Environmental planning and the field of remote sensing has been advanced by the ability to determine the physical properties of various earth components from great distances. Satellite technology provides information about the environment on a planetary scale. 

Satellites, orbiting the earth at a distance of hundreds of miles, gather physical, biological, and social/cultural characteristics and transmit representations (Images) to earth. These images accurately depict the spatial relationships of the complex earths surface. These earth images are valuable in determining the accurate past or current land activity for direct GIS application. 

There are thousands of satellites orbiting the earth. Since the late 1950's these electronic marvels have been a source of amazement to even the casual observer. Although few individuals have an understanding of the complex satellite technology we generally share a perception of national pride in the technical accomplishment. Our lives have been transformed forever by these orbiting communication and information platforms. Originally imaging satellites were created for military purposes. Oil, gas and mineral exploration soon followed the military lead. The advent of a stable earth observation platform soon interested all nations interested in planning and designing on a regional basis. 

Satellite images are used to "remote sense" the characteristics of the earth's surface.  An array of specialized sensors captures the earth's features from polar orbiting satellites and transmits the multi-spectral thematic information to ground stations.  The information is then process and sold by specific area and theme.    In conjunction with other information, satellites can provide much of the necessary data needed for good regional planning efforts. The different images are the RGB display products of different "band" combinations.

The Thematic Mapper Satellite image (above)  is showing a range of practical multi-spectural band display combinations. [6,6,6] [4,2,1] [6,2,1] [4,3,2] [7,4,2].   The satellite information is interpreted then used in conjunction with (for example) proposed road right-of-ways to determine the impact of alternative transportation and development strategies.

The necessity to determine change begins with a realization that the earths surface changes over time through natural phenomenon and human activity. Surface changes are compared in a "before and after" format determined by the needs of the GIS user. Change detection involves comparing two satellite images (or air photos) of the same location, using two separate dates. Obviously, the difference in the dates will depend on the purpose of the study.  Usually, the time difference is measured in years rather than days. For example, the dates must be of sufficient time difference for the subject and area of interest to be discernible. Seasonal differences such as fall-spring or summer-winter are valuable change detection strategies investigating elements such as seasonal water (high/low) or vegetative composition (leaf on/off). 

Shore line edge detection  Q: The hurricane has eroded the coastline. What is the land loss?

Agricultural crop rotational change  Q: Last year our area planted 5000 acres of cotton. How many acres of cotton are planted this year?

Military troop movements   Q: The enemy has placed troops along the border. Where are these troops located, and where are the best locations to attack?

Municipal growth  Q: Our town is growing since 1960. Where are the new housing locations as of 1990?

Forest disease  Q: Pine beetles have destroyed portions of the forest. What is the extent of the existing damage, and where are the beginnings of the next infections?

Forest harvest strategies  Q: There are 50,000 acres of forest as of 1950. Where have the trees been removed as of 1990.

1) Situations where information is unavailable. For example, there is only one set of air photos (or satellite images) available. 

2) Available images are not of the correct seasonal variation. For example, the need is agricultural, specifically how many acres are planted in wheat, within the given region. If the images are taken after the wheat harvest, and before the next planting, it is impossible to determine (by remote sensing techniques) how many acres are dedicated to wheat. 

3) Available images are taken in different, years but within the same month. This combination is best for comparing changes such as forest harvest, or municipal growth, but is not dependable.

4) The situation requires information about the ground surface and the tree canopy is "leaf on" making it impossible to view the ground features. 

5) Information is required in determining the biological health of vegetation and only normal color (not color infrared) imagery is available.