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Methods - Satellite

Satellite orbits

Satellite photography

Methods of Aerial Photography - Satellite

SATELLITE IMAGES:

Medium and high-resolution photographs taken from satellites orbiting high above the Earth are available for all locations in the UK and elsewhere in the world. These can be acquired from certain licensed, subscription-based sources and can be purchased, often at reasonable cost. Low-resolution images are also available from some sources at low or no cost, but while they provide a fascinating perspective of the world, the quality is usually of insufficient resolution for professional use.

High resolution satellite images for specific locations and at specific scales and magnifications can be acquired through us, if commercially available.

Currently, there are thought to be about 300 satellites orbiting the Earth, but in the next decade or so, many more will be operating or are planned to be launched. With hundreds of different types of instruments on board, they will increase the already vast amount of data and photographs being transmitted to Earth, some of which will be available commercially to the non-scientific community.

Apart from dedicated defence and surveillance satellites, many of the other satellites have meteorological and environmental observations are their primary objective, providing weather and climatic photographic data for national agencies. Other satellites provide a diverse range of other information such as telecommunications, scientific measurements and other commercially useful data.

As well as conventional 'visible' photographs, satellite images can be produced in the form of Infrared,enhanced infrared, composite visible/infrared, composite satellite/surface maps and water vapour images.

In addition to satellites operated by major governmental agencies, privately-owned and operated satellites provide a large amount of the photographs available commercially. One particular new satellite weighs about 725 kg and orbits the Earth once every 98 minutes at an altitude of approximately 400 miles (680 km). It is in a sun-synchronous orbit so it will pass a given longitude at about the same local time each day 10:30 a.m. The satellite orbit exactly repeats every 140 days.

However, since the sensor is capable of viewing land mass far from the area directly below the path of the satellite, a site can be imaged almost daily, although not always at 1-metre resolution. The satellite produces a number of different types of images (black and white and colour).

These include 1-meter resolution panchromatic, 1-metre resolution pan-sharpened, multispectral and 4-metre resolution multispectral (colour) images, which can be used for a wide variety of applications. These represent the highest resolution satellite imagery currently commercially available.


MAIN TYPES OF SATELLITE ORBITS
(
often described by their inclination (the angle between their orbital plane and the equatorial plane).

Geostationary Orbits (GEO, Geosynchronous):

Satellites orbit over the equator (zero degree inclination) at the same rate the Earth rotates, once every day. They orbit at a height of about 22,300 miles (36,000 km) above a fixed spot on the Earth's surface. This precise positioning allows continuous and consistent monitoring of a specific area. Geostationary satellite's cameras transmit their pictures in 'real time' and therefore provide an instantaneous record of the Earth, its geographical features and weather. A series of these photographs can also be displayed in continuous sequence to produce a movie effect.

Low Earth Orbits (LEO) Heights of approx 300 - 1000 km
and Medium Earth Orbits (MEO) Heights of approx 10,000 km.

An example of a LEO is a Polar Orbit. This closely parallel the earth's 0/180 meridian line (c. 90 degree inclination) and orbit at a much lower altitude of about 530 miles (850 km) providing more detailed information. They pass over the North and South poles each revolution. As the Earth rotates to the East beneath the satellite, each pass monitors an area to the West of the previous pass. These 'strips' of data can be pieced together to produce a picture of a very large area.

Elliptical Orbits: This follows an oval-shaped path and takes about 12 hours to circle the planet, with an inclination of about 64 degrees.

ADVANTAGES:Satellite images can show any proportion of the earth from a full view of one whole side of the planet down to close-up views of individual buildings. It is also possible to overlay a number of different feature sets on the image for specific analytical purposes.

DISADVANTAGES:The choice of images available is wide, but limited to the stock made available by NASA and the other international organisations for commercial use. High magnification images (ie down to street and building level) may not always be accessible for all areas and sometimes can be relatively expensive.

WORKING HEIGHT RANGE:400 - 23,000 miles, depending on the type of satellite and its orbit.

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