M. Di Bisceglie

Analysis of GNSS-R Delay-Doppler Maps from the UK-DMC satellite over the ocean

A study of the retrieval of sea surface roughness using Global Navigation Satellite System-Reflectometry (GNSS-R) from satellite is presented. Delay- Doppler Maps (DDMs) from the SSTL UK-DMC satellite are analyzed to retrieve directional Mean Square Slopes (MSSs). Results are compared to theoretically-derived MSSs and in situ measurements from co-located buoys of the National Data Buoy Center (NDBC), showing good agreement in most cases. Here, the whole DDM, a more complete source of information, is exploited for the first time using satellite GNSS-R data. These are potentially able to provide high spatial and temporal sampling, and therefore offer an improved way to observe wind and waves by means of a very modest instrument.

Canonical detection in spherically invariant noise

The paper deals with the detection of signals with unknown parameters in impulsive noise, modeled as a spherically symmetric random process. The proposed model subsumes several interesting families of noise amplitude distributions: generalized Cauchy, generalized Laplace, generalized Gaussian, contaminated normal. It also allows handling of the case of correlated noise by a whitening approach. The generalized maximum likelihood decision strategy is adopted, resulting in a canonical detector, which is independent of the amplitude distribution of the noise. A general method for performance evaluation is outlined, and a comprehensive performance analysis is carried out for the case of M-ary equal-energy orthogonal signals under several distributional assumptions for the noise. The performance is contrasted with that of the maximum likelihood receiver for completely known signals, so as to assess the loss due to the a-priori uncertainty as to the signal parameters. >

Cooperative sensor networks for voltage quality monitoring in smart grids

The paper intends to give a contribution toward the definition of a fully decentralized voltage quality monitoring architecture by proposing the employment of self organizing sensor networks. According to this para-digm each node can assess both the performances of the monitored site, computed by acquiring local information, and the global performances of the monitored grid section, computed by local exchanges of information with its neighbors nodes. Thanks to this feature each node could automatically detect local voltage quality anomalies. Moreover system operator can assess the system voltage quality index for each grid section by inquiring any node of the corresponding sensors network without the need of a central fusion center acquiring and processing all the node acquisitions. This makes the overall monitoring architecture highly scalable, self-organizing and distributed.

Simulation of L-Band Bistatic Returns From the Ocean Surface: A Facet Approach With Application to Ocean GNSS Reflectometry

We present the implementation of a facet-based simulator to investigate the forward scattering of L-band signals from realistic sea surfaces and its application to spaceborne ocean Global Navigation Satellite System (GNSS) Reflectometry. This approach provides a new flexible tool to assess the influence of the ocean surface roughness on scattered GNSS signals. The motivation stems from the study by Clarizia , which revealed significant differences between delay-Doppler maps (DDMs) obtained from UK-DMC satellite data and DDMs simulated with the Zavorotny-Voronovich (Z-V) model. Here, the scattered power and polarization ratio (PR) are computed for explicit 3-D ocean wave fields, using a novel implementation of the Kirchhoff approximation (KA), which we call the Facet Approach (FA). We find that the FA is consistent with the full KA and the Geometrical Optics (GO) used in the Z-V model, while being less computationally expensive than the KA and able to represent polarization effects not captured by the GO. Instantaneous maps of the bistatic normalized radar cross section computed with the FA show clear patterns associated with the underlying waves. The wave field is particularly visible in the PR, indicating that the scattering is generally dominated by the HH component, particularly from ocean wave troughs. Polarization effects show, for the first time, a strong correlation to the explicit sea surface from which the scattering originated. DDMs of the scattered power computed with the FA reveal patchy patterns and power distributions that differ from those obtained with Z-V and show closer similarities with observed DDMs from UK-DMC.

Optimum detection of fading signals in impulsive noise

This paper deals with the synthesis and the analysis of optimum receivers to detect one out of M equally likely, equi-energy, fading signals in impulsive noise, modelled as a compound Gaussian, possibly correlated process. We show that the conventional coherent and incoherent detectors are still optimum, independent of the noise as well as the fading probability density functions. The performance analysis has been carried on with reference to the general case of arbitrarily distributed disturbance: in order to simplify the analysis, asymptotical expressions have been developed for high signal-to-noise ratios as well as high signal space dimensionality. Interestingly enough, this allows separating the effect of the noise spikyness from that of the fading law. Results indicate that, for deep fading, the noise marginal distribution does not dramatically affect the error probability, nor is it influential on the limit operating characteristics corresponding to infinite signal space dimensions. For non-fluctuating signals, instead, the noise distribution plays a primary role: spiky noise usually produces performance impairment; moreover, the limit performance in impulsive disturbance may exhibit marked deviations from the well-known stepwise shape which is typical of Gaussian channels. >

CFAR detection of extended objects in high resolution SAR images

Presents a processing scheme for the constant false alarm rate (CFAR) detection of extended objects embedded in non-Gaussian disturbance. The proposed receiver exploits some relevant properties of the location-scale distributions for ensuring constant false alarm against Weibull clutter. The system has been specifically conceived for operating on high-resolution SAR images where space processing (but not time processing) is allowed.

Destriping MODIS data using IFOV overlapping

In this paper, we present a new destriping algorithm for MODIS images. The algorithm takes advantage of the observation redundancy due to the bow-tie effect. It estimates the equalization curve from single fields of view observed by multiple detectors. Results show that the strategy is correct in those regions where equalization curve is estimated in the low to moderate range of radiance

The Unmixing of Atmospheric Trace Gases From Hyperspectral Satellite Data

A new approach for the retrieval of the vertical column concentrations of trace gases, from hyperspectral satellite reflectances, is presented. The investigation moves from the general rationale of independent component analysis, but the constraint of perfect independence among sources is replaced by a minimum dependence concept that proves more reasonable for the application at hand. The unmixing of the gas spectra and their concentrations is achieved from linear mixtures obtained from the logarithm of the spectral reflectance. After a proper preprocessing stage aimed at reducing major residual dependences caused by atmospheric scattering, trace-gas retrieval is carried out through a minimization of a statistical cost function, subject to the physical constraint that the resulting spectra must be nonnegative. The experimental analysis relies on the retrieval of sulfur dioxide during volcanic emissions using data from the National Aeronautics and Space Administration Ozone Monitoring Instrument. To validate the procedure, reference reflectance spectra having a known profile of sulfur dioxide are generated with the MODerate resolution atmospheric TRANsmission software, and the retrieved concentration is compared with the theoretical one. Performance in the presence of shot and detector noise has also been analyzed starting from pure simulated spectral reflectances.

Simulation of GNSS-R returns for delay-DOPPLER analysis of the ocean surface

We present a new approach to the retrieval of sea surface roughness using GNSS-R. The steps through the simulation of the whole end-to-end microwave scattering of GNSS signals from the sea surface are explained, with emphasis on how to generate a linear sea surface and to implement the Kirchhoff Approximation (KA), as the large-scale part of the full scattering model. We illustrate some examples of radar cross sections calculated using the Kirchhoff scattering model, and how they change with respect to different polarizations. Their variations with geometry, sea state and spatial resolution are investigated and discussed.

Statistical characterization of the phase process in interferometric SAR images

In this paper we consider a statistical model for interferometric SAR images accounting for both the non-Gaussian statistics of the amplitude probability density function and for the most credited model for the interferometric phase distribution. At the basis of the model is the inapplicability of the central-limit theorem for resolution cells composed by a non-deterministic number of scatterers. Experimental results carried out on both single-pass and repeat-pass interferometric data show a very good agreement between the theoretically derived phase probability density function and the measured one.