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At the Naval Research Laboratory (NRL) in Washington, D.C., the
author discussed arctic problems with, the Head of the Polar
Oceanographic Division, the famous Arctic explorer and scientist,
Dr. Walt I. Wittmann. Dr. Wittmann mentioned that CRREL (Cold
Regions Research & Engineering Laboratory) started ice research by
means of Side-Looking Airborne Radar (SLAR) as early as in 1962,
in the K-band. Fig 8 shows a sample of side-looking radar imagery
collected by the U.S. Army CRREL in April, 1962. The imagery was
taken over the Arctic Basin pack ice north of Greenland from an
altitude of 18,300 m or about 60,000 feet. The area shown is 60
miles long and 30 miles wide or 1,800 square miles. A network of
leads and polynyas is readily discernible.
Dr. Wittmann further mentioned that the Naval Oceanographic Office
during April 1968 conducted a SLAR-experiment over the sea ice
fields north of Alaska. The purpose of this experiment was to
evaluate the application of the various frequencies of the NRL
four-frequency SLAR-system for mapping sea ice. The system had
four independent transmitters operating at X band (8910 MHz), C
band (4455 MHz), L band (1228 MHz), and P band (428 MHz) and a
four-channel receiver that was timeshared by the transmitters. In
addition to having vavelength capability from UHF to X band, the
system had the capabilities of polarization diversity, pulse width
variability (0.25 - 2.0 usec with P and L bands; 0.1 - 0.2 usec with
C and X bands), and pulse rate frequency flexibility (100-1463 pps).
This system, which had been operational since 1964, had a coherent
synthetic aperture mode ef operation that measured the spatial
characteristics of the energy backscattered from the illuminated
regions. Optical recorders were included in the system so that the
video output could be processed on an optical bench in the laboratory
to give a synthetic aperture map.
The shorter-wavelength X band radar appeared to have the greatest
potential for sea ice study when more definitive information is
required, such as mapping, distributions of stages of ice develop-
