Sampling - Field Sampling: Principles and Practices in Environmental Analysis - page 117

ocean temperatures are other common examples of uses of GIS. Recently, mapping
Pacific Ocean temperatures using remote sensing has been used to predict the occurrence
of La Niña or El Niño. Whenever data are entered into a GIS system from any source,
their accuracy must be checked. This is especially important if they are entered manually.
Today, satellites are the most important source of information for GIS. Satellites can
access various portions of the electromagnetic spectrum, allowing analysis and evaluation
of conditions on the Earth's surface. (For more information on satellite sensing, see the
previous section on remote sensing.) Having satellites use sensors to observe the Earth's
surface and having these data digitalized allows for easy insertion into GIS systems.
Satellite sensors are very versatile, and different satellites have sensors for different
portions of the electromagnetic spectrum. A well-know satellite used for remote sensing
is the Landsat TM (Thematic Mapper) satellite. It has a broad range of sensors, which
among other things can detect both different vegetation types and changes in them. These
changes can be related to changes in a plant's environment, including environmental
degradation. Airplanes equipped with sensors still play a role in remote sensing, and data
retrieved in this way can also be inserted into GIS systems.
In most cases, a sampling plan will not require the entity doing the sampling to
implement a GIS system. Desktop computers with GIS display and manipulation
software can be inexpensively obtained, however. The needed GIS data, including maps,
can thus be obtained from various sources and combined to obtain the information,
relationships, and analysis needed [10]. One important source is local GIS offices. It is
very common for even small cities, municipalities, and counties to have GIS systems, and
both the mapping and tax offices know who keeps these systems and where they are kept,
and there may even be a separate GIS office, which is often small and not easy to find. If
such an office exists, however, it is worthwhile finding because GIS personnel can be a
valuable resource in obtaining GIS data and in developing and executing a sampling plan.
5.6. SAMPLERS
There are many different types and constructions of samplers designed for each type of
media to be sampled. One of the most important considerations in deciding on the type
and construction of a sampler is the material that it is made of and whether or not it is
compatible with the type of material and contaminant being sampled. Figure 5.5 shows a
typical simple hand sampler, while Figure 5.6 shows a sampler mounted on a truck.
Additional