INTRODUCTION 



The following description of selected nnethods 

 and their partial evaluation is a detailed ac- 

 count of some of the instrunnentation and pro- 

 cedures which have been used by the author 

 in 1956-65 and by several of his colleagues in 

 the STOR (Scripps Tuna Oceanography Re- 

 search) Program in 1958-6Z in the eastern 

 tropical Pacific. Only abbreviated outlines of 

 these methods have been published (Holmes, 

 Schaefer, and Shimada, 1957; Holmes and 

 others, 1958; Holmes and Blackburn, 1960; 

 Blackburn, Griffiths, Holmes, and Thomas, 

 1962), and no accounts of statistical reliability 

 of the methods have appeared. Because data 

 obtained with these methods are being widely 

 used, and because I have completed a manu- 

 script that deals with the statistical and de- 

 scriptive interrelations of the variables 

 measured by these methods, an account 

 of the methods is believed to be timely and of 

 scientific value. 



INCIDENT SOLAR RADIATION 



Because of the importance of solar energy 

 in the photosynthetic process, incident solar 

 radiation upon a horizontal plane was measured 

 continuously on all STOR cruises. Although the 

 data have not beenused for heat-budget studies, 

 they have been analyzed here with a view toward 

 assessing the accuracy with which the daily 

 incident radiation total may be estimated by 

 indirect means. 



Instrumentation 



Eppley 10-junctionpyranometers, formerly 

 called pyrheliometers (The Eppley Laboratory, 

 Inc., Newport, R.I.), have beenused throughout 

 this investigation. 



The 180° pyranometer (Drummond, 1961) 

 was mounted above most of the vessel's super- 

 structure on a small metal base which was 

 shock-mounted to an identical pendulum- 

 balanced platform. Except in the roughest seas, 

 this gimbal's mounting maintained the instru- 

 ment in a nearly horizontal plane. 



The electromotive force generated by the 

 10-junction pyranometer, about 2 mv./ g, cal,/ 

 cm.2/rnin. (millivolts per gram calorie per 

 square centimeter per minute), was recorded 

 with a 0- to 10-mv. Speedomax Model G or H 

 recorder (Leeds and Northrup). Interference 

 originating from the vessel's radio transmitter 

 antenna during transmission was eliminated 

 by using shielded signal leads and appropriate 

 radio-frequency filters. 



The response of the Eppley instrument to 

 energy between 400 and 25,000 m^ is nearly 

 linear. Incident solar radiation active in algal 



Use of trade names in this publication does not imply 

 endorsement of commercial products. 



photosynthesis, 400 to 700 rrifi, was assumed 

 to average roughly 45 percent of the incident 

 energy recorded (Withrow and Withrow, 1956), 

 regardless of the degree of overcast. 



Daily radiation totals were obtained by in- 

 tegration of the unsmoothed daily records with 

 a polar planimeter. The accuracy of the daily 

 radiation totals is not precisely known. Sources 

 of error include: (a) calibrationerror; (b) fail- 

 ure of the pyranometer to maintain its cali- 

 bration; (c) recorder error; (d) failure tokeep 

 the pyranometer oriented in the same direction 

 at all times; (e) failure tokeep the pyranometer 

 horizontal under all sea conditions; and (f) in- 

 tegration errors. 



A rough estimate of the total error in the 

 daily radiation total, which includes the above- 

 mentioned sources of error, excepting items 

 a and b, was obtained in the following manner: 

 the solar radiation record for February 19, 

 1959, was integrated twice with a polar plani- 

 meter, once by use of the upper limit of the 

 pen excursion and once by use of the lower 

 limit of the pen excursion. The values obtained 

 were 525 and 478 g, cal./cm.^/da., respec- 

 tively. 



Qualitatively it has been noted for a constant 

 recorder-amplifier sensitivity that the amount 

 of pen excursion (i.e., the width of the trace) 

 appears to vary with sea conditions. During 

 darkness, regardless of sea state, the width 

 of the pen trace remained virtually constant 

 at 0.9 mm. On calm clear days the trace width 

 rarely exceeded 1 mnn., but on rough days it 

 averaged 2 mm., and once it reached an ex- 

 treme width of 5 mm. 



Had the central point of the pen excursions 

 been followed during the above integration, 

 the daily total would have equalled 501 g. cal./ 

 cm.*^ and the range would become - 24 g. cal./ 

 cm.^/day, or roughly i 5 percent of this value. 

 Since the sea on this particular day was ex- 

 tremely rough, I believe that the values for 

 the daily radiation totals are rarely in error 

 by more than t 5 percent. 



According to the pyranometer catalog issued 

 by the Eppley Laboratory, the probable error 

 for the pyranometer in the range 0.25 to 1.50 g. 

 cal./cm. 2/min. is t 1.5 percent. This figure 

 presumably covers calibration error and in- 

 cludes changes in pyranometer sensitivity 

 during the calibration period, as well as re- 

 corde r error. 



One of the two pyranometers used during 

 this study was recalibrated by the Eppley 

 Laboratory after 3 years of use at sea. The 

 change in sensitivity amounted to +0.12 mv. 

 (e.g., from 2.53 to 2.65 mv.) per g.cal./cm.^/ 

 min. Unfortunately, it is not known if this 

 change is typical for this class of instruments 

 or whether the change in sensitivity was 

 gradual or abrupt. As a result of this sensi- 

 tivity change, however, an undetermined num- 

 ber of the daily radiation totals will be roughly 

 5 percent too high. 



