## 6 Test Site and Data Set  
The test site is situated in the south part of Italy, see Figure 5 on the left, and covers a coastal area of about 90 km \(\times\) 100 km (see Figure 5 on the right). More specifically, it starts in the south of the Gulf of Gaeta, includes the Gulf of Naples with the Ischia, Procida and Capri Islands, and part of the Gulf of Salerno. In Figure 5 left, red placemarks were highlighted to delimitate the corners of the validation area of WRF-ARW wind model. The validation was performed at the sites that are vertices of a quadrangular containing the study area of this paper: Ponza, Cetraro, Palermo and Capo Comino. Moreover, [41] developed hindcast covering 32 years (from 1979 to 2010) and containing, among the other, the wind downscaled data used in the present study. In this work, we focused our study on the coast described above because it is an area densely urbanized and characterized by heavy maritime traffic. Hence, the analysis carried out could be functional for the study of the sea state and have an interesting outcome for the activities oriented toward the definition of a long-term strategy in support of sustainable growth in the marine and maritime sectors, i.e., those known as Blue Economy or Blue Growth. Moreover, the results on the surface current obtained in this work could also be useful for a meteorological analysis. Among the several available SAR sensors, in this work, we decided to use ENVISAT ASAR for its characteristics relative to the swath. As a matter of fact, ENVISAT, in case of the (standard) stripmap acquisition, provides seamless and continuous coverage over a single swath width up to 100 km. The swath analyzed in this work is shown on the right side of Figure 5 and delimitated by the yellow placemarks and red line. For the case of COSMO-SkyMed the swath width, still considering the stripmap acquisition, would have been approximatively halved in both directions. A more recent SAR sensor, which offers a very wide swath and operates in C-Band, is Sentinel-1 (S1), which can boast swath of about 250 km. S1 captures three sub-swaths using Terrain Observation with Progressive Scans SAR (TOPSAR) mode; this mode allows covering wide coastal areas for each single orbit. The operation mode provides, however, additional complexity in the estimation of Doppler centroid for the azimuth beam steering reasons, and would lead from burst to burst to the presence of  
Figure 5: The area of interest is located in the South part of Italy. The red placemarks show the corners of the validation area of WRF-ARW wind model (left side). On the right side, there is a zoom on the test site, delimitated by red line, which includes the south of the Gulf of Gaeta, the Gulf of Naples with the Ischia, Procida and Capri Islands, and part of the Gulf of Salerno. discontinuities in the estimation Doppler Anomaly due to the change on the borders of the antenna pointing: the discontinuities impacts also the final radial velocity product [28]. Following the above considerations, as the best choice for this area, we found 47 images acquired by ENVISAT over ascending orbits between 2002 and 2010 (i.e., almost the whole operative period of the sensor). The ENVISAT sensor operates at C-band (wavelength equal to 5.6 cm), in VV polarization. Such a sensor is characterized by a spatial resolution of 5 m by 20 m in azimuth and ground range, respectively. The dataset was screened for the presence of potential amplitude patterns related to the sea-air interface, in particular from the wind or from mass displacements of marine currents. Among them, a total of five images were selected for the subsequent numerical analysis on the Doppler characteristics, in particular, they span from 2004 to 2010 and are listed in Table 1 together with the indication of the available model/models. It is worth noting that the dataset presented had the aim of discussing the open issues, especially concerning the influence of wind on surface currents and hence, represents a case study, rather than a statistically significant analysis.