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Module 4 - Image Examples

A) Belize, Central America

Objectives

  1. Students will apply the skills they have learned in analyzing and interpreting radar image data to a data set from a tropical rain forest site.

Image data for this section is contained in the /DATA/MODS1TO5/MODULE04/IMAGES/BELIZE directory and should be copied over to your computer before beginning. The files you will need are:

An explanation of these images and their source follows. You may also find a directory within the /BELIZE directory, entitled /MOREBELL. This directory contains the different L-band polarization images which can be generated using Sigma0.

SEASATim.gif (261K GIF) - SEASAT radar image of the North-West corner of Belize, in Central America. The area is known as the Rio Bravo. The image was taken in 1978 and shows an area of about 100kmx100km. The white lines outline on the image are the borders with Guatemala, to the West (right side of image) and Yucatan, Mexico, to the North (top part of image). This area was settled by the Mayan civilization over a thousand years ago, and has Mayan ruins dotted all over it.

SEASATzm.gif (373K GIF) - A zoom-in of part of SEASATim.gif (261K GIF) showing more detail.

Mosaicim.gif (257K GIF) - radar image mosaic using AIRSAR data. P-band HH was colored red, L-band HV green and C-band VV blue to make this Red/Green/Blue overlay of AIRSAR data. The image was taken in 1990 and shows an area of about 50kmx50km. Comparing Mosaicim.gif with SEASATim.gif (261K GIF) you should be able to see two things immediately:

  1. By having different radar wavelengths you can see more features in the radar images. It's the difference between having color versus black and white.

  2. Between 1978 and 1990 a lot of deforestation occurred. These are the darker blue areas in Mosaicim.gif which have no match in SEASATim.gif. The bright red lines in some of the cleared areas are barbed wire fences which appear very bright at P-band.

Lbandful.gif (1,260K GIF) - L-band HH radar image of part of the image seen in the mosaic. This image is upside down when compared with the Mosaicim.gif image but was collected at the same time (April 1990) by the NASA/JPL AIRSAR imaging radar system. The radar was flying parallel to the top of the image and looking down and out to the left (i.e. down the page).

Belizkey.gif (8K GIF) - key to the radar image shown in Lbandful.gif. This schematic diagram, drawn to the same scale as the radar image, shows the size of the area covered (12.3kmx12.6km) and identifies some features seen in the radar image. Most of the image frame contains broadleaf upland forest, or tropical rain forest. At the top left is a small triangular shaped patch of a type of stunted forest, known as Bajo, which grows on poorly drained clay soils. The Bajo is separated from the upland forest by an escarpment, which rises about 100 feet. The most interesting feature in the image is a ranch known as Gallon Jug in the center right of the image, which was settled in about 1985, and contains: farmland (for raising corn and cattle); bare soil fields (just recently plowed); an area of regrowth, where the soil was too poor to support agriculture and the rancher is allowing the forest to grow back again; a recently bulldozed clear-cut, with trees still lying scattered on the ground; and a small coffee plantation. The coffee plantation was an area in the upland forest where the understory and middle canopy vegetation had been cleared, leaving only large trees. Although some coffee bushes had been planted, the forest floor was generally open. Also shown in the key is a local village where the ranch hands live, and two small lakes: Laguna Verde (green lagoon) and Laguna Seca (dry lagoon). Following the path of a small stream is a patch of flooded forest and marshland. Several dirt roads or tracks are indicated on the key as well.

VegmpByt.gif (16K GIF) - vegetation map of the Gallon jug area generated automatically from the AIRSAR data, using all three frequencies and all the different polarizations.

Comparing the vegetation map with the key shown in Belizkey.gif you should be able to see the following:

  1. The area of farmland is classified as low vegetation (light green).
  2. The area of bare soil is classified as no vegetation (blue).
  3. Most of the upland forest is classified as forest (bright green and yellow).
  4. The area of regrowth is classified as medium vegetation (dark green).
  5. The Laguna Verde is classified as no vegetation (blue).
  6. The Laguna Seca has patches of no vegetation (which may be open water), medium vegetation (D), and low vegetation (D). These are most probably sedge (1 to 2m high) and reeds (less than 1m high) growing above the waterline.
  7. The coffee plantation and the flooded area have a greater concentration of Forest (D), i.e. double-bounce forest (yellow), than the surrounding forest.
  8. The recently clear-cut area is unclassified (white)
Vegmpkey.gif (2K GIF) - key to the vegetation map shown in VegmpByt.gif. The color codes are: