We present an experiment investigating the physics of the atmospheric greenhouse effect that can be performed by undergraduate physics students. The students construct a three-channel spectral photometer to observe the infrared heat flux in the atmosphere. With this spectral photometer, the students observe the difference in heat flux between the portion of the IR spectrum that is absorbed by water vapor and carbon dioxide and the portion that is not absorbed by atmospheric constituents. The students discover that Earth's surface is warmed by radiation from the greenhouse gas absorption bands, and the radiation of heat to space is retarded by the absorption bands. One component of the experiment is performed on the ground and the other component is performed in the atmosphere using a high-altitude balloon. The students then compare their results to a simulation of infrared radiation transport in the atmosphere.

Topics
Infrared radiation, Thermal instruments, Black body radiation, Greenhouse gases, Greenhouse effect, Linear filters, Photometry, Absorption band, Students
1.
N.
Ekholm
, “
On the variations of the climate of the geological and historical past and their causes
,”
Q. J. R. Meteorological Soc.
27
,
1
–
62
(
1901
).
https://doi.org/10.1002/qj.49702711702
Google Scholar
Crossref
Search ADS
 
2.
Climate Change 2021: The Physical Science Basis
, edited by
V.
Masson-Delmotte
,
P.
Zhai
,
A.
Pirani
,
S. L.
Connors
,
C.
Péan
,
S.
Berger
,
N.
Caud
,
Y.
Chen
,
L.
Goldfarb
,
M. I.
Gomis
,
M.
Huang
,
K.
Leitzell
,
E.
Lonnoy
,
J. B. R.
Matthews
,
T. K.
Maycock
,
T.
Waterfield
,
O.
Yelekçi
,
R.
Yu
, and
B.
Zhou
, (
Cambridge U. P
.,
Cambridge
,
2021
).
Google Scholar
 
3.
K. E.
Trenberth
,
J. T.
Fasullo
, and
J.
Kiehl
, “
Earth's global energy budget
,”
Bull. Am. Meteorol. Soc.
90
,
311
–
324
(
2009
).
https://doi.org/10.1175/2008BAMS2634.1
Google Scholar
Crossref
Search ADS
 
4.
G. T.
Blanchard
,
F. A.
Adesina
,
W. C.
Belkwell
,
J. R.
Dyess
,
V. A.
Frabbiele
,
C. S.
McGibboney
, and
R. D.
Rumsey
, “
Balloon-borne two-channel infrared spectral photometer for observation of atmospheric greenhouse effect by undergraduates
,”
Am. J. Phys.
90
,
256
–
262
(
2022
).
https://doi.org/10.1119/10.0009284
Google Scholar
Crossref
Search ADS
 
5.
Those seeking to learn more about student ballooning are advised to inquire with their local Space Grant consortium <https://www.nasa.gov/stem/spacegrant/home/Space_Grant_Consortium_Websites.html> or the Stratospheric Ballooning Association <https://www.stratoballooning.org/>, which hosts the Academic High Altitude Conference.
6.
Laurie
McNeil
 and
Paula
Heron
, “
Preparing physics students for 21st-century careers
,”
Phys. Today
70
(
11
),
38
–
43
(
2017
).
https://doi.org/10.1063/PT.3.3763
Google Scholar
Crossref
Search ADS
 
7.
“
MLX90614 family Datasheet Single and Dual Zone Infra Red Thermometer in TO-39, Revision 13
,” available at <https://www.melexis.com/en/documents/documentation/datasheets/datasheet-mlx90614>.
8.
See the supplementary material at https://doi/org/10.1119/5.0135029 for a block diagram of the ground-based instrument, an Arduino script to control it, and a block diagram of the balloon-borne instrument.
9.
Note that Ts refers to the temperature of the MLX90614 sensor itself, not the effective radiation temperature measured by that sensor.
10.
We ran the model online at <http://climatemodels.uchicago.edu/modtran/>. We used the default parameters, except for the following: Temperature offset, 11.1; Locality, “1976 US Standard Atmosphere”; Altitude, 0; “Looking up.”
11.
A.
Berk
,
P.
Conforti
,
R.
Kennett
,
T.
Perkins
,
F.
Hawes
, and
J.
van den Bosch
, “
MODTRAN6: A major upgrade of the MODTRAN radiative transfer code
,”
Proc. SPIE
9088
,
90880H
(
2014
).
https://doi.org/10.1117/12.2050433
Google Scholar
Crossref
Search ADS
 
12.
Alexander
Berk
,
Patrick
Conforti
, and
Fred
Hawes
, “
An accelerated line-by-line option for MODTRAN combining on-the-fly generation of line center absorption with 0.1 cm-1 bins and pre-computed line tails
,”
Proc. SPIE
9471
,
947217
(
2015
).
https://doi.org/10.1117/12.2177444
Google Scholar
Crossref
Search ADS
 
13.
For more information about the LaACES program
, please visit <https://laspace.lsu.edu/laaces/>.
15.
We used the same parameters as above, with the exception of changing the temperature offset to 16.8 to account for the different surface temperature and changing the locality setting to “Cumulus Cloud Base.66 km Top 2.7 km.”
© 2023 Author(s). Published under an exclusive license by American Association of Physics Teachers.
2023
Author(s)

Supplementary Material

Supplementary materials- zip file
AAPT members receive access to the American Journal of Physics and The Physics Teacher as a member benefit. To learn more about this member benefit and becoming an AAPT member, visit the Joining AAPT page.