Safety arguments for next generation location aware computing

Concerns over the accuracy, availability, integrity and continuity of Global Navigation Satellite Systems (GNSS) have limited the integration of GPS and GLONASS for safety-critical applications. More recent augmentation systems, such as the European Geostationary Navigation Overlay Service (EGNOS) and the North American Wide Area Augmentation System (WAAS) have begun to address these concerns. Augmentation architectures build on the existing GPS/GLONASS infrastructures to support locationbased services in Safety of Life (SoL) applications. Much of the technical development has been directed by air traffic management requirements, in anticipation of the more extensive support to be offered by GPS III and Galileo. WAAS has already been approved to provide vertical guidance against ICAO safety performance criteria for aviation applications. During the next twelve months, we will see the full certification of EGNOS for SoL applications. This paper identifies strong similarities between the safety assessment techniques used in Europe and North America. Both have relied on hazard analysis techniques to derive estimates of the Probability of Hazardously Misleading Information (PHMI). Later sections identify significant differences between the approaches adopted in application development. Integrated fault trees have been developed by regulatory and commercial organisations to consider both infrastructure hazards and their impact on non-precision RNAV/VNAV approaches using WAAS. In contrast, EUROCONTROL and the European Space Agency have developed a more modular approach to safety-case development for EGNOS. It remains to be seen whether the European or North American strategy offers the greatest support as satellite based augmentation systems are used within a growing range of SoL applications from railway signalling through to Unmanned Airborne Systems. The key contribution of this paper is to focus attention on the safety arguments that might support this wider class of location based services

TreeWatch.net : a water and carbon monitoring and modeling network to assess instant tree hydraulics and carbon status

TreeWatch.net is an initiative that has been developed to watch trees grow and function in real-time. It is a water- and carbon-monitoring and modeling network, in which high quality measurements of sap flow and stem diameter variation are collected on individual trees. Automated data processing using a cloud service enables instant visualization of water movement and radial stem growth. This can be used to demonstrate the sensitivity of trees to changing weather conditions, such as drought, heat waves, or heavy rain showers. But TreeWatch.net's true innovation lies in its use of these high precision harmonized data to also parameterize process-based tree models in real-time, which makes displaying the much needed mechanisms underlying tree responses to climate change possible. Continuous simulation of turgor to describe growth processes and long-term time series of hydraulic resistance to assess drought-vulnerability in real-time are only a few of the opportunities our approach offers. TreeWatch.net has been developed with the view to be complementary to existing forest monitoring networks and with the aim to contribute to existing dynamic global vegetation models. It provides high-quality data and real-time simulations in order to advance research on the impact of climate change on the biological response of trees and forests. Besides its application in natural forests to answer climate-change related scientific and political questions, we also envision a broader societal application of TreeWatch.net by selecting trees in nature reserves, public areas, cities, university areas, schoolyards, and parks to teach youngsters and create public awareness on the effects of changing weather conditions on trees and forests in this era of climate change

Local versus Global Search in Channel Graphs

Previous studies of search in channel graphs has assumed that the search is global; that is, that the status of any link can be probed by the search algorithm at any time. We consider for the first time local search, for which only links to which an idle path from the source has already been established may be probed. We show that some well known channel graphs may require exponentially more probes, on the average, when search must be local than when it may be global.Comment: i+13 pages, 2 figure