Satellite Orbits and Celestial Mechanics Satellite Platforms, Sensors, and Products Sensor Calibrati

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Chapter 1
Guido CervoneEOS 121 Lecture I
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Characteristics of the Atmosphere

• Earths Atmosphere
• Thickness
• Composition
• Evolution
• Vertical Structure
• Other Planetary Atmospheres

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Characteristics of the Atmospehre
How tall is the atmosphere? Where does it
end? How can we measure it? How much does it
weight? Why does it look blue? What is it made
of? Where does it come from?
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The atmosphere is a mixture of gas
molecules, microscopically small suspended
particles of solid and liquid, and falling
precipitation. Meteorology is the study of the
atmosphere and the processes that cause what we
refer to as the weather.
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If we think of the atmosphere as a reservoir for
gas, the gas concentration in the reservoir will
remain constant so long as the input rate is
equal to the output rate. Under such conditions,
we say that the concentration of the gas exists
in a steady state.
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Thickness
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Thickness

• No definite boundary between the atmosphere and
  outer space.
• An altitude of 120 km marks the boundary where
  atmospheric effects become noticeable during
  reentry
• The Kármán line, at 100 km, is often regarded as
  the boundary between atmosphere and outer space

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Thickness

• The thickness of the atmosphere is very small
  compared to the thickness of the Earth

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Quiz

• If we were making a model of the Earth and the
  atmosphere, how thick would we represent the
  atmosphere if we made the Earth's radius 10
  meters and we assumed the atmosphere was 100 km
  thick, and the radius of the Earth 6350 km?
• 6.37 meters
• 16 dm
• 16 mm

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Chemical Composition

• Invisible gases
• Permanent gases
• Variable gases
• Dust and water droplets
• Continuous exchange with Earths surface

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Permanent gases account for the greater part of
the atmospheric mass99.999 percentand occur in
a constant proportion throughout the
atmospheres lowest 80 km (50 mi). Because of
its chemical homogeneity, this region within 80
km of Earths surface is called the homosphere.
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Variable gases are those whose distribution in
the atmosphere varies in both time and space. The
most abundant of the variable gases, water vapor,
occupies about one-quarter of 1 percent of the
total mass of the atmosphere. Most atmospheric
water vapor is found in the lowest 5 km (3 mi) of
the atmosphere.
Variable Gases of the Atmosphere
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Chemical Composition
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Water is constantly being cycled between the
planet and the atmosphere through the hydrologic
cycle. Water continuously evaporates from both
open water and plant leaves into the atmosphere,
where it eventually condenses to form liquid
droplets and ice crystals. These liquid and
solid particles are removed from the atmosphere
by precipitation as rain, snow, sleet, or hail.
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Water Vapor
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Another important variable gas is carbon dioxide
(.037). Increases in the carbon dioxide content
of the atmosphere may have some important
climatic consequences that could greatly affect
human societies. Carbon dioxide is removed from
the atmosphere by photosynthesis, the process by
which green plants convert light energy to
chemical energy (Box 1-1).
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CO2
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Plant Photosynthesis
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Plant Respiration

• Plants use of stored chemical energy to perform
  their life functions -- to grow, to transport
  nutrients, to reproduce, and to protect
  themselves
• They do this all the time (independently of
  sunlight), using oxygen from the air and sugars
  that they have stored inside to make carbon
  dioxide and water
• It is an almost reverse process of photosynthesis

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Plants and Carbon Dioxide

• When a plants, dies, the CO2 that stored is
  released into the atmosphere
• Sometimes, over geological timescale, plants are
  transformed into fossil fuels
• What happens thus when we burn fossil fuels?

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Methane

• Has been steadily increased over the past few
  years
• Why? What produces Methane?

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Vertical Distribution of Ozone (O3)
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Ozone in the Stratosphere

• In the upper stratosphere, ozone is generated
  when ultraviolet radiation (sunlight) strikes the
  stratosphere, dissociating (or "splitting")
  oxygen molecules (O2) to atomic oxygen (O). The
  atomic oxygen quickly combines with further
  oxygen molecules to form ozone
• O2 hv -gt O O (1)
• O O2 -gt O3 (2)
• (1/v wavelength lt 240 nm)

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Ozone in the Stratosphere

• Ozone in the stratosphere is important to our
  survival.
• In the stratosphere, ozone absorbs some of the
  potentially harmful ultra-violet (UV) radiation
  from the sun (at wavelengths between 240 and 320
  nm) which could otherwise lead to an increase in
  the incidence of skin cancer and also damage the
  Earth's eco-system in a variety of ways.
• Although the UV radiation splits the ozone
  molecule, ozone can reform through the following
  reactions resulting in no net loss of ozone.
• O3 hv -gt O2 O (3)
• O O2 -gt O3 (2)

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Ozone Hole
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The density of any substance is the amount of
mass of the substance contained in a unit of
volume. At lower altitudes, there is more
overlying atmospheric mass than is the case
higher up. Because air is compressible and
subjected to greater compression at lower
elevations, the density of the air at lower
levels is greater than that aloft.
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Density of the Atmosphere

• The density decreases with height
• At 16 km the density is 10 than at sea level
• At 50 km the density is only 1 than at sea level

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Mass

• 75 of the atmosphere's mass is within 11 km of
  the surface
• 99.99997 of the atmosphere's mass is within 100
  km of the surface
• Despite its thinness, its mass is 5.14 x 10 15
  kg

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Scientists divide the atmosphere into four
layers based not on chemical composition but
rather on how mean temperature varies with
altitude. The average temperature profile, called
the standard atmosphere, shows the four
layers troposphere, stratosphere, mesosphere,
and thermosphere.
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Variation of Temperature
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The troposphere is the lowest of the four
temperature layers. The troposphere is where the
vast majority of weather events occur and is
marked by a general pattern in which temperature
decreases with height. At the top of the
troposphere, a transition zone called the
tropopause marks the level at which temperature
ceases to decrease with height.
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Despite the strong tendency for temperature to
decrease with altitude in the troposphere, it is
not uncommon for the reverse situation to occur.
Such situations, where temperature increases with
height, are known as inversions.
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Above the tropopause is the stratosphere. Little
weather occurs in this region. In the lowest part
of the stratosphere, the temperature remains
relatively constant up to a height of about 20 km
(12 mi). From there to the top of the
stratosphere (called the stratopause), the
temperature increases with altitude. In the
upper stratosphere, heating is almost exclusively
the result of ultraviolet radiation being
absorbed by ozone.
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Ozone is the form of oxygen in which three O
atoms are joined to form a single molecule. The
small amount of it that exists in the the
stratosphere is absolutely essential to life on
Earth because it absorbs lethal ultraviolet
radiation from the sun. Near Earths surface it
is a major component of air pollution, causing
irritation to lungs and eyes and damage to
vegetation (Box 1-2).
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Above the mesosphere is the thermosphere, where
temperature increases with altitude to values in
excess of 1,500 C.
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High Temperature in Thermosphere

• The Thermosphere has very high temperature
• Molecules have very high kinetic energy
• However, the layer contains very little energy

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An additional layer, called the ionosphere, can
be defined based on its electrical
properties. This layer, which extends from the
upper mesosphere into the thermosphere, contains
large numbers of electrically charged particles
called ions. The ionosphere is important for
reflecting AM radio waves back toward Earth and
is responsible for the aurora borealis and the
aurora australis.
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It is generally believed that Earth was formed
perhaps 4.5 billion years ago. If an atmosphere
formed with Earth, it must have consisted of the
gases most abundant in the early solar
system including large amounts of hydrogen and
helium, the two lightest elements. If molecules
move with sufficient speed, known as their escape
velocity, they can overcome gravity and leave the
atmosphere. Light gases are more likely to
achieve escape velocity thus, the hydrogen and
helium were most readily lost.
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Differentiation of the early Earth

• When melting of the Earth began dense elements
  sank towards the center of and light elements
  rose towards the surface (forming minerals that
  make up the crust).

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Earth Forms

• Lighter material rose to surface crust denser
  sank to the core
• As the Earth cooled and differentiated, the crust
  became thicker and continents began to "grow" by
  plate tectonics
• First crust likely basaltic (like modern oceanic
  crust) and lacked continents
• At zones of subduction, intrusion of magma into
  overlying crust would have caused thickening to
  form continental crust.

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Earth Age

• Oldest continental igneous rocks are 3.8 billion
  years old.
• Oldest sedimentary rocks (sandstones) are 4.2
  billion years old.
• Therefore, granitic continental crust must have
  been present by 4.2 billion years ago.
• By 2.5 billion years ago, large continental
  masses were present.

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First Atmosphere

• Composition - Probably H2, He, neon, Ar
• These gases are relatively rare on Earth compared
  to other places in the universe and were probably
  lost to space early in Earth's history because
• gravity is not strong enough to hold lighter
  gases
• Earth still did not have a differentiated core
  (solid inner/liquid outer core) which creates
  Earth's magnetic field (magnetosphere Van Allen
  Belt) which deflects solar winds.
• Once the core differentiated the heavier gases
  stayed anchored

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Atmosphere by 4 billion years ago

• Virtually no O2
• Carbon dioxide CO2
• Water vapor H2O
• Nitrogen N2
• Hydrogen H2
• Hydrogen Chloride HCl
• Sulfur Dioxide SO2

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Origin of O2

• Some O2 came from
• 2H2O ultraviolet rays 2H2 O2
• Lost to space 2H2
• (Early sun with gt UV)
• More came from photosynthesis
• CO2 H2O light ( chlorophyll) (CH2O) O2

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Evidence for O2 and Cyanobacteria

• Photosynthesis requires chlorophyll, produced by
  some organisms (e.g., plants)
• The oldest that could produce chlorophyll are
  cyanobacteria single celled sea organisms that
  lacked an organized nucleus
• First cyanobacteria appeared about 3.5 bya and
  were anaerobic
• But very common in rocks lt about 2.5 bya
• There is strong correlation between O2 levels in
  the atmosphere and the development of life, on
  Earth. 

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http//www.ucmp.berkeley.edu/precambrian/precambri
an.html
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Cyanobacteria or"blue-green algae" go back to 3.5
by
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Oldest Fossil 3.5 bya

• Stromatolite Colony
• either blue-green algae or bacteria

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Oxygens Rise

• As Oxygen levels increased, aerobic organisms
  developed ? even more Oxygen
• Oxygen levels became high enough to support more
  complex life ? more oxygen
• By 600 million years ago Oxygen levels had almost
  reached modern levels, about 20 and O3 starts to
  form in stratosphere ?
• The evolution of land plants, resulted in a
  modest increase in O2
• Variation in O2 levels over the past 500 million
  years reflect changes in plant cover on Earth

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Variation in O2 over last 500 million years
reflects plant cover
Carboniferous warm, moist, tropical settings O2
levels almost doubled. Permian and Triassic arid
conditions on land O2 levels dropped to below
15.
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Rock Record O2 in the atmosphere has increased
with time

• Iron (Fe) is extremely reactive with oxygen. Fe
  in the rock record tells us much about
  atmospheric evolution.
• Archean - Find minerals that only form in
  non-oxidizing environments Pyrite (FeS2),
  Uraninite (UO2).
• Banded Iron Formation chert iron oxide, iron
  carbonate, iron silicate, iron sulfide. Major
  source of iron ore magnetite (Fe3O4), common in
  rocks 2.0 - 2.8 B.y.
• Red beds (continental siliciclastic deposits) are
  never found in rocks older than 2.3 B. y., but
  are common during Phanerozoic time. Red beds are
  red because of the highly oxidized mineral
  hematite (Fe2O3), that probably forms secondarily
  by oxidation of other Fe minerals that have
  accumulated in the sediment.

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American Museum of Natural History 2 billion
year old banded iron formation, Ontario
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Biological Evidence of O2 buildup

• Chemical building blocks of life could not have
  formed in the presence of atmospheric oxygen.
  Chemical reactions that yield amino acids are
  inhibited by presence of very small amounts of
  oxygen.
• Oxygen prevents growth of the most primitive
  living bacteria such as photosynthetic bacteria,
  methane-producing bacteria and bacteria that
  derive energy from fermentation. Conclusion -
  Since today's most primitive life forms are
  anaerobic, the first forms of cellular life
  probably had similar metabolisms.
• Today these anaerobic life forms are restricted
  to anoxic (low oxygen) habitats such as swamps,
  ponds, and lagoons.

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References

• http//willshare.com/willeyrk/creative/earthfax/ea
  rthfax.htm
• http//en.wikipedia.org/wiki/Earth
• http//www.crisp.nus.edu.sg/research/tutorial/atm
  os.htm
• http//ssdoo.gsfc.nasa.gov/education/lectures/magn
  etosphere/index.html
• http//rst.gsfc.nasa.gov/Front/tofc.html