Transcript PowerPoint file

Observing Climate - Remote
Sensing
Satellite Fundamentals
Types of Orbit
Lower Earth Orbits (LEO)
Polar Orbits
Medium Earth Orbits (MEO)
Highly Elliptical Orbits (HEO)
Geosynchronous Orbits (GEO)
6-1
Science Concepts
Circular Motion
Newton’s Laws of Motion
First Law
Second Law
Centripetal Acceleration
Acceleration of Gravity
Temporal Resolution
QuickTi me™ and a Sor enson Video decompr essor ar e needed to see this picture.
Climate and Global Change Notes
6-2
Satellite Observations
Newton’s Laws of Motion
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•
Forces are a vector quantity - they have a direction as well as a magnitude
Isaac Newton
(1643 to 1727)
Newton's Laws of Motion
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First Law
>
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An object's velocity (direction or speed) will remain
unchanged unless acted upon by a force
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Second Law
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Object's acceleration =
‡
net force
object's mass
Acceleration is defined as the change in velocity
with time and it also is a vector
a
=
(Change in velocity)
(Change in time)
=
http://www-groups.dcs.
st-and.ac.uk/~history/
Posters2/Newton.html
( V2 - V1)
( t2 - t1 )
Acceleration, i.e., a change in velocity can be change in
direction or speed or both
Climate and Global Change Notes
6-3
Satellite Observations
Circular Motion
•
An object in circular motion is constantly
changing direction - thus, constantly
accelerating
•
According to Newton’s Laws of Motion
circular motion requires that the object
have a center-seeking or “centripetal” force
•
Centripetal force is the force necessary to
accelerate an object in a curved path
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Centripetal force (CF) depends on the
motion, mass and path of the object
CF = (Mass of object) * (Velocity of object) 2
(Radius of circle)
B
A
String
Velocity
String
Centripetal
Force
Climate and Global Change Notes
C
6-4
Satellite Observations
Circular Motion (Con’t)
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Examples
CF = (Mass of object) * (Velocity of object) 2
(Radius of circle)
Climate and Global Change Notes
6-5
Satellite Observations
Velocity
Satellite Orbits
•
Force necessary for a satellite to orbit a planet
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Velocity
Centripetal
Force
Centripetal force (CF) needed to accelerate
satellite around a spherical planet is
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Centripetal
Force
Centripetal
Force
CF = (Mass of satellite) * (Velocity of satellite)
(Radius of satellite orbit)
Centripetal
Force
2
Velocity
Velocity
What replaces the string as the center-seeking force for the satellite?
>
>
Gravity must keep the satellite turning around the planet
Must have a balance between gravitational force and the
satellite’s centripetal force for the satellite to orbit the planet
(Gravitational Force) = (Centripetal Force)
Gravitational Force
toward Earth’s center
Climate and Global Change Notes
6-6
Satellite Observations
Gravitation Force
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Science quotes of 5th and
6th graders -
Gravitational force - attraction toward Earth
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The law of gravity says no
fair jumping up without
coming back down.
Force of attraction between two objects - in
this case the satellite and the Earth
Const * (Mass of Earth) * (Mass of satellite)
(Distance) 2
where “Distance” is the distance between the centers of the Earth and
the satellite, i.e., the radius of the satellite orbit.
Const = 6.67259 * 10 -11 m3 kg -1 s -2
Satellite Orbits (Con’t)
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Gravitational Force supplies the needed Centripetal Force for satellites. Thus,
(Orbital velocity) 2 =
Const * (Mass of Earth)
Radius of satellite orbit
Climate and Global Change Notes
6-7
Satellite Observations
Satellite Orbits (Con’t)
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Note that the Mass of the Earth is a constant, so
(Orbital velocity) 2 =
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Konstant
.
Radius of satellite orbit
Also recall that the definition of velocity is distance / time or d / t. The
distance a satellite make in orbiting the Earth is 2  ( Radius of the satellite
orbit ). Thus,
( Orbital velocity ) = 2  ( Radius of the satellite orbit )
Period of the orbit
or
(2  ( Radius of the satellite orbit )) 2 =
Konstant
.
2
( Period of the orbit )
Radius of satellite orbit
Solving for the Period yields
( Period of the orbit ) 2 = Konst ( Radius of the satellite orbit ) 3
Climate and Global Change Notes
6-8
Satellite Observations
Satellite Orbits
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Orbital velocity –
Velocity required
for an object to
orbit the Earth
at a specific radius
Science quotes of 5th and
6th graders When people run around
and around in circles we
say they are crazy. When
planets do it we say they
are orbiting.
Climate and Global Change Notes
6-9
Satellite Observations
Types of Orbits
•
http://www.thetech.org/exhibits_events/
online/satellite/4/4b/4b.1.html
Lower Earth Orbit (LEO)
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Orbit at 500 - 3,000 km above the Earth (definition varies)
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Used for reconnaissance, localized weather and imaging
of natural resources.
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Space shuttle can launch and retrieve satellites in this orbit
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Now coming into use for personal voice and data
communications
http://www.thetech.org/exhibits_events/
online/satellite/4/4a/4a.1.html
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Weather satellites
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Polar orbit - Note, as the satellite orbits, the Earth is turning
underneath. Current NOAA satellites orbit about 700 - 850 km
above Earth’s surface
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Orbital period about every 98 - 102 min
Climate and Global Change Notes
6-10
Satellite Observations
Types of Orbits (Con’t)
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Lower Earth Orbit (LEO) (Con’t)
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Weather satellites (Con’t)
>
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Examples
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Climate and Global Change Notes
6-11
Satellite Observations
Types of Orbits (Con’t)
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Lower Earth Orbit (LEO) (Con’t)
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International Space Station
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Specifications
‡
Slightly elliptical orbit, which varies from 351 km (218 miles) to
356 km (221 miles) from Earth
‡
Travels from west to east on an orbital inclination of 51.6°
‡
Orbital period 90-93 min
Climate and Global Change Notes
6-12
Satellite Observations
Types of Orbits (Con’t)
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Medium Earth Orbit (MEO)
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Orbit at 3,000 - 30,000 km (definition varies)
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Typically in polar or inclined orbit
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Used for navigation, remote sensing,
weather monitoring, and sometimes
communications
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GPS (Global Position System) satellites
‡ 24-27 GPS satellites (21+ active, 3+
spare) are in orbit at 20,000 km
(about 10,600 miles) above the Earth;
placed into six different orbital planes,
with four satellites in each plane
‡
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http://www.gisillinois.org/gps/G
PSDEF/sat.htm
One pass about every 12 h
Climate and Global Change Notes
6-13
Satellite Observations
Types of Orbits (Con’t)
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Highly Elliptical Orbits (HEO)
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Typically pass low (1,000 km) over the southern regions,
then loop high over the northern regions
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One pass every 4 to 12 h
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Used in communications to provide coverage of the higher
latitudes and the polar regions
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http://www.thetech.org/exhibits_events/
online/satellite/4/4d/4d.1.html
Climate and Global Change Notes
6-14
Satellite Observations
Types of Orbits (Con’t)
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Geosynchronous
http://www.thetech.org/exhibits_events/
online/satellite/4/4c/4c.1.html
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Orbital period of 1 day, i.e.,
satellite stays over the same
spot on the Earth
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Orbital radius is 42,164 km or 35,786 km above the Earth’s surface at
the Equator where the Earth’s radius is 6.378 * 106 m
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Used for many communication satellites;
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Cover a country like Australia
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Don’t require complex tracking dishes to receive the signals;
Note: satellite stay stationary relative to Earth
Climate and Global Change Notes
6-15
Satellite Observations
Types of Orbits (Con’t)
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Geosynchronous (Con’t)
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Weather satellites
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GOES (Geosynchronous Operational Environmental Satellites)
Satellite
Climate and Global Change Notes
Observing Climate - Remote
Sensing
6-16
Temporal Resolution
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What temporal and spatial resolution is needed for your problem
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View the same location at all times
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View the the whole globe every so often
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View a spot at high spatial resolution
Determines the satellite orbit you choose
Climate and Global Change Notes
6-17
Satellite Observations
Temporal Resolution
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What part of the globe can be viewed?
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The size of the field of view
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How often the satellite can revisit the same place?
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Length of time
the satellite is
on the sunny
side of the
planet.
Example
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11 Sept
4:55 UT 12 Sept
3:39 UT
2001
Climate and Global Change Notes