Radar Imagery : Looking from Space with Wavelengths 100000 Times Larger than the Ones of Visible Light

Article type: Research Article

Authors: Massonnet, D.

Affiliations: CNES (French Space Agency), 18 Avenue, E. Belin 31401, Toulouse CEDEX4, France

Abstract: Radar instruments are used to observe the Earth with radio waves. The resulting image reflects both the physical properties of the waves and the technological choices that have to be made to obtain a usable image from the raw data gathered by the instrument. We describe the way a radar image is obtained through computer as a two-fold image. The first part, the amplitude, conveys a similar, but different information than conventional imagery, such as the geometry of pixel layout on the ground and the estimation of the speed of mobile targets on land or sea. The second part, the phase, cannot be visualized by itself and gains value only through the comparison with the similar part of a companion image. An accurate description of terrain elevation can be obtained from the slight difference of point of view between the images. A much more accurate assessment of terrain displacement, down to millimeters, between the acquisition dates of the images can also be obtained. In addition, otherwise invisible meteorological phenomena can be mapped. We describe examples of the way these various pieces of information are obtained together or separately, as well as ways to combine the results into a singe color image.

Keywords: remote sensing, radar, interferometry, space geodesy, digital elevation models

Journal: Journal of Visualization, vol. 1, no. 3, pp. 239-253, 1998