Instrumentation and Metrology in Oceanography

399 Pages·2012·12.607 MB·English

by  Marc Le Menn(auth.)

Instrumentation and Metrology in Oceanography
Instrumentation
and Metrology
in Oceanography

Marc Le Menn
First published 2012 in Great Britain and the United States by ISTE Ltd and John Wiley & Sons, Inc.
Apart from any fair dealing for the purposes of research or private study, or criticism or review, as
permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced,
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© ISTE Ltd 2012

The rights of Marc Le Menn to be identified as the author of this work have been asserted by him in
accordance with the Copyright, Designs and Patents Act 1988.
____________________________________________________________________________________
Library of Congress Cataloging-in-Publication Data

Le Menn, Marc.
Instrumentation and metrology in oceanography / Marc Le Menn.
p. cm.
Includes bibliographical references and index.
ISBN 978-1-84821-379-1
1. Oceanographic instruments. 2. Oceanography--Measurement. I. Title.
GC41.L44 2012
551.46028'4--dc23
2012025490

British Library Cataloguing-in-Publication Data
A CIP record for this book is available from the British Library
ISBN: 978-1-84821-379-1
Printed and bound in Great Britain by CPI Group (UK) Ltd., Croydon, Surrey CR0 4YY
Table of Contents
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix
Chapter1.WhatWeMeasureandWhatWeProcess. . . . . . . . . . . . . . 1
1.1.Thequantitieswewanttoknow. . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.1.Velocityanddensity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1.2.Pressureanddepth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.1.3.Speedandmovement. . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.1.4.Timeandspace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.2.Linkingofessentialquantitiesinoceanography . . . . . . . . . . . . . . 10
1.2.1.Temperature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.2.2.Pressure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
1.2.3.Conductivityandsalinity . . . . . . . . . . . . . . . . . . . . . . . . . 22
1.2.4.Velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
1.2.5.Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
1.3.Calculationofdensity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
1.3.1.DensityandEOS-80 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
1.3.2.Laboratorydensitometers . . . . . . . . . . . . . . . . . . . . . . . . . 45
1.3.3.Densityandabsolutesalinity . . . . . . . . . . . . . . . . . . . . . . . 46
1.4.Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
1.4.1.Quantitiesthatwewanttoknow. . . . . . . . . . . . . . . . . . . . . 48
1.4.2.Linkingofessentialquantitiesinoceanography. . . . . . . . . . . . 49
Chapter2.MeasurementSystemsinPractice. . . . . . . . . . . . . . . . . . . 55
2.1.Determiningtemperature. . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
2.1.1.Principalinstruments. . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
2.1.2.Sensortechnologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
2.1.3.Thermaltransfers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
2.1.4.Responsetimeoftemperaturesensors. . . . . . . . . . . . . . . . . . 83
vi Instrumentation and Metrology in Oceanography

2.1.5. Viscous heating of temperature sensors . . . . . . . . . . . . . . . . . 88
2.2. Determining conductivity . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
2.2.1. Principle instruments used . . . . . . . . . . . . . . . . . . . . . . . . 89
2.2.2. Sensors’ technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
2.2.3. Response time of conductivity sensors . . . . . . . . . . . . . . . . . 102
2.2.4. Aligning the response times of temperature and
conductivity sensors and correcting thermal inertia . . . . . . . . . . . . . 105
2.2.5. Biofouling and protection of instruments . . . . . . . . . . . . . . . . 108
2.3. Determining pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
2.3.1. Piezoresistive pressure sensors . . . . . . . . . . . . . . . . . . . . . . 111
2.3.2. Piezoelectric pressure sensors . . . . . . . . . . . . . . . . . . . . . . 113
2.3.3. Errors in pressure sensor measurements . . . . . . . . . . . . . . . . 115
2.4. Determining velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
2.4.1. Principles of measurement . . . . . . . . . . . . . . . . . . . . . . . . 116
2.4.2. Instruments used at sea . . . . . . . . . . . . . . . . . . . . . . . . . . 123
2.5. Determining current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
2.5.1. Rotor current meters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
2.5.2. Doppler effect current meters . . . . . . . . . . . . . . . . . . . . . . . 129
2.5.3. Electromagnetic current meters. . . . . . . . . . . . . . . . . . . . . . 138
2.5.4. Doppler effect profilers . . . . . . . . . . . . . . . . . . . . . . . . . . 140
2.5.5. Directional referencing of current measurements . . . . . . . . . . . 151
2.5.6. Calibration of Doppler effect current meters . . . . . . . . . . . . . . 161
2.6. Determining time or measuring frequency . . . . . . . . . . . . . . . . . 163
2.6.1. The connection of clocks . . . . . . . . . . . . . . . . . . . . . . . . . 164
2.6.2. Time bases of instruments . . . . . . . . . . . . . . . . . . . . . . . . . 166
2.7. Determining position and movement . . . . . . . . . . . . . . . . . . . . . 171
2.7.1. The Argos system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
2.7.2. The global positioning system . . . . . . . . . . . . . . . . . . . . . . 178
2.8. Determining the height of water . . . . . . . . . . . . . . . . . . . . . . . . 190
2.8.1. Tide gauges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
2.8.2. Tide gauges with pressure sensors . . . . . . . . . . . . . . . . . . . . 199
2.8.3. Keying and uniting of tide gauges . . . . . . . . . . . . . . . . . . . . 202
2.9. Determining waves and swell characteristics . . . . . . . . . . . . . . . . 203
2.9.1. Factors relating to the origins and modeling of swell . . . . . . . . . 203
2.9.2. Instruments used to measure the state of the sea . . . . . . . . . . . . 207
2.10. Determining the turbidity or sea water’s optical properties . . . . . . . 220
2.10.1. Theoretical notions of the optical properties of sea water . . . . . 221
2.10.2. Measurement of apparent optical properties . . . . . . . . . . . . . 226
2.10.3. Transmissiometers and measurements of absorption . . . . . . . . 228
2.10.4. Nephelometers and turbidity sensors . . . . . . . . . . . . . . . . . . 232
2.10.5. Fluorimeters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236
2.11. Determining various physicochemical properties . . . . . . . . . . . . . 245
2.11.1. Notions of the chemical parameters of sea water . . . . . . . . . . 245
TableofContents vii
2.11.2.Insitumeasurementofdissolvedoxygen. . . . . . . . . . . . . . . 254
2.11.3.Insitumeasurementofdissolvedcarbon . . . . . . . . . . . . . . . 264
2.11.4.Insitumeasurementofsomeothercomponents . . . . . . . . . . . 269
2.12.Bibliographyandfurtherreading . . . . . . . . . . . . . . . . . . . . . . 277
2.12.1.Measuringtemperature. . . . . . . . . . . . . . . . . . . . . . . . . . 277
2.12.2.Measuringconductivity . . . . . . . . . . . . . . . . . . . . . . . . . 279
2.12.3.Measuringpressure. . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
2.12.4.Measuringvelocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
2.12.5.Measuringcurrent. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
2.12.6.Measuringtimeandfrequencies . . . . . . . . . . . . . . . . . . . . 283
2.12.7.Measuringdistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284
2.12.8.Measuringsealevel. . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
2.12.9.Measuringstateofsea . . . . . . . . . . . . . . . . . . . . . . . . . . 285
2.12.10.Measuringturbidityandopticalpropertiesofseawater. . . . . . 288
2.12.11.Measuringchemicalparameters. . . . . . . . . . . . . . . . . . . . 289
Chapter3.MeasurementsatSea. . . . . . . . . . . . . . . . . . . . . . . . . . . 295
3.1.Oceanographicvessels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295
3.1.1.Waysoflaunchinginstrumentsintothewater. . . . . . . . . . . . . 296
3.1.2.Waysofpositioningandprobing. . . . . . . . . . . . . . . . . . . . . 298
3.1.3.Waystotransmitdata . . . . . . . . . . . . . . . . . . . . . . . . . . . 303
3.1.4.Waystomakeoceanographicmeasurementsbyboat. . . . . . . . . 306
3.2.Moorings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309
3.2.1.Constraintsofmooringimplementation. . . . . . . . . . . . . . . . . 309
3.2.2.Generalitiesontheimplementationofmoorings . . . . . . . . . . . 310
3.2.3.Deploymentandrecoveryofmoorings . . . . . . . . . . . . . . . . . 325
3.3.Drifters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326
3.3.1.Historyandoperatingprinciples. . . . . . . . . . . . . . . . . . . . . 326
3.3.2.TheconceptandevolutionoftheArgoprogram . . . . . . . . . . . 328
3.3.3.Principlesforpositioningbyacousticsources. . . . . . . . . . . . . 332
3.3.4.Designandballastingofdrifters . . . . . . . . . . . . . . . . . . . . . 336
3.4.Instrumentedbuoysandunderwaterplatforms. . . . . . . . . . . . . . . 342
3.4.1.Instrumentedbuoys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342
3.4.2.Underwaterplatforms . . . . . . . . . . . . . . . . . . . . . . . . . . . 344
3.5.Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347
3.5.1.Oceanographicvessels. . . . . . . . . . . . . . . . . . . . . . . . . . . 347
3.5.2.Mooringsandanchoredfloats . . . . . . . . . . . . . . . . . . . . . . 348
3.5.3.Driftingfloats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349
3.5.4.Buoysandinstrumentedplatforms. . . . . . . . . . . . . . . . . . . . 351
Chapter4.EvolutionsandotherMeasurementConcepts . . . . . . . . . . . 353
4.1.Otherprocessesformeasuringsalinityanddensity . . . . . . . . . . . . 353
viii Instrumentation and Metrology in Oceanography

4.1.1. Relationship between density and refractive index . . . . . . . . . . 354
4.1.2. Measurement instruments of the refractive index . . . . . . . . . . . 357
4.2. Acoustic tomography of oceans and acoustic measurements . . . . . . . 362
4.2.1. General principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362
4.2.2. The instrumentation used . . . . . . . . . . . . . . . . . . . . . . . . . 365
4.3. The unmanned underwater vehicle: a new means for
ocean exploration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367
4.3.1. Energetic autonomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369
4.3.2.ROV and AUV displacement and positioning . . . . . . . . . . . . . 371
4.3.3. Autonomy in decision-making and communication . . . . . . . . . . 373
4.3.4. Gliders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374
4.4. Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377
4.4.1. Other processes for measuring salinity and density . . . . . . . . . . 377
4.4.2. Acoustic tomography of oceans and acoustic measurements . . . . 378
4.4.3. The UUV: new means for ocean exploration . . . . . . . . . . . . . . 379
Acronyms and Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387
Preface
The ocean is generally defined as “a vast stretch of salt water that covers the
greatest part of the globe”. However, the simplicity of this definition must not hide
the complexity of this environment, which oceanography attempts to decrypt. More
than just a stretch of salty water, it is a place with living rules, where study over
takes the biology. Within the science of oceanography, there are fields of study
focusingongeologyand chemistry, butitis the problems posedbythermal, optical
anddynamicpropertiesthatphysicaloceanographersseektoanswer.
Numerous models and theories attempt to describe and predict these properties.
To initiate and reinforce these, some measurements are necessary. The complexity
ofthisenvironmentanditshostilityaffectanotherfield:instrumentation.Inorderto
examine the complexity of this environment, specific technological developments
are necessary. These developments fall under the field of oceanographic
instrumentation.
This work mainly aims to describe the oceanographic instrumentation used to
determine the physical properties of the ocean through in situ measurements. With
thedevelopmentofspacesatellitetechnology,newsystemshaveappearedthathave
enabledustodiscovertheseproperties,creatinganewfield(thatwewillnotdiscuss
in this book): space oceanography. Space is a favored place from which we can
observetheocean,asitpermitslarge-scalestudy.
Theinstrumentsloadedonsatellitesusethepropertiesofelectromagneticwaves
to measure the thermal, optical and dynamic characteristics of the ocean.
Unfortunately, these waves are very rapidly absorbed or reflected by the oceanic
environment, so if ocean-predicting models use “spatial” data, the collection of in
situ observations remains an essential source of diagnostics to validate the models,
and it is always necessary to develop complementary equipment that permits the
studyofdeepwaterlayers.
x InstrumentationandMetrologyinOceanography
There are multiple fields of application for these studies. They concern the
evolutionoffundamentalknowledgeonthemovementofwatermasses,thecreation
of thermal or density anomalies, and the coupling between the ocean and the
atmospherethatleadtoabetterunderstandingofclimatechange.Thesealsoinclude
the development of acoustic technologies that have multiple civil and military
applications. The ocean is a favored environment for these technologies; however
thepropagationofacousticwavesisdependentonitsphysicalcharacteristics,sothe
use of tools that permit emission and reception (sonar, echo sounders, Doppler
current meters, etc.) must be optimized by measuring the properties of the
environmentifwewanttoachieveultimateaccuracies.
These accuracies cannot be achieved without the use of metrology. It is unusual
to associate oceanography with metrology, but this is the other field that this book
attempts to describe. Metrology is officially “the science of measurement and its
applications”,butitis,aboveall,thesciencethatallowsthereferencingofmeasured
data, and referencing is an essential part of oceanography when we want to ensure
the accuracy and replicability of measurements. Oceanography is probably the area
of physics where the requirements of the subject matter are greatest because the
acquisitionandinterpretationsofvariablesareoftenatthelimitsofourknow-how.
This book, first and foremost therefore, is for instrumentalists and metrologists
who want to know more about measurements in oceanography. It is also for
scientistswhowanttogatherinformationonoceanographicinstrumentation,andfor
allthoseforwhichthisisanareaofinterest.
All of the chapters of this book are enriched with practical and theoretical
details. Sections include recent relationships for the calculation of the physical
properties of sea water, the measurement of certain physicochemical properties
(carbonates,fluorimetry,etc.),suspendedparticulatematter,waysofpositioningand
probing in water, instrumented buoys, underwater platforms, etc. We also discuss
theprocessesofcalibrationoftheseinstruments,withoutwhichthesemeasurements
wouldnothaveallthelegitimacyweattachtothem.
MarcLeMenn
September2012
Chapter 1
What We Measure and
What We Process
1.1. The quantities we want to know
Measurements made in physical oceanography have two main aims: to improve
our fundamental knowledge of the ocean and the functioning of our planet; and to
optimize the use of acoustic tools, which also sometimes help us to gain knowledge
of the ocean.
The improvement of fundamental knowledge is integrated with the more general
topic of climate change. A global research program was launched in 1979 to try and
model this evolution: the World Climate Research Program (WCRP). The WCRP is
funded by the World Meteorological Organization (WMO) and UNESCO. To
maximize the efforts of different countries with regard to oceanographic
measurements, in 1982 the American National Science Foundation launched another
program called the World Ocean Circulation Experiment (WOCE). In 1989 it
created the WOCE Hydro-graphic Program Office, whose aim was to coordinate,
supervise and ensure the quality of measurements taken. To ensure the quality of
data collected, it was requested that “the standards to approach in terms of accuracy
and reproducibility for the one-time survey, are to be the highest possible under
current measuring techniques”. With “repeat surveys, these standards must be
approached sufficiently closely to achieve the appropriate regional goals”.
Instrumentation and Metrology in Oceanography Marc Le Menn
© 2012 ISTE Ltd. Published 2012 by ISTE Ltd.