## 2 Materials
### ICEYE Data  
Unlike ENVISAT, the ICEYE mission is a constellation of micro-satellites currently consisting of more than 30 X-Band SAR satellites orbiting Earth, capable of operating through different acquisition modes [50].  
The ICEYE satellites are in sun-synchronous orbit at an inclination of 97.7\({}^{\circ}\) with an orbital frequency of about 96 min. The first satellite of the constellation, ICEYE-X1, was launched in January 2018 [45]. The satellites work at X-band at a frequency of 9.65 GHz with left- and right-looking directions. Each satellite has a 17-day ground track repeat time, and as soon as all 48 satellites are in orbit, a twice-daily revisit time over the same locations on Earth is guaranteed.  
The ICEYE sensors are imaging only in vertical polarization (VV), offering products acquired in the following [51]:  
1. Stripmap mode (STRIP): It enables imaging any area on Earth at incidence angles of 15-30\({}^{\circ}\) with a ground spatial resolution of 3 m \(\times\) 3 m (azimuth \(\times\) range) and scene size of 50 km \(\times\) 30 km (azimuth \(\times\) range). The slant range resolution is 0.5 m based on the range bandwidth of 300 MHz and 1.5 m based on the range bandwidth of 100 MHz [45]. Although it is well known that the theoretical azimuth spatial resolution (in Stripmap mode) is given by half the antenna length (along the azimuth direction), the ICEYE azimuth pixel size of the SLC products is fixed to 3 m, whereas the azimuth antenna length is 3.2 m. This results from a system design parameters optimization that is carried out to reduce the azimuth ambiguities caused by aliasing. Accordingly, during the SLC product formation, an azimuth bandwidth reduction is performed [45].
2. Scan imagining mode (SCAN): It is a wide area imaging mode able to create a scene size of 100 km \(\times\) 100 km, with a ground resolution of 15 m \(\times\) 15 m at incidence angles of 21-29\({}^{\circ}\).
3. Spotlight mode (SPOT): It offers the finest resolution available with a ground resolution of 1.0 m \(\times\) 1.0 m, and it can image a scene of size 5 km \(\times\) 5 km at incidence angles of 20-35\({}^{\circ}\). The spot extended area (SLEA) mode provides the largest very-high resolution SAR imagery with ground resolution of 1.0 m \(\times\) 1.0 m and a scene size of 15 km \(\times\) 15 km, or slant resolution of 1.0 m \(\times\) 0.5 m (azimuth \(\times\) range) at incidence angles of 20-35\({}^{\circ}\).  
Figure 2: The area of interest for ENVISAT acquisition is located in the Gulf of Trieste in the Adriatic Sea, in the north part of Italy.  
Dwell mode (DWELL): It is characterized by a ground resolution from 50 cm and 1 m and a scene size of 5 km \(\times\) 5 km. Specifically, with its DWELL mode, ICEYE allows creating videos based on a single-pass radar acquisition. This capability enables a new dimension for analyzing in-scene motion [52; 53].  
Table 2 summarizes the main observational parameters of the ICEYE mission.  
The experiments carried out in our research with ICEYE data refer to a region over the Peru coastal area (South America) north of Lima, which is shown in Figure 3. In particular, the used SAR image was collected in Stripmap mode on 26 th January 2022 through an Ascending orbit. The SAR image covers a coastal area of about 50 km \(\times\) 30 km (azimuth \(\times\) range).  
By inspecting the archive of the available ICEYE data on [54], we identify a SAR image, related to an area in the Pacific Ocean, showing an interesting pattern which can be possibly related to a surface marine current. The scientific literature shows the capabilities of SAR to map sea currents in ocean regions mainly characterized by large flows [16].