Introduction to Field Sampling - Field Sampling: Principles and Practices in Environmental Analysis - page 20

followed, but also its speed. This provides valuable information that can dramatically
decrease the deleterious impact of spills such as those that occur when an oil tanker runs
aground.
All activities that use GPSs are termed precision. The use of GPS in farming activities
would be termed precision farming or precision agriculture. Weather stations having a
GPS receiver would be called precision weather stations. Field sampling using GPS
would be called precision sampling [19].
1.17. GEOGRAPHICAL INFORMATION SYSTEMS (GIS)
Satellite and any other digital information can be combined on an image of the Earth's
surface using a GIS. This is a computer program that allows any digital information about
the Earth's surface to be superimposed on a picture of that part of its surface (e.g.,
temperature and rainfall). In a like manner pollution concentration in a certain location
can be mapped on a picture, aerial photograph, or satellite image of that location using a
GIS system.
Although aerial photographs and satellite images are of the Earth's surface, it is also
possible, using GIS, to map any known information about subsurface features and thus
make a three-dimensional map of an area. Using GIS the location and movement of the
pollutant underground or in caves can be mapped using images of the Earth's surface as a
reference.
Geographical information systems are systems that allow not only the mapping of the
Earth's surface and subsurface, but also the relating of the data in these maps to other
data. It makes use of GPS, remote sensing, and other means of obtaining data about the
environment, including taking physical samples for analysis in the laboratory. All these
data can be related to a map of the area of concern and can then be used to analyze all the
data related to the area [20].
1.18. CONCLUSIONS
Before thinking about sampling a field or any part of the environment a firm grasp of
important characteristics of the environment relevant to sampling must be understood.
These characteristics must also be kept in mind while developing the sampling plan,
while carrying out the sampling, and during the transport and analysis of the samples.
The four most important considerations derive from the fact that the environment is four-
dimensional. The area to be sampled has length, width, and depth, and changes with time.
Samples must be obtained from various places on the surface and from the subsurface
using a well-developed plan taking these into consideration. The characteristics of
samples and the constituents they contain will vary over time. It is not acceptable to take
samples from part of an area one month and then a month later sample another part of the
area and put the analytical results from these two sampling times together and assume or
assert that they represent one sampling.