Polarization of scattered sunlight in deep water 42/ 



in the location and migration of animals of the whole photic /one. For these reasons 

 the extension of our knowledge of submarine polan/ccl light into deep water is a 

 matter relevant to several points of interest. 



The present report describes the results of photographic polarization measurements 

 down to 200 m which extend our information to depths in excess of ten times those 

 previously studied. It clearly proves that polarization of sunlight under water is nof 

 merely a superficial phenomenon but one which also must be reckoned witfi n 

 considerable depths. 



ACKNOWLEDGEMENTS 



The author is greatly indebted to a number of people who helped hnn in many 

 ways while preparing for and executing these measurements. Particular mention 

 should be made of various Staff members of the Woods Hole Oceanographic Institu- 

 tion and the Officers and Crew of R.V. Atlantis: Dr. C. O'D. Isflin, Mr. David 

 Owen, Mr. Richard Edwards, Mr. Lloyd Hoadley, Mr. Valentine Worthington 

 and Captain Scott Bray. Hearty thanks are also due to Miss Virginia Witmington, 

 Mr. Charles Robinson and Mr. Wallace Phelps of the Edwards Street Laboratory 

 at Yale University. 



EQUIPMENT AND PROCEDURE 



The data reported here were obtained in the southwest North Atlantic just west and 

 northwest of Bridgetown, Barbados, B.W.I. (13° N, 59° W) working from R.V. 

 Atlantis. Polarization measurements were made at 30, 60, 100, 150 and 200 m. The 

 average echo-sounding depth at the various stations was about 1,200 m so that no 

 effect of reflection or light scattering by the bottom could reasonably have influenced 

 the results, 



Secchi disc readings ranged from 22-26 m, indicating moderately clear oceanic 

 water in the upper layers. These depths correspond to vertical extinction coefhcients 

 of about 0-055-0-065 (Clarke, \9A\), or to overall transparency between Jkrlov's 

 (1951) types I and II oceanic water. The sea was moderate (Beaufort 2-3), confused 

 and occasionally had a large swell during the work. 



While the measurements were being made, the sun was shining on the sea surface 

 in all cases, although as work progressed on the 200 m station (No. 1 1 ). a high thin 

 overcast slowly cut down the direct sunlight from full to a point where shadows were 

 just visible. In all other cases the sky was either mainly clear overhead or nearly 

 completely clear. Stations were made at various sun's altitudes from 26-52'. 1 ho 

 latter was close to the local noon maximum for the period around December I when 



this work was done. 



In order that the results obtained may be eff"ectively presented, the optical equip- 

 ment used and the procedure for making the measurements will first be described. 



The basic units of equipment employed were (I) a special polarization analy/cr 

 and (2) a camera. The latter was arranged to record the interference figure produced 

 by the analyzer when it was traversed by polarized light. This analyzer, which has 

 been used before for visual observations (Waterman, 1954 a) is made up of two 

 essential optic components. The first of these is a calcite crystal about 3 5 mm thick 



