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5. Water Pollution 
Water pollution can be defined as substances, bacteria or other organisms present 
in such concentrations to impair the quality of water rendering it less suitable 
or unsuitable for its intended use and presenting a hazard to man or ihe eaviron- 
ment. -Seme of the main types of water pollutants are :- 
( i) organic wastes - contributed by sewage and industrial wastes; 
( ii) eutrophication - caused by the addition of plant nutrients that 
promote nuisance growths of aquatic plant life; 
(iii) synthetic - organic chemicals, such as detergents and pesticides; 
( iv) inerganic chemical and mineral substances - resulting from mining, 
manufacturing and agricultural processes; 
( v) oil and marine pollution; 
( vi) sediments - ag a result of erosion caused by land development ;and 
(vii) heated effluents- from the use of water for cooling purposes. 
Any two bodies of water that differ in quality have a unique distribution of 
reflected, emitted and absorbed radiation. These characteristics can be used 
to distinguish bodies of water and in some cases, to obtain information abcut 
ihe physical and chemical nature of the water. Most of the available techniques 
may be applied to the study of water pollution. Although only in rare cases is 
it possible to make a positive identification of a pollutant by remote sensing, 
the point of discharge can be detected, where the effluent goes and the general 
characteristics of its dispersion pattern. 
Most pollutants in water can be detected on colour photography because of the 
discolouration of the water. Even when receiving waters are high polluted, dis- 
charges at or near the surface are usually visible for at least a short distance 
from the release point. Colour infra-red film is only recommended for photo- 
interpretation of industrial sites when the photos are taken from high altitudes 
(more than 6,000 m.) to minimise the effects of atmospheric haze. It is, also, 
a very useful tool for evaluating the condition of floating aquatic vegetation, 
algal blooms and shoreline vegetation, where determining the presence or absence 
of vegetation is important. The idea! situation is the use of both colour and 
colonr infra-red photography taken simultaneously from low and medium altitude 
missions (van Genderen, 1975). 
The resolution factor of satellite imagery is an obvious problem in water pollution 
studies. Nevertheless, reports of the use of Landsat-1 imagery indicate that a 
great deal can be done with respect to water pollution analysis in spite of the 
limitations imposed. Water clarity is a distinguishable feature on satellite 
imagery. On colour composites clear water appears a deep blue, while water 
containing organic and suspended matter, a yellow or green colour and turbid 
waters as brown. In this way sedimentation can be mapped. Orbital imagery 
can indicate surface currents, which may affect pollution dispersal and has been 
successful in the detection of oil slicks. 
The distribution of relative surface temperatures can be plotted with infra-red 
line scanners. This will indicate currents and effluents, together with their 
degree of mixing. Infra-red line scanners can be used to monitor oil pollution 
as there is normally a teinperature difference between the oil slick and the 
surrounding water. The thickness of the oil is indicated by the density of the 
recorded image. 
Photography is, and will be, the most useful water quality remote sensing tool 
(Scherz, 1971). It is concluded from many studies that colour air photo- 
interpretation provides the most efficient and accurate means of locating outfalls 
and polluted waters, (Meyer and Welch, 1975).