RECENT DEVELOPMENTS IN TIDAL AND TIDAL 

 CURRENT MEASUREMENTS * 



U.S. Coast and Geodetic Survey 



Current Measuring Equipment 



During World War II, when a large part of its personnel and 

 equipment had been transferred to the Armed Forces, the U.S. Coast 

 and Geodetic Survey, in an effort to meet both military and civilian 

 requirements, devised several new instruments and procedures. One 

 of the most interesting of these is a radio current meter known as the 

 Roberts Radio Current Meter after its designer Capt. E. B. Roberts, 

 now Chief of the Division of Geophysics of the Bureau. The design 

 includes both the meter and a special buoy to support the meter and 

 house the radio transmitter. 



As often happens after field trials, the first design of this equip- 

 ment was found to have some features capable of being improved. 

 These improvements have been embodied in a revised design known as 

 Model II. However, Model I instruments are still being used with 

 satisfactory results. 



Equipment losses in congested harbor areas are likely to be high. 

 Buoys with attached equipment sometimes disappear without trace and 

 cannot be found by dragging. More often buoys are rammed by pass- 

 ing craft and set adrift. When found, if the meters are still attached, 

 they are usually badly damaged. Frequently the meter suspension cable 

 has been cut and all meters lost. Losses can be minimized to some 

 extent by publication of operations in local and weekly Notices to 

 Mariners. From time to time, it becomes necessary to replace equip- 

 ment lost in operation, and successful bidders have found it desirable 

 to make minor changes during construction. These have not changed 

 the basic design, but unless made by the same manufacturer, parts are 

 not always interchangeable. 



The introduction of this meter represented such a radical change 

 in standard methods for the determination of tidal current velocities 

 that it was necessary to prepare a special operating manual for it. This 

 manual has been revised periodically as improvements in equipment 



* Contribution from the U.S. Coast and Geodetic Survey, Department of Commerce, Wash- 

 ington, D.C., U.S.A. 



Presented by Capt. Andres O. Hizon, Director of the Bureau of Coast and Geodetic Sur- 

 vey, Republic of the Philippines. 



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