Use of coupled canopy structure dynamic and radiative transfer models to estimate biophysical canopy characteristics

Leaf area index (LAI) is a key variable for the understanding of several eco-physiological processes within a vegetation canopy. The LAI could thus provide vital information for the management of the environment and agricultural practices when estimated continuously over time and space thanks to remote sensing sensors.This study proposed a method to estimate LAI spatial and temporal variation based on multi-temporal remote sensing observations processed using a simple semi-mechanistic canopy structure dynamic model (CSDM) coupled with a radiative transfer model (RTM). The CSDM described the temporal evolution of the LAI as function of the accumulated daily air temperature as measured from classical ground meteorological stations.The retrieval performances were evaluated for two different data sets: first, a data set simulated by the RTM but taking into account realistic measurement conditions and uncertainties resulting from different error sources; second, an experimental data set acquired over maize crops the Blue Earth City area (USA) in 1998. Results showed that the proposed approach improved significantly the retrieval performances for LAI mainly by smoothing the residual errors associated to each individual observation. In addition it provides a way to describe in a continuous manner the LAI time course from a limited number of observations during the growth cycle.     

Mass-spring systems on the GPU

We present and analyze different implementations of mass-spring systems for interactive simulation of deformable surfaces on graphics processing units (GPUs). For the amount of springs we target, numerical time integration of spring displacements needs to be accelerated and the transfer of displaced point positions for rendering must be avoided. To fulfill these requirements, we exploit features of recent graphics accelerators to simulate spring elongation and compression on the GPU, saving displaced point masses in graphics memory, and then sending these positions through the GPU again to render the deformed surface. Two different simulation algorithms implementing scattering and gathering operations on the GPU are compared with respect to performance and numerical accuracy. We discuss GPU specific issues to be considered in simulation techniques showing similar computation and memory access patterns to mass-spring systems.     

Curvature-Driven PDE Methods for Matrix-Valued Images

Matrix-valued data sets arise in a number of applications including diffusion tensor magnetic resonance imaging (DT-MRI) and physical measurements of anisotropic behaviour. Consequently, there arises the need to filter and segment such tensor fields. In order to detect edge-like structures in tensor fields, we first generalise Di Zenzo’s concept of a structure tensor for vector-valued images to tensor-valued data. This structure tensor allows us to extend scalar-valued mean curvature motion and self-snakes to the tensor setting. We present both two-dimensional and three-dimensional formulations, and we prove that these filters maintain positive semidefiniteness if the initial matrix data are positive semidefinite. We give an interpretation of tensorial mean curvature motion as a process for which the corresponding curve evolution of each generalised level line is the gradient descent of its total length. Moreover, we propose a geodesic active contour model for segmenting tensor fields and interpret it as a minimiser of a suitable energy functional with a metric induced by the tensor image. Since tensorial active contours incorporate information from all channels, they give a contour representation that is highly robust under noise. Experiments on three-dimensional DT-MRI data and an indefinite tensor field from fluid dynamics show that the proposed methods inherit the essential properties of their scalar-valued counterparts.     

The conformal alpha shape filtration

Conformal alpha shapes are a new filtration of the Delaunay triangulation of a finite set of points in ℝ^d. In contrast to (ordinary) alpha shapes the new filtration is parameterized by a local scale parameter instead of the global scale parameter in alpha shapes. The local scale parameter conforms to the local geometry and is motivated from applications and previous algorithms in surface reconstruction. We show how conformal alpha shapes can be used for surface reconstruction of non-uniformly sampled surfaces, which is not possible with alpha shapes.     

Location Models for Augmented Environments

In this paper we describe two projects on contextualized computer systems and audio augmented environments we are currently working on at the Fraunhofer Institutes FIT and IMK. In this paper we will only focus on the world models and the augmentation layer. Both projects are based on completely different technologies, and use different representation methods and interaction facilities. While in hippie users are moving with small laptop computers or wearable computers with a small visual display, in LISTEN users will have only a wireless headphone displaying spatially rendered sound-scenes. Correspondence to: J. Goβmann, Fraunhofer-IMK, Schloss Birlinghoven, D-53754 St Augustin, Germany.     

A Microscopic Simulator for Freeway Traffic

In this contribution a micro-simulator for freeway traffic which is coupled to a stream of on-line data stemming from inductive loops is presented. In order to provide network-wide information about the current traffic state a cellular automaton traffic flow model is combined with the measured data. The framework is applied to the freeway network of North Rhine-Westphalia (NRW), where data from about 3,500 inductive loops are provided on-line minute by minute. Special attention is paid to the technical aspects of the simulation like the network structure. Results are presented and discussed.     

Market perspectives of stationary fuel cells in a sustainable energy supply system—long-term scenarios for Germany

Because of high efficiency, low environmental impacts and a potential role in transforming our energy system into a hydrogen economy, fuel cells are often considered as a key technology for a sustainable energy supply. However, the future framing conditions under which stationary fuel cells have to prove their technical and economic competitiveness are most likely characterised by a reduced demand for space heating, and a growing contribution of renewable energy sources to heat and electricity supply, which both directly limit the potential for combined heat and power generation, and thus also for fuel cells. Taking Germany as a case study, this paper explores the market potential of stationary fuel cells under the structural changes of the energy demand and supply system required to achieve a sustainable energy supply. Results indicate that among the scenarios analysed it is in particular a strategy oriented towards ambitious CO₂-reduction targets, which due to its changes in the supply structure is in a position to mobilise a market potential that might be large enough for a successful fuel cell commercialisation. However, under the conditions of a business-as-usual trajectory the sales targets of fuel cell manufacturers cannot be met.     

Quality change and mass loss of paddy during airtight storage in a ferro-cement bin in Sri Lanka

In Sri Lanka, prices for paddy fluctuate severely showing a minimum price at harvest. To benefit from higher prices, farmers strive to store paddy, but lack of facilities and poor storage management cause quantitative and qualitative losses by rodents, insects and microbial deterioration. To overcome these problems an airtight storage system, based on a ferro-cement bin, has been developed. The objective of this study was to evaluate the storage system in terms of paddy quality and mass loss. Before and after storage, samples were drawn from this bin and a control to analyse moisture content, thousand-grain mass, insect infestation, mould, germination rate and head rice yield. Additional samples were taken from different regions in the bin.Oxygen concentration dropped to 2.7% within 30 days and carbon dioxide rose to 9.1%. The change in gas composition was caused mainly by insect respiration. Ephestia cautella were found on the top layer in the bin and Sitophilus spp. and Rhyzopertha dominica in the bottom layer. The average infestation rate was 4.8 insects/kg. Most of the insects were dead at unloading. After 6 months storage, mass loss was 0.4% in the bin and 2.1% in the control. Head rice yield was 35.8% in the bin and 27.3% in the control. A significant amount of mould was found only in the control (0.85%). Germination rate, however, decreased from 85% to 0% in the airtight bin, whereas it was still 38% in the control. The study has shown that airtight ferro-cement bins provide a safe and convenient method for farmers in the tropics to preserve their harvest for later sale at a higher price. Further work is necessary to develop strategies for avoiding the decrease in germination capacity.     

Solar hydrogen

The intermittance and the geographical distribution of solar energy require means of storing and transporting it to the user's place. An ideal means of doing this is to split water in order to obtain hydrogen.Hydrogen is a carbon-free fuel which oxidizes to water as combustion product. The generated water becomes, together with renewable primary energy for splitting it, a source of clean and abundant energy in a carbon-free, natural cycle.Hydrogen is a fuel which can be transported over long distances and stored so that solar energy can be transported from energy rich countries over long distances in ships to Europe, stored underground or in containers and used in gaseous or liquid form in industry, households, power stations, motor cars and aviation.Solar energy as primary energy is discussed. A special form of it, the cheapest and by now largely available hydropower, is stressed.Techniques of hydrogen production, vectorisation and end use are discussed as well as safety aspects, costs and strategy for its implementation.