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Thermal sensors can provide information about conditions under the 
snow, as for example the presence of frozen cracks and polynyas, 
so-called ice-skylights, etc. They ought to be very useful for 
complementing ice charts, based on photographic as well as radar 
reconnaissance. 
4.4 Low Light-Level Television Systems 
  
In the same above-mentioned 1964 report the author further said 
that low light-level electro-visual systems, originally developed 
for spacecraft seeking astronomical data, or for such craft using 
the stars for navigational purposes, are supposed to be useful 
image intensifiers at ice reconnaissance in dark winters in high 
latitudes. As early as in 1960 noticeably good night pictures were 
published, spotted by IV, operating at 625 lines. The now (1964) 
improved cameras are airborne and fully transistorized. They use 
highly sensitive image orthicon tubes and appropriate objective 
lenses. 
The author then added that preliminary results, already gained with 
lightweight, closed-circuit television systems, designed to produce 
useful pictures of ground objects during cloudy, moonless nights, 
indicate that they ought to be useful night sensors also for de- 
picting ice conditions at sea. 
4.5 The Use of Satellites for Ice Studies 
  
As mentioned in paragraph 2.2 above, R.W. Popham, U.S. Weather 
Bureau, Washington, D.C., presented a paper to the Symposium on 
Photo Interpretation at Delft in September 1962 on "The Use of 
Satellites for Ice Studies", The use of meteorological satellites 
to obtain photographs of sea and lake ice for research and operatio- 
nal purposes was discussed in that paper. Television pictures obtained 
principally over Canadian east coast waters from the experimental 
TIROS (Television and Infrared Observation Satellite) satellites formed 
the basis of his studies. Satellite picture-acquisition methods were