a block (pulley) located at the end of a 5-m.- 

 long boom--or a 2-m. boom on SCOPE Expe- 

 dition (see Holn-ies et al,, 1958). The boom was 

 generally secured to the stern quarter of the 

 vessel, although on cruises TO-58-2 and 

 TO-59-1 (see Blackburn et al., 1962) it was 

 located amidships. The cable was marked with 

 colored tapes at spaced intervals which indi- 

 cated distance above the underwater detector 

 unit. Wire -angle measurements during a 

 lowering were made by visually superimposing 

 the edge of a conventional wire-angle in- 

 dicator with the support cable and reading 

 the angle. 



Electrical connection between the winch end 

 of the support cable and the associated deck 

 equipment was achieved in one of two ways. 

 With the hand-operated winch used on SCOPE 

 Expedition (Holmes et al., 1 958) and the motor- 

 driven winch used on SCOT Expedition (Holmes 

 and Blackburn, 1960), electrical connection 

 between the microammeter and detector was 

 made manually by inserting a polarized plug 

 in an appropriate socket on the winch spool. 

 A shorting plug was replaced by the micro- 

 annmeter plug between measurements. After 

 SCOT Expedition, gold-plated slip rings were 

 incorporated into the winch design so that 

 electrical continuity was maintained between 

 the microammeter and the detector at all 

 times. When measurements were not being 

 made, shorting of the photovoltaic cell as 

 recommended by the manufacturer was easily 

 accomplished by using the shorting position 

 on the scale switch incorporated in the Rawson 

 microammeter. 



During lowerings of the irradiance meter, 

 the annbient light incident upon the sea surface 

 was monitored by a gimbal-supported water- 

 proof deck cell mounted above the vessel's 

 superstructure. The light-sensitive element 

 and flux collector were the same type as those 

 used in the submarine irradiance meter. A 

 reducing screen of thin stainless steel with 

 equally spaced holes about 2 mm. in diameter 

 was placed between the cosine collector and 

 photovoltaic cell. No filter was used. The cur- 

 rent generated by the deck irradiance meter 

 was measured with a 0- to 1 -milliampere 

 meter of low resistance (about 50 ohms) or, 

 on TO-59-1 and subsequent cruises, with a 

 Rawson-type 501 meter. 



The current generated by the photovoltaic 

 cell in the submerged detector and by the deck 

 cell (see above) was measured with an in- 

 ternally damped Rawson microammeter, type 

 501 (Rawson Electrical Instrument Co., Cann- 

 bridge, Mass.). The damping feature (45- 

 second period), incorporated into the meter by 

 the manufacturer at my request, permits 

 measurement of irradiance levels near the 

 sea surface (upper 15-20 m.). In this depth 

 range, vessel surge and the focusing of inci- 

 dent specular energy from surface ripples 

 and waves produce a pulsating DC signal with 



a frequency of the order of 50 to 125 cycles 

 per minute (see Tyler, 1960; table 11). This 

 fluctuating signal makes measurements with 

 an undamped meter almost impossible. In the 

 deeper water the damping feature is useful on 

 occasion but is not necessary. 



The Rawson-type 501 meter is designed for 

 use with photovoltaic cells and possesses a 

 switch which allows the operator to short- 

 circuit the photovoltaic cell or select any one 

 of 5 scales (50, 100, 200, 500, and 1,000 

 microammeter), each having an internal re- 

 sistance of 100 ohms. 



These improvements do not affect the re- 

 liability of k nneasurements in general, and all 

 of the measurements obtained during this 

 investigation are considered comparable. A 

 brief discussion in another section, however, 

 mentions the adequacy of depth determina- 

 tions calculated from wire length-wire angle 

 relations, which incorporates information ob. 

 tained on cruise TO-60-1 with the depth- 

 sensing device. 



Characteristics of the Photovoltaic Cells 

 and Filters 



The photovoltaic cells and filters used to 

 measure attenuation coefficients possess elec- 

 trical and physical characteristics that affect 

 the precision and accuracy of the k values ob- 

 tained. 



The current generated by a Photronic cell 

 in a constant monochromatic light field is a 

 function of its sensitivity, the temperature, 

 and the external circuit resistance. Technical 

 information supplied by the manufacturer 

 shows that the percentage deviation in output 

 at the maximum and minimum light levels and 

 the temperature range (5-30° C.) encountered 

 in these studies does not exceed + 2 percent, 

 at the external resistance of the circuitry 

 (meter and photometer cable) used (105 + 1 

 ohm). The present data have not been corrected 

 for this temperature effect. 



Although the same microammeters have 

 been used and the detector design has re- 

 mained essentially constant during these in- 

 vestigations, a number of improvements have 

 been made in the design of the equipment. 

 These innprovements principally involved aux- 

 iliary equipment which permits the measure- 

 ment of attenuation coefficients in different 

 spectral regions, and ratios in the same spec- 

 tral region of upwelling, downwelling, and 

 horizontal irradiance. This additional work 

 may now be accomplished over the same two- 

 conductor cable without the return of the 

 detector units to the surface or changing the 

 orientation of individual detectors. Further- 

 more, a depth-sensing unit accurate to within 

 t 2 percent in the depth range 25 to 150 m. has 

 been developed which telemeters the depth 

 signal over the same two-conductor cable to a 

 deck component, where depth may be read 



