sufficient
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