Page 32 - Digital Analysis of Remotely Sensed Imagery

Overview 5

because of their subjectivity and personal bias. By comparison, the
computer can produce the same results with the same input no matter
who is performing the analysis. The only exception is the selection of
training samples, which could be subjective. However, the extent of
such human intervention is con-siderably reduced in the digital
environment.

Portability
As digital data are widely used in the geoinformatics community, the
results obtained from digital analysis of remote sensing data are
seldom an end product in themselves. Instead, they are likely to
become a component in a vast database. Digital analysis means that
all processed results are available in the digital format. Digital results
can be shared readily with other users who are working in a different,
but related, project. These results are fully compatible with other
existent data that have been acquired and stored in the digital format
already. This has profound repercussions for certain analyses that
were not possible to undertake before. For instance, the results of
digital analysis can be easily exported to a geographic information
system (GIS) for further analysis, such as spatial modeling, land cover
change detection, and studying the relationship between land cover
change and socioeconomic factors (e.g., population growth).

1.2.2 Disadvantages
Digital image analysis has four major disadvantages, the critical ones
being the initial high costs in setting up the system and limited
classification accuracy.
High Setup Costs
The most expensive component of digital image analysis is the high
initial cost associated with setting up the analysis system, such as
purchase of hardware and software. These days the power of
computers has advanced drastically, while their prices have tumbled.
Desktop computers can now perform jobs that used to require a
minicomputer. The same machine can be shared with others for many
other purposes in addition to image analysis, such as GIS spatial
analysis and modeling. Nevertheless, they depreciate very fast and
have a short life cycle. Hardware has to be replaced periodically.
Similar to hardware, the initial cost of purchasing software is also
high. Unlike hardware, software is never meant to be a one-off cost.
Software licensing policy usually needs to be renewed annually.
Additional costs may include subscription of ongoing user support
service so that assistance is available whenever the system runs into
problem.
The third cost is related to the purchase of data. Compared with
printed materials, satellite data are much more expensive. Although
the price of medium-resolution data has dropped considerably, it is