Image Sources for Informal Settlement Management

Informal settlements are a common feature of developing countries. In South Africa the improvement of living conditions in these settlements and the upgrading to formal housing types are regarded as being of central importance to the nation's development. Effective settlement improvement and upgrading activities, which we here term "management", require adequate spatial data. To date, the acquisition of spatial models of informal settlements has been based on conventional mapping techniques, and mostly on photogrammetry. Data are compiled using analogue or analytical methods. These are manual and hence require both considerable expertise and expensive equipment. Moreover, these methods are uneconomical over the often relatively small, densely populated areas covered by informal settlements and are also too expensive to employ with a regularity required to support such tasks as change detection. Alternative imaging sources and mapping techniques are therefore needed.
In this article we examine the problem of spatial information acquisition for informal settlement management from three perspectives: spatial information requirements, the role which imagery can play in satisfying these spatial information requirements, and effective imaging options. We focus on the potential of high resolution satellite imaging, small format digital aerial imagery and digital multispectral video systems for rapid mapping. We also discuss the example of automated shack extraction from aerial imagery.     

Characterization of the chemical structures of natural and synthetic aluminosilicate gels and sols by infrared spectroscopy

Infrared spectra in the 300–1400 cm^?1 region indicate that the non-crystalline products of interaction between hydroxyaluminium species and orthosilicic acid in dilute aqueous solutions of pH < 5 differ markedly in structure from those formed in near-neutral and alkaline solutions of pH > 6. The compound formed in acid solution has an infrared spectrum similar to imogolite, and is termed proto-imogolite; like imogolite, it contains orthosilicate groups and 6-coordinated aluminium, and has an ideal Si:Al ratio of around 0.5, but it can incorporate some excess alumina or silica and it does not have the regular tubular structure of imogolite. Compounds formed in alkaline solutions that are not too dilute have infrared spectra resembling the feldspathoid group of minerals and are termed hydrous feldspathoids. They incorporate a condensed tetrahedral framework with an Si:Al ratio greater than one, but can also contain 6-coordinated aluminium.Natural allophanes of the proto-imogolite and hydrous feldspathoid types exist. The allophane of weathered pumice, however, contains a condensed silicate anion that incorporates little tetrahedral aluminium. Proto-imogolite forms stable sols at pH < 5 and must play an important role in the transport of aluminium in acidic natural waters containing dissolved silica.     

The dependence of the climate sensitivity on convective parametrization: statistical evaluation

Two sensitivity experiments, in which CO₂ is instantaneously doubled, have been performed with a general circulation model to determine the influence of the convective parametrization on simulated climate change. We have examined the spatial structure of changes in the annual mean and annual cycle for surface temperature and precipitation for both experiments; similarly we have examined changes in the variance for these two fields. We have also computed a range of test statistics in order to obtain reliable measures of the signal-to-noise ratio in the climate change signal from each experiment. We have computed test statistics for the entire globe and for five different region and we contrast the global response with the response in the Australian region taken as a representative sample.We find that the highest signal-to-noise ratios in the change from 1 * CO₂ to 2 * CO₂ are for the change in surface temperature for both experiments with little difference in the global averages between the experiments. Globally averaged precipitation shows a greater noise level but perhaps the greatest contrast between experiments. There are generally significant increases in the temporal and spatial variability of precipitation in the change from the 1 * CO₂ to 2 * CO₂ and with some differences apparent between the two experiments. The temporal variability of surface temperature does not change significantly in any of the 2 * CO₂ cases, and there is little difference between the experiments. There is a significant decrease in the spatial variability of surface temperature in all 2 * CO₂ experiments in all cases and with significant differences in the seasonal variations between different experiments. The spatial variability of precipitation increases in all 2 * CO₂ cases and also with substantial differences in the seasonal variations between the experiments. There are accompanying significantly different spatial pattern correlations for both surface temperature and precipitation. In general we find that the global changes are fairly robust with the differences associated with convective parametrization schemes being very small. However, at the regional level, there are marked differences between experiments with changes both in the means and in the spatial and temporal variances but often with low levels of significance.     

Source structure and dynamics of Pc 1 pulsations at low latitudes

Structured Pc 1 signals propagate in the ionospheric F2 region duct from their secondary sources at high latitudes to lower latitudes. Propagation directions to low latitude stations can be inferred from measurements of polarization parameters. The analysis of five events recorded at two low latitude stations (L = 1.9) are presented. Direction of arrival measurements are used to investigate the spatial and temporal structure of Pc 1 sources. Results show a close relationship between the structure of events identified in the frequency-time representation and direction of arrival measurement patterns. Multiple sources are sometimes indicated.     

Spatial and temporal correlation of underwater sunlight fluctuations in the sea

A submerged linear array of photodetectors was used to measure sunlight irradiance fluctuations caused by ocean surface waves. Decorrelation times and lengths were found to be functions of depth. It was also found that the sensor depth selects a dominant temporal frequency from the random surface waves.     

Adsorption of As on hydroxy-Fe-montmorillonite complexes

DOI: 10.1360/03yd0553 Arsenic, a toxic element, is ubiquitous in the earth’s crust and may lead to health risks for humans. This may come about as a result of oxidative weathering and dissolution of As-containing minerals, use of ar-senical pesticides, excess use of some fertilizers and from mine drainage, smelter wastes and agricultural drainage water from certain arid regions. The dis-solved inorganic arsenic is transported in surface or2156 Science in China Ser. D Earth Sciences groun…     

Responses of the polar ionosphere to the Bastille Day solar event

Simultaneous observations at Zhongshan Station, Antarctica, are presented for the interval of 13–17 July 2000 to show responses of the polar ionosphere to the Bastille Day (14 July 2000) solar event. The polar ionosphere was highly disturbed, as shown by frequently large deviations of the geomagnetic H-component, large riometer absorption events and strong ULF waves. Associated with the huge solar proton event produced by the X5/3B flare, a polar cap absorption (PCA) was observed. It began at ∼ 10:40 UT on 14 July and ended at ∼ 19:40 UT on 17 July. Superposed on it, there was a large absorption event with a peak of 26 dB, starting at ∼ 03:00 UT and ending at ∼ 11:10 UT on 15 July. This kind of absorption was probably produced by an intense `cloud of energetic electrons' during an auroral substorm. The ULF waves were very intense during the main phase and the recovery phase of the severe magnetic storm on 15 and 16 July. The ionospheric absorption was so strong that the digisonde signal was blacked out most of the time. The ionosphere returned to normal in the afternoon on 17 July.