Ciro Bigongiari

Schematic View 17/05/2011Ciro Bigongiari 2 Photon Path Optical Beacon Optical Module Sea water

History  Calibob was derived from KM3 code  It was written in f90 language  It was recoded in f77 transforming all structures in common blocks (No need of f90 compiler)  On the assumption that the simulated light sources are nearly monochromatic all the dependencies on the wavelength were removed  La, Ls, β( θ) and n didn’t depend on λ  Recently reintroduced the dependence on λ of La, Ls and n trying to improve the Data-MC agreement 17/05/ Ciro Bigongiari

LED Spectrum 17/05/2011Ciro Bigongiari 4 From AVAGO CB30 Datasheet Peak wavelength 470 nm Sigma 15nm Slightly asymmetric Values confirmed by measurements in Valencia lab ANTARES LED

Code structure (I)  Three step package: GEN, HIT, CAL  GEN  Simulates photon emission and photon propagation through sea water up to a maximum distance (350 m)  No absorption simulated at this stage  Photon position, direction, transit time and wavelength on 34 spherical shells (10 m step) centred on the light source are recorded  Some more histograms and ntuples saved for debugging purposes 17/05/ Ciro Bigongiari

Code structure (II)  Three step package: GEN, HIT, CAL  HIT  Simulates absorption by weighting photons  Weight = exp(-PhotonPath/AbsorptionLength)  Simulates photon detection by an optical module at different position/direction w.r.t. to the optical beacon  Stores detection probability tables  CAL  Reads in detector geometry  Loops over OB flashes and optical modules  Stores hits in ASCII format 17/05/ Ciro Bigongiari

Optical Beacons  Light emission from point-like light sources  Angular distribution of emitted photons  Uniform  Cleaved LED  Laser + Glass Rod  Time distribution of emitted photons  Gaussian  LED pulse  Wavelength distribution of emitted photons  Gaussian  LED spectrum 17/05/ Ciro Bigongiari

Optical Modules  Photon detection by optical modules is simulated exactly in the same way as in KM3  Angular acceptance  Glass transmission  Gel transmission  Photo-conversion efficiency 17/05/ Ciro Bigongiari

Sea Water (I)  Absorption:  Absorption is simulated by weighting photons  The absorption length is calculated rescaling the Smith&Baker parameterization 17/05/2011Ciro Bigongiari 9 WARNING: in this way L A can be larger than SmithBaker( λ) which should be an upper limit (pure water).

Absorption length 17/05/2011Ciro Bigongiari 10 λ Ref = 470 nm L Ref = 60 m

Sea Water (II)  Scattering:  The scattering length is calculated rescaling the Kopelevich parametrization with Vs = Vl = /05/2011Ciro Bigongiari 11 The values of V S and V L presently used are different from the ones used in KM3 which are outside the allowed region (Mobley )

Scattering Length 17/05/2011Ciro Bigongiari 12

Sea Water (III)  Refraction Index:  The refraction index is a function of photon wavelength and water temperature, pressure and salinity. We fixed  T = 13.1 ºC P = 220 barS = % 0 17/05/2011Ciro Bigongiari 13 A = B = C = D = e6

Refraction Index 17/05/2011Ciro Bigongiari 14

Sea Water (IV)  Volume Scattering Function:  β = β( θ,λ) is a function of scattering angle and photon wavelength  The dependence on λ has not be considered so far β = β( θ)  Usually we use the so-called PARTIC model 17/05/2011Ciro Bigongiari 15 WARNING: Petzold’s measurements were performed at 514 nm

Scattering Angle 17/05/2011Ciro Bigongiari 16 η = 0.17  = 0.767

Volume Scattering Function 17/05/2011Ciro Bigongiari 17 V.Haltrin Appl.Opt.38(33)-1999

Comparison 17/05/2011Ciro Bigongiari 18 New Old

Summary & Outlook  Reintroduced absorption length, scattering length and refraction index dependence on wavelength  No big improvement found. To be investigated further  Dependence of volume scattering function still to be implemented.  Continue comparison with KM3 17/05/2011Ciro Bigongiari 19

Water Models  There are some recently developed water models with a reasonably low number of parameters. For example  Kopelevich’s  Haltrin’s  Morel’s  Zege – Katsev – Prikcach  Should we try a more recent water model ?  Can they be used for very deep waters ? 17/05/2011Ciro Bigongiari 20

Smith&Baker ? 17/05/2011Ciro Bigongiari 21 ………………………… In the visible part of the spectrum, recent studies from Sogandares and Fry (1997) and Pope and Fry (1997), based on different measuring techniques, provided very precise measurements of pure water absorption from 380 to 700 nm. The results obtained by these authors emphasized that Smith and Baker (1981) formulation strongly overestimated the actual a w ( λ ) in particularly below 490 nm. At 380 nm Pope and Fry (1997) values are about 2 times lower. Such differences between Smith and Baker (1981) and Pope and Fry (1997) formulations have been attributed to biases in the former measurements induced by organic impurities absorption and scattering effects. Moreover, Pope and Fry (1997) confirmed the existence of seventh and eighth harmonics of the OH stretch at 449 and 401 nm and the presence of the absorption minimum at 420 nm as previously observed by Sogandares and Fry (1997). The data by Pope and Fry (1997) are currently considered as the reference value and are widely used in bio-optical modeling and remote sensing applications in the visible……… (Vantrepotte&Mélin2006).