Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Eyk Bösche et al. BBC2 Workshop, Oktober 2004:...
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Eyk Bösche Eyk Bösche et al. et al. BBC2 Workshop, Oktober BBC2 Workshop, Oktober 200 200 4 4 : : Simulation of skylight polarization with the DAK model and comparisons with measurements 18.10.200 4 E. Bösche 1 , P. Stammes 2 , R. Preusker 1 , T. Ruhtz 1 , J. Fischer 1 1 (Institute for Space Sciences, Free University of Berlin) 2 (Royal Netherlands Meteorological Institute, De Bilt, The Netherlands) Simulation of skylight polarization with the DAK model and comparisons with measurements
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Transcript of Eyk Bösche et al. BBC2 Workshop, Oktober 2004: Eyk Bösche et al. BBC2 Workshop, Oktober 2004:...
Eyk
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hop
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hop
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ktob
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0044 :
: S
imul
atio
n of
sky
light
pol
ariz
atio
n
with
the
DA
K m
odel
and
com
par
ison
s w
ith
mea
sure
men
ts
18.10.2004
E. Bösche1, P. Stammes2, R. Preusker1, T. Ruhtz1, J. Fischer1
1(Institute for Space Sciences, Free University of Berlin)2(Royal Netherlands Meteorological Institute, De Bilt, The Netherlands)
Simulation of skylight polarization with the DAK model and comparisons with
measurements
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hop
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: S
imul
atio
n of
sky
light
pol
ariz
atio
n
with
the
DA
K m
odel
and
com
par
ison
s w
ith
mea
sure
men
ts
18.10.2004
Overview
• Introduction
• Mie-Simulations
• DAK-Simulations
• First comparison with measurements
• Outlook
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hop
, O
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: S
imul
atio
n of
sky
light
pol
ariz
atio
n
with
the
DA
K m
odel
and
com
par
ison
s w
ith
mea
sure
men
ts
18.10.2004
Introduction
• Radiative forcing by tropospheric aerosols depends on their optical properties like optical thickness, single scattering albedo and phase function.
• Basic idea:
• Spectral resolved VIS and NIR measurements of the diffuse sunlight at various directions in the suns principal plane with inclusion of polarization.
• Comparison of measurements and radiative transfer simulations
• Comparison allows to draw conclusions on:
• the size distribution,
• the refractive index
• and vertical distribution of aerosols.
• From the knowledge of the size distribution and the refractive index the single scattering albedo and the phase function can be derived.
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hop
, O
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0044 :
: S
imul
atio
n of
sky
light
pol
ariz
atio
n
with
the
DA
K m
odel
and
com
par
ison
s w
ith
mea
sure
men
ts
18.10.2004
Mie-Simulations (1/4)
• First mie-calculations have been performed with the following standard input parameters:• wavelength 675 nm• real and imaginary part of the refraction index of 1.5 and 0.006• log normal size distribution with a sigma of 1.8• mode radius of 0.1 microns
• To analyse how sensitiv the mie calculations are to changes of one of these parameters, each parameter was changed in a certain range, while the rest of the parameters remaind constant.
• The mie simulations serve as input for the DAK-simulations
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: S
imul
atio
n of
sky
light
pol
ariz
atio
n
with
the
DA
K m
odel
and
com
par
ison
s w
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mea
sure
men
ts
18.10.2004
Mie-Simulations (2/4)
Mode radius variation
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2 W
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hop
, O
ktob
er 2
00 2
0044 :
: S
imul
atio
n of
sky
light
pol
ariz
atio
n
with
the
DA
K m
odel
and
com
par
ison
s w
ith
mea
sure
men
ts
18.10.2004
Mie-Simulations (3/4)
Abs(Im(m)) variation
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hop
, O
ktob
er 2
00 2
0044 :
: S
imul
atio
n of
sky
light
pol
ariz
atio
n
with
the
DA
K m
odel
and
com
par
ison
s w
ith
mea
sure
men
ts
18.10.2004
Mie-Simulations (4/4)
Re(m) variation
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hop
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0044 :
: S
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n of
sky
light
pol
ariz
atio
n
with
the
DA
K m
odel
and
com
par
ison
s w
ith
mea
sure
men
ts
18.10.2004
DAK-Simulations (1/5)
• The DAK-simulations have been performed for multiple scattering and the following standard input parameters:
• a surface albedo of 0.15
• an optical thickness of 0.39
• a standard midlatitude atmospheric profile• and the mie-aerosol (output of the mie-simulations) was put in the
first layer (first one km) • while varying the optical thickness the standard mie aerosol was used.
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hop
, O
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0044 :
: S
imul
atio
n of
sky
light
pol
ariz
atio
n
with
the
DA
K m
odel
and
com
par
ison
s w
ith
mea
sure
men
ts
18.10.2004
DAK-Simulations (2/5)
Mode radius variation
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hop
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2 W
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hop
, O
ktob
er 2
00 2
0044 :
: S
imul
atio
n of
sky
light
pol
ariz
atio
n
with
the
DA
K m
odel
and
com
par
ison
s w
ith
mea
sure
men
ts
18.10.2004
DAK-Simulations (3/5)
Abs(Im(m)) variation
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0044 :
: S
imul
atio
n of
sky
light
pol
ariz
atio
n
with
the
DA
K m
odel
and
com
par
ison
s w
ith
mea
sure
men
ts
18.10.2004
DAK-Simulations (4/5)
Re(m)
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sky
light
pol
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with
the
DA
K m
odel
and
com
par
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s w
ith
mea
sure
men
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18.10.2004
DAK-Simulations (5/5)
Optical thickness variation
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: S
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sky
light
pol
ariz
atio
n
with
the
DA
K m
odel
and
com
par
ison
s w
ith
mea
sure
men
ts
18.10.2004
Comparisons with measurements (1/5)
• For the first comparison of simulations and measurements data from the BBC2 campagne have been used, taken at Cabauw, 8 Mai 2003, the Netherlands.
• Measurement geometry: principal plane• Wavelength: 675nm• Sunelevation angle: 17.65°
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2 W
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er 2
00 2
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: S
imul
atio
n of
sky
light
pol
ariz
atio
n
with
the
DA
K m
odel
and
com
par
ison
s w
ith
mea
sure
men
ts
18.10.2004
Comparisons with measurements (2/5)
FUBISS-POLAR scans, Cabauw, 08 May 2003 FUBISS-POLAR zenith, Cabauw, 08 May 2003
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: S
imul
atio
n of
sky
light
pol
ariz
atio
n
with
the
DA
K m
odel
and
com
par
ison
s w
ith
mea
sure
men
ts
18.10.2004
Comparisons with measurements (3/5)
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hop
, O
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er 2
00 2
0044 :
: S
imul
atio
n of
sky
light
pol
ariz
atio
n
with
the
DA
K m
odel
and
com
par
ison
s w
ith
mea
sure
men
ts
18.10.2004
Comparisons with measurements (4/5)
Mode radius variation Abs(Im(m)) variation
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erB
BC
2 W
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hop
, O
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er 2
00 2
0044 :
: S
imul
atio
n of
sky
light
pol
ariz
atio
n
with
the
DA
K m
odel
and
com
par
ison
s w
ith
mea
sure
men
ts
18.10.2004
Comparisons with measurements (5/5)
Re(m) variation Optical thickness variation
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: S
imul
atio
n of
sky
light
pol
ariz
atio
n
with
the
DA
K m
odel
and
com
par
ison
s w
ith
mea
sure
men
ts
18.10.2004
OUTLOOK…
• Investigate the effect of different size distributions (e.g bimodal)• Implementation of the k-distribution in DAK (O2A-Band)• First sensitivity studies of radiance and polarization to aerosols in the
absorbtion bands (O2A-Band)• Sensitivity to aerosol optical thickness• Sensitivity to aerosol altitude• Sensitivity to aerosol size parameters
• Size distribution• Effective radius• Effective variance
• Sensitivity to aerosol refractive index• Surface albedo effects
• Final aim: an retrieval algorithm for aerosol optical properties from polarization measurements.
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2 W
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erB
BC
2 W
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hop
, O
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er 2
00 2
0044 :
: S
imul
atio
n of
sky
light
pol
ariz
atio
n
with
the
DA
K m
odel
and
com
par
ison
s w
ith
mea
sure
men
ts
18.10.2004
ENDE
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0044 :
: S
imul
atio
n of
sky
light
pol
ariz
atio
n
with
the
DA
K m
odel
and
com
par
ison
s w
ith
mea
sure
men
ts
18.10.2004
Measurement-equation ...
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2
1
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1
11
v
v
v
v
n
nU
Q
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MSS
• Interaction of a light wave with an optical unit (e.g. polarizer, lense or even a scattering particle) can be described by a linear transformation of the Stokes-Vector
• Negligence of the circular component V• Supposition of an ideal sensor• FUBISS-POLAR measures only intensities
))(2sin)(2cos(2
1111 UQII
