Absorption of sunlight by atmospheric sodium using a Fabry-Perot spectrometer and a sodium vapour cell
Neo, Yee Pan
A low-resolution Fabry-Perot spectrometer was used in conjunction with a sodium vapour cell to observe the terrestrial absorption by sodium. By observing the variation of absorption with the solar elevation, the sodium abundance was determined. The abundances of sodium obtained were in the range between 10 X 109 and 20 X 109 atoms/cm2 column. Recent dayglow results obtained by Blamont and Donahue (1961) have indicated that the sodium abundance in the daytime is three to four times higher than during twilight. The present results tend to support the dayglow observation by Blamont and Donahue (1961). However, previous work by Zwick and Shepherd (1961) and McNutt and Mack (1963) have both indicated no enhancement of sodium during the daytime as compared to twilight. The apparent contradiction between these sets of results has not yet been resolved. As an additional result, the residual intensities at the bottom of the Fraunhofer D-lines were found to be 6.37 ± 0.19% and 5.41 ± 0.25% for the D1 and D2 lines respectively.