I. MARINE GEOPHYSICS 
Seismology 
Reflection measurements were made at all three stations using 
portable exploration seismographs and geophone pick-ups on the ice. This 
method produced excellent measurements of the ocean depth and dip. The 
energy source for these measurements was usually } pound of dynamite exploded 
at a depth of ten feet or near the base of the ice. The primary problem 
in this field work was deeping the shot hole free of broken ice. The ten 
foot depth was found te be helpful. Shallower shots broke out the hole 
and deeper shots produced bubble pulses with undesirably long interval. A 
light bulb with quilts over it was usually sufficient at the top of the ice 
hole to keep it unfrozen when not in use. Thaw wires down the hole were 
also partially successful. be 
The reflection records produced information on sub-bottom as well 
as bottom reflecting horizons. These sub-bottom reflections are characterized 
as a low frequency arrival after the bottom reflection. Im order to study the 
relative amplitude of these arrivals it was found desirable to use linear 
amplification and no automatic gain control. For deep water work it was also 
desirable to use no filters so that no events were missed. In shallow water 
it is sometimes necessary to use filters to eliminate the surface waves and 
water noise from the shot. The seismic reflection medsurements produce 
valuable information on depth and dip but the profile is not continuous. 
A precision depth recorder was used at Station Charlie to provide continuous 
depth sounding. This proved a successful method for use on ice floes and the 
records do not suffer from the irregularities due to ship motion which occur 
on records taken from research vessels. The drifting ice station cannot 
produce the amount of bathymetric data that a submarine cruising beneath the 
ice can. But the data is probably more precise as to position and depth. 
