of the air wave. These waves are called air-coupled flexural waves. The equation 

 for 7 becomes 



ya = Hi/C 



from which the ice thickness can readily be determined. 



Other Physical Properties 



HEAT FLOW THROUGH A SNOW-COVERED ICE SHEET 



The heat flow per unit time per unit area through a snow-covered ice sheet, 

 which is bounded on one side by an isothermal reservoir of water and on the other 

 side by the atmosphere, is given by the relation* 



where 



w = heat flux 



k ^= thermal' conductivity 



T = temperature 



Z = thickness of the ice sheet 



When the thermal conductivity is not constant but varies through the ice sheet, 

 the ice sheet and the corresponding snow cover must be divided into thin layers. 

 By a consideration of the thermal conductivity of each individual ice layer, it is 

 possible to write the following relation for the heat conducted through the snow- 

 covered ice sheet 



T„ — Ti T„ — Ti 



w = — 



RESISTIVITY OF SEA ICE 



The resistivity method of measuring the resistance of sea-water ice consists of 

 sending an electric current into the ice sheet and measuring the potential between 

 a set of electrodes placed in the ice within the eilective area of the current. The 

 Wenner method^ of electrode arrangements (fig. 1) was used in making the 

 measurements. 



Theoretical investigations based on the distribution of electric current in the 

 ground are nearly all based on the assumption that the layers are horizontal and 

 homogeneous in the horizontal plane. If the ground has uniform electrical prop- 

 erties for an infinite distance in a vertical direction, the resistivity, using the elec- 

 trode arrangement in figure 1, is given by 



p = I'KU (V/I) 



where 



p = resistivity in ohm-centimeters 

 a = electrode separation in centimeters 

 V = voltage in millivolts 

 / = current in milliamperes 



For the case of nonuniform properties in a vertical direction, the equation no 

 longer gives the true resistivity. In such a case, the resistivity determined from the 

 measurements is called the apparent resistivity. 



