DUAL-POLARIZED SAR DATA FOR OIL SPILL DETECTION

In this study the capability of the co-polarized phase difference (CPD) for oil spill observation has been investigated. A simple and effective filtering technique, based on the standard deviation (σ) of the CPD Synthetic Aperture Radar (SAR) image, has been implemented. First experiment, accomplished over SIR-C/X-SAR C-Band data, have shown different sensitivity of the filtering technique with respect to oil spills and biogenic oil lookalikes. Since this technique needs only HH and VV data it can be applied also on dual-polarized data such as those provided by the ASAR operated on board on the ENVISAT satellite and the forthcoming COSMO-SKYMED. Key words: SAR; dual-polarized data; oil spill

Measurements of Backscattering from a Dihedral Corner in a Reverberating Chamber

In this paper, the backscattering of a dihedral corner is evaluated by measurements accomplished within the reverberating chamber (RC) of the Università degli Studi di Napoli Parthenope, formerly Istituto Universitario Navale (IUN). The obtained results are found in good agreement with those of a previous very accurate model, whose validity was assessed by anechoic chamber measurements

Wind speed retrieval from the Gaofen-3 synthetic aperture radar for VV- and HH-polarization using a re-tuned algorithm

In this study, a re-tuned algorithm based on the geophysical model function (GMF) C-SARMOD2 is proposed to retrieve wind speed from Synthetic Aperture Radar (SAR) imagery collected by the Chinese C-band Gaofen-3 (GF-3) SAR. More than 10,000 Vertical-Vertical (VV) and Horizontal-Horizontal (HH) polarization GF-3 images acquired in quad-polarization stripmap (QPS) and wave (WV) modes have been collected during the last three years, in which wind patterns are observed over open seas with incidence angles ranging from 18° to 52°. These images, collocated with wind vectors from the European Centre for Medium-Range Weather Forecast (ECMWF) reanalysis at 0.125° resolution, are used to re-tune the C-SARMOD2 algorithm to specialize it for the GF-3 SAR (CSARMOD-GF). In particular, the CSARMOD-GF performs differently from the C-SARMOD2 at low-to-moderate incidence angles smaller than about 34°. Comparisons with wind speed data from the Advanced Scatterometer (ASCAT), Chinese Haiyang-2B (HY-2B) and buoys from the National Data Buoy Center (NDBC) show that the root-mean-square error (RMSE) of the retrieved wind speed is approximately 1.8 m/s. Additionally, the CSARMOD-GF algorithm outperforms three state-of-the-art methods – C-SARMOD, C-SARMOD2, and CMOD7 – that, when applied to GF-3 SAR imagery, generating a RMSE of approximately 2.0–2.4 m/s

Detection of Wind Turbines in Intertidal Areas Using SAR Polarimetry

The detection of wind turbines in a strong clutter background is analyzed at variance of polarimetric synthetic-aperture radar (SAR) configurations. The area of interest is the intertidal zone near Jiangsu, China and two detectors are used, the polarimetric notch filter (PNF) and a change detector that optimizes the ratio between covariance matrices. The detection performance is quantitatively analyzed using the receiver operating characteristic (ROC) curve, while the scattering mechanisms that characterize wind turbines are analyzed using the Yamaguchi decomposition. Experimental analysis shows that: 1) wind turbines result in a nontrivial scattering mechanism and 2) full-polarimetric measurements achieve the best detection performance independently of the two detectors

On the Evaluation of the Shielding Effectiveness of an Electrically Large Enclosure

The shielding effectiveness (SE) has become a fundamental step in testing active or passive electric devices. The Reverberating Chamber (RC) is a well- established method for determining the SE since has the advantage to expose the material to a more realistic environment. In this paper the SEe of electrically large enclosures with a metallic mesh grid in a RC is evaluated. Enclosures made with metallic mesh are considered. In particular, it is shown that the SE of a material is unable to provide complete information for the SEe of an electrically large enclosure made with the same material. Moreover, this latter one is related to the loading conditions within the enclosure itself. Measurements accomplished at RC of the Università di Napoli Parthenope (formerly Istituto Universitario Navale, IUN) confirm the physical soundness of the proposed approach

On the trade-off between enhancement of the spatial resolution and noise amplification in conical-scanning microwave radiometers

The ability to enhance the spatial resolution of measurements collected by a conical-scanning microwave radiometer (MWR) is discussed in terms of noise amplification and improvement of the spatial resolution. Simulated (and actual) brightness temperature profiles are analyzed at variance of different intrinsic spatial resolutions and adjacent beams overlapping modeling a simplified 1-D measurement configuration (MC). The actual measurements refer to Special Sensor Microwave Imager (SSM/I) data collected using the 19.35 and the 37.00 GHz channels that match the simulated configurations. The reconstruction of the brightness profile at enhanced spatial resolution is performed using an iterative gradient method which allows a fine tuning of the level of regularization. Objective metrics are introduced to quantify the enhancement of the spatial resolution and noise amplification. Numerical experiments, performed using the simplified 1-D MC, show that the regularized deconvolution results in negligible advantages when dealing with low-overlapping/fine-spatial-resolution configurations. Regularization is a mandatory step when addressing the high-overlapping/low-spatial-resolution case and the spatial resolution can be enhanced up to 2.34 with a noise amplification equal to 1.56. A more stringent requirement on the noise amplification (up to 0.6) results in an improvement of the spatial resolution up to 1.64.Peer ReviewedPostprint (author's final draft

Retrieval of phenological stages of onion fields during the first year of growth by means of C-band polarimetric SAR measurements

The phenological stages of onion fields in the first year of growth are estimated using polarimetric observables and single-polarization intensity channels. Experiments are undertaken on a time series of RADARSAT-2 C-band full-polarimetric synthetic aperture radar (SAR) images collected in 2009 over the Barrax region, Spain, where ground truth information about onion growth stages is provided by the European Space Agency (ESA)-funded agricultural bio/geophysical retrieval from frequent repeat pass SAR and optical imaging (AgriSAR) field campaign conducted in that area. The experimental results demonstrate that polarimetric entropy or copolar coherence when used jointly with the cross-polarized intensity allows unambiguously distinguishing three phenological intervals.This work was partially supported by the Spanish Ministry of Economy and Competitiveness (MINECO) and EU FEDER, under Project TEC2011-28201-C02-02

A dual-polarimetric approach to earthquake damage assessment

In this study, a novel physical approach is proposed to detect damages due to earthquakes using dual polarimetric (DP) coherent Synthetic Aperture Radar (SAR) imagery. An optimization method, aimed at enhancing scattering basis differences between measurements collected before and after the event, is designed exploiting Lagrange optimization of the difference between two polarimetric covariance matrices. A meaningful showcase is presented to demonstrate the soundness of the proposed approach that consists of processing Sentinel–1 C–band scenes related to 2016 Central Italy Earthquake. The proposed approach, which is contrasted with the conventional coherence based single– and dual–polarization approaches, results in the best sensitivity to damages

On the Ability of PolSAR Measurements to Discriminate Among Mangrove Species

In this article, a polarimetric synthetic aperture radar (PolSAR) feature is analyzed to discriminate among different mangrove species. This feature, which is related to the Wishart distance, maximizes the contrast among mangrove species optimizing the ratio between quadratic forms. The discrimination performance is assessed both against ground truth and by intercomparing it with conventional model-based decomposition features. Results obtained by processing actual $L$ - and $C$ -band full-polarimetric synthetic aperture radar scenes collected by ALOS-PALSAR-2 and RADARSAT-2 missions show that the proposed approach achieves accurate enough discrimination performance to differentiate two out of the four mangrove species. In addition, results suggest using a multifrequency PolSAR approach to maximize discrimination performance