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According to the World Bank data catalogue, 6 , 862 records of reservoirs and their associated dams are present summing up a capacity of 6 , 197 km3 of water. They play a crucial role in providing potable and irrigation water and, therefore, it is of paramount interest to effectively monitor such critical infrastructures. An effective approach is based on satellite remote sensing and, in particular, on the Synthetic Aperture Radar (SAR). In this paper, we critically investigate the use of polarimetric SAR measurements for reservoirs' waterline estimation. Measurements of the novel COSMO-SkyMed Second Generation (CSG) X-band quad-polarimetric SAR related to the San Giuliano reservoir, in the South of Italy, are used to carry out an electromagnetic analysis of the different polarimetric scattering returns. Experimental results show that the cross-polarized channel, as well as the inter-channel phase, are noisy and, therefore, uninformative when used to design coherent polarimetric waterline extraction methods. From an electromagnetic viewpoint, this is due to the peculiarities of the reservoirs that call for low surface roughness and negligible wave pattern that, at once, result in a joint combination of un-tilted Bragg scattering and specular reflection. This implies that a low co-polarized backscatter and a cross-polarized signal largely below the system noise floor are to be expected. As a consequence, waterline extraction approaches that do not exploit the inter-channel phase, the so-called incoherent approaches, are shown to outperform the coherent ones. [ABSTRACT FROM AUTHOR]

Forest fires burn various natural ecosystems worldwide and can harm the environment and human life. Accordingly, real-time monitoring of this phenomenon and early decision-making warning is vital. Active remote sensing systems, such as Synthetic Aperture Radar (SAR) sensors, provide an excellent opportunity for burn mapping because they can penetrate through clouds and smoke day and night. In this study, the potential of Sentinel-1 SAR data was investigated by deploying a deep convolutional neural network (CNN) based framework to map burn progression dynamically, in both supervised and transfer manners. Accordingly, an optimized deep architecture was designated to use SAR data features with high sensitivity to map the burned areas. The proposed method includes three main steps: 1) extraction of SAR indices, 2) training deep CNN model with a limited number of scenes and 3) assessing the transferability of the CNN for estimating burn progression for any unseen scene. Sentinel-1 SAR indices of log-ratio, radar burn difference (RBD), and difference of dual-polarization SAR vegetation index (ΔDPSVI) were obtained to be fed to the CNN. To validate the efficiency of the proposed approach, two fire events, i.e. the Derazno fire in Iran (2021) and the Rossomanno-Grottascura-Bellia fire in Italy (2017), were considered. For the scenes including training samples, the proposed method improved the overall accuracies (OAs) of classical machine learning techniques (i.e. SVM and RF) significantly (more than 4%). However, the improvement was minor when compared to a CNN using only log-ratio as the input channel (log-ratio CNN). For the scenes without training samples (unseen dates), the investigated transferred model performed substantially better (3% higher OA) compared to the other machine learning methods and the log-ratio CNN. This finding approves that the obtained SAR indices boost the transferability of the CNN model for burn progression mapping at unseen scenes. [ABSTRACT FROM AUTHOR]

This study analyzes the ability of polarimetric Synthetic Aperture Radar (PolSAR) measurements to quantify post-earthquake damages. To achieve this goal, a twofold task is addressed: on one side a processing chain, which exploits multi-polarization SAR features, and a decision-tree classifier is proposed to quantify the levels of damage in earthquake-affected urbanized areas using dual-polarimetric (DP) SAR imagery. On the other side, a new damage index is developed that allows a fair spatial inter-comparison of building-by-building information, collected via ground surveys on the damaged areas, and SAR-derived damage maps. The proposed rationale is showcased using measurements related to the Central-Italy Earthquake occurred in 2016 where both Sentinel-1 DP imagery and ground-based information are available. Experimental results demonstrate the soundness of the proposed approach. The main outcomes can be summarized as follows: a) DP features perform better than single-polarization ones; b) DP features exhibit a larger sensitivity to lower damage grades if compared to the single polarization (SP) feature; c) the accuracy of the estimated damage levels depends on the requested granularity in the damage maps; d) the accuracy obtained using DP features spans from ∼ 52 % up to ∼ 71 % when five and two damage classes are considered, respectively. [ABSTRACT FROM AUTHOR]