SLAR--FOR CLEAR AS WELL AS CLOUDY WEATHER
Louis F. Dellwig, Professor of Geology, University of Kansas,
Remote Sensing Laboratory, Lawrence, Kansas 66045
Janet E. Bare, Associate Scientist, University of Kansas,
Remote Sensing Laboratory, Lawrence, Kansas 66045
Ron Gelnett, Motorola Aerial Remote Sensing, Inc., 4350 E.
Camelback, Phoenix, Arizona 85018.
In 1965 the geoscience community was introduced to a new scientific
tool, Side Looking Airborne Radar, a military development with a capability
of "seeing" through clouds. Earlier, recognition of the potential value of
radar for geoscience investigations was revealed by Cameron (1964) who syste-
matically photographed the PPI scope of an RAF bomber over the frozen
St. Lawrence River to demonstrate the potential value of this tool for moni-
toring river, lake and sea ice, and later (1965) over Scotland to identify
faults previously undetected.
With the inception of the NASA program in 1965, the Westinghouse AN/APQ-97
radar was utilized to image selected targets throughout the United States with
the analysis of imagery resulting in the documentation of a mapping potential
and the revelation of geoscience data not otherwise obtainable. An early
climax in documenting system potential was reached with the topographic and
geological mapping of Darien Province, Panama (Viksne et al., 1969; MacDonald,
1969) under the auspices of the Army Corps of Engineers, Engineering Topographic
Laboratory of Ft. Belvoir, Virginia.
Shortly thereafter, Westinghouse Aerospace launched a commercial imaging
program with a per square mile price that reversed the enthusiasm for the use
of this new tool and reduced its utilization to mapping in areas in which no
other sensor could acquire data because of hostile weather conditions.
However, because of improvements in technology and a significant reduction in
cost, an increase in utilization of commercial SLAR later resulted. By 1975
it could be demonstrated that SLAR, properly utilized as a reconnaissance tool,
was competitive with aerial photography in terms of price (Figure 1). Such a
comparison is valid only from the standpoint of price, in as much as the two
sensors record data in different regions of the electromagnetic spectrum,
responding to different characteristics of the target. Also emphasized by
the comparison curves is the primary function of the one as a reconnaissance
tool and the other for more detailed data collection. After SLAR had been
established as a reconnaissance mapping tool, attention was temporarily
diverted from its utilization in terrain mapping with the launching of
LANDSAT 1. Faced with an imaging system which, given the 18 day interval
repetitive coverage, one might expect would ultimately generate an image over
any portion of the earth's surface over which it passed, earth scientists
anticipated a data source which would prove to be the panacea for all of their
problems. However, even today after six years of data collection with not only
LANDSAT 1 but now 2 and 3 there are areas in tropical countries for which a
reasonably cloud-free image of modest quality is yet to be obtained.
