vlvnt 09 – vladimir zhukov 4-th international workshop on very large volume neutrino telescopes...

VLVnT 09 – Vladimir Zhukov

4-th International Workshop on Very Large Volume Neutrino Telescopes for the Mediterranean Sea

LIGHT TRANSMISSION MEASUREMENTS WITH LAMS in the MEDITERRENIAN SEA

Vladimir Zhukovon behalf of the KM3NeT collaboration

Introduction


One of the important tasks of particle physics and astrophysics in coming years is the detection of high energy cosmic neutrinos. In order to build a deep under water Cherenkov neutrino telescope the knowledge of the water optical characteristics is mandatory.

Monitoring of the water optical properties

Choice of the telescope siteInput parameters for Monte Carlo and

reconstructions

Introduction


In case of very clear Mediterranean water the optical base of the instrument should be long enough (10 and more meters) in order to minimize the errors of measurements. Since the KM3NeT is an open geometry experiment we are using non-collimated light beam to measure the transmission length Lβ = 1/β, β is the transmission coefficient.

The quantity Lβ can be derived by the relation

I(λ,R) = [I0(λ)/4πR2]exp[- R/Lβ(λ)] ,

where R is the path of light.

Optical parameters

Introduction


Measure intensity at two known distances RS and RL (indexes S and L mean “short” and “long”) the transmission length Lß can be derived by the ratio of intensities

IS / IL = (RL/ RS )2 exp [(RL – RS)/Lβ ]

In this case we don’t care for knowledge of I0 and internal optical parameters of the instrument.

Optical parameters

NESTOR collaboration has built a transmissometer with optical base of changeable length - LAMS = Long Arm Marine Spectrophotometer

Transparency of water have been investigated. Measurements have been performed in Ionian Sea in site near Pylos (April and October 2008, and May 2009) and in sites near Capo Passero (May 2009).

Construction of the LAMS


•Long rigid Ti-frame

•Two VITROVEX glass spheres with light source and photo-detector inside

Photo detector

10

m, 1

5 m

, 1

7 m

an

d 2

2 m

VITROVEX glass sphere

VITROVEX glass sphere

Pressure meter

Ti- frame

Light source

LAMS Mechanical Structure



• Two plane HAMAMATSU S6337-01 photodiodes, large sensitive area of 324 mm2 .

• DAQ has two different channels.• Photocurrent converted to voltage & digitized.• Data taking rate ~70 Hz.• Data stored on SD memory card

Photo-detector

Light Source• LED matrix, 8 groups of LEDs, 8 Wavlengths• Wavelength range 375nm – 520nm.• Each LED group turned on sequentially for 10s.• Between groups 2s off, and 14s off between rounds.• Autonomous, controlled by microcontroller.

λm(nm) 376 386 400 425 445 463 502 520

Number of LEDs 15 15 7 4 4 7 8 15

FWHM (nm) 13 14 14 17 18 27 31 32



LAMS Lab test 1/R2-law The relation between photodiode signal and distance from light source to detector is obtained in the tests in air.

The attenuation of intensity due to geometrical spreading of light beam follows the 1/R2 law perfectly.

I L/I S = (R S

/R L)2

I L/I S = (R S

/R L)2

LAMS deployments MAY 2009


In May 2009 the system was deployed in sites • Site 1 near Capo Passero (36 11.019’N / 16 06.017’E), depth 3350 m • Site 2 near Capo Passero (36 11.910’N / 15 45.922’E), depth 3600 m • Site near Pylos 4.5D(36O 31.336’ N / 21O 25.635’ E), depth 4300 m

NEMO(Near Capo Passero)

NESTOR(Near Pylos

LAMS deployments


Measurements were taken continuously during deployment with the system stationary at specific depths and during motion.

The depth was determined by means of the wire length and verified by pressure meter data.

The length of LAMS was changed on the deck of ship by adding or removing additional parts of the frame.

R = 10 m, 15 m, 17 m and 22 m were used

Data analysis


• A mean value of the intensity is calculated for all distances between the source and the photo-detector.

• A fit to the mean values with exponential relation

provides the transmission length Lβ = 1/β, β is the transmission coefficient. R is the distance between light source and detector

I(λ,R) = [I0(λ)/4πR2]exp[- R/Lβ(λ)]

Results


Measurements of the Pylos 4.5D and Capo Passero 1 Sites

Site 1 near Capo Passero (36 11.019’N / 16 06.017’E)

Site near Pylos (36o 31.336’ N / 21o 25.635’ E)

Data from May 2009

Results


Measurements of the Pylos 4.5D and Capo Passero 2 Sites

Site near Pylos (36o 31.336’ N / 21o 25.635’ E)

Site 2 near Capo Passero (36 11.910’N / 15 45.922’E )

Data from May 2009

Site 1 near Capo Passero (36 11.019’N, 16 06.017’E)Depth: 3100m (seabed: 3350m)

Site 2 near Capo Passero (36 11.910’N, 15 45.922’E)Depth: 3000m (seabed: 3600m)

Site near Pylos (36o 31.336’N, 21o 25.635’E)Depth: 3000m (seabed: 4300m)

Data from May 2009


Results

Transmission length at similar depths per Site

Depth (m)

3100, Capo Passero 1

3100


3000, Pylos 4.5D

After all this depths

the telescope is located

Data from May 2009

Results




4100, Pylos 4.5D

Depth (m)

Transmission length at deepest depth per Site

Results


Transmission lengths from LAMS May 2009 deployments

Depth (m) 2000 2500 3000 3100 3400 4100

Wavelength (nm) Transmission length (m) at site Capo Passero 1

375.7 18.5 18.8 18.3

385.7 22.0 22.4 21.8

400.3 26.3 26.5 25.6

425.0 32.7 32.6 30.8

445.4 38.3 37.2 35.0

462.6 41.9 40.3 37.6

501.6 27.0 26.4 25.2

519.5 20.6 20.2 19.7

Wavelength (nm) Transmission length (m) at site Capo Passero 2

375.7 16.5 17.0 18.2 17.4

385.7 19.4 20.1 21.8 20.7

400.3 22.6 23.4 25.7 24.3

425.0 27.3 28.8 32.2 30.8

445.4 30.9 32.4 36.5 35.7

462.6 34.3 36.2 41.4 39.9

501.6 23.6 24.4 26.0 25.7

519.5 18.3 18.8 19.9 19.7

Wavelength (nm) Transmission length (m) at site Pylos 4.5D

375.7 19.5 20.2 20.4 20.4 19.7

385.7 22.9 24.1 24.4 24.4 23.6

400.3 26.8 28.3 28.8 28.8 27.6

425.0 32.8 34.3 35.7 36.1 34.1

445.4 36.5 39.1 40.5 41.1 39.2

462.6 40.2 43.6 45.1 45.6 44.1

501.6 26.3 27.1 27.7 28.1 27.1

519.5 19.7 20.3 20.3 20.7 20.1

Lβ Lβ = 1.20Capo Pas.1 3100 m

(Lβ Lβ )3 = 1.73Pylos 4.5D4100 m

Capo Pas.1 3100 m

Transmission length ratio (at 463 nm – near the maximum transparency)

Therefore the volume observed by one OM in the Pylos 4,5D site is larger than in the Capo Passero site. This allows one to use a smaller number of OMs for a detector built at the Pylos 4.5D site than for the same detector built in Capo Passero site for the same sensitive volume, or in other words for the same number of optical modules one can achieve a larger sensitive volume at the Pylos site than at the Capo Passero site.

Results

Lβ Lβ = 1.14

(Lβ Lβ )3 = 1.50

Pylos 4,5D4100 m

Pylos 4,5D4100 m

Capo Pas.2 3400 m

Capo Pas.2 3400 m


λ (nm) 375 385 400 425 445 463 502 520

Lβ P4.5/Lβ CP1 1.11 1.12 1.13 1.16 1.16 1.20 1.10 1.09

Lβ P4.5/Lβ CP2 1.17 1.18 1.19 1.17 1.15 1.14 1.09 1.05

Pylos 4,5D4100 m

Results


LAMS 2009

Attenuation of pure water [2]

Wavelength (nm)

Comparison with attenuation

NESTOR 1992[1]

Pylos 4.5 D Site

Summary


The water transparency in the visible region of spectrum in the various depths in the Pylos 4.5D and Capo Passero sites has been investigated with Long Arm Marine Spectrophotometer.

It is established that the optical properties of both sites do not differ considerably, but for all wavelengths and on all depths water in the Pylos 4.5D site is a bit more transparent. The maximum excess is 1.2 times, and is observed for 463 nm at a depth of 3400 m.

BACKUP SLIDES

Results


Extraction of parameters Lsct and Labs

bca

bcosc

cos

сb

λ, nm, C, m-1

*)

β, m-1 <cosθ>**)

b, m-1 Lsct , m a, m-1 Labs , m

425 0.031 0.028 0.70 0.004 233 0.027 37

445 0.028 0.024 0.72 0.006 180 0.022 45

463 0.026 0.022 0.74 0.005 200 0.021 48

baс

Smith & Baker 1981 (clearest sea water)

λ (nm) 420 440 460

b (m-1) 0.0061 0.0049 0.0041

*) S.A.Khanaev et al. 1992 **)M.Jonasz and G.Fournier Light Scattering by Particles in Water, Elsevier 2007 Ocean Optics. Physical Optics of Ocean. Nauka, Moscow 1983 (in Russian)

S.A.Khanaev et al. Measurements of water transparency South-West of Greece. 2nd NESTOR INTERNATIONAL WORKSHOP. OCTOBER 19-21, 1992 in PYLOS-GREECE

G.Riccobene et al. Deep sea water inherent optical properties in The Southern Ionian Sea. arXiv: astro-ph/0603701 v1 25 Mar 2006

R. Smith and K. Baker. Optical properties of the clearest natural waters (200 – 800 nm) Appl.Opt. V20, N2, 1981

References

Ocean Optics. Physical Optics of Ocean. Nauka, Moscow, 1983, pp. 225, 226, 234 (in Russian, A.S Monin editor.

M.Jonasz and G.Fournier Light Scattering by Particles in Water, Elsiver 2007


vlvnt 09 – vladimir zhukov 4-th international workshop on very large volume neutrino telescopes...

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