Imaging Radars for Geoscience Use

Properties of a side-looking airborne radar (SLAR) designed for geoscience rather than military use are presented. The speckled nature of usual single-frequency radar images may be reduced by averaging in azimuth and by averaging in range or transmitting excess range bandwidth. With synthetic aperture systems, averaging is possible in both range and azimuth, but only range averaging (excess bandwidth) is reasonable with most real-aperture systems. Multispectral sensing appears to offer advantages for radar comparable with those for photography, on the basis of experimental spectral response curves. Matching the transfer characteristics of receiver, recorder, and film is necessary to achieve quality images. Special techniques may be necessary to permit discriminating targets of similar radar return while at the same time allowing for the very wide total range of returns. The calibration necessary to achieve repeatable results and permit use of automatic data processing may be obtained by inserting a stepped sample of transmitter signal into the receiver to place calibration blocks on the image. Both multiple look-angle coverage with a single flight line and stereo can be achieved by use of fore-and-aft squinted antennas for alternate transmissions.