Institut für Umweltphysik Universität Heidelberg High resolution spectroscopy of the Oxygen A-band in zenith-scattered light; Implications for cloudy sky

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


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


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


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


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)


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


Inferred Lévy Indices(Pfeilsticker, JGR, 1999)


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)


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)


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


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)


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

Documents

Institut für Umweltphysik Universität Heidelberg High resolution spectroscopy of the Oxygen A-band in zenith-scattered light; Implications for cloudy sky