Terminology and units in optical oceanography

Abstract

This document presents fundamental terms describing the transfer of radiative energy and relevant optical properties of natural waters. These are primarily based upon the terminology of the “Système International d'Unités (SI)”; and the “International Commission on Illumination (CIE).’’ Quantities and Symbols as proposed in the present terminology follow and extend the terminology that was recommended by the Committee on Radiant Energy in the Sea (of the International Association of Physical Oceanography, IAPO), as published by Jerlov (1968, Optical Oceanography Elsevier Oceanography Series, Vol. 5; 1976, Marine Optics Elsevier Oceanography Series, Vol. 14).     

Sigmoidal particle density distribution in a subplinian scoria fall deposit

A general expression to describe particle density distribution in tephra fall deposits is essential to improve fallout tephra mass determination and numerical modelling of tephra dispersion. To obtain particle density distributions in tephra fall deposits, we performed high-resolution componentry and particle density analyses on samples from the 2006 subplinian eruption of Tungurahua volcano in Ecuador. Six componentry classes, including pumice and scoria, have been identified in our sample collection. We determined the class of 300 clasts in each 0.5? fractions from ?4.5? to 3.5? and carried out water pycnometry density measurements on selected size fractions. Results indicate that the mean particle density increases with ? up to a plateau of ~2.6?g/cm³ for clasts finer than 1.5?. The density of scoria and pumice increases between ?3 and 1?, while dense particle density is sub-constant with grainsize. We show that the mean particle density ?? of the vesicular fractions is a function of grainsize i (? scale) given by a sigmoidal law: $ \mu (i)={{{K+\beta }} \left/ {{\left( {1+\alpha {e^{-ri }}} \right)}} \right.} $ , where K, ??, ?? and r are constants. These sigmoidal distributions can be used to determine accurately the load of each componentry class and should be applicable to many tephra deposits and for modelling purposes.     

Building frequency fluctuations from continuous monitoring of ambient vibrations and their relationship to temperature variations

Building frequencies (fundamental and higher modes) are a critical parameter especially in the field of structural health monitoring mainly based on the stability of the structural dynamic parameters of individual building (frequencies, damping and modes shape). One of the most used methods to find out these parameters is based on the use on ambient vibration analysis. In this work, we study the fluctuations over a month period of the fundamental frequencies (transverse and longitudinal) of a 3.5-story RC-building made of 2 identical units connected by a structural joint. Time independent building frequencies is a strong assumption; as illustrated by our experiment showing that over an observation period of a month, building frequencies fluctuate of about 3.5 %. A clear correlation is found between the building frequency fluctuations and temperature variations, with a phase-shift interpreted as the characteristic time of heat diffusion within the walls. This allows: (1) determining the thermal diffusivity of the structure, (2) inferring its relative stiffness variations, and (3) showing that its Young modulus varies linearly with temperature.     

Deep sea in situ excess pore pressure and sediment deformation off NW Sumatra and its relation with the December 26, 2004 Great Sumatra-Andaman Earthquake

The swath bathymetric data acquired during the “Sumatra Aftershocks” cruise from the Sunda trench in the Indian Ocean to the north of the Sumatra Island imaged several scars and deposits. In situ pore pressure measurements using the Ifremer piezometer and coring demonstrate that high excess pore pressure and sediment deformation was generated by a recent event in the scar of the slope failure zone identified by J.T. Henstock and co-authors. This excess pore pressure is localized in the upper sedimentary layers and is not related to an interplate subduction process. Numerical simulations of the hydrological system that take into account the hydro-mechanical properties of the upper sediment layer show that the excess pore pressure and sediment deformations could be generated at the time of the December 26, 2004 Great Sumatra Earthquake. The Sumatra Aftershocks team: J.-C. Sibuet, S. Singh, R. Apprioual, N.C. Aryanto, J. Begot, A. Cattaneo, A.P.S. Chauchan, R. Creach, J. Crozon, A. Domzig, N. Falleau, D. Graindorge, F. Harmegnies, Y. Haryadi, F. Klingelhoffer, S.K. Kolluru, J.-Y. Landuré, C. Le Lann, J. Malod, A. Normand, G. Oggian, C. Rangin, D. Restunin Galih, J.-L. Schneider, N. Sultan, M. Taufik, M. Umber and H. Yamaguchi.     

From marginal to conditional probability functions of parameters in a conceptual rainfall–runoff model: an event-based approach

ABSTRACT

A parameter estimation strategy for a conceptual rainfall–runoff (CRR) model applied to a storm sewer system in an urban catchment (Chassieu, Lyon, France) is proposed on the basis of event-by-event Bayesian local calibrations. The marginal distribution formed by locally-estimated parameters is divided into conditional functions, clustering the event-based parameters based on their transferability to similar rainfall events. The conditional functions showed to be consistent with an observed bimodality in the marginal representation, reflecting two different hydrological conditions mainly related to the magnitude of the rainfall intensities (high or low). The improvements achieved by expressing the parameter probability functions into a conditional form are shown in terms of accuracy (Nash-Sutcliffe efficiency criterion), precision (average relative interval length) and reliability (percentage of coverage) for simulating flow rate in 255 and 110 calibration/verification events.     

Influence of instruments on the H/V spectral ratios of ambient vibrations

For an optimal analysis of the H/V curve, it appears necessary to check the instrument signal to noise ratio in the studied frequency band, to ensure that the signal from the ground noise is well above the internal noise. We assess the reliability and accuracy of various digitizers, sensors and/or digitizer-sensor couples. Although this study is of general interest for any kind of seismological study, we emphasize the influence of equipment on H/V analysis results. To display the impact of the instrumental part on the H/V behavior, some series of tests have been carried out following a step-by-step procedure: first, the digitizers have been tested in the lab (sensitivity, internal noise...), then the three components sensors, still in the lab, and finally the usual user digitizers-sensors couple in lab and outdoors. In general, the digitizer characteristics, verified during this test, correspond well to the manufacturer specifications, however, depending on the digitizer, the quality of the digitized waveform can be very good to very poor, with variation from a channel to another channel (gain, time difference etc.). It appears very clearly that digitizers need a warming up time before the recording to avoid problems in the low-frequency range. Regarding the sensors, we recommend strongly to avoid the use of “classical” accelerometers (i.e., usual force balance technology). The majority of tested seismometers (broadband and short period, even 4.5 Hz) can be used without problems from 0.4 to 25 Hz. In all cases, the instrumentation should be checked first to verify that it works well for the defined study aim, but also to define its limit of use (frequency, sensitivity...).