Detection of multiplicative noise in stationary random processes using second- and higher order statistics

This paper addresses the problem of detecting the presence of colored multiplicative noise, when the information process can be modeled as a parametric ARMA process. For the case of zero-mean multiplicative noise, a cumulant based suboptimal detector is studied. This detector tests the nullity of a specific cumulant slice. A second detector is developed when the multiplicative noise is nonzero mean. This detector consists of filtering the data by an estimated AR filter. Cumulants of the residual data are then shown to be well suited to the detection problem. Theoretical expressions for the asymptotic probability of detection are given. Simulation-derived finite-sample ROC curves are shown for different sets of model parameters

Remote Sensing

This dual conception of remote sensing brought us to the idea of preparing two different books; in addition to the first book which displays recent advances in remote sensing applications, this book is devoted to new techniques for data processing, sensors and platforms. We do not intend this book to cover all aspects of remote sensing techniques and platforms, since it would be an impossible task for a single volume. Instead, we have collected a number of high-quality, original and representative contributions in those areas

Diurnal Variability Of Underwater Acoustic Noise Characteristics in Shallow Water

The biggest challenge in the underwater communication and target locating is to reduce the effect of underwater acoustic noise (UWAN). An experimental model is presented in this paper for the diurnal variability of UWAN of the acoustic underwater channel in tropical shallow water. Different segments of data are measured diurnally at various depths located in the Tanjung Balau, Johor, Malaysia. Most applications assume that the noise is white and Gaussian. However, the UWAN is not just thermal noise but a combination of turbulence, shipping and wind noises. Thus, it is appropriate to assume UWAN as colored rather than white noise. Site-specific noise, especially in shallow water often contains significant non-Gaussian components. The real-time noise segments are analyzed to determine the statistical properties such as power spectral density (PSD), autocorrelation function and probability density function (pdf). The results show the UWAN has a non-Gaussian pdf and is colored. Moreover, the difference in UWAN characteristics between day and night is studied and the noise power at night is found to be more than at the day time by around (3-8dB)

An investigation into the dynamical and statistical properties of dominant ocean surface waves using close-range remote sensing

Denne avhandlingen er basert på forskningsresultat som behandler statistiske og dynamiske egenskaper av dominante vinddrevne overflatebølger i åpent hav. Med uttrykket dominante bølger refererer vi her til de største bølgene, med størst energi, i en gitt sjøtilstand. Bølgedrevne prosesser er viktige både i klimasammenheng via atmosfære--hav interaksjon som drives i stor grad av bølgebrytning, samt for kommersiell og rekreasjonell offshorevirksomhet p.g.a. risikoen for å bli utsatt for f.eks. ekstreme enkeltbølger. Både bølgebrytning og ekstrembølgestatistikk er i skrivende stund ufullstendig representert i teoretiske og numeriske modeller. Arbeidet som presenteres i denne avhandlingen undersøker de ovennevnte temaene ved bruk av bølgeobservasjoner som er primært samlet inn på Ekofiskfeltet i den sentrale delen av Nordsjøen. Observasjonsdatasettene består av en langtidstidsserie av laser-altimetermålinger og stereoskopiske videodata fra Ekofisk, samt videomålinger av brytende bølger fra et forskningstokt i nordre Stillehavet. Forskningsresultatene er presentert i artikkelform med to publiserte verk og ett innlevert manuskript. Det blir påvist en tydelig forbindelse mellom økt bølgebrytning og dominante bølgegrupper, et resultat som tidligere har blitt påvist i laboratorie- og modelleksperiment, men sjeldent ved bruk av feltobservasjoner. Tredimensjonale stereo-rekonstruksjoner viser også at ekstreme bølgekammer, både brytende og ikke-brytende, følger nylig utviklet teori om ikke-lineær bølgegruppedynamikk. Dette funnet har konsekvenser f.eks. for estimering av geometriske og kinematiske bølgeegenskaper såsom steilhet og kamhastighet fra endimensjonale tidsseriemålinger. Som følge av en langtidsanalyse av endimensjonal bølgestatistikk blir det vist at enrettet, langkammet og bratt sjø mest sannsynlig leder til ekstreme enkeltbølger med statistiske egenskaper som avviker systematisk fra ordinære statistiske modeller. Tredimensjonal, kortsiktig tid-rom-statistikk av ekstreme bølgekammer blir også undersøkt v.h.a. stereomålingene fra Ekofisk. Her blir det vist at statistiske modeller utvidet fra endimensjonale til tredimensjonale bølgefelt i snitt er velegnet til å beskrive forekomsten av de høyeste bølgekammene, spesielt for relativt store tid-rom segment.The research presented in this thesis characterizes statistical and dynamical aspects of dominant wind-generated surface gravity waves inferred from field observations in intermediate-to-deep water. Dominant waves are the most energetic waves in a sea state, and as such, understanding their behavior is important in both engineering and geophysical contexts. Large waves impart considerable impact forces on marine structures such as oil and gas platforms and offshore wind turbines, and these forces may multiply manyfold when waves break. Wave breaking in deep water, often referred to as whitecapping, is also a key, though incompletely understood, process regulating the transfer of momentum, gas and heat across the air-sea interface, and must thus be accurately parameterized in large-scale weather and climate models. Current theory holds that the wave breaking process is closely linked kinematically and dynamically to the group structure inherent in ocean surface wave fields. Wave group dynamics is also believed to govern the characteristic shape and motion of so-called extreme or rogue waves, whose correct statistical description is central to many offshore activities. The work presented herein shows, using state-of-the-art stereoscopic imaging techniques employed at the Ekofisk platform complex in the central North Sea, that large-scale wave breaking activity in the open ocean is strongly enhanced in dominant wave groups. The topic of wave group-modulated wave breaking has received considerable attention in the past two decades from theoretical, numerical and laboratory perspectives; however, quantitative field studies of the phenomenon remain comparatively rare. The current results also support the general notion that the dominant waves in a given sea state regulate the breaking of shorter waves. The statistics of extreme wave crest elevations is investigated using a novel long-term laser altimeter data set, also located at the Ekofisk field. The validity of the extreme values is verified using a newly developed despiking methodology, and the quality controlled data set, which covers storm events over an 18-year period, is used to investigate the effects of wave steepness and directionality on crest height statistics. Narrow directional spread combined with high wave steepness is found to lead to crest height statistics that deviate the most from standard linear and second-order formulations. Finally, geometric wave shape and crest speed dynamics are analyzed for the highest wave crests encountered in three-dimensional, spatially and temporally resolved segments of the stereo-reconstructed sea surface fields. The directly measured crest steepness is found to conform to the classical breaking limit of Stokes, whereas crest steepness estimated from one-dimensional time series measurements using the linear gravity-wave dispersion relation are systematically higher. This may be at least in part explained by the observation that the directly measured crest speed just before, during and after the moment of maximum crest elevation slows down compared to the linear gravity-wave phase speed estimate. For the first time, the crest speed slowdown is shown with field measurements to apply to both breaking and non-breaking dominant wave crests.Doktorgradsavhandlin

Group sizes, activity patterns and acoustic production of three delphinid species in Azores

Os repertórios acústicos de três espécies de delfinídeos, com especiação simpátrica sazonal e que são geralmente avistadas durante o Verão no arquipélago dos Açores, foram estudados e comparados. Os assobios de Tursiops truncatus, Delphinus delphis e Stenella frontalis foram gravados através de um hidrofone conectado a um gravador com uma frequência de amostragem de 96 kHz. Esta recolha de dados ocorreu entre 24 de Agosto a 14 de Outubro de 2019 ao redor das ilhas do Faial e do Pico. Para além das gravações acústicas efetuadas, foram também registados diferentes padrões de atividade e o tamanho dos grupos para cada espécie. O número de assobios nas gravações acústicas foi contado através de um programa de modo a que as suas taxas de emissão pudessem ser calculadas. Do número total de assobios foram selecionados 484 para Tursiops truncatus (n = 175), Stenella frontalis (n = 282) e Delphinus delphis (n = 27) onde foram medidos e comparados os parâmetros acústicos e os perfis de modulação de frequência entre as três espécies. Ao analisar estatisticamente os resultados, Tursiops truncatus apresentou uma taxa de emissão média significativamente maior do que Delphinus delphis, Stenella frontalis não obteve diferenças significativas nos valores das taxas de emissão entre os padrões de atividade e para cada espécie não houve correlação entre o tamanho dos grupos e as taxas de emissão. No entanto, as três espécies de golfinhos apresentaram diferenças significativas tanto nos parâmetros acústicos como nos perfis de modulação de frequência dos assobios. Palavras-The whistle repertoires of three seasonally sympatric delphinid species, that are commonly sighted during the summer in the Azores Archipelago, were study and compared. Tursiops truncatus, Delphinus delphis and Stenella frontalis whistles were recorded using a hydrophone connected to a recorder with a 96 kHz sampling frequency. These data collection occurred from August 24th to October 14th, 2019 around the Faial and Pico islands. Besides the acoustic recordings performed, it was also registered different activity patterns and the groups size for each species. A program was used to count the number of whistles in the acoustic recordings so that the whistle emission rates could be calculated. From the total number of whistles 484 were selected for Tursiops truncatus (n = 175), Stenella frontalis (n = 282) and Delphinus delphis (n = 27) where acoustic parameters and frequency contours were measured and compared among the three species. When the results were statistically analyzed, Tursiops truncatus exhibited an average emission rate significantly higher than Delphinus delphis, Stenella frontalis did not present significant differences in the emission rate values between the activity patterns and for each species there was no correlation between the groups size and the emission rates. However, the three dolphin species presented significant differences in both whistle acoustic parameters and frequency contours.Dissertação de Mestrado apresentada no ISPA – Instituto Universitário para obtenção de grau de Mestre na especialidade de Biologia Marinha e Conservaçã

Diurnal seismicity cycle linked to subsurface melting on an ice shelf

ABSTRACTSeismograms acquired on the McMurdo Ice Shelf, Antarctica, during an Austral summer melt season (November 2016–January 2017) reveal a diurnal cycle of seismicity, consisting of hundreds of thousands of small ice quakes limited to a 6–12 hour period during the evening, in an area where there is substantial subsurface melting. This cycle is explained by thermally induced bending and fracture of a frozen surface superimposed on a subsurface slush/water layer that is supported by solar radiation penetration and absorption. A simple, one-dimensional model of heat transfer driven by observed surface air temperature and shortwave absorption reproduces the presence and absence (as daily weather dictated) of the observed diurnal seismicity cycle. Seismic event statistics comparing event occurrence with amplitude suggest that the events are generated in a fractured medium featuring relatively low stresses, as is consistent with a frozen surface superimposed on subsurface slush. Waveforms of the icequakes are consistent with hydroacoustic phases at frequency ${\bf \gt} \bf 75\,{\bf Hz}$ and flexural-gravity waves at frequency $\bf {\bf \lt}25\,{\bf Hz}$. Our results suggest that seismic observation may prove useful in monitoring subsurface melting in a manner that complements other ground-based methods as well as remote sensing.</jats:p

Space-based remote imaging spectroscopy of the Aliso Canyon CH_4 superemitter

The Aliso Canyon gas storage facility near Porter Ranch, California, produced a large accidental CH_4 release from October 2015 to February 2016. The Hyperion imaging spectrometer on board the EO-1 satellite successfully detected this event, achieving the first orbital attribution of CH_4 to a single anthropogenic superemitter. Hyperion measured shortwave infrared signatures of CH_4 near 2.3 μm at 0.01 μm spectral resolution and 30 m spatial resolution. It detected the plume on three overpasses, mapping its magnitude and morphology. These orbital observations were consistent with measurements by airborne instruments. We evaluate Hyperion instrument performance, draw implications for future orbital instruments, and extrapolate the potential for a global survey of CH_4 superemitters