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Losler M.,Agency Systems | Haas R.,Chalmers University of Technology | Eschelbach C.,Frankfurt University of Applied Sciences
Journal of Geodesy | Year: 2013

The Global Geodetic Observing System (GGOS) requires sub-mm accuracy, automated and continual determinations of the so-called local tie vectors at co-location stations. Co-location stations host instrumentation for several space geodetic techniques and the local tie surveys involve the relative geometry of the reference points of these instruments. Thus, these reference points need to be determined in a common coordinate system, which is a particular challenge for rotating equipment like radio telescopes for geodetic Very Long Baseline Interferometry. In this work we describe a concept to achieve automated and continual determinations of radio telescope reference points with sub-mm accuracy. We developed a monitoring system, including Java-based sensor communication for automated surveys, network adjustment and further data analysis. This monitoring system was tested during a monitoring campaign performed at the Onsala Space Observatory in the summer of 2012. The results obtained in this campaign show that it is possible to perform automated determination of a radio telescope reference point during normal operations of the telescope. Accuracies on the sub-mm level can be achieved, and continual determinations can be realized by repeated determinations and recursive estimation methods. © 2013 Springer-Verlag Berlin Heidelberg. Source


Creutzfeldt B.,German Research Center for Geosciences | Guntner A.,German Research Center for Geosciences | Wziontek H.,Agency Systems | Merz B.,German Research Center for Geosciences
Geophysical Journal International | Year: 2010

Temporal gravimeter observations, used in geodesy and geophysics to study the Earth's gravity field variations, are influenced by local water storage changes (WSC). At the Geodetic Observatory Wettzell (Germany), WSC in the snow pack, top soil, unsaturated saprolite and fractured aquifer are all important terms of the local water budget. In this study, lysimeter measurements are used for the first time to estimate the hydrological influence on temporal gravimeter observations. Lysimeter data are used to estimate WSC at the field scale in combination with complementary observations and a hydrological 1-D model. From these estimated WSC, we calculate the hydrological gravity response. The results are compared to other methods used in the past to correct temporal gravity observations for the local hydrological influence. Lysimeter measurements significantly improve the independent estimation of WSC and thus provide a better way of reducing the local hydrological effect from gravimeter measurements. We find that the gravity residuals are caused to a larger extent by local WSC than previously stated. At sites where temporal gravity observations are used to study geophysical processes beyond local hydrology, the installation of a lysimeter is recommended. © 2010 The Authors Journal compilation © 2010 RAS. Source


Blondell S.J.,University of Queensland | Kitter B.,University of Queensland | Griffin M.P.,Agency Systems | Durham J.,University of Queensland
AIDS and Behavior | Year: 2015

Migrants, particularly from low- and middle-income countries, are at a heightened risk of adverse HIV outcomes. HIV testing may improve these outcomes. We reviewed and synthesised studies into migrants and HIV testing (outcome variable), published between January 1997 and April 2014. Papers using quantitative, qualitative and mixed methods designs, and samples with adult (≥18 years) migrants from low- and middle-income countries in high-income countries were included in the paper. Of 3155 papers retrieved, 31 met the inclusion criteria and are included in the review. A large number of barriers and facilitators to HIV testing were identified across the individual, social and structural levels. A number of study design and methodological issues, however, inhibited a comprehensive synthesis. There is no doubt that addressing HIV testing in migrants in high-income countries is complex; however, it has important implications for individual, community and population health, and a strong, empirically based response is warranted. © 2015, Springer Science+Business Media New York. Source


Cheng B.-N.,Lincoln Laboratory | Wheeler J.,Lincoln Laboratory | Hung B.,Agency Systems
IEEE Communications Magazine | Year: 2013

The increased usage of net-centric IP applications at the tactical edge has pushed DoD communications systems to maximize bandwidth efficiency amid a limited availability of RF spectrum. One method of increasing bandwidth efficiency (especially with the desire to move to IPv6), is the use of IP header compression (IPHC) to compress headers from the network layer and above into small identifiers before sending to the link layer. Although widely used in cell phone technology, the tactical edge provides some unique challenges to traditional IPHC techniques including highly dynamic links and link conditions due to potential jamming threats and difficult environments, multi-hop scenarios due to lack of infrastructure, and a highly diverse set of radio systems lacking interoperability. In this article, we examine two common IP header compression schemes, Robust Header Compression (RFC 5225) and IP Header Compression (RFC 2507) and one experimental scheme, MANET IP header compression, and identify their current use and applicability in the tactical edge. Furthermore, we identify some challenges in implementing header compression schemes in emerging systems. © 2013 IEEE. Source


Knab J.J.,Agency Systems
IEEE Transactions on Aerospace and Electronic Systems | Year: 2012

Today, the Wideband Global SATCOM (WGS) system employs a new concept of adjusting the transponder power gain of individual links. A simple optimum method is derived for selecting these individual channel gains to minimize the amount of transponder power utilized. This new method directly solves a set of simple nonlinear equations and does not utilize any search algorithms or matrix inversions thus allowing it to be used with any number of links in a transponder. © 2006 IEEE. Source

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