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Satellite Orbits Satellite Meteorology/Climatology Professor Menglin Jin.
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Transcript of Satellite Orbits Satellite Meteorology/Climatology Professor Menglin Jin.
Satellite Orbits
Satellite Satellite Meteorology/ClimatologyMeteorology/Climatology
Professor Menglin JinProfessor Menglin Jin
Satellite Orbits
At what location is the satellite looking?At what location is the satellite looking? When is the satellite looking at a given When is the satellite looking at a given
location?location? How often is the satellite looking at a How often is the satellite looking at a
given location?given location? At what angle is the satellite viewing a At what angle is the satellite viewing a
given location?given location?
Atmospheric Remote Sensing Sensors, Satellite Platforms, and Orbits
Atmospheric Remote Sensing Sensors, Satellite Platforms, and Orbits
Satellite orbits and platformsSatellite orbits and platforms
• Low Earth orbitLow Earth orbit
– Sunsynchronous and repeat coverageSunsynchronous and repeat coverage
– PrecessingPrecessing
• Geosynchronous orbitGeosynchronous orbit Sensor scanning modesSensor scanning modes
• Whiskbroom and pushbroom scannersWhiskbroom and pushbroom scanners
• Active and passive microwave radiometersActive and passive microwave radiometers
Types of orbits
Sunsynchronous orbitsSunsynchronous orbits: An orbit in which the : An orbit in which the satellite passes every location at the same time satellite passes every location at the same time each dayeach day• Noon satellites: pass over near noon and midnightNoon satellites: pass over near noon and midnight
• Morning satellites: pass over near dawn and duskMorning satellites: pass over near dawn and dusk
• Often referred to as “polar orbiters” because of the Often referred to as “polar orbiters” because of the high latitudes they crosshigh latitudes they cross
• Usually orbit within several hundred to a few Usually orbit within several hundred to a few thousand km from Earththousand km from Earth
Types of orbits
Geostationary (geosynchronous) orbitsGeostationary (geosynchronous) orbits: : An An orbit which places the satellite above the orbit which places the satellite above the same location at all timessame location at all times• Must be orbiting approximately 36,000 km Must be orbiting approximately 36,000 km
above the Earthabove the Earth• Satellite can only “see” one hemisphereSatellite can only “see” one hemisphere
SectorSatellites in Orbit
(+mode) Operator LocationLaunch date Status
MTSAT-1R (Op) Japan 140°E 2/26/05 Fully functionalMTSAT-2 (B) Japan 145°E 2/18/06 Back-up to MTSAT-1RGOES-9 (B) USA/NOAA 160°E 5/99 Dissemination not
activatedEast-Pacific GOES-11 (Op) USA/NOAA 135°E 5/00 GOES-West
GOES-10 (B) USA/NOAA 60°W 4/97 South America coverageGOES-12 (Op) USA/NOAA 75°W 7/01 GOES-EastGOES-13 (P) USA/NOAA 89.5°W 5/06 In commissioning
Meteosat-6 (B)EUMETSAT 10°E 11/93 Rapid scan anomalyMeteosat-7 (B)EUMETSAT 0°E 2/97 To be relocated to 57.5°E
Meteosat-8 (Op)EUMETSAT 3.4°W 8/28/02 EUMETCASTMeteosat-9 (P)EUMETSAT 6.5°W 12/21/05 In commissioning
Meteosat-5 (Op)EUMETSAT 63°E 3/91 Functional but high inclination mode
GOMS-N1 (B) Russia 76°E 11/94 Standby since 9/98FY-2C (Op) China/CMA 105°E 10/19/04 Functional
Kalpana-1 (Op) India 74°E 9/12/02 DedicatedINSAT-3A (Op) India 93.5°E 4/10/03 Operational
West-Pacific
West-Atlantic
East-Atlantic
Indian Ocean
Geosynchronous Meteorological SatellitesWMO Member States
Low Earth Orbit Concepts
Equator
South Pole
Ground track
Ascending node
Inclination angle
Descending node
Orbit
Perigee
Apogee
Orbit
Sun-Synchronous Polar Orbit
Satellite
Orbit
Earth Revoluti
on
• Satellite orbit precesses (retrograde)– 360° in one year
• Maintains equatorial illumination angle constant throughout the year– ~10:30 AM in this example
Equatorial illuminatio
n angle
Sun-Synchronous Orbit of Terra
Spacing Between Adjacent Landsat 5 or 7 Orbit Tracks at the Equator
Timing of Adjacent Landsat 5 or 7 Coverage Tracks
Adjacent swaths are imaged 7 days apart
Polar-Orbiting Satellite in Low Earth Orbit (LEO)
Example from Aqua
A precessing low-A precessing low-inclination (35inclination (35°°), low-), low-altitude (350 km) orbit altitude (350 km) orbit to achieve high spatial to achieve high spatial resolution and capture resolution and capture the diurnal variation of the diurnal variation of tropical rainfalltropical rainfall– Raised to 402 km in Raised to 402 km in
August 2001 August 2001
Tropical Rainfall Measuring Mission Orbit (Precessing)
TRMM Coverage
1 day coverage 2 day coverage
The orbital period of a satellite around a The orbital period of a satellite around a planet is given byplanet is given by
where where 00 = orbital period (sec)= orbital period (sec)
RRpp == planet radius (6380 km for Earth)planet radius (6380 km for Earth)
HH == orbit altitude above planet’s surface (km)orbit altitude above planet’s surface (km)
ggss == acceleration due to gravity (0.00981 km sacceleration due to gravity (0.00981 km s-2-2 for for Earth)Earth)
Definition of Orbital Period of a Satellite
T0 2(Rp H )Rp H
gs Rp2
SatelliteAltitude
(km)Inclination
(°)Orbital Period
(min)Repeat
Coverage Orbits/dayJason-1 1336 66 112.3 10 12.8Meteor-3M/SAGE III 1020 99.5 105.5 13.7Landsat 1-3 907-915 99.2 103.1 18 14.0SPOT 832 98.7 101.5 26 14.2NOAA 850 98-99 102-104 11 14.0QuikScat 803 98.6 100.9 14.3ACRIMSAT 720 98.1 99.1 14.5Landsat 4-7 705 98.2 98.8 16 14.6Terra, Aqua, Aura 705 98.2 98.8 16 14.6
ICESat 600 94 96.6 – 14.9UARS 585 57 96.3 – 14.9ERBS 610 57 96.8 – 14.9SORCE 640 40 97.5 – 14.8TRMM 402 35 92.6 – 15.6TRMM 350 35 91.5 – 15.7
Orbital Characteristics of Selected MissionsLow Earth Orbit & Precessing Missions
Ellipse An ellipse is defined as follows: For two given points, the An ellipse is defined as follows: For two given points, the focifoci, ,
an ellipse is the an ellipse is the locuslocus of points such that the of points such that the sumsum of the of the distance to each focus is distance to each focus is constantconstant..
BTW, Locus-A word for a BTW, Locus-A word for a setset of of pointspoints that forms a that forms a geometric figuregeometric figure or or graphgraph
Kepler’s laws
1. Satellites follow an elliptical orbit with the Earth as one 1. Satellites follow an elliptical orbit with the Earth as one focusfocus
PerigeeApogee
Foci
Period of orbit
Valid only for circular orbits (but a good Valid only for circular orbits (but a good approximation for most satellites)approximation for most satellites)
Radius is measured from the center of the Earth Radius is measured from the center of the Earth (satellite altitude+Earth’s radius)(satellite altitude+Earth’s radius)
Accurate periods of elliptical orbits can be Accurate periods of elliptical orbits can be determined with Kepler’s Equation determined with Kepler’s Equation
T2= r342
Gme
Period of orbit
Gravitational constant Mass of the Earth
Radius of the orbit
Sunsynchronous image (SMMR)
Geostationary Image (GOES-8)
Space-time sampling
GeostationaryGeostationary• Fixed (relatively) field of viewFixed (relatively) field of view• View area of about 42% of Earth’s surfaceView area of about 42% of Earth’s surface
SunsynchronousSunsynchronous• Overlapping viewsOverlapping views• See each point at several viewing anglesSee each point at several viewing angles
Other orbits (“walking orbits”)Other orbits (“walking orbits”)• Passes each location at a different time of dayPasses each location at a different time of day• Earth Radiation Budget SatelliteEarth Radiation Budget Satellite• Useful when dirunal information is neededUseful when dirunal information is needed
Scanning techniques VidicomVidicom
• Like television camera; “sees” everything at onceLike television camera; “sees” everything at once SwingingSwinging
• Results in a zig-zag pattern of scanningResults in a zig-zag pattern of scanning SpinningSpinning
• Satellite spins in order to create imageSatellite spins in order to create image PushbroomPushbroom
• Multiple scanning elements, relies on forward motion of satelliteMultiple scanning elements, relies on forward motion of satellite