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La Spezia, Italy

Camps A.,Polytechnic University of Catalonia | Font J.,Polytechnic University of Catalonia | Font J.,CSIC - Institute of Marine Sciences | Corbella I.,Polytechnic University of Catalonia | And 39 more authors.
Remote Sensing | Year: 2012

This work summarizes the activities carried out by the SMOS (Soil Moisture and Ocean Salinity) Barcelona Expert Center (SMOS-BEC) team in conjunction with the CIALE/Universidad de Salamanca team, within the framework of the European Space Agency (ESA) CALIMAS project in preparation for the SMOS mission and during its first year of operation. Under these activities several studies were performed, ranging from Level 1 (calibration and image reconstruction) to Level 4 (land pixel disaggregation techniques, by means of data fusion with higher resolution data from optical/infrared sensors). Validation of SMOS salinity products by means of surface drifters developed ad-hoc, and soil moisture products over the REMEDHUS site (Zamora, Spain) are also presented. Results of other preparatory activities carried out to improve the performance of eventual SMOS follow-on missions are presented, including GNSS-R to infer the sea state correction needed for improved ocean salinity retrievals and land surface parameters. Results from CALIMAS show a satisfactory performance of the MIRAS instrument, the accuracy and efficiency of the algorithms implemented in the ground data processors, and explore the limits of spatial resolution of soil moisture products using data fusion, as well as the feasibility of GNSS-R techniques for sea state determination and soil moisture monitoring. © 2012 by the authors. Source

Lund B.,University of Miami | Graber H.C.,University of Miami | Horstmann J.,NURC | Terrill E.,University of California at San Diego
International Geoscience and Remote Sensing Symposium (IGARSS) | Year: 2012

In this paper we evaluate different methods to retrieve wind information from marine radar data. In contrast to traditional in-situ sensors, marine radar wind data cover a large area and therefore are much less susceptible to air flow distortion by the platform. Unlike previous studies that have been limited to fixed-platform data, this study includes data from a quasi-stationary and moving platform. Images collected with a standard marine HH-polarized X-band radar operating at grazing incidence angle exhibit a single intensity peak in the upwind direction. Marine radar images that are averaged over about 1 min may also show wind streaks, which are usually well-aligned with the mean surface wind direction. Here, we use both phenomena to retrieve wind directional information and compare results to determine the best approach under the given conditions. To retrieve wind speeds, an empirical model function which relates average backscatter intensity to wind speed is developed. © 2012 IEEE. Source

Anderson S.D.,Georgia Institute of Technology | Sabra K.G.,NURC | Zakharia M.E.,French National Center for Scientific Research | Sessarego J.-P.,Georgia Institute of Technology
Journal of the Acoustical Society of America | Year: 2012

The development of low-frequency sonar systems, using, for instance, a network of autonomous systems in unmanned vehicles, provides a practical means for bistatic measurements (i.e., when the source and receiver are widely separated) allowing for multiple viewpoints of the target of interest. Time-frequency analysis, in particular, Wigner-Ville analysis, takes advantage of the evolution time dependent aspect of the echo spectrum to differentiate a man-made target, such as an elastic spherical shell, from a natural object of the similar shape. A key energetic feature of fluid-loaded and thin spherical shell is the coincidence pattern, also referred to as the mid-frequency enhancement (MFE), that results from antisymmetric Lamb-waves propagating around the circumference of the shell. This article investigates numerically the bistatic variations of the MFE with respect to the monostatic configuration using the Wigner-Ville analysis. The observed time-frequency shifts of the MFE are modeled using a previously derived quantitative ray theory by Zhang [J. Acoust. Soc. Am. 91, 1862-1874 (1993)] for spherical shell's scattering. Additionally, the advantage of an optimal array beamformer, based on joint time delays and frequency shifts is illustrated for enhancing the detection of the MFE recorded across a bistatic receiver array when compared to a conventional time-delay beamformer. © 2012 Acoustical Society of America. Source

Hollett R.D.,NURC
Proceedings of the Institute of Acoustics | Year: 2010

Mine-Penetration Sonar is proposed as a candidate, next-generation minehunter system for enhanced detection and classification of proud and buried seabed mines. The system concept is based on high-resolution target imagery in the low frequency regime (< 30 kHz), by means of backprojection of broadband returns (5-30 kHz), over a broad sector of aspect angles about the target (90-degree sector or more). It is proposed that: 1) in the low frequency regime, the mine casing is readily penetrated, as the thickness is reduced to a fraction of the incident wavelengths; 2) the target scattering is dominated by the coherent field, as the mine is constructed of acoustically-smooth, homogeneous components, both exterior and interior; 3) in the low frequency regime, the coherent field is considerably widened (about the specular), particularly from the interior components, and amenable to broad-sector backprojection. The system design is based on low frequency broadband, broad-sector SAS, capable of high-resolution imagery (typically, 3 cm × 3 cm). The system is envisaged as bi-modal: 1) in its primary mode of operation, the system is run as a strip-map or bottom survey SAS, with initial detection and classification of mine-like objects based on interior imagery; 2) in its secondary mode, the system is run as a spotlight or target-classification SAS on targets of interest, for spectral analysis of response with aspect, template matching, etc. (based on reutilization of the data acquired in primary mode). The system simulations are based on simple modelling of interior components of typical mines and the backprojection of their coherently-scattered returns. The interior components are modelled by means of the boundary element method with the additional simplification of boundary impenetrability (Kirchhoff approx.). It is proposed that the basic acoustic field scattered by the mine interior is sufficiently well represented and that any effects of penetrability are easily evaluated. The simulated target imagery is based on the filtered backprojection algorithm (for echo inversion), and dB levels in the imagery presented as target backscattering strengths, for direct comparison with known bottom backscattering strengths and evaluation of target echo-to-reverberation ratios in the imagery. Source

Mourre B.,NURC | Alvarez A.,NURC
Deep-Sea Research Part I: Oceanographic Research Papers | Year: 2012

The benefits of piloting a glider during a 6-day period via an adaptive sampling procedure in a 80×60km 2 marine area are assessed under a fully operational framework. The glider trajectory was adapted to reduce the ocean temperature uncertainties predicted by the operational 3-D super-ensemble model in the Ligurian Sea in August 2010. Two sets of real time model predictions are compared, which assimilate observations from (1) the adaptive-sampling-driven glider and (2) an independent glider flying in the same area. The piloting algorithm was able to successfully guide the glider along the planned trajectories. These were nevertheless not fully completed due to un-predicted adverse currents faced along the transects. Despite operational constraints and model prediction errors, the adaptive sampling procedure is shown to meet the proposed objective, i.e. a reduction of the 48-h model temperature uncertainty predicted in the upper 200m. Moreover, measurements collected during the last 48-h forecast cycle from (i) an ocean mooring, (ii) a repeated ScanFish transect and (iii) more irregularly distributed platforms, all indicate that the actual prediction error is lower in the simulation assimilating the data from the adaptive sampling. Quantitatively, the total root-mean-square error is reduced by 18% at the end of the field experiment in comparison with the control simulation. © 2012 NATO Undersea Research Centre. Source

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