MILLIAMPERES 



BAnERY SUPPLY 



CURRENT POTENTIAL 



ELECTRODE | ■ ELECTRODE i i 



^ — ° — A* — 



Figure 1. Wenner method of dc resistivity measurements. 



MEASUREMENTS, WINTER 1954 BERING 

 SEA EXPEDITION 



Equipment and Procedures 



Measurements of the longitudinal plate-wave velocity and of the ice thickness 

 by the air-coupled flexural-wave method were made in a sea-ice sheet. The equip- 

 ment consisted of Electro-technical model EVS 2-A geophones, a six-channel Brush 

 recorder, modified Brush amplifiers with limiters, and a shot-break circuit em- 

 ploying a portable transmitter-receiver radio system. The icebreaker lay to in the 

 ice sheet for a period of one to three days at three locations. At the first two 

 stations, insufficient data were obtained because of difficulties encountered with 

 equipment operation in cold temperatures. At the third station, satisfactory rec- 

 ords were obtained. 



Two sets of geophones, 91.44 meters (100 yards) apart, were buried in the ice 

 for detecting the longitudinal plate-wave velocity. Each set consisted of three geo- 

 phones oriented in the three vector directions. No effort was made to obtain dis- 

 persion curves, since the ship was at each location for only a short time. Hence, 

 it was decided to standardize on 457.2 meters (500 yards) and 914.4 meters (1000 

 yards) as the distance from the first geophone set to the point where the explosive 

 charges were detonated. Two additional geophones were placed on top of the ice 

 sheet for detecting the air-coupled flexural waves. The surface of the ice sheet 

 was, in general, very smooth. Measurements made in this ice sheet are presented 

 in table 1. Figure 2 presents a schematic arrangement of geophones and shot-blast 

 stations. 



