of downward vertical motion. Water vapor imagery
can detect these motions without clouds present.
Circulation patterns in the upper atmosphere,
including the jet stream, are easily identified using WV
imagery.
Q15.
Q16.
Q17.
Q18.
Q19.
Q20.
Q21.
Q22.
Q23.
Q24.
REVIEW QUESTIONS
What is the image-scanning sensor of a satellite
called?
Which sensor would provide higher resolution
data, one with a spatial resolution of 1 kilometer
or one with a spatial resolution of 4 kilometers?
Consider two objects, one cold the other hot.
Which object is emitting electromagnetic energy
at relatively longer wavelengths?
The majority of the radiation emitted by the
earth is known by what term?
In the visible spectrum, what color has the
longest wavelength?
Of the following objects, sand or grass, which
one would have a higher albedo?
What are the major advantages of infrared
imagery?
How do relatively cold objects appear on IR
imagery?
How do high humidity areas appear on water
vapor images?
What are the advantages of water vapor
imagery?
IMAGERY ENHANCEMENT
LEARNING OBJECTIVES: Identify various
types of user-defined and predefined satellite
enhancement curves.
Identify information
contained in the GOES legend and temperature
scale.
Most satellite data processors have the capability
to assign colors or various gray shades to specific JR
imagery energy readings. When an image is produced
by using either color or an alternating gray shade rather
than the straight black-to-white or white-to-black
shading, the color or gray shade assignment is called an
enhancement. An enhanced satellite image allows the
user to see specific details of an image with better
definition. Infrared imagery is often enhanced to
better define a small range of critical temperatures.
TYPES OF ENHANCEMENT CURVES
Unenhanced imagery displays a linear transition of
gray shades from black (warm) to white (cold). It is a
steady increase in brightness that produces little
contrast. Enhanced imagery displays a transition of
mostly non-linear gray shades. The result is an
improved contrast of various key temperatures that
makes specific temperature assessment much easier.
There are two methods of enhancing satellite imagery:
brilliance inversions and thresholding (curves).
Brilliance inversion enhancements use a range of gray
shades (or color) to identify a range of specific
temperatures. With threshold enhancements, a single
gray shade is used to identify a whole range of
temperatures. In other words, all the temperatures in
a particular range have the same gray contour. Figure
1-14 shows enhanced infrared images.
User-Defined Enhancement Curves
When possible, enhancement curves should be
locally developed and evaluated. Most satellite
receiving equipment used by the Navy, such as the
AN/SMQ-11, allow for the creation of custom
designed enhancement curves. Keep in mind that
when you are developing enhancement curves, you
should limit the number of features to be enhanced.
You must allow for enough detail as possible without
making the display too confusing. There are always
compromises between simple enhancement curves,
which sacrifice detail but can quickly be interpreted in
an operational environment, and complex curves,
which maximize information content but require more
time to interpret.
Figure 1-15 is a graphic illustration of a basic
enhancement curve table. Count values as input would
be plotted on the horizontal axis, and modified count
values for the final display would be plotted on the
vertical axis. These count values range from 0 to 255,
where 0 appears as black and 255 appears as white.
Values in between produce varying shades of gray. By
adding, deleting, and positioning points within the
graph, an input color or gray shade is mapped to an
output color or gray shade. As points of reference, six
count values on the horizontal axis correspond to the
six sets of temperatures at the bottom of the graph.
Count values on the vertical axis result in the gray
shade range as referenced at the right of the graph. The
1-14
