Satellite imagery

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Satellite imagery consists of photographs of Earth or other planets made by means of artificial satellites.

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[edit] History

Image:TIROS-1-Earth.png
First television image of Earth from space transmitted by the TIROS-1 weather satellite.
The first satellite photographs of Earth were made August 14, 1959 by the US satellite Explorer 6. The first satellite photographs of the Moon might have been made on October 6, 1959 by the Soviet satellite Luna 3, on a mission to photograph the far side of the Moon. The Blue Marble photograph was taken from space in 1972, and has become very popular in the media and among the public. Also in 1972 the United States started the Landsat program, the largest program for acquisition of imagery of Earth from space. Landsat 7, the most recent Landsat satellite, was launched in 1999. In 1977, the first real time satellite imagery was acquired by the USA's KH-11 satellite system.

All satellite images produced by NASA are published by Earth Observatory and are freely available to the public. Several other countries have satellite imaging programs, and a collaborative European effort launched the ERS and Envisat satellites carrying various sensors. There are also private companies that provide commercial satellite imagery. In the early 21st century satellite imagery became widely available when affordable, easy to use software with access to satellite imagery databases became offered by several companies and organizations.

[edit] Uses

Image:Crops Kansas AST 20010624.jpg
Satellite photography of the countryside of Haskell County, Kansas, United States.

Satellite images have many applications in agriculture, geology, forestry, biodiversity conservation, regional planning, education, intelligence and warfare. Images can be in visible colours and in other spectra. There are also elevation maps, usually made by radar imaging. Interpretation and analysis of satellite imagery is conducted using software packages like ERDAS Imagine or ENVI. Some of the first image enhancement of satellite photos was conducted by the U.S. Government and its contractors. For example ESL Incorporated developed some of the earliest two dimensional Fourier transforms applied to digital image processing to address NASA photos as well as national security applications.

[edit] Resolution and data

The resolution of satellite images varies depending on the instrument used and the altitude of the satellite's orbit. For example, the Landsat archive offers repeated imagery at 30 meter resolution for the planet, but most of it has not been processed from the raw data. Landsat 7 has an average return period of 16 days. For many smaller areas, images with resolution as high as 10 cm can be available. DigitalGlobe's QuickBird satellite provides the world's highest resolution commercial satellite imagery. The 60 cm resolution of QuickBird's images allows the satellite to distinguish between objects on the ground that are at least 60 cm apart.

Satellite imagery is sometimes supplemented with aerial photography, which has higher resolution, but is more expensive per square meter. Satellite imagery can be combined with vector or raster data in a GIS provided that the imagery has been spatially rectified so that it will properly align with other data sets.

[edit] Disadvantages

Because the total area of the land on Earth is so large and because resolution is relatively high, satellite databases are huge and image processing (creating useful images from the raw data) is time-consuming. Depending on the sensor used, weather conditions can affect image quality: for example, it is difficult to obtain images for areas of frequent cloud cover such as mountain-tops.

Commercial satellite companies do not place their imagery into the public domain and do not sell their imagery; instead, one must be licensed to use their imagery. Thus, the ability to legally make derivative products from commercial satellite imagery is minimized.

Privacy concerns have been brought up by some who wish not to have their property shown from above. Google Maps responds to such concerns in their FAQ with the following statement: "We understand your privacy concerns... The images that Google Maps displays are no different from what can be seen by anyone who flies over or drives by a specific geographic location." Though there is no way to definitively know about Google's intent, the second part of the statement is provable.

[edit] Moving images

In 2005 the Australian company Astrovision (ASX: HZG) announced plans to launch the first commercial geostationary satellite in the Asia-Pacific. It will provide true color, real-time live satellite feeds, with down to 250 metres resolution over the entire Asia-Pacific region, from India to Hawaii and Japan to Australia. They intend to provide this content to users of 3G mobile phones, over Pay TV as a weather channel, and to corporate and government users.

[edit] See also

Image:Flat earth night.png
Composite image of Earth at night

[edit] External links

bg:Спътникова фотография de:Satellitenbild es:Imagen satelital ko:위성 사진 hu:Műholdfelvétel nl:Satellietfoto ja:衛星画像 pt:Imagem de satélite ru:Спутниковая фотосъемка zh:卫星地图

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