ASSURE: a model for the simulation of urban expansion and intra-urban social segregation

Numerous cities in developing regions worldwide are expanding at a tremendous rate. This requires adequate strategies to address the needs of these growing cities with diverse populations. Nonetheless, the development of urban policies is often hampered by the lack of reliable data or insight in the socio-spatial dynamics of this urban expansion. This paper therefore presents ASSURE, a spatially and temporally explicit model that can simulate urban growth and intra-urban social segregation, taking into account alternative policy strategies and expected social dynamics. The model has a flexible structure that allows incorporating specific city conditions that influence residential decision-making and adapting the simulation to the data available. This, in combination with the transparent model structure, makes ASSURE a potentially valuable decision support tool for urban planning. The potential is demonstrated with an example where the urban growth of and social segregation in Kampala (Uganda) is simulated based on (semi-)quantitative and qualitative data for ca. 800 households collected through interviews. The results of the simulations show that depending on the scenario, the spatial segregation and accessibility problems will evolve highly differently.     

Ten Years of Development of Equipment for Measurement of Atmospheric Radioactive Xenon for the Verification of the CTBT

Atmospheric measurement of radioactive xenon isotopes (radioxenon) plays a key role in remote monitoring of nuclear explosions, since it has a high capability to capture radioactive debris for a wide range of explosion scenarios. It is therefore a powerful tool in providing evidence for nuclear testing, and is one of the key components of the verification regime of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The reliability of this method is largely based on a well-developed measurement technology. In the 1990s, with the prospect of the build-up of a monitoring network for the CTBT, new development of radioxenon equipment started. This article summarizes the physical and technical principles upon which the radioxenon technology is based and the advances the technology has undergone during the last 10 years. In contrast to previously used equipment, which was manually operated, the new generation of radioxenon monitoring equipment is designed for automated and continuous operation in remote field locations. Also the analytical capabilities of the equipment were strongly enhanced. Minimum detectable concentrations of the recently developed systems are well below 1 mBq/m³ for the key nuclide ¹³³Xe for sampling periods between 8 and 24 h. All the systems described here are also able to separately measure with low detection limits the radioxenon isotopes ^131mXe, ^133mXe and ¹³⁵Xe, which are also relevant for the detection of nuclear tests. The equipment has been extensively tested during recent years by operation in a laboratory environment and in field locations, by performing comparison measurements with laboratory type equipment and by parallel operation. These tests demonstrate that the equipment has reached a sufficiently high technical standard for deployment in the global CTBT verification regime.     

Creating Surface Flux Maps from Airborne Measurements: Application to the Mackenzie Area GEWEX Study MAGS 1999

The objective of this study is to produce two-dimensional maps of the sensible and the latent heat fluxes from airborne measurements, based on the analysis of a flight pattern, called grid flights. A footprint model with along-wind and cross-wind components was used to project the measured fluxes onto the surface map. The method was applied to measurements over Arctic tundra during the Mackenzie Area GEWEX (Global Energy and Water Cycle Experiment) Study (MAGS) 1999. The resulting flux estimates were computed by integration of a wavelet transform, and corrected for long wavelength losses using information from 100 km long regional runs that were conducted close to the grid flights. The random flux error was estimated based on the flight length that is represented in each map element, and a map resolution of 3 × 3 km was chosen in order to keep the average random error of the latent heat flux below 25%. The random error of the sensible heat flux was smaller by a factor of 1.4 on average. An analysis of airborne flux measurements at different altitudes showed no significant increase of flux estimates for measurement heights below 90 m. Thus, the fluxes measured at heights between 48 and 64 m were not corrected for vertical flux divergence. The resulting flux maps provide quantitative two-dimensional estimates of the energy exchange between the surface and the atmosphere during the snow melt period in an Arctic environment, which are well-suited for calibration and validation of numerical models.     

Evolution of contourite systems in the late Cretaceous Chalk Sea along the Tornquist Zone

Based on integration of seismic reflection and well data analysis this study examines two major contourite systems that developed during the late Cretaceous in the southern Baltic Sea. The evolution of these Chalk Sea contourite systems between the Kattegat and the southern Baltic Sea started when Turonian to Campanian inversion tectonics overprinted the rather flat sea floor of the epeiric Chalk Sea. The Tornquist Zone and adjacent smaller blocks were uplifted and formed elongated obstacles that influenced the bottom currents. As a consequence of the inversion, the sea floor west of the Tornquist Zone tilted towards the north‐east, creating an asymmetrical sub‐basin with a steep marginal slope in the north‐east and a gentle dipping slope in the south‐west. A south‐east directed contour current emerged in the Coniacian or Santonian along the south‐western basin margin, creating contourite channels and drifts. The previously studied contourite system offshore Stevns Klint is part of this system. A second, deeper and north‐west directed counter‐flow emerged along and parallel to the Tornquist Zone in the later Campanian, but was strongest in the Maastrichtian. This bottom current moderated the evolution of a drift‐moat system adjacent to the elevated Tornquist Zone. The near surface Alnarp Valley in Scania represents the Danian palaeo‐moat that linked the Pomeranian Bay with the Kattegat. The previously studied contourite system in the Kattegat represents the north‐western prolongation of this system. This study links previous observations from the Kattegat and offshore Stevns Klint to the here inferred two currents, a more shallow, south‐east directed and a deeper, north‐west directed flow.     

Routine analysis of sediment pore water of high ionic strength

Pore water of sediments plays an important role in aquatic systems as mediator and as the reactive zone between the sediment and surface water. Sediment pore waters with high ionic strength from acidified pit lakes were investigated to obtain information about the influence on the lake water quality. The analysis of soluble reactive phosphorus, nitrate, ammonium, silica, dissolved organic carbon, ferrous iron, sulfate, chloride, sodium, potassium, calcium, magnesium, manganese, and total dissolved iron was predetermined as the dataset required for evaluation of water quality. The data collection procedure was optimised by designing a methodology for stabilisation, dilution of pore water samples and adaptation of analytical methods. The developed methodology was evaluated with respect to the effort required in the laboratory under routine conditions. In the first round of analyses, 72% of 638 individual analyses from a random selection of pore water profiles were found to be within the calibration ranges. Remedial actions to handle the remaining 28% of invalid analytical results are exemplified. Differences between comparative analyses of some ions by continuous flow analysis, ion chromatography, and atomic emission spectroscopy were evaluated. The majority of results measured by ion chromatography differed on a highly significant level from results measured by atomic emission spectroscopy. Possible reasons, originating from the extreme sample matrix, are discussed. Finally, the designed methodology and the results of the method comparison are used to recommend the selection of analytical methods under specific conditions.     

Monitoring the Dynamics of the Ionosphere–Plasmasphere System by Ground-Based ULF Wave Observations

Cross-spectral analysis of ULF wave measurements recorded at ground magnetometer stations closely spaced in latitude allows accurate determinations of magnetospheric field line resonance (FLR) frequencies. This is a useful tool for remote sensing temporal and spatial variations of the magnetospheric plasma mass density. The spatial configuration of the South European GeoMagnetic Array (SEGMA, 1.56 <  L <  1.89) offers the possibility to perform such studies at low latitudes allowing to monitor the dynamical coupling between the ionosphere and the inner plasmasphere. As an example of this capability we present the results of a cross-correlation analysis between FLR frequencies and solar EUV irradiance (as monitored by the 10.7-cm solar radio flux F10.7) suggesting that changes in the inner plasmasphere density follow the short-term (27-day) variations of the solar irradiance with a time delay of 1–2 days. As an additional example we present the results of a comparative analysis of FLR measurements, ionospheric vertical soundings and vertical TEC measurements during the development of a geomagnetic storm.