## 5 Discussion and Conclusions  
In this work, we have shown the preliminary results achieved by analyzing a set of SAR data collected by recently launched ICEYE SAR micro-satellites for the estimation of marine current velocity, using the DCA methodology. In recent years, many private space companies have invested heavily in innovative and low-cost space radar platforms, which can be exploited for this kind of application. Specifically, micro-satellite constellations (100-500 kg [24]) for SAR missions, such as the Surrey Satellite Technology Limited's (SSTL) NovaSAR [58], the ICEYE-X1, X2, and X3 [45], and the Capella Space's Capella X-SAR [59] have the potential to provide improved monitoring capabilities to traditional SAR missions on larger platforms, in terms of shorter revisit times, innovative acquisition modes, flexibility and redundancy of the measurements, and lower costs. One of the main benefits of the micro-satellite approach is the ability to operate with many spacecraft at a reasonable cost [60]. In addition, future bistatic space-based SAR missions, such as the European Space Agency's (ESA) C-band Harmony mission [61] and the Italian Space Agency's (ASI) X-band PLATINO-1 mission [62; 63], will provide significant added value for Earth observation applications compared to more conventional monostatic SAR systems, particularly in the context of marine monitoring. Historically, ENVISAT data have been widely used for marine environment monitoring [13; 16]. Therefore, since to our knowledge the literature lacks surface marine velocity estimation by using micro-satellite SAR data and particularly ICEYE data, this work is aimed at providing operational indications for this aim when applying the DC estimation method in [30] on micro-satellite X-Band SAR data. Consequently, based on the experience gained with C-Band ENVISAT data, we compare the quality indicator related to theoretical STD [31] and the one estimated on real data in different operative conditions, i.e., different DC estimation windows. A further comparison between ENVISAT and ICEYE data is provided concerning the achievable spectral and velocity resolution with the above-said specific parameters selection. The general aim is to provide to the reader with straightforward parameter selections that allow to achieve comparable performance results to those of the well-evaluated ENVISAT data. In order to achieve a superior DC estimation (the lowest standard deviation according to [31]), when considering ICEYE data, our experiments indicate that utilizing a DC estimation window size of \(400\times 400\) (see Table 4) is optimal. From the perspective of marine applications, the resolution of the surface radial velocity is a crucial parameter. Therefore, given that the wavelength of the X-Band radar is smaller than that of the C-Band (see Table 2), this results in superior radial VR (see Equation (7)) as evidenced by the results presented in Section 4. The discrepancy in radial velocity resolution between ENVISAT and ICEYE is amplified as the DC estimation window size diminishes. This is a noteworthy phenomenon from a marine perspective, as there is a potential benefit in achieving low radial velocity resolution to ensure compatibility with in situ measurement instruments. In the event that a particular marine application necessitates an enhanced velocity resolution value, this study also demonstrates that it is feasible to achieve favorable outcomes by extending the DC estimation window while maintaining a reasonable degree in terms of STD. A more detailed analysis including the application of ocean modeling techniques and/or real data acquired from in situ measurement instruments can provide a quantitative evaluation of the relation between the local ocean dynamic and the information derived from SAR.