Multi-spectral image


Multi-spectral image

Multi-spectral imaging is a technology originally developed for space-based imaging. Multi-spectral imaging can capture light from frequencies beyond the visible light range, such as infrared. This can allow extraction of additional information that the human eye fails to capture with its receptors for red, green and blue.

Multi-spectral images are the main type of images acquired by Remote sensing (RS) radiometers. Multi-spectral is the opposite of panchromatic. Usually satellites have 3 to 7 or more radiometers (Landsat has 7). Each one acquires one digital image (in remote sensing, called a "scene") in a small band of visible spectra, ranging 0.7 µm to 0.4 µm, called red-green-blue (RGB) region, and going to infra-red wavelengths of 0.7 µm to 10 or more µm, classified as NIR-Near InfraRed, MIR-Middle InfraRed and FIR-Far InfraRed or Thermal. In the Landsat case there are 7 scenes comprising a 7 band multi spectral image.

This technology has also assisted in the interpretation of ancient papyri such as those found at Herculaneum, by imaging the fragments in the infrared range (1000nm). Often the text on the documents appears to be as black ink on black paper to the naked eye. At 1000nm, the difference in light reflectivity makes the text clearly readable. It has also been used to image the Archimedes Palimpsest by imaging the parchment leaves in bandwidths from 365-870 nm and then using advanced digital image processing techniques to reveal the under text of Archimedes work.

pectral bands

The wavelengths are approximate; exact values depend on the particular satellite's instruments:
* Blue, 450-515..520 nm, used for atmospheric and deep water imaging. Can reach within convert|150|ft|m deep in clear water.
* Green, 515..520-590..600 nm, used for imaging of vegetation and deep water structures, up to convert|90|ft|m in clear water.
* Red, 600..630-680..690 nm, used for imaging of man-made objects, water up to convert|30|ft|m deep, soil, and vegetation.
* Near infrared, 750-900 nm, primarily for imaging of vegetation.
* Mid-infrared, 1550-1750 nm, for imaging vegetation and soil moisture content, and some forest fires.
* Mid-infrared, 2080-2350 nm, for imaging soil, moisture, geological features, silicates, clays, and fires.
* Thermal infrared, 10400-12500 nm, uses emitted radiation instead of reflected, for imaging of geological structures, thermal differences in water currents, fires, and for night studies.
* Radar and related technologies, useful for mapping terrain and for detecting various objects.

pectral band usage

For different purposes, different combinations of spectral bands can be used. They are usually represented with red, green, and blue channels. Mapping of bands to colors depends on the purpose of the image and the personal preferences of the analysts. Thermal infrared is often omitted from consideration due to poor spatial resolution, except for special purposes.
* True-color. Uses only red, green, and blue channels, mapped to their respective colors. A plain color photograph. Good for analyzing man-made objects. Easy to understand for beginner analysts.
* Green-red-infrared, where blue channel is replaced with near infrared. Vegetation, highly reflective in near IR, then shows as blue. This combination is often used for detection of vegetation and camouflage.
* Blue-nearIR-midIR, where blue channel uses visible blue, green uses near-infrared (so vegetation stays green), and mid-infrared is shown as red. Such images allow seeing the water depth, vegetation coverage, soil moisture content, and presence of fires, all in a single image.Many other combinations are in use. Near infrared is often shown as red, making vegetation covered areas appear red.

Multispectral Data Analysis Software

* MicroMSI endorsed by the NGA.
* Opticks - an open source remote sensing application.

ee also

* Hyperspectral imaging
* Full Spectral Imaging
* Remote sensing
* Spy satellite

References

* Harold Hough: Satellite Surveillance, Loompanics Unlimited, 1991, ISBN 1-55950-077-8


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • multi-spectral imagery — The image of an object obtained simultaneously in a number of discrete spectral bands. Also called MSI …   Military dictionary

  • Image resolution — describes the detail an image holds. The term applies equally to digital images, film images, and other types of images. Higher resolution means more image detail. Image resolution can be measured in various ways. Basically, resolution quantifies …   Wikipedia

  • Image analysis — is the extraction of meaningful information from images; mainly from digital images by means of digital image processing techniques. Image analysis tasks can be as simple as reading bar coded tags or as sophisticated as identifying a person from… …   Wikipedia

  • Image sensor — A CCD image sensor on a flexible circuit board …   Wikipedia

  • Digital image — A digital image is a numeric representation (normally binary) of a two dimensional image. Depending on whether or not the image resolution is fixed, it may be of vector or raster type. Without qualifications, the term digital image usually refers …   Wikipedia

  • MSIA — Multi Spectral Image Analyzer NASA …   Acronyms

  • MSIA — Multi Spectral Image Analyzer ( > NASA Acronym List ) …   Acronyms von A bis Z

  • Hyperspectral imaging — collects and processes information from across the electromagnetic spectrum. Unlike the human eye, which just sees visible light, hyperspectral imaging is more like the eyes of the mantis shrimp, which can see visible light as well as from the… …   Wikipedia

  • Remote sensing application — A remote sensing application is a software application that processes remote sensing data. Remote sensing applications are similar to graphics software, but they enable generating geographic information from satellite and airborne sensor data.… …   Wikipedia

  • MicroMSI — for Windows is a remote sensing imagery analysis program designed for use in introductory courses in remote sensing, developed by the National Geospatial Intelligence Agency. MicroMSI for Windows is a public domain program and can be freely… …   Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.