1. 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 Zhukov on behalf of the KM3NeT collaboration

2. Introduction VLVnT 09 – Vladimir Zhukov 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 site Input parameters for Monte Carlo and reconstructions

3. Introduction VLVnT 09 – Vladimir Zhukov 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 L β = 1/β, β is the transmission coefficient. The quantity L β can be derived by the relation I(λ,R) = [I 0 (λ)/4πR 2 ]exp[- R/L β (λ)], where R is the path of light. Optical parameters

4. Introduction VLVnT 09 – Vladimir Zhukov Measure intensity at two known distances R S and R L (indexes S and L mean “short” and “long”) the transmission length L ß can be derived by the ratio of intensities I S / I L = (R L / R S ) 2 exp [(R L – R S )/L β ] In this case we don’t care for knowledge of I 0 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).

5. Construction of the LAMS VLVnT 09 – Vladimir Zhukov LAMS Mechanical Structure

6. Construction of the LAMS VLVnT 09 – Vladimir Zhukov Two plane HAMAMATSU S6337-01 photodiodes, large sensitive area of 324 mm 2. 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. λ m (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

7. Construction of the LAMS VLVnT 09 – Vladimir Zhukov LAMS Lab test 1/R 2 -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/R 2 law perfectly. I L /I S = (R S /R L ) 2

8. LAMS deployments MAY 2009 VLVnT 09 – Vladimir Zhukov 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(36 O 31.336’ N / 21 O 25.635’ E), depth 4300 m NEMO (Near Capo Passero) NESTOR (Near Pylos

9. LAMS deployments VLVnT 09 – Vladimir Zhukov 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

10. Data analysis VLVnT 09 – Vladimir Zhukov 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 L β = 1/ β, β is the transmission coefficient. R is the distance between light source and detector I(λ,R) = [I 0 (λ)/4πR 2 ]exp[- R/L β ( λ)]

11. Results VLVnT 09 – Vladimir Zhukov 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 (36 o 31.336’ N / 21 o 25.635’ E) Data from May 2009

12. Results VLVnT 09 – Vladimir Zhukov Measurements of the Pylos 4.5D and Capo Passero 2 Sites Site near Pylos (36 o 31.336’ N / 21 o 25.635’ E) Site 2 near Capo Passero (36  11.910’N / 15  45.922’E ) Data from May 2009

13. 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 (36 o 31.336’N, 21 o 25.635’E) Depth: 3000m (seabed: 4300m) Data from May 2009 VLVnT 09 – Vladimir Zhukov Results Transmission length at similar depths per Site Depth (m) 3100, Capo Passero 1 3100 3000, Capo Passero 2 3000, Pylos 4.5D

14. After all this depths the telescope is located 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: 3400m (seabed: 3600m) Site near Pylos (36 o 31.336’N, 21 o 25.635’E) Depth: 4100m (seabed: 4300m) Results VLVnT 09 – Vladimir Zhukov 3100, Capo Passero 1 3400, Capo Passero 2 4100, Pylos 4.5D Depth (m) Transmission length at deepest depth per Site

15. Results VLVnT 09 – Vladimir Zhukov Transmission lengths from LAMS May 2009 deployments Depth (m)200025003000310034004100 Wavelength (nm)Transmission length (m) at site Capo Passero 1 375.718.518.818.3 385.722.022.421.8 400.326.326.525.6 425.032.732.630.8 445.438.337.235.0 462.641.940.337.6 501.627.026.425.2 519.520.620.219.7 Wavelength (nm)Transmission length (m) at site Capo Passero 2 375.716.517.018.217.4 385.719.420.121.820.7 400.322.623.425.724.3 425.027.328.832.230.8 445.430.932.436.535.7 462.634.336.241.439.9 501.623.624.426.025.7 519.518.318.819.919.7 Wavelength (nm)Transmission length (m) at site Pylos 4.5D 375.719.520.220.4 19.7 385.722.924.124.4 23.6 400.326.828.328.8 27.6 425.032.834.335.736.134.1 445.436.539.140.541.139.2 462.640.243.645.145.644.1 501.626.327.127.728.127.1 519.519.720.3 20.720.1

16. L β L β = 1.20 Capo Pas.1 3100 m (L β L β ) 3 = 1.73 Pylos 4.5D 4100 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 L β L β = 1.14 (L β L β ) 3 = 1.50 Pylos 4,5D 4100 m Pylos 4,5D 4100 m Capo Pas.2 3400 m Capo Pas.2 3400 m VLVnT 09 – Vladimir Zhukov λ (nm)375385400425445463502520 L β P4.5 /L β CP1 1.111.121.131.16 1.201.101.09 L β P4.5 /L β CP2 1.171.181.191.171.151.141.091.05 Pylos 4,5D 4100 m

17. Results VLVnT 09 – Vladimir Zhukov LAMS 2009 Attenuation of pure water [2] Wavelength (nm) Comparison with attenuation NESTOR 1992[1] Pylos 4.5 D Site

18. Summary VLVnT 09 – Vladimir Zhukov 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.

19. BACKUP SLIDES

20. Results VLVnT 09 – Vladimir Zhukov Extraction of parameters L sct and L abs λ, nm,C, m -1 *) β, m -1 **) b, m -1 L sct, m a, m -1 L abs, m 4250.0310.0280.700.0042330.02737 4450.0280.0240.720.0061800.02245 4630.0260.0220.740.0052000.02148 Smith & Baker 1981 (clearest sea water) λ (nm)420440460 b (m -1 )0.00610.00490.0041 *) 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)

21. 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