A Comparison of Airborne GEMS/SAR with Satellite-Borne Seasat/SAR Radar Imagery—The Value of Archived Multiple Data Sets
Authors: Hanson BC , Dellwig LF 
Published: February 2009

In an effort to define ideal system and operational parameters for both side-looking airborne radar (SLAR) and synthetic-aperture radar (SAR), early investigators relied on multiple data sets acquired by systems having diverse system and operational parameters. However, the problems resulting from the use of diverse parameters were often intensified by temporal or seasonal contrasts. More recently, data sets from the multiple-frequency, multiple-polarization radar operated initially by the Environmental Research Institute of Michigan (ERIM), and subsequently by the Canadian Centre for Remote Sensing (CCRS), have enhanced the capability of analysts to define optimum parameters for a wide variety of applications. Such studies led to the definition of parameters for the shuttle imaging radar-A (SIR-A) system, deployed aboard the space shuttle in 1981, and to the modification of that system for follow-up SIR missions.
The desire to develop and orbit an “ideal” system, along with the recent development and operation of systems with improved resolution and dynamic range, has caused interest in available, archived data to decline to a considerable degree. Data sets generated by radar systems having recognized contrast in their system and operational parameters are becoming increasingly available in many areas throughout the world. Given an understanding of the unique capabilities of the systems generating such imagery, data may emerge that are not available in the imagery produced by a single system. Thus, not only might unique data be provided, but information may also be revealed solely as a result of the strong contrast in the system and operational parameters of the radar with which the imagery is generated.
To demonstrate the value of using radar imagery from systems having diverse parameters, X-band images of the Northern Louisiana Salt Dome area, generated by the airborne Goodyear electronic mapping system (GEMS) operating with an incidence angle of 75° to 85° and a resolution of 12 m, were analyzed in conjunction with imagery generated by the satellite-borne L-band Seasat/SAR operating with a contrasting incidence angle of 23° and a resolution of 25 m. The result was that otherwise unobtainable data became accessible when (1) adjustments were made for the time lapse between the two missions, and (2) supporting ground data were acquired concerning the physical and vegetative characteristics of the terrain in the study area. Included among such data were additional information relative to land management activities, improved delineation of the drainage net, better definition of surface roughness in cleared areas, and swamp identification.
The relatively low cost of such archival imagery as Seasat/SAR, SIR-A and -B, X-band imagery flown for the U.S. Geological Survey, and X-band imagery produced by Strategic Air Command systems should prompt investigators to utilize such data in conjunction with mission-specific, commercially generated imagery to augment existing input on geotechnical projects. What has been revealed in the area investigated may be only a fraction of what might be revealed at negligible cost in an area-extensive study.