Location Based Social Networks – Definition,Current State of the Art and Research Agenda

The growing penetration of GPS equipped smartphones allowing users to constantly share geographic information on their current whereabouts has led the way to an augmentation of existing Social Network Sites with location‐based features or the creation of new ones exclusively around geographic information. Within these Location Based Social Networks vast amounts of geographic information are allocated, which attracted the attention of researchers with various scientific backgrounds. This article presents a comprehensive definition of this special type of Social Network Site and an overview of research activities, which are currently conducted using the data. Finally, a research agenda for GIScience is drawn from existing research directions.     

The variability of the large-amplitude internal wave field on the Australian North West Shelf

Observations are presented of large-amplitude internal waves (LAIWs) generated by the steepening of the internal tide on the Australian North West Shelf (NWS) over a 4-month period extending from strongly stratified summer conditions to weakly stratified winter conditions. The observations are from a site in water depth of 124 m where current and temperature measurements were made from a fixed vertical mooring and a benthic L-shaped spatial array. The observations show the LAIWs at this site to be characterized by strong seasonal variability, with energetic LAIWs of depression being dominant during summer and weaker LAIWs of elevation being dominant during the winter months as the stratification weakens, the upper mixed layer deepens, and the thermocline is close to the bottom. Waves were also seen to propagate from a range of directions towards the observation site. Modeling using the Regional Ocean Modeling System (ROMS v2.1) revealed that internal tide generation in the area occurred at water depths of between 400 and 600 m along an arc of approximately 120 km in length, some 70 km to the northwest of our experimental site. The results demonstrate both the 3D nature as well as the seasonal variation of the LAIW field.     

Present and Future Observing Trends in Atmospheric Magnetoseismology

With modern imaging and spectral instruments observing in the visible, EUV, X-ray, and radio wavelengths, the detection of oscillations in the solar outer atmosphere has become a routine event. These oscillations are considered to be the signatures of a wave phenomenon and are generally interpreted in terms of magnetohydrodynamic (MHD) waves. With multiwavelength observations from ground- and space-based instruments, it has been possible to detect waves in a number of different wavelengths simultaneously and, consequently, to study their propagation properties. Observed MHD waves propagating from the lower solar atmosphere into the higher regions of the magnetized corona have the potential to provide excellent insight into the physical processes at work at the coupling point between these different regions of the Sun. High-resolution wave observations combined with forward MHD modeling can give an unprecedented insight into the connectivity of the magnetized solar atmosphere, which further provides us with a realistic chance to reconstruct the structure of the magnetic field in the solar atmosphere. This type of solar exploration has been termed atmospheric magnetoseismology. In this review we will summarize some new trends in the observational study of waves and oscillations, discussing their origin and their propagation through the atmosphere. In particular, we will focus on waves and oscillations in open magnetic structures (e.g., solar plumes) and closed magnetic structures (e.g., loops and prominences), where there have been a number of observational highlights in the past few years. Furthermore, we will address observations of waves in filament fibrils allied with a better characterization of their propagating and damping properties, the detection of prominence oscillations in UV lines, and the renewed interest in large-amplitude, quickly attenuated, prominence oscillations, caused by flare or explosive phenomena.     

Resonantly Damped Surface and Body MHD Waves in a Solar Coronal Slab with Oblique Propagation

The theory of magnetohydrodynamic (MHD) waves in solar coronal slabs in a zero-β configuration and for parallel propagation of waves does not allow the existence of surface waves. When oblique propagation of perturbations is considered, both surface and body waves are able to propagate. When the perpendicular wavenumber is larger than a certain value, the body kink mode becomes a surface wave. In addition, a sausage surface mode is found below the internal cutoff frequency. When nonuniformity in the equilibrium is included, surface and body modes are damped by resonant absorption. In this paper, first, a normal-mode analysis is performed and the period, the damping rate, and the spatial structure of the eigenfunctions are obtained. Then, the time-dependent problem is solved, and the conditions under which one or the other type of mode is excited are investigated.     

Is area affected by flood or stagnant water independently associated with poorer health outcomes in urban slums of Dhaka and adjacent rural areas?

This study investigated the association of flood/stagnant water (FSW) with various health outcomes among respondents living in urban slums of Dhaka and adjacent rural areas. We also assessed the differences of individual-, household- and area-level characteristics between the FSW-affected and non-affected areas. Bangladesh as a whole and slums in the megacity of Dhaka in particular are severely affected by the FSW. Data were collected from 3,207 subjects (aged 10+ years) through baseline surveys conducted in March 2008 and 2009. Twelve big slums in Dhaka and three adjacent villages were selected as study areas. Face-to-face interviews using a multidimensional pre-tested questionnaire were conducted by the trained university graduates. We performed various types of analyses ranging from the simple frequency analysis to the multivariable-adjusted logistic regression modelling. Our empirical findings suggest that slums were more affected by the FSW as compared to the rural areas. People living in the FSW-affected areas were more vulnerable in terms of individual-, household- and area-level characteristics than non-affected people. Age was also significantly associated with various health outcomes. According to multivariable analyses controlled for various factors, the FSW-affected people reported significantly higher likelihoods of health symptoms (namely fever, cold/cough, weakness), communicable diseases (namely diarrhoea and gastric disease) and poor mental well-being as compared to the non-affected people. Only the burden of non-communicable diseases was lower in the FSW-affected areas than the non-affected areas. Our findings lead us to conclude that the FSW-affected area is an independent risk factor for various physical and mental health problems. Urban slums are more affected than rural areas by the FSW. Therefore, we underscore the necessities of well-designed and comprehensive public health interventions focusing on individual, community and higher levels of interventions to reduce the FSW-related health and other consequences among the people living in the FSW-affected areas and urban slums in the rapidly growing city of Dhaka, Bangladesh.     

A parcel formulation of Hamiltonian layer models

Starting from the three-dimensional hydrostatic primitive equations, we derive Hamiltonian N-layer models with isentropic tropospheric and isentropic or isothermal stratospheric layers. Our construction employs a new parcel Hamiltonian formulation which describes the fluid as a continuum of Hamiltonian ordinary differential equations bound together by integral transport laws. In particular, we show that this parcel Hamiltonian structure is compatible with the stacking of layers under isentropic or isothermal constraints. The appeal of the parcel formulation is the simplification of various calculations, in particular the derivation of the continuum Poisson bracket and the proof of the Jacobi identity. A comparison and connection is made between the Hamiltonian dynamics of fluid parcels and the Hamiltonian system of partial differential equations. The parcel formulation can be seen as a precursor and tool for the study of Hamiltonian numerical schemes.     

Spatiotemporal Dynamics of a Páramo Ecosystem in the Northern Ecuadorian Andes 1988-2007

Páramo is a term used to describe tropical alpine vegetation between the continuous timberline and the snow line in the Northern Andes. Páramo environments provide important species habitat and ecosystem services. Changes in spatial extent of the páramo ecosystem at Pambamarca in the Central Cordillera of the northern Ecuadorian Andes were analysed using multi-temporal Landsat TM/ETM+ satellite data. The region suffered a loss of 1826.6 ha or 20% of the total area at a rate of 100 ha/annum during 1988-2007 period. It is found that permanent páramo cover decreased from 8350 ha in 1988 to 5864 ha in 2007 at a fairly constant rate(R2=0.94). This loss is attributed to expansion of commercial agriculture and floriculture in the valleys coupled with increased population pressure. Land at higher elevations has been cleared for small scale agriculture. Loss of the páramo ecosystem will exert a number of negative impacts on ecosystem services and livelihoods of the local population at Pambamarca.     

Rapid orbit determination of LEO satellites using IGS clock and ephemeris products

Different types of GPS clock and orbit data provided by the International GPS Service (IGS) have been used to assess the accuracy of rapid orbit determination for satellites in low Earth orbit (LEO) using spaceborne GPS measurements. To avoid the need for reference measurements from ground-based reference receivers, the analysis is based on an undifferenced processing of GPS code and carrier-phase measurements. Special attention is therefore given to the quality of GPS clock data that directly affects the resulting orbit determination accuracy. Interpolation of clock data from the available 15 min grid points is identified as a limiting factor in the use of IGS ultra-rapid ephemerides. Despite this restriction, a 10-cm orbit determination accuracy can be obtained with these products data as demonstrated for the GRACE-B spacecraft during selected data arcs between 2002 and 2004. This performance may be compared with a 5-cm orbit determination accuracy achievable with IGS rapid and final products using 5 min clock samples. For improved accuracy, high-rate (30 s) clock solutions are recommended that are presently only available from individual IGS centers. Likewise, a reduced latency and more frequent updates of IGS ultra-rapid ephemerides are desirable to meet the requirements of upcoming satellite missions for near real-time and precise orbit determination.     

Efficient GOCE satellite gravity field recovery based on least-squares using QR decomposition

We develop and apply an efficient strategy for Earth gravity field recovery from satellite gravity gradiometry data. Our approach is based upon the Paige-Saunders iterative least-squares method using QR decomposition (LSQR). We modify the original algorithm for space-geodetic applications: firstly, we investigate how convergence can be accelerated by means of both subspace and block-diagonal preconditioning. The efficiency of the latter dominates if the design matrix exhibits block-dominant structure. Secondly, we address Tikhonov-Phillips regularization in general. Thirdly, we demonstrate an effective implementation of the algorithm in a high-performance computing environment. In this context, an important issue is to avoid the twofold computation of the design matrix in each iteration. The computational platform is a 64-processor shared-memory supercomputer. The runtime results prove the successful parallelization of the LSQR solver. The numerical examples are chosen in view of the forthcoming satellite mission GOCE (Gravity field and steady-state Ocean Circulation Explorer). The closed-loop scenario covers 1 month of simulated data with 5 s sampling. We focus exclusively on the analysis of radial components of satellite accelerations and gravity gradients. Our extensions to the basic algorithm enable the method to be competitive with well-established inversion strategies in satellite geodesy, such as conjugate gradient methods or the brute-force approach. In its current development stage, the LSQR method appears ready to deal with real-data applications.     

In-flight performance analysis of the CHAMP BlackJack GPS Receiver

JPL's BlackJack receiver currently represents the most widely used geodetic grade GPS receiver for space applications. Using data from the CHAMP science mission, the in-flight performance of the BlackJack receiver has been assessed and the impact of various software updates performed during the 2.5 years since launch is described. Key aspects of the study comprise the channel allocation, anomalous data points, and the noise level of the code and carrier data. In addition, it has been demonstrated that the code measurements collected onboard the CHAMP satellite are notably affected by multipath errors in the aft-looking hemisphere, which can be attributed to cross-talk between the occultation antenna string and the primary precise orbit determination antenna. For carrier smoothed 10 s normal points, the code noise itself varies between a minimum of 5 cm at high elevations and 0.5 m (C/A) to 1.0 m (P₁, P₂) at 10° elevation. Carrier-phase data exhibit representative errors of 0.2 to 2.5 mm. The results of the CHAMP GPS data analysis contribute to a better understanding and possible improvement of the BlackJack receiver and support the design of optimal data editing and weighting strategies in precise orbit determination applications.