Light velocity at new wavelengths Method New wavelengths Corrections Results Public plot

Method Optical Beacon run: Flash light from a given position Measure time when light reaches PMT => velocity of light in water and refractive index Advantage of light from Optical Beacons: Small light dispersion, because of small wavelength range (around 10 nm) Light emitted at wavelength (red new data) 385, 400, 440, 460, 470, 505, 518 and 532 nm

Method: Times versus distances Fit linear function => v_measured n=v_vacuum/v_measured

Additional runs Old analysis (69 runs taken between 5.5.2008 and 31.3.2010) : Light emitted at wavelength 400, 470 and 532 nm New analysis (Runs taken the 24.11, 13.12, 23.12, 5.1, 17.1) Light emitted at wavelength 385, 400, 440, 470, 505, 518 nm Laser runs taken at similar period 532 nm Calibration used 2010:V6.5 for new analysis

New Measurements Data at 400 nm (5 runs) Data at 518 nm (5 runs) Similar for other wavelengths

Wavelength measured with calibrated spectrometer Laser 532 nm 385 nm 460 nm Normalized curves Curves with different width Wavelength [nm] Measure by Diego Real & Francesco Urbano Plot by Juan Zuniga

Absorption length distribution Some Optical Beacon emit light with large range of wavelengths take into account that each wavelength has his own: 1) light velocity => measured 2) absorption => use to correct Input: Wavelength distribution at emission place (distribution from spectrometer) Take into account absorption Output: at detection place (shifted distribution used in public plot)

Change of wavelength distribution through absorption Laser 532 nm Light curve emitted 385 nm 460 nm Drastic change Expected light curve at 120 meters

Evolution of wavelength peak values as function of distance Plot by Juan Zuniga Most wavelength with small changes Largest change for 518 nm 518 nm at 0 m 490 nm at 120 m Width of wavelength distribution also change (not shown for clarity) Analysis range between 100 m and 250 m

Scattering as function of wavelength Higher limit given by Mobley Lower limit given by Mobley Plot by Ciro Bigongiari Ciro suggests to take for all wavelength a minimum scattering value of 10 m and a maximum scattering value given by Mobley

MC with different scattering lengths for systematic evaluation Shorter scattering length -> larger measured refraction index Variation 0.7% Fit range in MC different then in data 0.7% 0.5%

Comparison of parametric formula and measurement Errors for refraction index => 0.7% (scattering) Errors for wavelength distribution from absorption corrections

Conclusion New runs with additional wavelength Absorption changes the measured wavelength distribution => apply corrections for final plot Still to do: systemics analyze more data