Browsing by Author "Lehtola, Ville"

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  • Bearing estimation using foghorn sounds
    (2025-03-01) Gorad, Ajinkya; Zhao, Zheng; Vallet García, José M.; Lehtola, Ville; Hammarberg, Toni; Ramm-Schmidt, Henrik; Islam, Saiful; Thombre, Sarang; Särkkä, Simo
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Situational awareness is critical for safe navigation and autonomous ship operations. To improve safety and automate navigation, multi-sensor systems could involve sound-based direction-finding of foghorns. In this paper, we study the performance of a three-microphone array in bearing estimation when a distant foghorn is audible. We adopt an approach which utilizes Hilbert transforms to obtain phase delay from filtered sounds, and get bearing estimate by minimization of an energy function. We compare this approach with a cross correlation method and GPS-based ground-truth bearing. We present results from simulated tests, laboratory tests with synthetic foghorn sounds, and field tests done on a cruise vessel in the Gulf of Finland. The results suggest that vessel bearing estimation is possible through foghorn sounds received by the microphone array. Best accuracy of 7∘ is achieved in bearing estimation using Hilbert transform approach with target-to-receiver distance of 3.2 km, and processing time of 19 ms for 1 second of sound information. We provide recommendations on how the sound could play an important role in multi-sensor systems. It can be concluded that sound sensory information is useful in autonomous navigation.
  • Dynamics of single biopolymer translocation and sedimentation
    (2010) Lehtola, Ville
     Aalto-yliopiston teknillinen korkeakoulu | Doctoral dissertation (article-based)
    In this Thesis the dynamics of translocation and sedimentation of a single biopolymer (typically DNA, RNA or a protein) is studied. A coarse-graining paradigm is invoked to justify the various computational models by use of which the results are obtained. The transport of biopolymers through a nano-scale pore in a membrane is a ubiquitous process in biology. Experimental interest in translocation process focuses on its potential applicability in ultra-fast sequencing of DNA and RNA molecules. Polymer translocation has been under intense study for over a decade. Inspite of the vast theoretical research, the experimental results on the driven case have not been explained. We claim that the reason for this is that the translocation process must be treated as (at least) two dynamically distinct cases, where the dynamics takes place either close to or out of equilibrium. Here, we find that the latter case corresponds to the experiments. We make a comprehensive investigation on how the process can be discriminated based on its dynamics, and define and use some indicators to this end. In addition, we study the role of hydrodynamics, and find it to govern the dynamics when the process takes place out of equilibrium. Sedimentation is a natural process induced by gravity that can be applied experimentally in a quickened form by the use of ultracentrifuges, and which is similar to electrophoresis. Our study on behavior of single polymers under non-equilibrium conditions falls within the rapidly developing field of nano- and microfluidics that has important applications in "lab-on-a-chip" based technologies. In polymer sedimentation, we study the settling of the polymer in a steady-state in the limit of zero Péclet number, i.e. where no thermal fluctuations exist. The hydrodynamic coupling of the polymer beads leads to chaotic time-dependent behavior of the chain conformations that in turn are coupled with the velocity fluctuations of the polymer's center of mass.
  • The Effect of Wind on Tree Stem Parameter Estimation Using Terrestial Laser Scanning
    (2016-06-07) Vaaja, Matti; Virtanen, Juho-Pekka; Kurkela, Matti; Lehtola, Ville; Hyyppä, Juha; Hyyppä, Hannu
     A4 Artikkeli konferenssijulkaisussa
    The 3D measurement technique of terrestrial laser scanning (TLS) in forest inventories has shown great potential for improving the accuracy and efficiency of both individual tree and plot level data collection. However, the effect of wind has been poorly estimated in the error analysis of TLS tree measurements although it causes varying deformations to the trees. In this paper, we evaluated the effect of wind on tree stem parameter estimation at different heights using TLS. The data consists of one measured Scots pine captured from three different scanning directions with two different scanning resolutions, 6.3 mm and 3.1 mm at 10 m. The measurements were conducted under two different wind speeds, approximately 3 m/s and 9 m/s, as recorded by a nearby weather station of the Finnish Meteorological Institute. Our results show that the wind may cause both the underestimation and overestimation of tree diameter when using TLS. The duration of the scanning is found to have an impact for the measured shape of the tree stem under 9 m/s wind conditions. The results also indicate that a 9 m/s wind does not have a significant effect on the stem parameters of the lower part of a tree (<28% of the tree height). However, as the results imply, the wind conditions should be taken into account more comprehensively in analysis of TLS tree measurements, especially if multiple scans from different positions are registered together. In addition, TLS could potentially be applied to indirectly measure wind speed by observing the tree stem movement.
  • Liikkuvan kameran reaaliaikainen georeferointi
    (2012-12-17) Penttinen, Topi
     Insinööritieteiden korkeakoulu | Bachelor's thesis
  • Localization corrections for mobile laser scanner using local support-based outlier filtering
    (2016) Lehtola, Ville; Virtanen, Juho-Pekka; Rönnholm, Petri; Nüchter, Andreas
     A4 Artikkeli konferenssijulkaisussa
  • Motorized panoramic camera mount – calibration and image capture
    (2016) Kauhanen, Heikki; Rönnholm, Petri; Lehtola, Ville
     A4 Artikkeli konferenssijulkaisussa
  • Polymer Scaling and Dynamics in Steady-State Flow
    (2006) Lehtola, Ville
     Helsinki University of Technology | Master's thesis
    Diplomityössä tutkitaan yhtä karkeistettua vakiovirtauksessa olevaa polymeeriä. Systeemi on epätasapainossa gravitaation vuoksi, joka vaikuttaa nestettä raskaampiin polymeerin osasiin. Polymeeri on kokoonpuristumattomassa nesteessä, jota mallinnetaan ratkaisemalla Navier-Stokesin yhtälöä multigrid metodilla. Kahta fysikaalista muuttujaa käytetään selittämään polymeerin käytöstä. Gyraatiosäde RG kuvaa polymeerin tilavuutta ja diffuusiotekijä D polymeerin liikkuvuutta nesteessä. Systeemin skaalautuvuutta tutkitaan määrittämällä skaalauseksponentit näille muuttujille. Gyraatiosäteen virtauksensuuntainen komponentti vz = 0.785 skaalautuu eri tavalla kuin kohtisuora v1 = 0.445. Tulos SAW:lle tasapainosysteemissä on v = 0.588. Työssä esitetään Floryn teoriaan pohjautuva argumentti, joka selittää vakiovirtauksen osuuden symmetriarikkoon. Vaikka simuloidussa systeemissä ei ole lainkaan lämpöliikettä, polymeerin osien (Kuhnin segmentit) vuorovaikutus aiheuttaa epätriviaaleja fluktuaatioita polymeerin massakeskipisteelle. Tämän takia massakeskipisteelle määritetään efektiivinen diffuusiotekijä D, joka kuvaa segmenttien vuorovaikutuksesta aiheutuvaa liikettä. Tässä työssä havaittiin, että efektiivinen diffuusiotekijä D skaalautuu polymeerin pituuden N funktiona, siten että D kasvaa N:n kasvaessa Tämä käytös on täysin päinvastaista tasapainosysteemissä olevan polymeerin termiseen diffuusioon verrattuna.
  • Polymer scaling and dynamics in steady-state sedimentation at infinite Peclet number
    (2007) Lehtola, Ville; Punkkinen, O.; Ala-Nissilä, T.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    We consider the static and dynamical behavior of a flexible polymer chain under steady-state sedimentation using analytic arguments and computer simulations. The model system comprises a single coarse-grained polymer chain of N segments, which resides in a Newtonian fluid as described by the Navier-Stokes equations. The chain is driven into nonequilibrium steady state by gravity acting on each segment. The equations of motion for the segments and the Navier-Stokes equations are solved simultaneously using an immersed boundary method, where thermal fluctuations are neglected. To characterize the chain conformation, we consider its radius of gyration RG(N). We find that the presence of gravity explicitly breaks the spatial symmetry leading to anisotropic scaling of the components of RG with N along the direction of gravity RG,∥ and perpendicular to it RG,⊥, respectively. We numerically estimate the corresponding anisotropic scaling exponents ν∥≈0.79 and ν⊥≈0.45, which differ significantly from the equilibrium scaling exponent νe=0.588 in three dimensions. This indicates that on the average, the chain becomes elongated along the sedimentation direction for large enough N. We present a generalization of the Flory scaling argument, which is in good agreement with the numerical results. It also reveals an explicit dependence of the scaling exponents on the Reynolds number. To study the dynamics of the chain, we compute its effective diffusion coefficient D(N), which does not contain Brownian motion. For the range of values of N used here, we find that both the parallel and perpendicular components of D increase with the chain length N, in contrast to the case of thermal diffusion in equilibrium. This is caused by the fluid-driven fluctuations in the internal configuration of the polymer that are magnified as polymer size becomes larger.
  • Sisätilan mallinnus - Case Startup Sauna
    (2015-06-08) Tähtinen, Suvi
     Insinööritieteiden korkeakoulu | Master's thesis
    Tässä työssä tarkastellaan sisätilojen kolmiulotteista mallinnusta käyttäen kolmea erilaista kuvausmenetelmää tilatiedon keräämiseen. Lisäksi pohditaan tiedonkeruun ja -käsittelyn prosesseja ja eri menetelmin tuotetun tilatiedon laatua. Vertailussa on kolme kolmiulotteista pistepilveä. Yksi on tuotettu laserkeilaimella, toinen fotogrammetrisesti valokuvista ja kolmas Matterportin syvyyskamera-pilvipalveluyhdistelmällä. Mallinnuskohteena on Espoossa sijaitseva Startup Sauna. Työssä on pohdittu käytettävyyttä ja perusteltu, miksi perinteinen valokuvaus ja Matterport-kuvaus soveltuvat käytettävyydeltään mallinnustyössä aloittelijoille, ja miksi laserkeilaus puolestaan ei sovellu. Testatuin menetelmin on varsinaisen pistepilvidatan lisäksi mahdollista saada aikaan kolmiulotteisia visuaalisia esityksiä kohteesta. Pistepilvien jatkoprosessointi teksturoiduiksi pintamalleiksi ulottuu tämän työn ulkopuolelle.