Evaluation of vegetative criteria for near-surface groundwater detection using multispectral mapping and GIS techniques in semi-arid Botswana

The critical need to consider all options in the search for groundwater in semi-arid areas has promoted work on the possible association of near-surface groundwater and vegetation characteristics using a combination of remote-sensing data and geographic information systems (GIS) techniques. Two vegetative criteria (dense woody cover and abundance of deep-rooting species) are identified as being indicative of near-surface groundwater, and their spatial distribution is tested against the location of aquifers in southeast Botswana. Vegetative criteria classes were combined in a GIS environment with the distribution of geomorphic units and bedrock geology to determine the degree of coincidence with assumed or known aquifers. Results indicate that the distribution of dense woody vegetation as mapped from Thematic Mapper imagery has some potential in identifying especially surficial but also bedrock near-surface groundwater sources in mostly naturally vegetated semi-arid areas. Dense woody cover classes tend to select aquifers in topographically higher areas while classes comprising some deep-rooting species tend to select low-lying aquifers such as those occurring in fossil valleys. Deep-rooting species, however, are less successful as a vegetative criterion. Although various technical refinements are suggested, this work shows that vegetative criteria mapping can however be used in conjunction with conventional geological/geophysical techniques to enhance the prospects for groundwater location in relatively undisturbed semi-arid areas.     

Effect of attachment configuration on the trapping efficiency of Vaseline-coated slide catchers for windblown particles

There are various types of the windblown sediment traps developed for wind tunnel and field studies. One of the main supports expected from these traps is in measuring surface dust concentrations to appropriately derive flux equations. The measurement performance and accuracy of a trap is very important and depends strictly upon the physical characteristics and the behaviors of dust grains with air flows. This paper presents the measurement results of static pressure distribution (SPD) of wind flow around Vaseline-coated slide (VCS) catchers with an aim of finding out whether or not particle trapping efficiency (η) of the VCS is related to the SPD. The SPD was evaluated by a wind reduction coefficient (R _c) in a series of wind tunnel experiments with different VCS settings which have different attachment configurations on a pole. Three VCS configurations were considered: a configuration on a circular plastic pole (CPP) and two configurations on wooden square poles (WSP₁ and WSP₂, respectively). Thus, the primary contribution of this work was to experimentally analyze the effect of the different attachment configurations on the SPD, and the secondary objective was to determine the effect of the SPD on the η. It was shown that spatial correlation and spatial pattern of the R _c were different in the surrounding area of each configuration, and ANOVA and DUNCAN tests indicated that η(s) of WSP₁, WSP₂, and CPP were different at the significant level of P ≤ 0.05 with the mean of 0.94 ± 0.09, 0.63 ± 0.14, and 1.13 ± 0.07, respectively. Additionally, the amount of PM₂₀, PM₄₀, PM₆₀, PM₈₀, and PM₁₀₀ trapped by the configurations of WSP₁, WSP₂, and CPP considerably varied depending upon the particular aerodynamic circumstances associated with every configuration.     

Temporal and spatial variability of cross-fault groundwater-level differences: the impact of fault-induced permeability reduction,precipitation and evapotranspiration

Hydrogeology Journal - Faults in the Roer Valley Rift System (Netherlands, Belgium, and Germany) act as barriers to lateral groundwater flow in unconsolidated sedimentary aquifers. This causes a...     

An all-sky camera battery for x-ray astronomy

The increasing number of interesting variable X-ray sources asks for an instrument for continuously monitoring the brightness of the most important X-ray sources over the whole sky. We describe a system consisting of a set of identical large position-sensitive detectors, mounted on the sides of a polyhedral satellite. Each counter is illuminated through a large diaphragm, with binary shadow characteristics. By holographic methods the X-ray image of the observed part of the sky could be derived from the illumination of each detector by multiplex analysing methods. The satellite should have fairly coarse (half a degree accuracy) three-axial stabilization, and an on-board computersteered data accumulation system. A relation is derived between the number of transparent holes in the diaphragm, the total count rate, and the flux of the faintest observable source. It appears that for a diaphragm with a few hundred transparent holes (detector geometrical area ≈10³ cm²) an integration time of approximately 6 min is needed in order that sources with a count rate of 0.01 cm^?2 s^?1 should still be observable with a confidence limit of 99%.     

Structure of sunspots

The sunspot models published so far do not reproduce the observed run of the umbral continuum intensities over the entire spectral range 0.5 < < 4 m. Moreover, in several previous models is the temperature gradient smaller than both the adiabatic and the radiative equilibrium gradient.Agreement between intensities computed from acceptable models and measured intensities can be obtained by introducing an additional opacity for 0.8 m, which is probably caused by the crowding of atomic and molecular lines. We present a new umbral model atmosphere with a wavelength dependent opacity enhancement factor which explains the continuum intensities and also reproduces plausible center-to-limb variations and line profiles. This model is in radiative equilibrium down to _0.5 = 1.5, with an effective temperature of 4000 ± 100K. For the deeper superadiabatic layers a small but probably significant departure from radiative equilibrium is indicated by the intensities in the range 1.5 < < 2.4 m.The uncertainties in the present model and the effect of the additional opacity on line profiles are briefly discussed.     

Improved values for the solar micro- and macro-turbulent filter functions

The contributions of any arbitrary photospheric velocity field to (macroturbulent) line displacement, and to (microturbulent) line broadening can be expressed by the macro- and micro-turbulent filters f _M (k) and f _t(_k), where _k is the wavenumber of the energy spectrum in which the line-of-sight component of the velocity field can be decomposed. As a correction to a previous computation of f _M and f _t we give in this Note improved values for the filter functions for weak lines in LTE. An example of the way to use the filter functions is given.     

Reflections on solar variability

The Sun is a variable star in many respects: there are secular varitions related to the general solar evolution, and - as discovered in recent years - there are many short period variations of which the 5 min and 160 min pulsations are the most important ones. Magnetic fields in the outer convective mantle play a dominant role in the 22-years cycle. The origin of solar magnetic variability is a key problem in astrophysics. The relation between solar variability and changes in the Earth's climate is a crucial element in climatology.Introductory talk to the 14th ESLAB Symposium: Physics of Solar Variations, 16–19 September, 1980, Scheveningen, The Netherlands.