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Remote Sensing of the Ocean
and Atmosphere:
John Wilkin
[email protected]
IMCS Building Room 214C
732-932-6555 ext 251
Orbits and
Measurement Geometry
Johannes Kepler (1571 – 1630)
German mathematician,
astronomer and astrologer
1. Planets move in elliptical
orbits with the sun as one
focus
2. the radius vector from the
sun to the planet sweeps
out equals areas in equal
times
3. T2 : R3 ratio is constant for
all planets, where T is
orbital period and R is semimajor axis of the orbit
Epoch (UTC):
10:07:53 AM, Monday, January 28, 2008
Eccentricity:
0.0005362
Inclination:
51.6418°
Perigee Height:
334 km
Apogee Height:
341 km
Right Ascension of
Ascending Node:
22.2238°
Orbit Number at Epoch:
52631
Revolutions per Day:
15.77540422
Nov 5, 2007 view from Space Shuttle
Stewart, R. H., 1985, Methods of Satellite Oceanography, University of California Press, 360 pp.
Stewart, R. H., 1985, Methods of Satellite Oceanography, University of California Press, 360 pp.
http://spaceflight.nasa.gov/realdata/elements
See graphics of orbital elements and data for ISS
Jason-1 launch from Vandenburg Air Force Base, California
Orbit: http://www.aviso.oceanobs.com/en/missions/current-missions/jason-1/orbit/index.html
Launch: http://www.youtube.com/watch?v=Z4WHOSF2Ktg
Other launches:
Delta-II (Themis):
http://www.youtube.com/watch?v=p_pAhPecto0
Ariane:
http://www.youtube.com/watch?v=OfONuo3h3t0
http://www.youtube.com/watch?v=kYUrqdUyEpI
Jason-2 OSTM
http://www.youtube.com/watch?v=cf0loVEs_lo
Topex/Poseidon launched with Ariane rocket
http://sealevel.jpl.nasa.gov/gallery/tiffs/videos/launch.mov
Pegasus vehicle aircraft launch
http://www.youtube.com/watch?v=QRHiTvRHHd8
OSTM / Jason-2 Boost Profile
Space craft separation:
Hohmann Transfer
Maneuver to different inclination
http://en.wikipedia.org/wiki/Hohmann_transfer
http://www.nytimes.com/2007/02/06/science/space/06orbi.html?emc=eta1
On Jan 11, 2007, China tested an antisatellite rocket. The initial collision added
800 to 1000 pieces of space junk to the
current total of detectable objects.
How many detectable objects (< 4
inches) are in orbit?
Collisions between existing debris
generate additional pieces of debris.
There is concern that eventually a chain
reaction will ensue (the Kessler
syndrome) littering the low earth orbit
(LEO) with debris making it almost
impenetrable to new satellite launches for
fear of collision.
http://www.nytimes.com/2007/02/06/science/20070206_ORBIT_GRAPHIC.html
Kessler, D. J., and Burton G. Cour-Palais. "Collision frequency of artificial satellites – The creation of a debris
belt." Journal of Geophysical Research Vol. 83 (June 1978): 2637-2646.
http://spaceflight.nasa.gov/realdata/elements
See graphics of orbital elements and data for ISS
Sidereal day = time it takes for Earth to rotate through 360o
This is slightly shorter than a solar day (24 hours)
There are 365.25 solar days in a year but 366.25 sidereal days
Sidereal day = 365.25/366.25*24 = 29.93 hours
solar
sidereal
http://en.wikipedia.org/wiki/Sidereal_time
SeaWiFS daily
coverage
Terra satellite, MODIS instrument, coverage of all instrument
swaths during a single day ( 01/28/2006 )
Jason
altimeter
satellite
ENVISAT
35-day repeat
Equatorial separation of
Jason groundtracks is 315 km
Scan geometry
• zenith angle w.r.t. satellite nadir
• look angle and solar zenith
angle w.r.t local vertical
• Fixed solid angle Field of View
(FOV) such as for an optical lens,
gives elliptical footprint off-nadir
and varying spatial resolution in
the scan
View satellite orbits and ground tracks at:
http://science.nasa.gov/realtime/jtrack/Spacecraft.html
Internet resources on orbits and satellites
•
http://science.nasa.gov/realtime/jtrack/Spacecraft.html
Shows ground tracks and 3-D orbits for all satellites
– Notice the clusters of satellites in the major categories or orbits
•
•
•
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Geostationary
Polar orbiting (NOAA, Topex, ERS, Envisat)
Low Earth orbit (Iridium, HST, ISS)
GPS
– Unusual orbits (especially ground track)
• Chandra
• IMAGE
• CRRES (in a geosynchronous transfer orbit)
•
http://heavens-above.com
Shows predicted orbits and visibility magnitudes and star charts of pass
trajectories for all satellites
– See Homework 1
•
http://tinyurl.com/11-670-451-homework-1
http://spaceflight.nasa.gov/realdata/elements
– See graphics of orbital elements and data for ISS
•
Real-time satellite tracking at http://www.n2yo.com