j) Spectral Calculation
It is an indispensable prerequisite for the
•
development of optical gas sensors,
•
the propagation of optical or infrared radiation through the atmosphere or
•
studies of TeraHertz femtosecond pulse propagation through dense gases
to
have
detailed
spectral
information
about
the
investigated
molecules
and
also
about
possible
candidates, which are overlapping in their spectra with the studied gas.
Therefore,
we
developed
a
program
for
fast
computation
and
display
of
molecular
spectra
on
a
PC
Microsoft
Windows®
platform
(Harde&Pfuhl
[1];
Harde
et
al.
[2]).
This
program,
which
we
named
MolExplorer,
takes
advantage
of
a
database,
in
which
the
relevant
parameters
for
the
calculation of a spectrum are stored . The Mol
Explorer works with two different databases:
•
The
HITRAN08
database
contains
the
39
most
prominent
molecules
in
the
atmosphere
and
has
stored
2.714
Mio
spectral
lines
of
these
gases.
3
further
gases
(SF
6
,
ClONO
2
and
CF
4
)
with
additional
2.981
Mio
lines
are
found
in
a
supplementary
folder
of
the
database.
HITRAN
is
an
acronym
for
Hi
gh-Resolution
Tran
smission
Molecular
Absorption
Database
and
is
a
compi
-
lation
of
spectroscopic
parameters
to
predict
and
simulate
the
transmission
and
emission
of
light in the atmosphere (Rothman et al. [3, 4]).
•
The GEISA-03-database (Gestion et Etude des Informations Spectroscopiques Atmosphé-
riques: Management and Study of Atmospheric Spectroscopic Information) contains more
than 1.6 Mio transitions of 42 molecules which are of interest for studies of the terrestrial as
well as other planetary atmospheres (Jacquinet-Husson et. al. [5, 6]).
The
MolExplorer
calculates
the
molecular
absorption
and
models
the
attenuation
of
radiation
in
the
atmosphere
or
under
laboratory
conditions.
Within
seconds
it
provides
survey
spectra
from
mm-waves
up
to
the
ultra
violet
as
well
as
selected
parts
with
highest
spectral
resolution,
this
for
the most relevant gases and pollutants in the atmosphere (see: MolExplorer Manual, Harde [7] ).
For
this
the
user
has
to
specify
the
molecules
or
isotopologues
of
interest,
the
spectral
range
and
resolution,
the
respective
partial
pressures
or
concentrations,
the
buffer
gas
pressure
(when
re
-
quired), and perhaps additionally the temperature. The rest is accomplished by the MolExplorer.
The
lower
screen
shot
shows
the
panel
and
graphical
display
of
the
MolExplorer,
in
this
ex
-
ample
for
a
spectral
calculation
around
2
µm
for
three
CO
2
isotopologues,
which
can
be
distin
-
guished by colored markers.
Some Additional Options
•
Direct comparison of spectra from the HITRAN- or GEISA-database.
•
Import
of
measurements
or
other
calculations
and
fit
to
these
spectra
with
HITRAN-
or
GEISA-data.
•
Convolution of spectra with different instrument functions.
•
Propagation
of
radiation
through
the
atmosphere
under
preselected
elevation
angles
and
over
specified
path
lengths,
accounting
for
changes
in
pressure
and
temperature
broaden
-
ing of spectral lines and lineshapes with altitude above surface.
•
Consideration of Mie scattering and free-space-dam
ping over the path length.
•
Radiation
transfer
calculations
without
or
with
cloud
overcast
in
up-
and
down
direction
for
three climate zones.
References & Publications
1.
H. Harde, J. Pfuhl
MolExplorer: A Tool for Computation and Display of Molecular Spectra from the HITRAN and GEISA Database
Helmut-Schmidt-University, 1995 - 2018
2.
H. Harde, J. Pfuhl, M. Wolff, H. Groninga
MolExplorer: A New Tool for Computation and Display of Spectra from the HITRAN Database,
Session 5 (Database), 9th HITRAN Database Conference, Harvard-Smithsonian Center for Astrophysics,
Cambridge, MA, USA, 25.-28. June 2006
http://cfa-www.harvard.edu/hitran/HITRAN_conf06_presentations/Session5/5.5-Harde.pdf
3.
L. S. Rothman et.al., “The HITRAN Molecular Spectroscopic Database and HAWKS; 1996 Edition”, J. Quant.
Spectrosc. Radiat. Transfer 60, 665–710 (1998)
4.
L. S. Rothman et.al., “The HITRAN 2008 molecular spectroscopic database”,
J. Quant. Spectrosc. Radiat. Transfer 110, 533–572 (2009),
http://www.hitran.com or http://www.cfa.Harvard.edu
5.
N. Jacquinet-Husson et. al., “The 2003 edition of the GEISA/IASI spectroscopic database“,
J. Quant. Spectrosc. Radiat. Transfer 95, 429-467 (2005)
6.
http://ara.lmd.polytechnique.fr/htdocs-public/products/GEISA/HTML-GEISA/IasiDatabase_pres.pdf: “The 2003
Edition of GEISA: A Spectroscopic Database System for the Second Generation Vertical Sounders Radiance
Simulation”
7.
H. Harde, Manual of MolExplorer, Helmut-Schmidt-University, 2012
Physics & Climate