04-07-2013, 04:02 PM
Remote Sensing: Photographic vs. Non-Photographic Systems
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Summary
The intention of site-specific management is to optimize grower inputs on areas much smaller than the entire field.
These areas may be as small as a few square meters in size. To manage a field on such a scale, data would have to be
collected on a similar or smaller scale. To collect the data by hand would be very time consuming, labor intensive,
and destructive. This is the role remote sensing systems can play in site-specific management. The purpose of this
guideline is to compare the advantages and disadvantages for two types of remote sensing systems: photographic and
non-photographic. It is also intended to provide basic information about remote sensing and how to deal with the data
obtained.
Introduction
“Remote sensing is defined as the acquisition of
information about an object without being in physical
contact with it” (Elachi, 1987). A simple example is when
our eyes sense the reflected light from an object and our
brain interprets the information. In this example, our eye
is the detector and our brain is the computer that makes
sense out of what was detected. Remotely sensed information
can be in the form of potential fields, force distribution,
acoustic waves, or electromagnetic energy. The main
focus of remote sensing in agriculture is the interaction of
plants and soil with electromagnetic energy. The sensors
utilized can be grouped into two main categories, photographic
and non-photographic. Both provide information
about electromagnetic energy and how it interacts with
the surface being viewed.
Sensor Type
The sensors common to agricultural applications are
most generally airborne systems and are grouped as
photographic and non-photographic.
Photographic Sensors Photographs can be thought of
as consisting of a network of many tiny electromagnetic
energy detectors. The photographic spectrum utilized by
these detectors ranges from 0.3 mm to 0.9 mm. For black
and white film, the individual detectors are the grains of
silver halide in the film emulsion. Color and color IR film
contains no silver. Rather, the image is created when light
interacts with chemicals on the film. The absorption
characteristics of the three dye layers (yellow, magenta,
and cyan) generate the various colors. The developed film
will provide information about the variability within a
grower’s field.
If the desire is to compare images over time or relate
reflectance values to crop/soil conditions, then calibration
of the image is required. For quick calibration of images
over the same field select several objects for which
reflectance does not change over time. Choose the image
that will be considered your base map. All other images of
the same area will be calibrated to the base map. Adjust
the entire image by applying the equation that describes
the relationship between the brightness of each object in
the base map and the brightness of those objects for each
of the other images.