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 - l.l 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.
At the receiving stations the video-band data were transferred to
a 70 mm film and enlarged to photographic pictures of about
23 x 23 cm, on the scale of 1:1 000 000. On a comparison with
topographic maps the correspondence was striking.
4.5.2 Southern Ice Limit Charts
After the XIIth International Congress in Ottawa, July-August
1972, the author of this report had the opportunity to visit the
Canadian High Arctic for some weeks' arctic research and ice
reconnaissance. From there he visited the US Fleet Weather
Facility at Suitland, Washington, D.C., for the purpose of Ice-
chart studies.
There they make excellent ice charts on the basis of satellite
pictures, air reconnaissance - photographic as well as visual and
radar reconnaissance - and observations from ships, ice islands and
coastal stations, etc. Some of these very lucid ice charts show
the ice situation in the Northern Hemisphere. They are published
weekly, and called "Southern Ice Limit'"-charts. Others are prognostic
charts, called "Western and Eastern Arctic 30-day Forecast", pub-
lisched twice a month.
The first-mentioned ice charts are divided into two groups, Western
and Eastern Arctic Analysis, respectively. The westerly "Southern
Ice Limit"-charts show the ice conditions between about 85° W. and
85° E., the easterly ones between about 125° E., and 125? w.
The varying ice concentration over a defined area is given as the
ratio in oktas of the sea surface actually covered by ice to the
total area of sea surface, both ice-covered and ice-free.