## 8 Discussion and Conclusions  
SAR sensors have significant applications in the marine sector due to the high sensitivity to different phenomena occurring under and above the sea surface. SAR data can be used to extract the sea radial surface velocity, a key variable in maritime scenario. In the present work, we investigated the potentialities and the limitation in the extraction from ENVISAT data of information about the sea currents in the coastal area of the Gulf of Naples (South Italy) in the Mediterranean Sea. In the cases examined in the previous section, rather typical of the area considered, we have seen that the wind shaped the Doppler Anomaly derived from the analysis of the SAR images. One of the reasons of that is the weakness of the surface currents, which, according to the ocean model hindcast (Figure 11), roughly range between \(\pm\) 5 cm/s, which is similar to the resolution of the Doppler Anomaly derived from SAR. Despite the inability to quantify the effect of circulation currents on the Doppler measurements, the study does provide evidence of the effects in terms of the observed Doppler patterns. Doppler Anomaly measured form SAR image shows some differences with the model-derived one, a fact that may be ascribed to the coarse spatial resolution of the wind's model, which was adopted both to force the Doppler Geophysical Model Functions [28] (D-GMF) and as a first guess to the retrieve wind field from SAR (D-GMF). The results presented in this paper suggest that this well known issue [53; 54] could be partly overcome. The coarse spatial resolution of external data could indeed be refined by wind/Doppler approach that highlights changes in wind direction, as shown in this paper. By combining D-GMF and W-GMF with an atmospheric wind model, a wind vector fine map could be thus obtained. Once all the above problems are solved, the Doppler contribution produced by the D-GMF should be subtracted to that derived from SAR, to perform a validation of the residual Doppler Anomaly. Future investigations of the effects of wind and currents on SAR derived surface currents should thus consider coastal regions for which current data (e.g., from moored Acoustic Doppler Current Profiler velocity data [55], High-Frequency Radar currents (e.g., [56]), are available for a direct quantitative comparison. It should be remarked that over large areas (as those studied here) that cannot be sensed by the coastal HF radars, there is the need of a more detailed ocean surface modelling assimilating the available in-situ data, possible nowadays with the enhanced computer facilities and the data assimilation techniques. Along this line, altimetry-derived surface currents (e.g., [57; 58]) can be exploited also in coastal regions [59] as an additional source of information. The work along these lines would provide a contribution to the exploitation of SAR derived currents products to the advance of coastal ocean observing systems [60]. For research articles with several authors, a short paragraph specifying their individual contributions must be provided. The following statements should be used \"Conceptualization, V.Z. and G.F.; methodology, V.Z., F.D.S., G.D.C. and G.F.; software, V.Z., F.D.S., A.C., G.F.; validation, V.Z., F.D.S. and A.C.; data curation, V.Z. and F.D.S. ; writing--original draft preparation, V.Z., F.D.S., G.D.C., G.F.; writing--review and editing, V.Z., F.D.S., A.C., S.Z., G.D.C., and G.F.; supervision, G.D.C and G.F.; funding acquisition, S.Z., G.D.C., G.F. All authors have read and agreed to the published version of the manuscript. This research started with funding of the Italian Space Agency (ASI), under the project agreement J/055/09/0, and of the Italian Ministry of Education, University and Research Italian (MIUR) under the RITMARE flagship project; it achieved recent funding under the Contract ASI n\({}^{\circ}\) 217-I-E.0: \"Progetto Premiale \"Rischi Naturali indotti dalle Attivita Umana--COSTE\".