Day 4—Use Multispectral Imaging Techniques to Examine Remote Sensed Images

Clockwise from top left: Undisturbed Amazonian tropical rain forest (photo credit: Don Deering); deforestation stage 1 (photo credit: D. Morton); deforestation stage 2 (photo credit: D. Morton); deforestation stage 3 (photo credit: G. van der Werf).
Tropical forests cover less than ten percent of our planet's land surface, but are home to more than half of all species on Earth. The incredibly rich biodiversity of these forests provide a wide variety of resources for the entire world, including food supplies, shelter, spices, raw industrial materials, powerful medicines, and more. However, the delicate balance and productivity of these tropical forest ecosystems are being jeopardized by widespread deforestation. In fact, it is believed that rain forests could completely disappear within the next 100 years if deforestation continues at its current rate.

Part of Mato Grosso, Brazil on August 6, 1992, captured by the Thematic Mapper on NASA's Landsat 5 satellite (top) and the same area on July 28, 2006, captured by the ASTER instrument on NASA's Terra satellite (bottom).
Satellite technology is one of the key components in the effort to monitor, study, and limit the extent of deforestation. The images to the right are false-color satellite images showing changes in vegetation in the Mato Gosso region of Brazil. In these images, red indicates vegetation, and the brightness of the color indicates the density of the vegetation. The most striking difference between the two images is the widespread clearing of forestsseen as gray-beige rectanglesthat occurred between 1992 and 2006.

Satellites allow scientists to observe large tracts of land over long periods of time. The Landsat satellites have helped document deforestation and land cover changes in the Amazon since the 1970s. Satellite observations of tropical forests are made at multiple wavelengths. The most effective wavelengths for studying vegetation are those at the red end of the visible spectrum or longer. Red wavelengths are used to measure "greenness" since healthy plants will absorb red (and near infrared) wavelengths for photosynthesis, and stressed plants will reflect more of those wavelengths back into space. Even longer wavelengths (e.g., microwave and radar) are able to penetrate clouds and haze to observe the rainforests below and monitor changes in land cover and usage. Today you will learn analysis techniques for working with true and false color images.

Day 4 Goals

  • Understand how color images are captured and reproduced.
  • Understand how satellite data helps us investigate deforestation.
  • Learn how data collected at different wavelengths can be combined in different orders to highlight surface features on Earth.
  • Share your ideas about how you might use Landsat data in your classroom teaching.

Day 4 Tasks

  1. Deconstruct and reconstruct color images.
  2. Combine three Landsat spectral bands to produce true and false color composites.
  3. Locate a Landsat image of interest to you.
  4. Contribute to an online discussion centered on using Landsat data in your teaching.