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