1. gp:neral requikp]mp:nts 



(Change 1) 171) 



The lialf-liourly velocities and directions ob- 

 served at eacli deptli shall be recorded on Form 

 270, Record of Current Observations. All 

 record books, chronograph tapes, and plotted 

 curves shall be forwai-ded to tlie AVasliington 

 Office as soon as practicable after lerniination 

 of each station. 



If a survey vassel or current buoy is to be 

 anchored in or near traffic lanes, tlie Com- 

 mander of the Coast Guard district in which 

 project is hx-ated shall be j^iven ;idvance notice 

 and requested to publish same in his Ivocal 

 Notice to Mariners. 



1-48 Oceanography. — Periodic measure- 

 ments of temperatures and salinity are re- 

 quired to compute velocity corrections to 

 echo soundings (see 5-114 to 118), except 

 in areas where satisfactory bar checks can 

 be obtained to the maximum depth of hy- 

 drography. The frequency of observations is 

 a matter that must be left to the hydrog- 

 rapher's judgment, but it must be borne in 

 mind that, to comply with the requirements, 

 the average temperature from surface to 

 bottom used to correct any sounding must be 

 within 2 degrees of the actual mean tempera- 

 ture. At least one serial temperature and 

 salinity should be observed in the deepest 

 part of the area surveyed each month (see 

 3-116). 



Nansen bottles and precision type revers- 

 ing thermometers should be used when avail- 

 able and salinities deterinined on a .salinity 

 bridj^e. The Sigsbee water cup with hydrome- 

 ters and the Tanner-Sigsbee reversing fi-ame 

 and tliennonieter shall be used when the heavier 

 equipment is not available. 



The project instructions may require 

 oceanographic observations in addition to 

 the temperature and salinity observations 

 required for reduction of soundings. Repeat 

 observations should be made during the sea- 

 son to provide data on seasonal changes. The 

 program of observations at each station 

 shall be in accordance with instructions con- 

 tained in Chapter 2, H.O. Publication 607 

 and outlined as follows; 



(a) Nansen-bottle samples at International 

 depth intervals from surface to bottom or 

 to a depth specified by project instructions. 

 Salinity samples may be retained until time 

 is available for their analysis. 



(b) Bottom sample at all stations regard- 

 less of depth. Samples by Phleger Corer are 

 preferred. All samples shall be retained for 

 future analysis. 



(c) Secchi disc readings. 



(d) Sea and swell observations in accord- 

 ance with H. 0. Publication 606-e. 



