satellite images

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

History

The first satellite photographs of Earth were made April 1, 1960 by the weather satellite TIROS-1. 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. 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. Other countries have their own satellite imaging programs. There are also private companies that provide commercial satellite imagery. Blue Marble was a project for mapping the visible color of the Earth with about 1-km resolution. The colourful resulting images from Blue Marble have become very popular in the media and among the public. 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.

Uses

Satellite images have many applications in agriculture, geology, forestry, 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. Analysis of satellite imagery is conducted by specialists known as Photographic Interpreters or PIs.

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.

Resolution and data

The resolution of satellite images varies depending on the instrument used and the altitude of the satellite's orbit. For most cities in the world photos with resolution of 10 meters or better are available. For areas outside cities the resolution can be 100-500 meters. Most of the Earth is imaged with resolution of 1 km or better. For many smaller areas images with resolution as high as 10 cm can be available. Satellite imagery is 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.

Disadvantages

Because the total area of the land on Earth is so large and because resolution is relatively high, satellite databases are huge and creating these images is time-consuming. The sun is the major source of light for such photography, and thus weather conditions and time-of-day must be at a premium to create reasonable images. 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.

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.

See also

• Object-oriented image classification (of satellite imagery)
• SRTM
• MODIS
• GLOBE
• Virtual globe
  • NASA World Wind
  • Google Earth
• TerraServer-USA
• Terraserver.com
• Google Maps
• Virtual Earth
• Stratellite
• Pictometry

External links

• Blue Marble - the most detailed true-color image of the entire Earth to date.
• World Wind - an open source 3D Earth-viewing software developed by NASA that accesses NASA JPL database
• Google Earth - Google's commercial 3D Earth-viewing software- Free.
• Google Maps satellite imagery
• TerraServer-USA - formerly Microsoft TerraServer, a repository of free satellite images of the United States
• GlobeXplorer - library of satellite imagery and maps
• Satellite Imaging Corp. - Gallery of satellite images