1. INTRODUCTION
The exploration of the rich natural resources, such as oil, gas and miner-
als, continues to increase all over the world. That is the case also concerning
the Arctic and other areas where the sea is often blocked by floating ice. In
many cases the ice situation involves severe problems to the extraction of the
resources and to the transportation of the products to suitable markets, concern-
ing surface shipping as well as under-ice navigation.
In any case the best possible position-fixing and a true knowledge of pre-
vailing ice conditions as well as the bathymetry is obligatory, and reliable ice
forecasts desirable. Advanced remote-sensing techniques therefore are of great
importance.
In a report, entitled "Applications of Remote Sensing to Oceanography & Sea
Ice" by Ragnar Thorén, prepared as a paper to the 14th Congress of the Interna-
tional Society of Photogrammetry, Hamburg 1980, the author introductively de-
scribes the remarkable evolution of the remote-sensing technique during the last
decades. In the twenties and thirties remote-sensing techniques were introduced,
including radio navigation and photography for picturing the ice situation. It
may be mentioned that, as early as 1930, the author successfully used very low
frequency radio for reaching submarines at a depth of 30 metres (in the Baltic
Sea). In 1933 he introduced infrared photography for navigation and reconnais-
sance in hazy weather with limited visibility. Later radar systems were devel-
oped, and in the fifties television-transmitted pictures from satellites were
used for the purpose of receiving information concerning the distribution of the
sea ice in different areas. In his book "Picture Atlas of the Arctic" (Elsevier
Scientific Publishing Company, Amsterdam - London - New York, 1969), he also
gives "View-points on radio communicätion systems and submarines operating under
ice".
When using very low frequency (VLF) radio there are good possibilities of
reaching submarines in transit beneath the polar pack ice, not only with ordi-
nary messages but with navigational signals as well. The communication, however,
is always limited to one-way transmission - from shore stations to under-ice
submarines. Heavy ice, very nearly free of salt, facilitates, as a matter of
fact, the receiving conditions of submerged submarines. As an example may be
mentioned that the depth of penetration in salt-free ice at about 15 kc is about
100 times greater than in sea water with a salinity of 30 /oo (corresponding to
the average salinity of the surface layer of the Polar Basin). Because of that,
the receiving conditions at one and the same diving-depth must be more favoura-
ble if the submarine leaves open water and moves in beneath an ice field. There-
fore, radio transmission on the VLF» and to under-ice submarines may always be
of current interest in the Arctic.
At the IXth International Congress in London, 1960, the chairman of the
working group "Interpretation of Ice", Captain Ragnar Thorén, Royal Swedish Na-
vy, called attention to the Soviet progress in high-altitude photography, which
he presumed to become of outstanding importance for Arctic research in a near
future.
In the early sixties satellites were more commonly used for ice studies and
some years later for making excellent ice charts (by the US Fleet Weather Facil-
ity at Suitland, Washington, D.C. The title of Fleet Weather Facility was of-
ficially changed to "Naval Polar Oceanography Center" on 29 October 1979).
In an Invited Paper to the ISP Commission VII at he Xth International Con-
gress in Lisbon, September 1964, entitled "The Application of Aerial Photo Inter-
pretation in the Scientific Field of Ice met at Sea" by Ragnar Thorén, the author
780
a i TA
uud ELS [5S 0 sS = Z
a " "s
^ mr in
7x5 0000 Boo no >B
— Y ASO ee 1 0 - sz o0 c
et ‘nu (UM o o" o m PM mA m9
