Transcript Introduction - San Jose State University

Satellite Orbits
Satellite Meteorology/Climatology
Professor Menglin Jin
Satellite Orbits
At what location is the satellite looking?
 When is the satellite looking at a given
location?
 How often is the satellite looking at a
given location?
 At what angle is the satellite viewing a
given location?

Atmospheric Remote Sensing Sensors,
Satellite Platforms, and Orbits


Satellite orbits and platforms
• Low Earth orbit
– Sunsynchronous and repeat coverage
– Precessing
• Geosynchronous orbit
Sensor scanning modes
• Whiskbroom and pushbroom scanners
• Active and passive microwave radiometers
Special Orbits
Orbital parameters can be tuned to produce
particular, useful orbits
• Geostationary
• Geosynchronous
• Sunsynchronous
• Altimetric
Types of orbits

Sunsynchronous orbits: An orbit in which the
satellite passes every location at the same time
each day
• Noon satellites: pass over near noon and midnight
• Morning satellites: pass over near dawn and dusk
• Often referred to as “polar orbiters” because of the
high latitudes they cross
• Usually orbit within several hundred to a few
thousand km from Earth
Types of orbits

Geostationary (geosynchronous) orbits: An
orbit which places the satellite above the
same location at all times
• Must be orbiting approximately 36,000 km
above the Earth
• Satellite can only “see” one hemisphere
Altimetric Orbits
• Ascending
and descending orbits should
cross at 90º
– Designed so that orthogonal
components of surface slope will have
equal accuracy
• Orbital inclination depends on location of
altimetric needs
Geosynchronous Meteorological Satellites
WMO Member States
Sector
West-Pacific
East-Pacific
West-Atlantic
East-Atlantic
Indian Ocean
Satellites in Orbit
(+mode)
MTSAT-1R (Op)
MTSAT-2 (B)
GOES-9 (B)
Operator
Japan
Japan
USA/NOAA
Location
140°E
145°E
160°E
Launch
date
2/26/05
2/18/06
5/99
GOES-11 (Op)
GOES-10 (B)
GOES-12 (Op)
GOES-13 (P)
Meteosat-6 (B)
Meteosat-7 (B)
Meteosat-8 (Op)
Meteosat-9 (P)
Meteosat-5 (Op)
USA/NOAA
USA/NOAA
USA/NOAA
USA/NOAA
EUMETSAT
EUMETSAT
EUMETSAT
EUMETSAT
EUMETSAT
135°E
60°W
75°W
89.5°W
10°E
0°E
3.4°W
6.5°W
63°E
5/00
4/97
7/01
5/06
11/93
2/97
8/28/02
12/21/05
3/91
GOMS-N1 (B)
FY-2C (Op)
Kalpana-1 (Op)
INS AT-3A (Op)
Russia
China/CMA
India
India
76°E
105°E
74°E
93.5°E
11/94
10/19/04
9/12/02
4/10/03
Status
Fully functional
Back-up to MTSAT-1R
Dissemination not
activated
GOES-West
South America coverage
GOES-East
In commissioning
Rapid scan anomaly
To be relocated to 57.5°E
EUMETCAST
In commissioning
Functional but high
inclination mode
Standby since 9/98
Functional
Dedicated
Operational
Low Earth Orbit Concepts
Descending node
Ascending
node
Perigee
Ground track
Orbit
Inclination
angle
Equator
Orbit
South Pole
Apogee
Sun-Synchronous Polar Orbit
Earth
Revolution
Equatorial
illumination
angle
Satellit
e Orbit
• Satellite orbit precesses (retrograde)
– 360° in one year
• Maintains equatorial illumination angle constant throughout the year
– ~10:30 AM in this example
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
Tropical Rainfall Measuring
Mission Orbit (Precessing)
 A precessing
lowinclination (35°),
low-altitude (350
km) orbit to achieve
high spatial
resolution and
capture the diurnal
variation of tropical
rainfall
– Raised to 402 km in
August 2001
TRMM Coverage
1 day coverage
2 day coverage
Definition of Orbital Period of a
Satellite
The orbital period of a satellite around a
planet is given by
T0  2( R p  H )
R p  H 
2
gs R p
where 
T0 = orbital period (sec)
Rp =planet radius (6380 km for Earth)
H =orbit altitude above planet’s surface (km)
gs =acceleration due to gravity (0.00981 km s-2 for Earth)
Orbital Characteristics of Selected Missions
Low Earth Orbit & Precessing Missions
Satellite
Jason-1
Meteor-3M/SAGE III
Landsat 1-3
SPOT
NOAA
QuikScat
ACRIMSAT
Landsat 4-7
Terra, Aqua, Aura
ICESat
UARS
ERBS
SORCE
TRMM
TRMM
Altitude
(km)
1336
1020
907-915
832
850
803
720
705
705
Inclination
(°)
66
99.5
99.2
98.7
98-99
98.6
98.1
98.2
98.2
600
585
610
640
402
350
94
57
57
40
35
35
Orbital Period
(min)
112.3
105.5
103.1
101.5
102-104
100.9
99.1
98.8
98.8
96.6
96.3
96.8
97.5
92.6
91.5
Repeat
Coverage
10
18
26
11
16
16
–
–
–
–
–
–
Orbits/day
12.8
13.7
14.0
14.2
14.0
14.3
14.5
14.6
14.6
14.9
14.9
14.9
14.8
15.6
15.7
Ellipse

An ellipse is defined as follows: For two given points, the foci, an
ellipse is the locus of points such that the sum of the distance to
each focus is constant.

BTW, Locus-A word for a set of points that forms a geometric
figure or graph
Kepler’s laws
1. Satellites follow an elliptical orbit with the Earth
as one focus
Foci
Apogee
Perigee
Period of orbit
Period of orbit
2
4

T2=
r3
Gme
Gravitational constant



Radius of the orbit
Mass of the Earth
Valid only for circular orbits (but a good
approximation for most satellites)
Radius is measured from the center of the Earth
(satellite altitude+Earth’s radius)
Accurate periods of elliptical orbits can be
determined with Kepler’s Equation
Sunsynchronous image (SMMR)
Geostationary Image (GOES-8)
Geostationary satellites
•Meteosat
•GOES
•Operational
•Specific wave bands
•Specific use
•High temporal frequency
Space-time sampling

Geostationary
• Fixed (relatively) field of view
• View area of about 42% of Earth’s surface

Sunsynchronous
• Overlapping views
• See each point at several viewing angles

Other orbits (“walking orbits”)
• Passes each location at a different time of day
• Earth Radiation Budget Satellite
• Useful when dirunal information is needed
Imaging Systems
Cross-track scanner
• Whiskbroom scanner
• Pushbroom sensor
•
Cross-track Scanner
• “back and forth” motion of the foreoptics
• scans each ground resolution cell one-by-one
• Instantaneous Field of View (IFOV) of
instrument determines pixel size
• Image is built up by movement of satellite
along the orbital track and scanning acrosstrack
Along-track scanner
(“Pushbroom)
• Linear array of detectors (aligned cross-track)
– reflected radiance passes through a lens and onto a line of
detectors
• Image is built up by movement of the satellite along its orbital
track (no scanning mirror)
• Area array can also be used for multi-spectral remote sensing
– dispersion used to split light into narrow spectral
bands and individual detectors
Scanning techniques

Vidicom
• Like television camera; “sees” everything at once

Swinging
• Results in a zig-zag pattern of scanning

Spinning
• Satellite spins in order to create image

Pushbroom
• Multiple scanning elements, relies on forward
motion of satellite
Getting the Data to the Ground
• On-board
recording and pre-processing
• Direct telemetry to ground stations
– receive data transmissions from satellites
– transmit commands to satellites (pointing,
turning maneuvers, software updating
• Indirect transmission through Tracking
and Data Relay Satellites (TDRS)