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What Happens to Energy When It Hits a Target on the Ground?
While some light is absorbed by the atmosphere, other light is scattered
by it. Scattering occurs due to particles in the atmosphere and is thus always
present, but also unpredictable. Particles will absorb energy and redirect it
back out in random directions, causing scattering. There are three types of
scattering that can occur: The first of these is Rayleigh scattering, which
occurs when the particles causing the scattering are significantly smaller
than the wavelengths being affected. Keeping in mind that the visible-light
wavelengths are smaller than one-millionth of a meter, Rayleigh scattering is
caused by molecules in the atmosphere. In addition, shorter wavelengths are
scattered to a much greater degree than longer wavelengths. This explains
why the sky is blue during the day: The shorter blue wavelengths are scattered far more than the longer red wavelengths. However, at sunset or sunrise, sunlight has a longer way to travel to reach Earth, and thus with all of
the blue wavelengths already scattered, we see the reds and oranges of longer
wavelengths as the Sun goes out of view.
Another type of scattering is Mie scattering, when the particles causing
the scattering are roughly the same diameter as the wavelengths they’re scattering (this would include things like dust or smoke). Last is nonselective
scattering, where what’s causing the scattering is larger than the wavelengths being scattered (such as water droplets or clouds) and scatters all
wavelengths equally. Nonselective scattering also explains why we see clouds
as being white—the visible colors of blue, green, and red are all scattered the
same, thus taking on the color of white (equal levels of red, green, and blue
will produce the color white).
What Happens to Energy When It Hits
a Target on the Ground?
After absorption and scattering by the atmosphere, the wavelengths that correspond to the windows finally make it to Earth’s surface and interact with
targets there. One of three things can happen to that energy (on a wavelengthby-wavelength basis)—it can either be transmitted through the target, it can
be absorbed by the target, or it can be reflected off the target. Transmittance
occurs when a wavelength of energy simply passes through a surface to interact with something else later. Think of light passing through a windshield of
a car—most of the light will pass through the glass to affect things in the car
rather than the windshield itself.
Absorption occurs when the energy is trapped and held by a surface
rather than passing through or reflecting off it. Think of walking across a
blacktop parking lot during a hot summer day—if you don’t have something
on your feet, they’re going to hurt from the heat in the pavement. Since the
blacktop has absorbed energy (and converted it into heat), it’s storing that
heat during the day. Absorption also explains why we see different colors.
For instance, if someone is wearing a bright green shirt, there’s something in
the dyes of the shirt’s material that is absorbing all other colors (that is, the
Rayleigh scattering
scattering of light
caused by atmospheric
particles smaller than
the wavelength being
scattered.
Mie scattering
scattering of light
caused by atmospheric
particles the same size
as the wavelength
being scattered.
nonselective
scattering scattering
of light caused by
atmospheric particles
larger than the
wavelength being
scattered.
transmittance when
light passes through a
target.
absorption when light
is trapped and held by
a target.
What Happens to Energy When It Hits a Target on the Ground?
While some light is absorbed by the atmosphere, other light is scattered
by it. Scattering occurs due to particles in the atmosphere and is thus always
present, but also unpredictable. Particles will absorb energy and redirect it
back out in random directions, causing scattering. There are three types of
scattering that can occur: The first of these is Rayleigh scattering, which
occurs when the particles causing the scattering are significantly smaller
than the wavelengths being affected. Keeping in mind that the visible-light
wavelengths are smaller than one-millionth of a meter, Rayleigh scattering is
caused by molecules in the atmosphere. In addition, shorter wavelengths are
scattered to a much greater degree than longer wavelengths. This explains
why the sky is blue during the day: The shorter blue wavelengths are scattered far more than the longer red wavelengths. However, at sunset or sunrise, sunlight has a longer way to travel to reach Earth, and thus with all of
the blue wavelengths already scattered, we see the reds and oranges of longer
wavelengths as the Sun goes out of view.
Another type of scattering is Mie scattering, when the particles causing
the scattering are roughly the same diameter as the wavelengths they’re scattering (this would include things like dust or smoke). Last is nonselective
scattering, where what’s causing the scattering is larger than the wavelengths being scattered (such as water droplets or clouds) and scatters all
wavelengths equally. Nonselective scattering also explains why we see clouds
as being white—the visible colors of blue, green, and red are all scattered the
same, thus taking on the color of white (equal levels of red, green, and blue
will produce the color white).
What Happens to Energy When It Hits
a Target on the Ground?
After absorption and scattering by the atmosphere, the wavelengths that correspond to the windows finally make it to Earth’s surface and interact with
targets there. One of three things can happen to that energy (on a wavelengthby-wavelength basis)—it can either be transmitted through the target, it can
be absorbed by the target, or it can be reflected off the target. Transmittance
occurs when a wavelength of energy simply passes through a surface to interact with something else later. Think of light passing through a windshield of
a car—most of the light will pass through the glass to affect things in the car
rather than the windshield itself.
Absorption occurs when the energy is trapped and held by a surface
rather than passing through or reflecting off it. Think of walking across a
blacktop parking lot during a hot summer day—if you don’t have something
on your feet, they’re going to hurt from the heat in the pavement. Since the
blacktop has absorbed energy (and converted it into heat), it’s storing that
heat during the day. Absorption also explains why we see different colors.
For instance, if someone is wearing a bright green shirt, there’s something in
the dyes of the shirt’s material that is absorbing all other colors (that is, the
Rayleigh scattering
scattering of light
caused by atmospheric
particles smaller than
the wavelength being
scattered.
Mie scattering
scattering of light
caused by atmospheric
particles the same size
as the wavelength
being scattered.
nonselective
scattering scattering
of light caused by
atmospheric particles
larger than the
wavelength being
scattered.
transmittance when
light passes through a
target.
absorption when light
is trapped and held by
a target.