Abstract
It has often been reported and is now well established that the traditional definition of Instantaneous Frequency (IFt) fails in the presence of multicomponent signals. New definitions of IFt have recently been proposed, in an attempt to cope with the difficulties of the traditional one. In this paper, we will address the reasons for failure of the traditional definition, show that it can also fail with monocomponent signals, and show how its behaviour can be predicted for any type of signal, thus generalizaing previous results. We will also analyse the performance in noise of one of the recently proposed definitions of IFt.

Abstract
A procedure for parameter estimation of multicomponent Polynomial Phase Signals is presented. This scheme, while restricted to high SNR's, has the advantage of being extremely simple. It is also insensitive to the equal-coefficient identifiability problem of HAF (High-order Ambiguity Function) based methods. It poses, however, some restrictions on the component amplitudes. Its performance in noise is investigated, and confirmed with several examples.

Abstract
Due to the complexity of underwater transients and background interference, model based approaches to transient detection/classification are often not practical. This has motivated an interest for data-driven, model-free methods. One such method was presented in [2] and modified in [1], where it was applied to the detection of underwater transients. In this article, we will extend that approach, to allow its use in the more demanding environment of a brown water environment, where background noise is constituted by a multitude of different interferences, non-white, and highly non-stationary. Also, the assumption of linear separability amongst the transients and the background noise in the time-frequency or related domains will be discarded, leading to the use of an additional classifier stage. A technique to minimize the number of prototypes on this classifier will be presented. The developed methods are used to detect and classify real underwater transients, recorded off the Portuguese coast. Estimation of the overall error rate of the method is obtained using cross-validation with the available data set, showing that these methods can effectively be used in real environment situations.

Abstract
The failure of the traditional definition of instantaneous frequency (IFt) in the multicomponent case has been often reported, We will determine the reasons for failure of this definition, That will enable us to understand and integrate all previously reported cases in a simple unified theory. As a direct consequence, we will be able to extrapolate and predict the behavior of the traditional definition for any type of multicomponent signal.

Abstract
The need to generate random wave fields with a pre-determined spectrum is a common one. One of the typical applications requiring this capability is the need to interface spectral and deterministic models. The spectra and integral parameters produced as output of spectral models must often be transformed into wave fields which can be used as input to deterministic models (e.g. Navier-Stokes based numerical models). Also, the instantaneous statistics of the produced wave field must be controlled. This is typically the case when the objective is to evaluate the influence of these statistics in the appearance of certain wave phenomena. In this article we propose a parametric based approach to the wave field generation. Not only is this a computationally efficient way of generating local elevation sequences, but it also enables perfect control of both the instantaneous and spectral characteristics of the generated waves. Two examples of applications will be given. One, where the developed generator will be used to investigate the influence of the spectral model and the instantaneous statistics of the wave field in extreme wave generation. A second example will be the generation of a boundary field for a Navier-Stokes based model starting from the spectral output of the SWAM model.

Abstract
Current practices and major trends in unmanned aircraft systems (UAS) for maritime operations are presented along with projections of future UAS maritime applications. First, various aspects of UAS program management, including organization, operator responsibilities, program operation, and overall program costs, are reviewed. Next, maritime aircraft missions and required capabilities are outlined, and current practices for both manned and unmanned aircraft are described. Technological trends relating to UAS are also discussed, focusing on developments relevant to maritime UAS operations. This information provides a background for assessing potential future maritime UAS operations. Trends including miniaturization of sensors and computer systems, high energy density of power sources, and increased subsystem standardization and modularity will have important effects in the future. However, another significant trend is towards increased system autonomy via new command and control frameworks that facilitate integration of UAS into higher level maritime observing systems through new concepts of operation for networked systems and new business models. © Springer Science+Business Media Dordrecht 2015.