772 EIGHTH PACIFIC SCIENCE CONGRESS 



and methods have occurred. The latest revision was made in early 

 1952. It will be revised again to include improved procedures devel- 

 oped during the 1952-53 seasons. 



At present, research is underway toward improved designs for the 

 transmitter and chronograph. Considerable work has been done on 

 the design of a low-velocity highly sensitive meter for use on the bot- 

 tom. Work is also in progress on an automatic recording system for 

 these meters. 



Field Methods 



As indicated earlier, this meter is a wartime development, con- 

 ceived as the solution of the problem of economical and rapid deter- 

 mination of surface current velocities of interest to marine navigators. 

 The laborious and time-consuming methods involving the anchoring 

 of vessels or barges on current stations could no longer be employed 

 for lack of men and floating equipment. The Roberts Radio Current 

 Meter provided an economical and relatively easy method for making 

 current observations from surveying vessels engaged in hydrographic 

 or other surveys within radio range of the buoy transmitters. The 

 design of this equipment was based on the concept of single-meter oper- 

 ation. To permit satisfactory handling from small craft, weights were 

 kept to a minimum. At first, normal operating procedure consisted of 

 streaming a buoy with one meter attached— usually at some level 12 to 

 40 feet below the surface. At receiving stations, whether ashore or 

 afloat, it is necessary to tune manually receivers to the frequency of 

 each transmitter. This limits observations in radio-congested areas to 

 six or seven meters for a single receiving station, as six or more clear, 

 unobstructed frequency channels are difficult to find. Interruptions 

 in transmission make records difficult to process— oftentimes worthless. 



For marine transportation, surface current velocities are of para- 

 mount interest, and the Roberts Radio Current Meter was used at 

 first to determine these. Because of its light weight it tends to lift 

 in proportion to the strength of the current in velocities greater than 

 about 2 knots. A tendency to sheer is noticeable in velocities of 3 

 knots. A leader was devised for attachment to the buoy anchor cable 

 to obviate these tendencies. It was found desirable to use this leader 

 regardless of the velocity because it causes the meter to pivot about a 

 point of the anchor cable and produces more consistent results in cur- 

 rent direction measurements. 



.Although the buoy, as designed, has a strong planing lift, it must 

 be carefully streamed to insure satisfactory operation in strong cur- 

 rents. The lightest cable of adequate strength must be used. It has 

 also been found desirable to attach buoy \vings at the sides and bow. 



