Satellite Imagery

Jan 16, 2010

SOFAB Satellite Spacecraft & Imagery:

• A satellite unmanned spacecraft revolves around earth in a circular or elliptical path. These unmanned satellite spacecraft carry a variety of sensory equipment that scans Earth and electronically communicates the data back to Earth ground stations. The path a satellite follows is an orbit within a given trajectory path.
• There are three types of satellite imagery in use at present these are Optical, Thermal (Infra Red) and Radar. Each type has its specialized uses.
• Optical is good for high resolution images but has drawbacks where it will only give good images during daylight and no cloud cover conditions.
• Thermal is acceptable for both night and day but also is disrupted with cloud cover.
• Radar will provide images both day and night and with cloud cover. Radar is best suited for collecting images of sea or water related targets rather than land generally images are in black and white. Radar images are in black and white however they can be provided in color by using up to three satellites and combining the images as layers and then using computer generated color to provide color images.

What Are the Types of Satellite Orbits?
There are three basic kinds of orbits, depending on the satellite's position relative to Earth's surface:

• Geostationary Orbits (also called geosynchronous or synchronous) are orbits in which the satellite is always positioned over the same spot on Earth. Geostationary satellites orbit at a speed that enables them to remain constantly over the same area of Earth. This position provides constant "viewing" of a specific area of Earth. Many geostationary satellites are above a band along the equator, with an altitude of about 22,223 miles, or about a tenth of the distance to the Moon. The "satellite parking strip" area over the equator is becoming congested with several hundred television, weather and communication satellites! This congestion means each satellite must be precisely positioned to prevent its signals from interfering with an adjacent satellite's signals. Television, communications and weather satellites all use geostationary orbits. Geostationary (Fixed orbit) satellites are generally used for environmental, weather and other such observations and will provide low resolution of 100 to 1,000s of meters. Geostationary orbits are why a DSS satellite TV dish is typically bolted in a fixed position.

• The scheduled Space Shuttles use a much lower, Asynchronous Orbit, which means they pass overhead at different times of the day. Asynchronous Observation satellite Orbit’s typically orbiting at altitudes from 300 to 600 miles (480 to 970 km), are used for tasks like photography. Asynchronous Orbit (Rotating orbit) is the best satellite for high resolution imagery. A constellation of satellites will provide more images per day. Observation satellites such as the Landsat 7 perform tasks such as:
• Mapping
• Ice and sand movement
• Locating environmental situations (such as disappearing rainforests)
• Locating mineral deposits
• Finding crop problems

• In a Polar Orbit, the satellite generally flies at a low altitude and passes over the planet's poles on each revolution. Many of these satellites operate in Sun-synchronous orbits. The Sun-synchronous orbits are designed so that the satellite passes over the same terrain at the same time each day. The polar orbit remains fixed in space as Earth rotates inside the orbit. As a result, much of Earth passes under a satellite in a polar orbit. Because polar orbits achieve excellent coverage of the planet, they are often used for satellites that do mapping and photography.

• The International Space Station is in a LEO Orbit that varies from 319.6 km (199 mi) to 346.9 km (216 mi) above the Earth's surface. The most popular image it produces are infrared images.

• LEO Orbit: The commonly accepted definition for LEO Orbit is between 160 - 2,000 km.

Types of available satellites:

1. Weather satellites help meteorologists predict the weather or see what's happening at the moment. Typical weather satellites include the TIROS, COSMOS and GOES satellites. The satellites generally contain cameras that can return photos of Earth's weather, either from fixed geostationary positions or from polar orbits.
2. Communications satellites allow telephone and data conversations to be relayed through the satellite. Typical communications satellites include Telstar and Intelsat. The most important feature of a communications satellite is the transponder -- a radio that receives a conversation at one frequency and then amplifies it and retransmits it back to Earth on another frequency. A satellite normally contains hundreds or thousands of transponders. Communications satellites are usually geosynchronous.
3. Broadcast satellites broadcast television signals from one point to another (similar to communications satellites).
4. Scientific satellites perform a variety of scientific missions. The Hubble Space Telescope is the most famous scientific satellite, but there are many others looking at everything from sun spots to gamma rays.
5. Navigational satellites help ships and planes navigate. The most famous are the GPS NAVSTAR satellites.
6. Rescue satellites respond to radio distress signals (read this page for details).
7. Earth observation satellites observe the planet for changes in everything from temperature to forestation to ice-sheet coverage. The most famous are the LANDSAT series.
8. Military satellites are up there, but much of the actual application information remains secret. Intelligence-gathering possibilities using high-tech electronic and sophisticated photographic-equipment reconnaissance are endless. Applications may include:
   • Relaying encrypted communications
   • Nuclear monitoring
   • Observing enemy movements
   • Early warning of missile launches
   • Eavesdropping on terrestrial radio links
   • Radar imaging
   • Photography (using what are essentially large telescopes that take pictures of militarily interesting areas).

Satellite Imagery:

• High resolution images to military standard are taken from an orbit of 36km giving a resolution down to 20 Centimeters per pixel, these are normally military satellites and have a shorter life due to burn out from the earth’s atmosphere as they are very close to the outer atmosphere. They also carry a high fuel payload for continued orbit adjustment.
• Higher orbits of 600km and higher will provide resolutions of 0 to 1metre and also 0 to 4metres. These are mainly commercial satellites widely used for commercial purposes.
• In general, the higher the orbit, the longer the satellite can stay in orbit. At lower altitudes, a satellite runs into traces of Earth's atmosphere, which creates drag. The drag causes the orbit to decay until the satellite falls back into the atmosphere and burns up. At higher altitudes, where the vacuum of space is nearly complete, there is almost no drag and a satellite can stay in orbit for centuries
• In order to provide as close to live images as possible a constellation is required with a minimum of three satellites however the more you put into orbit the closer to real time images you can achieve.
• Images from commercial satellites typically cover between 10 to 100 square kilometers per image collection depending on tasking.
• Commercially available images are rarely current unless a license has been granted for current images; Google Earth and other similar viewers can contain images over three years old. Some images are also manually altered to avoid showing sensitive areas such as military and key installations of national importance.
• Commercial satellites are tasked by many organizations ranging from governments through to private enterprise for mapping, agriculture, demographics through to river flow and land mass movement etc.
• Costs of images vary depending on date of acquisition, amount of details and number of images required: Cost show in chart attached.

Trust Middle East Company Ltd can provide the following services. Please email us for the latest prices:

1. 10km x 10km resolution of 1m.
2. 7km x 7km resolution of 1m.
3. 40km x 40km stripmap resolution of 3m.
   • Up to 4 images per day of the same area can be provided for the above services.
   • Data can be delivered by Hard Disc, DVD-R 4.7gb or by FTP server download
   • Images sizes vary but average between 300mb to 5gb.

Note:

For Total Control and images when required without queuing for slot times with satellites the only option is to launch your own constellation of satellites, this is costly and can take up to 6 years before the first satellites are in orbit.