geostationary and sun-synchronous

Orbital characteristics of Remote sensing satellite geostationary and sun-synchronous

Orbits in Remote Sensing

Orbit = the path a satellite follows around the Earth.
The orbit determines what part of Earth the satellite can see, how often it revisits, and what applications it is good for.
Remote sensing satellites mainly use two standard orbits:
- Geostationary Orbit (GEO)
- Sun-Synchronous Orbit (SSO)

Geostationary Satellites (GEO)

Characteristics

Altitude: ~35,786 km above the equator.
Period: 24 hours → same as Earth's rotation.
Orbit type: Circular, directly above the equator.
Appears "stationary" over one fixed point on Earth.

Concepts & Terminologies

Geosynchronous = orbit period matches Earth's rotation (24h).
Geostationary = special type of geosynchronous orbit directly above equator → looks fixed.
Continuous coverage: Can monitor the same area all the time.

Applications

Weather satellites (e.g., INSAT, GOES) → continuous monitoring of clouds, storms, cyclones.
Telecommunication & broadcasting → because the antenna can always point at the same satellite.

Sun-Synchronous Satellites (SSO)

Characteristics

Altitude: ~600–900 km (Low Earth Orbit).
Period: ~90–100 minutes (around 14 orbits per day).
Orbit inclination: near-polar (~98°).
Passes the same spot at the same local solar time every day → ensures consistent sunlight conditions.

Concepts & Terminologies

Near-polar orbit: passes close to the poles → covers almost all Earth's surface.
Sun-synchronous = orbit shifts slightly every day so the satellite crosses each location at the same local solar time → ideal for comparing images over time.
Revisit cycle = how often the satellite passes over the same area (e.g., every 5–16 days depending on mission).

Applications

Earth observation & remote sensing (Landsat, Sentinel, IRS, Cartosat, ResourceSat).
Environmental monitoring: forests, agriculture, urban growth, glaciers.
Disaster management: floods, earthquakes, landslides.

GEO vs. SSO (Simplified Comparison)

Feature	Geostationary (GEO)	Sun-Synchronous (SSO)
Altitude	~36,000 km	600–900 km
Coverage	Fixed area, ~⅓ of Earth	Global (pole-to-pole)
Revisit time	Continuous over one region	Same spot daily at same solar time
Best for	Weather, communication	Earth observation, mapping
Examples	INSAT, GOES, Meteosat	Landsat, Sentinel, IRS, Cartosat

Geostationary satellites stay fixed over one region → great for real-time monitoring (weather, communication).
Sun-synchronous satellites orbit pole-to-pole and give global coverage with consistent sunlight → great for mapping and scientific studies.

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