Table of Contents

RADARSAT-1 Climate Change

A Science Unit for Grades 11 and 12

RADARSAT Image Analysis

Satellites image the Earth's surface in a variety of ways, covering a wide range of wavelengths. Almost every satellite imaging technique uses reflected sunlight or infrared thermal radiation to create images. Full colour images are created by combining images taken through colour filters. RADARSAT is the exception to this rule... RADARSAT uses a self-generated microwave beam to illuminate the Earth's surface. Images are generated by the analysis of the microwave echo.

A sketch illustrating an image created from a NOAA polar orbiter

Satellites which see the Earth in the visible part of the electromagnetic spectrum often cannot see the Earth's surface because of cloud cover. High angle solar illumination also creates extensive shadow artefacts while other angles of illumination can create direct sun reflections. Of course, visible light observations are impossible at night.

A sketch illustrating an image created from a RADARSAT polar orbiter

RADARSAT observations can be made at any time during the satellite's orbital pass and are not affected by cloud cover.

All images are monochromatic, although "false" multicolour images are available. However most RADARSAT images are printed in multi-level gray scale. Note the ships, the causeway, the airport, and the volcanic crater which are not seen in the upper image.

Of course the sketches above are rather simplistic. They have been drawn to illustrate the basic elements of a satellite image. Real images are rather more complex. It takes a "trained" eye to notice the extensive detail in an image processed from a real dataset.

To give you some practice working with real RADARSAT data, the following exercise is provided.

Student Assignment

About NOAA polar orbiters

The NOAA series of weather satellites create their images from a single optically-sensitive detector. This detector rotates. As it does it scans in an E-W direction creating an image raster line. The forward motion of the spacecraft (polar orbit) constantly advances the raster lines. This enables the satellite to generate a constant, uninterrupted image throughout the entire orbit. Like RADARSAT, NOAA satellites also use sun-synchronized orbits.