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A Novel Signal Model and Estimation Method for Acoustic Doppler Current Meters

Lagö, Thomas L LU (1999) In TVBA 1007.
Abstract (Swedish)
Popular Abstract in Swedish

Denna avhandling behandlar den process där man beräknar undervattensströmmar från ljud som reflekteras från en utsänd ljudpuls, precis som när en fladdermus bedömer omgivningen genom att lyssna på ekot. En ton skickas ut under en kort tid, och det Dopplerskift som uppkommer från rörliga föremål i vattnet kan sedan omsättas till vattenhastiget eller ström. Föremål som rör sig bort från mätaren kommer att sänka tonen något, och föremål som rör sig mot mätaren kommer att öka tonen något. Den klassiska modellen för denna beräkning är baserad på ett antagande att tidssignalen är Gaussisk, pga att amplituden har en Rayleigh-fördelning och att fasen i signalen skall vara slumpmässig. Detta i sin tur är... (More)
Popular Abstract in Swedish

Denna avhandling behandlar den process där man beräknar undervattensströmmar från ljud som reflekteras från en utsänd ljudpuls, precis som när en fladdermus bedömer omgivningen genom att lyssna på ekot. En ton skickas ut under en kort tid, och det Dopplerskift som uppkommer från rörliga föremål i vattnet kan sedan omsättas till vattenhastiget eller ström. Föremål som rör sig bort från mätaren kommer att sänka tonen något, och föremål som rör sig mot mätaren kommer att öka tonen något. Den klassiska modellen för denna beräkning är baserad på ett antagande att tidssignalen är Gaussisk, pga att amplituden har en Rayleigh-fördelning och att fasen i signalen skall vara slumpmässig. Detta i sin tur är baserat på att man antar att det ljud som reflekteras kommer från många ungefär lika stora bubblor som är slumpmässigt fördelade i den vattenvolym som studeras. Det är rimligt att ifrågasätta om denna modell är rätt. Därför har en stor del av denna avhandling ägnats åt att studera riktiga tidssignaler från flera olika platser, tre i Sverige och en i Hongkong. Denna ganska omfattande studie har visat att den signal som erhålls inte uppfyller ett Gaussantagande. Analysen visar istället att signalen är mer sinusliknande. En ny signalmodell har därför tagits fram, där den reflekterade signalen beskrivs med hjälp av ett antal sinussignaler som summeras tillsammans.



Det är vanligt att man inom dagens vetenskap tar till avancerade matematiska modeller för att beskriva denna process, men dessa bidrar inte till förståelsen av den fysikaliska processen, eller hur beräkningen av Dopplerskiftet skall gå till. I detta arbete har fokus legat på att ta fram en enkel signalmodell som är knuten till de fysikaliska fenomenen samt att presentera en robust men enkel metod att beräkna Dopplerskiftet, dvs vattenströmmens storlek.



Denna nya matematiska modell för den reflekterade signalen används sedan för att testa olika beräkningsmetodet för Dopplerskiftet. En ny beräkningsmetod, kallad estimator, har sedan tagits fram. Denna nya metod har fått namnet Symmiktosmetoden, och är en olinjär estimator med goda egenskaper för denna typ av signaler. Denna metod jämförs sedan med den klassiska kovariansmetoden för både riktiga undervattensdata såväl som för simulerade signaler. Symmiktosmetoden är inte baserad på ett Gaussiskt antagande, vilket kovariansmetoden är och detta gör att den blir mer robust och ger bättre skattningar för de flesta typer av data. Metoden är enkel att implementera och är intuitiv, vilket har varit ett av målen med detta arbete. Enkelhet men samtidigt en robust estimator trots svåra signalförhållanden ledde till Symmiktosmetoden™.



En stor databas med insamlade data från fyra platser har använts i arbetet: Trubaduren, Almagrundet, Fladen och Ma-Wan, Hongkong. Dessa data har sedan använts för att beräkna ett stort antal statistiska mått som ANOVA, högre ordningens moment, histogram och normalfördelningskurvor. Klassiska signalbehandlingsmetoder har genomförts såväl som icke-linjär filtrering av data med hjälp av en nyutvecklad analysmetod: Multiple Peak Count Analysis, MPCA. Den senare presenteras grafiskt i både 2D och 3D-format. De olika estimeringsmetoderna; kovariansmetoden och Symmiktosmetoden har också testats för dessa riktiga data såväl som för simulerade signaler. (Less)
Abstract
This thesis deals with the process of estimating underwater current from the backscattering signal transmitted from an ultrasonic transducer. The narrowband sinusoidal burst signal is Doppler-shifted due to the current, and this information is converted into current. The traditional mathematical model for this Doppler process is based on the assumption that the backscattering time signal is Gaussian, due to the Rayleigh backscattering amplitude with random phase. This is based on the assumption that the backscattering is due to many randomly distributed bubbles with about equal size. It is reasonable to question whether this assumption holds for real life signals. Therefore, part of the work discussed in this thesis has concentrated on... (More)
This thesis deals with the process of estimating underwater current from the backscattering signal transmitted from an ultrasonic transducer. The narrowband sinusoidal burst signal is Doppler-shifted due to the current, and this information is converted into current. The traditional mathematical model for this Doppler process is based on the assumption that the backscattering time signal is Gaussian, due to the Rayleigh backscattering amplitude with random phase. This is based on the assumption that the backscattering is due to many randomly distributed bubbles with about equal size. It is reasonable to question whether this assumption holds for real life signals. Therefore, part of the work discussed in this thesis has concentrated on looking at real life data, and has investigated whether the Gaussian assumption holds for the background noise and the Doppler signal received. It has been found that this is not generally the case. Thus, a different mathematical model has been sought which describes the Doppler signal in a more realistic way. Such a model has been developed, and is presented.



When studying the work of other researchers, it has been noticed that some of the more recent modeling work relies on elaborate mathematics, but does not contribute much to the understanding of the physics, nor the effects on the estimation process. Again, and this is emphasized, the aim has been to develop a simple signal model and a simple estimation method that performs well. The latter is important since the complexity of the system needs to be low. This is because systems are often battery operated and a long battery life is needed as the systems are positioned out in the water.



The new mathematical model for the backscattering signal is subsequently used to test different estimator approaches, and to investigate their behavior for different types of complexity in the Doppler signal. A new estimator, the Symmiktos Method™ estimator, has been developed, which is a non-linear estimation method. The estimator performance is compared with the covariance method, which is based on the Gaussian model assumption. The Symmiktos Method™ is based on a more complex Doppler signal model. The result is that the Symmiktos Method™ is more robust to changes in the signal complexity. Also, the method is quick and easy to implement, an important factor in real-life use. Otherwise the method becomes a theoretical method with very little practical use, and this has not been the intention with this work. The work should be viewed as a practical approach to solving a difficult signal processing application problem, where cost, size, simplicity and performance are very important for the end result.



A large data set from four locations, Trubaduren, Almagrundet, Fladen and Ma-Wan, Hongkong has been collected. This data base was used when performing elaborate statistical analyses like ANOVA, higher order moments, histograms and normal probability plots. Classical signal processing has been performed as well as non-linear filtering using Multiple Peak Count Analysis, MPCA. The latter is presented in both a 2D and a 3D format. Different estimation methods are compared, including the Symmiktos Method™. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • Professor Fuller, Chris R.
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Doppler Profiler, Acoustic Doppler, Gaussian Backscattering Model, ADCM, ADCP, The Symmiktos Method, Estimation, Doppler, Current, MPCA., Technological sciences, Teknik, Electromagnetism, optics, acoustics, Elektromagnetism, optik, akustik
in
TVBA
volume
1007
pages
526 pages
publisher
Technical Acoustics, LTH, Box 118, 221 00 LUND,
defense location
LTH, V-huset, Sal D
defense date
1999-04-23 10:00
external identifiers
  • other:ISRN: LUTVDG/TVBA--99/1007--SE
ISSN
0281-8477
ISBN
0281-8477
language
English
LU publication?
yes
id
bf373e0e-06d5-4587-93a1-d3bfc0a18194 (old id 19313)
date added to LUP
2007-05-24 14:25:26
date last changed
2016-09-19 08:44:59
@phdthesis{bf373e0e-06d5-4587-93a1-d3bfc0a18194,
  abstract     = {This thesis deals with the process of estimating underwater current from the backscattering signal transmitted from an ultrasonic transducer. The narrowband sinusoidal burst signal is Doppler-shifted due to the current, and this information is converted into current. The traditional mathematical model for this Doppler process is based on the assumption that the backscattering time signal is Gaussian, due to the Rayleigh backscattering amplitude with random phase. This is based on the assumption that the backscattering is due to many randomly distributed bubbles with about equal size. It is reasonable to question whether this assumption holds for real life signals. Therefore, part of the work discussed in this thesis has concentrated on looking at real life data, and has investigated whether the Gaussian assumption holds for the background noise and the Doppler signal received. It has been found that this is not generally the case. Thus, a different mathematical model has been sought which describes the Doppler signal in a more realistic way. Such a model has been developed, and is presented.<br/><br>
<br/><br>
When studying the work of other researchers, it has been noticed that some of the more recent modeling work relies on elaborate mathematics, but does not contribute much to the understanding of the physics, nor the effects on the estimation process. Again, and this is emphasized, the aim has been to develop a simple signal model and a simple estimation method that performs well. The latter is important since the complexity of the system needs to be low. This is because systems are often battery operated and a long battery life is needed as the systems are positioned out in the water.<br/><br>
<br/><br>
The new mathematical model for the backscattering signal is subsequently used to test different estimator approaches, and to investigate their behavior for different types of complexity in the Doppler signal. A new estimator, the Symmiktos Method™ estimator, has been developed, which is a non-linear estimation method. The estimator performance is compared with the covariance method, which is based on the Gaussian model assumption. The Symmiktos Method™ is based on a more complex Doppler signal model. The result is that the Symmiktos Method™ is more robust to changes in the signal complexity. Also, the method is quick and easy to implement, an important factor in real-life use. Otherwise the method becomes a theoretical method with very little practical use, and this has not been the intention with this work. The work should be viewed as a practical approach to solving a difficult signal processing application problem, where cost, size, simplicity and performance are very important for the end result.<br/><br>
<br/><br>
A large data set from four locations, Trubaduren, Almagrundet, Fladen and Ma-Wan, Hongkong has been collected. This data base was used when performing elaborate statistical analyses like ANOVA, higher order moments, histograms and normal probability plots. Classical signal processing has been performed as well as non-linear filtering using Multiple Peak Count Analysis, MPCA. The latter is presented in both a 2D and a 3D format. Different estimation methods are compared, including the Symmiktos Method™.},
  author       = {Lagö, Thomas L},
  isbn         = {0281-8477},
  issn         = {0281-8477},
  keyword      = {Doppler Profiler,Acoustic Doppler,Gaussian Backscattering Model,ADCM,ADCP,The Symmiktos Method,Estimation,Doppler,Current,MPCA.,Technological sciences,Teknik,Electromagnetism,optics,acoustics,Elektromagnetism,optik,akustik},
  language     = {eng},
  pages        = {526},
  publisher    = {Technical Acoustics, LTH, Box 118, 221 00 LUND,},
  school       = {Lund University},
  series       = {TVBA},
  title        = {A Novel Signal Model and Estimation Method for Acoustic Doppler Current Meters},
  volume       = {1007},
  year         = {1999},
}