Linear systems theory and its relationship to ocean acoustics

The article of record as published may be found at https://doi: 10.1121/1.2028979The purpose of this talk is to demonstrate the consistency and relationships between linear systems theory and the physics of propagation of small‐amplitude acoustic signals in fluid media. Using the principles of linear, time‐variant, space‐variant filter theory and time‐domain and spatial‐domain Fourier transforms, derivations of the solutions of the linear, three‐dimensional, inhomogeneous wave equation for (1) an unbounded isospeed fluid medium, (2) and unbounded fluid medium with speed of sound an arbitrary function of depth, and (3) a full‐wave, pulse‐propagation model for three‐dimensional wave propagation in a Pekeris waveguide are presented. Characterizing a fluid medium as a linear filter is valid since this involves trying to solve the linear wave equation. Computer simulation results are presented.Work supported by ONR, Code1 1250 and the Naval Postgraduate Schoo

Phase structured wavefields with phase singularities and bispectral properties

The work presented in this dissertation can be subdivided into two parts. The first part illustrates the novel use of a 37 actuator segmented deformable mirror for the creation of optical vortex beams ranging in topological charge from 1 to 10. The segmented deformable mirror offers a dynamic, polarization independent alternative for creating vortex beams with arbitrary charge. An optical vortex mode purity comparison between the deformable mirror and multi-step diffractive phase plates with 16 and 32 discrete steps is carried out both analytically and in simulation. Computer simulations show the intensity and phase of the vortices generated with the two methods. The deformable mirror, by being reconfigurable, shows better mode purity for high charge OVs, while the static phase plate mode efficiency declines due to the fixed number phase quantization. The second part of the dissertation reviews the concept of the bispectrum (3rd order polyspectrum) and the possibility of creating partially spatially coherent beams with nonzero bispectral characteristics. Numerical simulations show that bispectral properties encoded in an input wavefield are invariant upon propagation in free space. This result opens the possibility of using the bispectrum as a new degree of freedom for encoding information in a wavefield

Array processing based on time-frequency analysis and higher-order statistics

Ph.DDOCTOR OF PHILOSOPH

Ecosystem Monitoring and Port Surveillance Systems

International audienceIn this project, we should build up a novel system able to perform a sustainable and long term monitoring coastal marine ecosystems and enhance port surveillance capability. The outcomes will be based on the analysis, classification and the fusion of a variety of heterogeneous data collected using different sensors (hydrophones, sonars, various camera types, etc). This manuscript introduces the identified approaches and the system structure. In addition, it focuses on developed techniques and concepts to deal with several problems related to our project. The new system will address the shortcomings of traditional approaches based on measuring environmental parameters which are expensive and fail to provide adequate large-scale monitoring. More efficient monitoring will also enable improved analysis of climate change, and provide knowledge informing the civil authority's economic relationship with its coastal marine ecosystems

A New Concept of Fractional Order Cumulant and It-Based Signal Processing in alpha and/or Gaussian Noise

In this article, the concept and definitions of the Fractional Order Moment (FOM) and Fractional Order Cumulant (FOC) are proposed, which is based on the fractional derivative of the fractional order Moment-generating function and the fractional order Cumulant-generating function of stochastic processes. The moment and cumulant are defined on an expanded set from positive integer to the whole positive real. This development not only provides a new technology for signal processing, also complements the existing theory in the field. The properties of the FOC have been derived, and their uniformity and particularity with the High Order Cumulant are compared and commented. In addition, the transformation between the FOM and the FOC are derived and discussed in detail. As one of the applications of the new concept to the α and Gaussian processes, a new method of suppressing α and Gaussian noise is proposed. Furthermore, a FOC-based parameter estimation algorithm is developed for the non-minimum phase ARMA processes in α and/or Gaussian noise. Simulation examples are used to demonstrate the effectiveness of the proposed parameter estimation algorithm

Measuring ocean surface velocities with the KuROS and KaRADOC airborne near-nadir Doppler radars: a multi-scale analysis in preparation of the SKIM mission, Submitted to Ocean SCience, July 2019

Surface currents are poorly known over most of the oceans. Satellite-borne Doppler Waves and Current Scatterom-eters (DWCS) can be used to fill this observation gap. The Sea surface KInematics Multiscale (SKIM) proposal, is the first satellite concept built on a DWCS design at near-nadir angles, and now one of the two candidates to become the 9th mission of the European Space Agency Earth Explorer program. As part of the detailed design and feasibility studies (phase A) funded by ESA, airborne measurements were carried out with both a Ku-Band and a Ka-Band Doppler radars looking at the sea surface at 5 near nadir-incidence in a real-aperture mode, i.e. in a geometry and mode similar to that of SKIM. The airborne radar KuROS was deployed to provide simultaneous measurements of the radar backscatter and Doppler velocity, in a side-looking configuration , with an horizontal resolution of about 5 to 10 m along the line of sight and integrated in the perpendicular direction over the real-aperture 3-dB footprint diameter (about 580 m). The KaRADOC system has a much narrower beam, with a circular footprint only 45 m in diameter. 10 The experiment took place in November 2018 off the French Atlantic coast, with sea states representative of the open ocean and a well known tide-dominated current regime. The data set is analyzed to explore the contribution of non-geophysical velocities to the measurement and how the geophysical part of the measured velocity combines wave-resolved and wave-averaged scales. We find that the measured Doppler velocity contains a characteristic wave phase speed, called here C 0 that is analogous to the Bragg phase speed of coastal High Frequency radars that use a grazing measurement geometry, with little 15 variations ∆ C associated to changes in sea state. The Ka-band measurements at an incidence of 12 • are 10% lower than the theoretical estimate C 0 2.4 m/s for typical oceanic conditions defined by a wind speed of 7 m/s and a significant wave height of 2 m. For Ku-band the measured data is 1 https://doi. 30% lower than the theoretical estimate 2.8 m/s. ∆ C is of the order of 0.2 m/s for a 1 m change in wave height, and cannot be confused with a 1 m/s change in tidal current. The actual measurement of the current velocity from an aircraft at 4 to 18 • incidence angle is, however, made difficult by uncertainties on the measurement geometry, which are much reduced in satellite measurements