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

2. 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

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

5. Additional runs Old analysis
(69 runs taken between and ) :
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

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

7. 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

8. 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)

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

10. 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 m
490 nm at 120 m
Width of wavelength
distribution also change
(not shown for clarity)
Analysis range between
100 m and 250 m

11. 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

12. 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%

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

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