90 



Arctic throughout late winter and spring. Quick, reliable methods ar«=> needed 

 for determining from the air the thickness of the snow cover, the smoothness of 

 the ice and its thickness or load bearing strength. Methods should preferably 

 be instrumental as visual observations are not trustworthy in snow areas. The 

 upturned edges of local pressure ice, freeboard at edges of broken ice, and color 

 are useful indications of thickness, but the "personal" factor is great. Seismic 

 methods for determining ice thickness and other mechanical properties have 

 been tried on various types of ice by Ewing, Crary, Press (Press and others, 

 1951) and others. The inhomogeneities and irregular thickness of sea ice can 

 be expected to complicate any physical measurements, and averaging methods 

 may not indicate the critical extremes. The large size, and apparently uniform 

 character of freshly frozen, unbroken ice of the leads favor satisfactory meas- 

 ments of this ice, however. Preference for gear is completely plane enclosed, 

 trailed, or non-captive in this order. 



Conventional oceanographic equipment can be used from landed planes, 

 but should be light in weight, compact, simple to operate, and positive in action 

 at extremely low temperatures. Power, or its equivalent in gear and fuel, must 

 be evaluated in terms of weight. Aside from normal oceanographic procedures, 

 provision must be made for penetrating the ice to the water below. Ice spuds 

 or chisels, augers and chain saws have been used. The newer hand power aug- 

 ers cut quite rapidly and give a core Z to 4 inches in diameter, suitable for 

 studying the internal structure and connposition of the ice. Larger holes are re- 

 quired for lowering oceanographic gear. On Project Skijump (Holmes and 

 Worthing, 1951) these were quickly made using a power chain saw and breaking 

 the last several inches with an ice chisel. The winch was kept in the plane and 

 the hydrographic wire was rigged out the parachute door over a boom to permit 

 lowering the gear vertically. Cabin heaters kept the compartment warm enough 

 to insure proper functioning of the reversing bottles and thermometers. 



As in the case of the ice breaker and the submarine, the present ocea- 

 nographic work is largely limited by the vehicle and is not due to lack of specific 

 oceanographic instrumentation. The plane landing on ice can supplement the 

 ship by occupying widely spaced stations well inside the pack perimeter, taking 

 advantage of late winter and spring conditions. This combined geographic and 

 seasonal gap cannot easily be filled by surface vessels. 



Helicopters can be used from ship or beach for on-ice landings. They 

 are excellent for short range reconnaissance and shuttle service from icebreak- 

 ers. Their light load capacity, cramped space, short range, and inability to 

 take off and land in strong winds limits the oceanographic tasks that they can 

 perform. Logistically they cannot operate as independent units. 



Long range reconnaissance aircraft fill quite a different need in sea ice 

 studies than those satisfied by planes for making on-ice landings. These larger 

 aircraft can describe the distribution of the ice; defining its limits, the season- 

 al and annual changes, the density and arrangement of the ice cover, and the 

 character of the ice including form, size, surface characteristics and the like. 

 Visual and electronic observations amplified by photography are commonly used. 



Planes were used extensively during the war years to scout the ice of the 

 North Atlantic from the Scotian Banks through the Greenland Sea to Bear Island. 

 This dates the first approach to synoptic observations over that large area. The 

 primary problems at that time were seeing the ice visually or by radar, deter- 

 mining the position of the plane and the relative position of the ice, and evaluat- 

 ing the character of the ice in terms of ships' operations. 



Visual sightings were reliable in times of good visibility but ice could 



