PHYSICS
2122
CHAPTER
34- Electromagnetic Waves
Interference Interference Demonstrator
NASA Observatorium Education-Reference
Module-Landsat's Thematic Mapper Bands The multispectral
remote sensing instruments carried on the Landsat and other
satellites measure the amount of energy reflected and emitted in
several discrete portions, or bands, of the EM spectrum. The
various visible and infrared bands were chosen to measure
reflected and emitted energy in areas of the spectrum that
correspond to known responses of the target materials. These
include specific characteristics of land, vegetation, water,
rocks, and temperature.
Virtually
Hawaii: Remote Sensing ExampleWhy satellite images have different colors
In Virtually Hawaii, we show you a large number of images taken
from aircraft and spacecraft that have unusual colors compared to
the ones we can see with our eyes. Often, we are asked "why
is one part of the image red and the other blue?". This is
because we have chosen to use display three different wavelengths
on our computer screen where the surface is highly reflective
(bright) at these wavelengths. These colors are the result of
using instruments that study different parts of the spectrum to
the part that our eyes can see. While we do not want to give you
a complete course in physics, we thought that you might like to
have a bit of the background to these remote sensing images.
Wave propagation reflection/refraction
When a beam of light impings at some angle on the smooth flat
surface of an optically dense medium, the wave "sees" a
vast array of very closely spaced atoms that will somehow scatter
it. (At the wavelengths of light -- d=500nm -- the Earch's
atmosphere at STP has about 106 molecules in such a d3-cube). As
the wavefront descends, it excites one scatterer after another,
each of which reradiates a stream of photons that can be thought
of as a hemispherical wavelet in the incident medium. Because the
wavelength is so much greater than the separation between the
molecules, the wavelets advance together and add constructively
in only one directions, and there is one well-defined reflected
beam. The wavelets bend as they cross the boundary, because of
the speed change.
Reflection
and Refraction of Wave
Reflection and Refraction of Wave When a beam of light impings at
some angle on the smooth flat surface, the wave "sees"
a vast array of very closely spaced atoms that will somehow
scatter it. As the wavefront descends, it excites one scatterer
after another. The wavelets advance together and add
constructively in only one directions, and there is one
well-defined reflected beam. This java applet try to let you
visualize it for reflected and refracted wave. (Fu-Kwun Hwang)
Electromagnetic
Spectrum Light is a form of
electromagnetic radiation. Other forms of electromagnetic
radiation include radio waves, microwaves, infrared radiation,
ultraviolet rays, X-rays, and gamma rays. All of these, known
collectively as the electromagnetic spectrum, are fundamentally
similar in that they move at 186,000 miles per second, the speed
of light. The only difference between them is their wavelength,
which is directly related to the amount of energy the waves
carry. The shorter the wavelength of the radiation, the higher
the energy.
False Color Which would you rather do: watch TV in
color or in black and white? Which usually looks better: a
picture of your pet in black and white or in color? Unless you
have a Dalmatian, most of us would choose color, wouldn't we?
That's because we can see differences among objects in color much
better than we can see those same details in black and white.
Reflected infrared energy Reflected infrared energy and about the
infrared oart of the spectrum.
Color Mixing You have all had experience with color
mixing. When you were a kid, and you needed a color that was not
in your box of crayons, what did you do? Right: you used two
crayons, and mixed the colors! Look at how changing the incident
angle of light on a water drop changes the resulting spectrum of
light.