but passes unaltered the lower -frequency signals produced by the 

 larger and longer waves. The output of the filter unit then is recorded 

 either on magnetic tape or on a direct- writing recorder. The surface 

 wave record is obtained by a double integration of this output. (See 

 Reference VII- 29.) 



This wave buoy was not designed to be a refined instrument; the 

 cost has been kept at around $100 to $200, and it probably could be 

 brought lower by mass production. Thus the buoy can be considered 

 as expendable if necessary. The transmitter is subject to some 

 frequency drift, and the tuner needs occasional retuning. An error 

 exists in the acceleration information obtained, because the lever 

 arm of the accelerometer does not remain horizontal as the float 

 assembly rides up and down the waves. 



d. Inductance- type and capacitance-type wave poles 



These two wave poles were developed at the Woods Hole 

 Oceanographic Institution and are similar in general operation to the 

 electric wave staff of the Hydrographic Office (Reference VII-8). 

 One pole is a capacitance type; the other is an inductance type. The 

 two poles differ from the one used at the Hydrographic Office in that 

 no damping disc is required; damping is attained by flooding tanks 

 which are component parts of the poles. The capacitance pole radios 

 data back to a ship, but the inductance pole requires a connecting 

 cable. Both poles resonate at 38 seconds; however, some undesirable 

 bouncing occurs at around 19 seconds. These two poles seldom are 

 used except in fairly calm seas. At the Woods Hole Oceanographic 

 Institution, the Tucker accelerometer (see below) has been installed 

 on the ATLANTIS, and this instrument is used in preference to the 

 two wave poles. 



e. Ship-borne wave recorder 



This instrument, designed by Tucker at the National Institute 

 of Oceanography, measures waves directly aboard ship. It combines 

 the sea pressure at a point on the hull of the ship with the vertical 

 displacement of this point which is obtained by double integration of 

 the output of a vertical accelerometer. No equipment has to be put 

 outboard. This instrument has been tested by taking 2,500 wave records 

 and has proven fairly satisfactory. However, the extremely uncertain 

 response of the system to wave periods of less than seven seconds is 

 a disadvantage. (See Reference VII- 27.) 



VII- 11 



