442 Table 153 



RELATION BETWEEN ILLUMINATION AND TOTAL RADIATION 



In the spring and summer of 1924, Kimball ' made comparisons at Washington, D. C, 

 between the illumination on a horizontal surface as measured with a photometer and the 

 total solar and sky radiation falling on a horizontal surface as measured with a thermo- 

 electric pyrheliometer. Table 153 gives the illumination in foot-candles corresponding to 

 a total solar and sky radiation of 1 calorie per square centimeter per minute as a function 

 of the sun's zenith distances, for cloudless skies. For overcast conditions Kimball obtained 

 a mean value of 7440 foot-candles for each calorie per square centimeter per minute. He 

 concludes that with cloudless skies the factor 6700 will on the average give the daylight 

 intensity within ± 5 percent. With cloudy skies the factor averages higher, probably not 

 far from 7000. 



Illumination equivalent of 1 calorie per square centimeter per minute 



Sun's zenith distance 



25° 47.3° 60.0° 67.6° 70.7° 73.6° 75.7° 77.4° 78.7° 

 Illumination 

 equivalent (ft.-c.) 7000 6740 6470 6320 6260 6220 6200 6200 6200 



1 Kimball, H. H., Month. Weath. Rev., vol. 52, p. 473, 1924. 



Table 154 

 ALBEDO OF VARIOUS SURFACES 



Table 154 presents a summary of values of the albedo of various surfaces obtained by a 

 representative group of observers. In the column headed "Type of observation," measure- 

 ments of the albedo in the visible spectrum made with photometers are indicated by v, 

 measurements of the total albedo made with pyrheliometers, pyranometers, etc., are indi- 

 cated by t, measurements made from aircraft by a, and measurements made on the ground 

 by g. Richardson * gives a theoretical discussion of the use of photometers. 



Descriptive terms follow the usage of the individual writers. 



Surface 



Type of 

 observation 



Albedo 



% 



3-A 



6-10 



5-10 



3-7 



3-5 



4 



6 

 14 

 30 

 46 



Observer 



KH 

 TH 

 L 

 TH 

 L 

 A 

 A 

 A 

 A 

 A 



Bay va 



" and river va 



Inland waters va 



Ocean va 



deep va 



near shore, solar elevation 47° tg 



" , " " 43° tg 



" , " " 20° tg 



" , " " 12° tg 



" , " " sr tg 



(Also see Table 155, Reflectivity of a Water Surface.) 



Forest, green va 



" va 



" va 



' ' , snow-covered ground va 



Ground, bare va 



" , " , very white va 



" , " , some trees va 



" , wet, 70-85% bare ta 



" , moist, 70-95% bare ta 



Black mold, dry tg 



" , wet tg 



Sand, dry tg 



1 Richardson, L. F., U. G. G. I. Sect. d. Meteor., Troisieme Assemblee Generate, Prague, 1927. 

 University Press, Cambridge, 1928. 



{continued) 



3-6 



4-10 



3-5 



10-25 



10-20 



11 

 7 



8-9 

 9-12 



14 

 8 



18 



KH 



TH 



L 



KH 



L 



KH 



KH 



F 



F 



A 

 A 



SMITHSONIAN METEOROLOGICAL TABLES 



