Visualization of Water Services in Africa: Data Applications for Nexus Governance - Governing the Nexus: Water, Soil and Waste Resources Considering Global Change - page 190

source software solution that was explicitly developed to support decision-makers
in developing countries. 4 As one potential application for using mobile phones or
other GPS devices, WPM is discussed in Sect. 2.6.3 .

2.3.3 Quasi-continuous Data

Several technologies for quasi-continuous measurements of environmental proper-
ties exist. The methods are suitable for earth (near-) surface measurements
(2D 4D) such as characterization of topography, vegetation, soil and surface or

subsurface water bodies. Some of the selected methods can account for depth (3D) or
temporal information (4D) through time-lapse measurements (time series). Tech-
nologies that have the potential for being applicable in regions where limited data is
still an issue are mainly geophysical methods (Hartemink et al. 2008 ) such as:

- 3D -

Near-surface hydrogeophysical methods, which are applied for quasi-con-
tinuous local to large-scale measurements of the surface and subsurface. Their
purpose is the characterization, mapping and monitoring of soils, geological
features and groundwater processes (Binley et al. 2010 ). The medium to large-
scale quasi-continuous mapping is not obtainable with traditional point-based

￿

field measurement approaches. Geophysical methods additionally are helpful in
assessing water quality and monitoring of underground contamination move-
ments (Binley et al. 2010 ). However, geophysical measurements generally
require an adequate number of

field samples to verify and to assign real soil/
underground property values to the geophysical data. This veri cation process is

historically called ground truthing in remote sensing, but nowadays transferable
to general geophysical measurements (Hargrave 2009 ). Methods comprise:
Electromagnetic induction ( EMI ) , Seismic methodology, Geoelectrics (Fig. 4 ),
Ground Penetrating Radar ( GPR ). The physical variables measured by geo-
physical methods such as electrical conductivity can be produced by different
combinations of underground material properties (equi nality in

context of geophysical soil mapping means that different combinations of
material compositions (water, salt and clay content) cause similar measurement
values/results. For instance, areas with high clay content have high electrical
conductivities similar to areas with high water content. Due to the equi

nality). Equi

nality of
the geophysical measurement results, the data and image interpretation should
be carried out in combination with auxiliary methods (models of physical
relationship between geophysical data and hydrological property) or ground
truthing (e.g. water sample) (van Dam 2012 ; Binley et al. 2010 ). An extensive
review of hydrogeophysical methods, their advantages and limitations is pro-
vided by Reynolds ( 2011 ), Rubin and Hubbard ( 2005 ), Kn

ö

del et al. ( 2005 ) and

Binley et al. ( 2010 ).

4

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