An Introduction to Remotely Sensed Data Analysis - Sampling Spatial Units for Agricultural Surveys - page 63

Chapter 4
An Introduction to Remotely Sensed Data
Analysis

4.1 Introduction

Remote sensing (RS) is an important tool for studying natural resources and the
environment. There is an extremely large number of possible applications for
remotely sensed data: identifying potential archaeological sites, drought and flood
damage assessment, land use monitoring and management, and crop inventory and
forecasts, amongst others. RS observations have become crucial for protecting the
global environment, reducing disaster losses, and achieving sustainable

development.
RS is defined as the technique for deriving information about the Earth s surface

and estimating geo-bio-physical properties using electromagnetic radiation
(Canada Centre for Remote Sensing 2003 ). The data are acquired without physical
contact with the Earth. This process involves making observations using sensors
(i.e., cameras, scanners, radiometer, radar, and so on) mounted on platforms (i.e.,
aircraft and satellites) that are a considerable height from the Earth

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s surface, and
recording the observations on a suitable medium (i.e., images on photographic films
and videotapes, or digital data on magnetic tapes). Then, the observation data are
typically stored and manipulated using computers.
A digital image is an extremely useful way to synthesize and display a large
amount of data that could not otherwise be analyzed. The great advantage of digital
data is that they can be computationally processed for either machine assisted
information extraction or visual enhancement. This processing makes the data
more interpretable to a human analyst. Generally, an analyst is referred to as a
photo-interpreter.
The images can be recorded, for example, by meteorological satellites that
observe scenes of thousands of square miles, or by electron microscopes that
work on scales of a nanometer or less (see the next section for more information).
The output of a digital image is typically a square grid divided into smaller boxes,
also known as square pixels (i.e., picture elements). The element associated with

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