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1993-04-21
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OFFICE OF PUBLIC INFORMATION
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIFORNIA. TELEPHONE (213) 354-5011
FOR RELEASE TUESDAY, June 15, 1976
Accurate continuous mapping of Arctic ice floes by air-
borne imaging radar has been proven feasible by a team of Jet Pro-
pulsion Laboratory scientists, working jointing on a National
Aeronautics and Space Administration program with colleagues from
the United States and Canada.
In a series of flights over the Beaufort Sea north of
Alaska, radar imagery from a 30,000-foot altitude determined that
ice floes drifted up to 40 kilometers (25 miles) in five days of
mid-summer.
But more importantly, according to Dr. Charles Elachi,
JPL team leader, the radar experiment showed that this type of
geographic measuring could be done from an Earth-orbiting satel-
lite such as SEASAT, which JPL will launch for NASA in the spring
of 1978. The SEASAT will have onboard an imaging radar which is
being developed at JPL.
The accuracy of measurement is expected to be the same--
over 95 percent--even though SEASAT will be in an 800-kilometer
(500-mile) high polar orbit. Working with well-defined ground
points may make the radar accuracy virtually 100 percent, project
scientists believe.
Dr. William Campbell of the U.S. Geological Survey and
Dr. Rene Ramseier of the Canadian Department of the Environment
were prominent co-investigators on Project Aidjex (Arctic Ice
Dynamics Joint Experiment).
For the August, 1975 flights the JPL L-band radar was
used on the NASA CV-990 aircraft from Ames Research Center,
operating from Fairbanks.
Average daily ice floe drift recorded was 6.5 kilome-
ters, roughly four miles, eastwardly and 2.9 km (1.1 miles) in a
southerly direction. It was even possible for the radar to
determine the amount of rotation of individual ice floes induced
by winds and currents. The analytical technique used in the
determination of the ice motion was developed by Dr. Franz
Leberl, an Austrian scientist in residence at JPL. This
technique was first developed for lunar cartography using Apollo
17 radar imagery.
With the opening of the north Alaska coast to oil ex-
ploration, maintenance of ports and shipping lanes will require
better knowledge of ice problems in the Artic Ocean, of which the
Beaufort Sea is a part. The AIDJEX missions are establishing
radar's capability to differentiate between new (first-year) sea
ice, older sea ice, and open water, as well as rate of drift on a
global basis.
Elachi's JPL colleagues, besides Dr. Leberl, include
Dr. M. L. Bryan, Tom G. Farr and Elmer McMillan. Dave Billiue
and Gene Samuel were contractor technicians on the project.
The team predicted satellite radar would be more accu-
rate and convenient for mapping the top of the world. Among the
reasons given:
~<~ The swath width of a SEASAT radar image will be
100 km (62 miles) compared to the 12 km (7.5
miles) swath width of the aircraft radar.
~<~ Satellite radar's angle of incidence will vary
only 6 degrees compared to a 55-degree variation
in some aircraft radar scans.
~<~ The orbit of SEASAT will be smoother than the
flight path of the plane and its radar will have
an internal geometry system, which will help
reduce mapping error possibilities.
Earlier in April, 1975, the JPL radar flew over the
Bering Sea area and studied the ice-covered tundra lakes of south-
west Alaska. Elachi and Bryan reported that the equipment was
able to determine whether or not most of these lakes were frozen
completely to the bottom. Their colleague on this study was Dr.
W. F. Weeks of the Cold Regions Research and Engineering
Laboratories, Hanover, N.H.
Similar measurements of lakes in northern Alaska this
spring verified the technique. The experimenters say that radar
will help to determine which of the shallow lakes are suitable as
year-round sources of fresh water or should be considered for the
possible stocking of fish.
Another potential application is to pinpoint the lakes
frozen all the way to the bottom so that they may be used as land-
ing strips for heavy transport aircraft. This activity is expect-
ed to grow drastically in the next few years as more oilfields in
north Alaska are opened for exploration.
SEASAT, the scientists predicted, will be able to pro-
vide a complete radar map of Alaska in a few weeks time, permitt-
ing such lakes to be mapped on a continuous basis.
The JPL radar system can discern objects as small as 25
meters across, irrespective of cloud cover, sun illumination, or
platform altitude. The L-band instrument operates at 1200 mega-
hertz frequency (25 centimeter wavelength). The final outputs of
the system are recorded on 70-millimeter negative film transparen-
cies which are arranged to form mosaics for mapping purposes.
Computer processing produces other data required--such as relative
and absolute ice motion during the period between different
flights.
####
BB-6/8/76
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