Digital Signal Processing Reference
In-Depth Information
specific locations on the Earth's surface. To obtain information about, for example, spatial extent and
causes of water quality problems (such as the effects of land-use practices), computer-based GISs are
valuable tools. They can be used for data presentation, analysis and interpretation. Geographical
information systems allow the georeferencing of data, analysis and display of multiple layers of
geographically referenced information and have proven their value in many aspects of water pollution
control.
GIS uses a computer database to store large quantities of spatial and temporal data. This allows the
integration of diverse types of information into a form that makes it possible to consider different
approaches to land management and environmental problems before making management decisions.
Spatial data is information that describes how a specific feature is located or distributed in space. This
type of information can include watershed boundaries, slope, aspect, contour, soil type, stream
location, waterbodies boundaries and land use/land cover. The use of GIS allows us to process and
evaluate these data. Without this type of computer tool, such large amounts of data would be very
difficult to interpret. Information stored in a GIS will come from a variety of sources. The greater the
quantity and quality of the information, the more complete the GIS database will be.
“GIS” at its broadest has become a term to refer to any and all computer-based activities that focus on
geographic information; “GIS data” is often used as shorthand for digital geographic information; and
the redundant “GIS system” is becoming the preferred term for the software itself (Goodchild, 1999).
The “GIS system” requirements of most (current) monitoring systems are, in fact quite small (usually
limited to handling georeferenced site information, spatial mapping, and limited map overlaying). If
we go into broader types of application, GIS is used as a link between data sets and modeling tools or
it is even used as a standalone modeling tool in some water quality assessment studies. The general
believe in water management is that GIS systems are only for specialised activities because the
learning requirements are substantial, the hardware and software cost are high and only specialists can
efficiently use such systems (Ongley, 1997). But nowadays several studies and conducted research
shows the extensive use and the importance of this tool in specialized analysis and detailed studies in
the field of water in general and in the environmental and water quality studies in specific.
For example, GIS as a standalone tool have been used to provide water quality information on:
Location, spatial distribution and area affected by point-source and non-point source pollution.
Correlations between land cover and topographic data with environmental variables, such as
surface run-off, drainage and drainage basin size.
Mapping of water quality parameters.
Presentation of monitoring and modelling results at a geographic scale.
A typical GIS system consists of:
A data input system which collects and processes spatial data from, for example, digitised map
information, coded aerial photographs or satellite images, and geographically referenced data,
such as water quality data.
A data storage and retrieval system.
A data manipulation and analysis system which transforms the data into a common form
allowing for spatial analysis.
A data reporting system which displays the data in graphs or maps showing spatial reference
of information.
The application of GIS as a processing tool for remote sensing data will be explained also in the
coming sections of this chapter.
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