Page 31 - Digital Analysis of Remotely Sensed Imagery

4 Cha pte r O n e

the results are much more objective than visual ones that are strongly
influenced by the interpreter’s knowledge and expertise in the subject
area concerned, as well as personal bias. The results, nevertheless, are
quantitative and can be exported to other systems for further analysis
without much additional work. This ease of portability is achieved at
the expense of purchasing and maintaining expensive and sophisticated
computer hardware and software.

1.2.1 Advantages
Digital image processing has a number of advantages over the
conventional visual interpretation of remote sensing imagery, such as
increased efficiency and reliability, and marked decrease in costs.

Efficiency
Owing to the improvement in computing capability, a huge amount
of data can be processed quickly and efficiently. A task that used to
take days or even months for a human interpreter to complete can be
finished by the machine in a matter of seconds. This process is sped
up if the processing is routinely set up. Computer-based processing is
even more advantageous than visual interpretation for multiple
bands of satellite data. Human interpreters can handle at most three
bands simultaneously by examining their color composite. However,
there is no limit as to the number of bands that can be processed in
image classification. Moreover, the input of many spectral bands will
not noticeably slow the processing.
Flexibility
Digital analysis of images offers high flexibility. The same processing
can be carried out repeatedly using different parameters to explore
the effect of alternative settings. If a classification is not satisfactory, it
can be repeated with different algorithms or with updated inputs in a
new trial. This process can continue until the results are satisfactory.
Such flexibility makes it possible to produce results not only from
satellite data that are recorded at one time only, but also from data
that are obtained at multiple times or even from different sensors. In
this way the advantages of different remote sensing data can be fully
exploited. Even non-remote sensing data can be incorporated into the
processing to enhance the accuracy of the obtained results.

Reliability
Unlike the human interpreter, the computer’s performance in an
image analysis is not affected by the working conditions and the
duration of analysis. In contrast, the results obtained by a human
interpreter are likely to deteriorate owing to mental fatigue after the
user has been working for a long time, as the interpretation process is
highly demanding mentally. The results are also likely to be different,
sometimes even drastically, if obtained by different interpreters,