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A multispectral image is created by measuring energy at various wavelengths and using different colors to represent the energy present along each separate wavelength. The assorted grayscale images, known as bands, receive a different color and are combined to create a composite image. For example, Band A might be colored red, while Band B is colored blue and Band C is colored green. Put them together and the color patterns formed on the composite image allow the viewer to identify surface features of the object.
A satellite image that details such features as mountains, buildings and water across wide swaths of land is a prime example of a multispectral image and one of the most common uses of multispectral technology. The United States’ Landsat satellite program has provided a vast array of multispectral images since its first satellite launch in 1972. That satellite relays huge amounts of data back to Earth on a continual basis. Landsat 7, the newest Landsat satellite, is in an orbit that allows it to re-image a 2-degree portion of Earth every 16 days.
Information provided by Landsat multispectral images is valuable in a range of fields, including hydrology, environmental monitoring and land-use assessment. Many countries rely on information from the US-based program and have set up stations to directly receive the information. The stations allow those countries the opportunity to receive the information almost as soon as it is gathered, without the delay of waiting for NASA to process and redistribute the images. NASA approves the stations with the agreement that the stations will provide the data to those who need it within their region.
Multispectral imaging from space got its start in 1968, when NASA included it in the Apollo 9 mission. It wasn’t long before unmanned satellites designed specifically for multispectral imaging were launched. Technology hasn’t stopped advancing in the decades since, and hyperspectral imaging that can capture so-called narrow bands of information — as compared to multispectral imaging’s broad bands — now provides even more detailed data for scientists and others.
Hyperspectral imaging can capture a swath width as relatively tiny as 11 kilometers, or less than 7 miles. The problem with such imaging long had been rate of speed required of equipment traveling on fast-moving air and space vehicles. The vehicle’s speed left too little time for the equipment to focus and create such a detailed image. Scientific advances have erased that barrier.
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