A simple photometer constructed from an LED and an op amp can be used to measure light in a number of physical situations. A variety of LEDs exist to investigate different wavelength ranges. Combined with an inexpensive transit, the LED photometer can be used to carry out skylight studies and atmospheric optical depth measurements. The activities described in this paper can help students understand why the sky is blue and introduce students to the basics of radiation scattering and planetary atmospheres.
REFERENCES
1.
G. E.
Shaw
, “Sun photometry
,” Bull. Am. Meteor. Soc.
64
, 4
–10
(1983
).2.
Scattering in the Atmosphere, edited by C. Bohren (SPIE Press, Bellingham, WA, 1989). This reference includes many interesting articles on atmospheric optics.
3.
4.
K.L. Coulson, Polarization and Intensity of Light in the Atmosphere (A. Deepak Publishing, Hampton, VA, 1988).
5.
F.M. Mims III, Engineer's Mini-Notebook Environmental Projects (Siliconcepts, USA, 1995).
6.
A National Semiconductor LF411CN was used in the circuit.
7.
Y. B.
Acharya
, A.
Jayaraman
, S.
Ramachandran
, and B. H.
Subbaraya
, “Compact light-emitting-diode sun photometer for atmospheric optical depth measurements
,” Appl. Opt.
34
, 1209
–1214
(1995
).8.
The LEDs were purchased from Digikey Corp. and are manufactured by Lumex. Lumex part numbers Super Red SSL-LX5093SRC/E and Mega-brite Green SSL-LX100133XGC.
9.
Nasco can be contacted at custserv@eNASCO.com.
10.
http://www.wmo.ch/web/arep/reports/gaw153.pdf.
11.
M. D.
King
, D. M.
Byrne
, B. M.
Herman
, and J. A.
Reagan
, “Aerosol size distribution obtained by inversion of spectral optical depth measurements
,” J. Atmos. Sci.
35
, 2153
–2167
(1978
).For the earliest discussion of such a procedure, see
A.
Angstrom
, “On the atmospheric transmission of Sun radiation and on dust in the air
,” Geograf. Ann.
12
, 130
–159
(1929
). This article is reprinted in Ref. 2.12.
See, for example,
A. S.
Zakey
, M. M.
Abdelwahab
, and P. A.
Makar
, “Atmospheric turbidity over Egypt
,” Atmos. Environ.
38
, 1579
–1591
(2004
) and the references therein.13.
http://www.pnl.gov/aisu/pubs/eemw/papers/ipccreports/workinggroup1/index.htm.
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2006
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