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Institut für Umweltphysik Universität Heidelberg
High resolution spectroscopy of the Oxygen A-band in zenith-scattered light; Implications for cloudy sky photon
path length
T.Scholl, U.Nägele , U.Platt, and K.Pfeilsticker
Institut für Umweltphysik, Universität Heidelberg, INF 229, D-69120 Heidelberg
Overview:
-Instrumentation
-Method
-Evaluation Example
-Summary / Outlook
Institut für Umweltphysik Universität Heidelberg
Setup / Geometry
ANDO R C C D C AM ERA(2048 x 512 p ixe l)
Ground
v
FOV = 1°
RT SmoothingH
H
H: vertical cloud extension
Short integration time required:
Previous measurements: 900 sec
BBC measurements: ~ 2 sec
Institut für Umweltphysik Universität Heidelberg
Spectrograph CCD Detector
•Sopra UHRS 1500 Fastie-Ebert
•F = 1500 mm
•110 x 220 mm2, 316 g/mm Echelle
•f/13.5
•Temp. const. +/- 1K
•ca. 500 kg
Resolution(@770nm): 9.6 pm (5ch, 1.93pm/ch)
Spectral Range: ca. 4 nm
•2048x512 pixel
•27.6 x 6.9 mm2 (13.5 m)
•QE ca. 45% @ 770nm
•R/O noise 2e-/pixel
•FI, Marconi (EEV)
•TE cooling –90°C
Institut für Umweltphysik Universität Heidelberg
Setup / Geometry
ANDO R C C D C AM ERA(2048 x 512 p ixe l)
Ground
v
FOV = 1°
RT SmoothingH
H
H: vertical cloud extension
Short integration time required:
Previous measurements: 900 sec
BBC measurements: ~ 2 sec
Institut für Umweltphysik Universität Heidelberg
Radiative Smoothing Scales
08:00 10:00 12:00 14:000
1x104
2x104
3x104
4x104
5x104
6x104a) October 08, 98
-1 1 3 5 7 9 11 13 15
2-12
2-10
2 -8
2 -6
2 -4
2 -2
20
L = 17-25 kmSmoothing
regime
Large scale
regime
Intermediate
regime
=1.64
2=0.48
a) October 08, 98
<|
(r
;n)|
2>
2 22 2 2 2 2 2 2
Savigny et al. , 2002Scale parameter rTime (UTC)
Radiometer HDRAD (760nm)
Institut für Umweltphysik Universität Heidelberg
Lévy Indices
α: Lévy (transport) index; α = 1 direct transmission, 1< α < 2 anomalous diffusion, α = 2 classical diffusion Observables are: <L> (oxygen A band spectroscopy), H radar/Lidar, Inferred quantities: τ and α
ergo transport index α (describing a mean) can be inferred !
11
11
HL
MFP
Lgg
HMFP
Institut für Umweltphysik Universität Heidelberg
Inferred Lévy Indices(Pfeilsticker, JGR, 1999)
Institut für Umweltphysik Universität Heidelberg
Measurement
768.0 768.5 769.0 769.5 770.0 770.50.0
0.2
0.4
0.6
0.8
1.0
K I
Mg ISi I
Tra
nsm
issi
on
Wavelength (nm)
Sept.17, 2001 10:30:32 UTC
=14 pm, integration time = 1.5 sec
- Data available from Sept.6 – 25, 2001- ~ 150.000 spectra were measured (~9GB)- Integration time ranging from 0.5 - 5 sec (variable light intensity)
Institut für Umweltphysik Universität Heidelberg
Data Analysis
High Spectral Resolution
Searched quantityp(l) ?
Spectrum
Measurement withgiven spectral
resolution
Measured Spectrum
Nonlinear Least
Square Fit (10min, 1GHz)
Modeled Spectrum
Spectroscopic Model Temp., Pressure Profile
x T(p(aj), i ( )
Solar Fraunhofer p(l) Model Oxygen Absorption Spectrum Lines (VOD)
Low Spectral ResolutionBest estimate p(l)
Convolution with instrument function
768.0 768.5 769.0 769.5 770.0 770.5 771.0 771.50.0
0.2
0.4
0.6
0.8
1.0
Ni I
(?)
Ni I
Co
IF
e II
Fe
I
K I
Si I
Si I
Mg
I
Si I
Si IS
i IC I
Si I
I 0
Wavelength / nm
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.50
10
20
30
40
50
60
70
767.20 767.25 767.30 767.35 767.40 767.45 767.500.00E+000
2.00E-024
4.00E-024
6.00E-024
Wavelength (nm)
Institut für Umweltphysik Universität Heidelberg
Evaluation Example
768.0 768.5 769.0 769.5 770.0 770.50.0
0.2
0.4
0.6
0.8
1.0
Tra
nsm
issio
n
Wavelength (nm)
MEASUREMENT Model (Fit)
768.0 768.5 769.0 769.5 770.0 770.5
-0.02
-0.01
0.00
0.01
0.02
0.03
0.04
Re
sid
ua
l
Wavelength (nm)
Model
Residual
Institut für Umweltphysik Universität Heidelberg
Sensitivity Test
1 2 3 4 5 6 7
0.0
0.5
1.0
1.5
2.0
2.5
?
?
model: Gamma <l> = 2.615 +/- 0.039
<l2> = 9.177 +/- 0.717<l> = 2.682 +/- 0.038
<l2> = 7.227 +/- 0.223p(l
)
Pathlengths l
free Fraunhofercoefficient fixed Fraunhofercoefficient
768.0 768.5 769.0 769.5 770.0 770.5
-0.03
-0.02
-0.01
0.00
0.01
0.02
0.03
0.04
Re
sid
ua
l
Wavelength (nm)
Institut für Umweltphysik Universität Heidelberg
Summary
• Spectral retrieval software works, but needs some improvements (wavelength dependent convolution)
• Better time resolution (15 min few seconds) and better spectroscopical resolution ( 20pm 9.5 pm)
• Better understanding and sensitivity test for retrieval method necessary • Determination of <L>, <L2>, ...• Combination with , LWC, H, ...• ..............
Outlook
Recommended