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mentioned: "The airborne Ice Observer nowadays generally has effective radar at
his disposal, suitable for ice reconnaissance under all conditions, in thick fog
and dark polar nights as well. The radar picture is studied directly on the
screen, and, when required, recorded automatically in a photographic way. It is
possible to measure the dimensions of polynyas, leads and cracks, etc., in radar
pictures, further to observe pressure ridges, and to determine the difference
between polar ice and young ice, etc. A pack ice area always has a distinct de-
marcation at any given time between the open sea and the ice. This so-called ice
edge shows up quite well on the radar screen, also when the ice concentration is
characterized as open or very open pack." He further stressed that "Side-Looking
Radar" ought to be useful for mapping and surveillance of the Polar Ice Pack and
mentioned that a recently developed Synthetic-Aperature Radar provided extremely
high resolution with a relatively small antenna. The author also informed on
"Passive Microwave Radiometry", "Low Light-Level Televisions Systems", and "The
Use of Satellites for Ice Studies".
At the XIIth ISP-Congress in Ottawa, 1972, there was a great interest in
satellite-carried sensors, and the Canadians showed their sincere satisfaction
when the first Canadian ERTS-picture (ERTS = Earth Resources Technology Satel-
lite) could be demonstrated at this Photogrammetric World Congress. It was taken
on July 27 from NASA's ERTS-1 at an altitude of 920 km. The satellite was equip-
ped with two systems for remote sensing, l:o a multispectral scanner, scanning
within four different spectral-zones, viz. green (0.5-0.6 um) red (0.6-0.7), and
the short-wavy infrared bands 0.7-0.8 and 0.8-1.1 um; 2:0 a three-colours TV-
camera with a resolution of about 80 m, working on the spectral-bands 0.475-0.575,
0.58-0.68 and 0.69-0.83 um.
In accordance with ITU "Radio Regulations", Geneva 1959, the succeeding
bands in the electromagnetic frequency spectrum comprise frequency ranges as
follows: LF (1ow frequency) 30-300 kHz, VLF (very low frequency) 3-30 kHz, and
ELF (extremely low frequency) 3:102 Hz - 3 kHz.
As regards the ELF-band there was an interesting announcement, published in
the September 1979 issue of DEFENSE ELECTRONICS, entitled "VLF and ELF communica-
tions with ballistic missile submarines (TACAMO)". In view i.a. of the fact that
LF and VLF communications suffer from jamming vulnerability in higher degree
than extremely low-frequency communications, it is mentioned in the announcement
that signals at ELF frequencies can penetrate seawater to a depth of several
hundred feet. The words "several hundred feet" point to a remarkable increase of
the penetrating depth in sea water - 300 ft. (more than 90 m), for instance, is
about twice the depth (measured from the upper edge of the conning tower to sea
level) which submarines normally use when navigating beneath ridged-ice zones,
where downward-projecting ridges, so-called ice keels, always may be expected.
To the above-mentioned ISP-Congress in Ottawa the Chairman of the American
Underwater Photography Committee, Gomer T. MeNeil, presented an Invited Paper on
the subject "Underwater Photography", including cameras, films, and lighting ad-
vancements, etc. In the same paper there was an article concerning "remote under-
water systems on towed vehicles" by Joseph Pollio, illustrated with photos clearly
demonstrating the importance of side-scan sonar imagery. Television and photog-
raphy systems as well as side-scan sonar, altitude sonar, and slant range trans-
ponder equipment were discussed, emphasizing that the bottom topography is always
of great interest to the under-ice navigator. Thus, innovations in Underwater
Photography is of special importance.
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