## 4 Results  
This section presents the experimental results achieved by using ENVISAT ASAR and ICEYE data. For our experiments, among the different DC estimators present in the literature and discussed in Section 3.1, DC estimation are carried out by using the method based on the calculation of the azimuth autocorrelation function proposed in [30]. DC estimates are determined over the entire scene using three different sliding windows, corresponding to a coverage on the ground of (about) 1 km \(\times\) 1 km, 2 km \(\times\) 2 km and 2.5 km \(\times\) 2.5 km (see Table 4). Figure 5 shows the histograms of the estimated DC STD for ENVISAT ASAR (Figure 5A) and ICEYE (Figure 5B) data considering the three windows reported in Table 4. Of note, for each dataset, the theoretical STD (according to Equation (1)) decreases as the size of the aforementioned DC estimation windows increases. This is evidenced by the fact that the histogram peaks shift towards the left as the estimation window size increases. \begin{table}
\begin{tabular}{l c c c c c} \hline \hline  & \begin{tabular}{c} **Window** \\ **Size** \\ **(az \(\times\) rg)** \\ \end{tabular} & \begin{tabular}{c} **Ground** \\ **Covered** \\ **Area [km\({}^{2}\)]** \\ \end{tabular} & \begin{tabular}{c} **Expected** \\ **DC** \\ **STD Value [Hz]** \\ \end{tabular} & \
\begin{tabular}{c} **Measured** \\ **DC** \\ **STD Value [Hz]** \\ \end{tabular} &
\begin{tabular}{c} **Error** \\ **(Exp.-Meas.) [Hz]** \\ \end{tabular} \\ \hline ENVISAT & 256 \(\times\) 64 & 1.3 \(\times\) 1.3 & 4.48 & 5.15 & 0.67 \\ ICEYE & 400 \(\times\) 400 & 1.2 \(\times\) 1.2 & 4.43 & 4.62 & 0.19 \\ \hline ENVISAT & 426 \(\times\) 106 & 2.1 \(\times\) 2.1 & 2.7 & 3.61 & 0.91 \\ ICEYE & 600 \(\times\) 600 & 1.8 \(\times\) 1.8 & 2.95 & 3.87 & 0.92 \\ \hline ENVISAT & 512 \(\times\) 128 & 2.5 \(\times\) 2.5 & 2.24 & 3.34 & 1.1 \\ ICEYE & 800 \(\times\) 800 & 2.4 \(\times\) 2.4 & 2.22 & 3.56 & 1.34 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Expected and measured STD for ENVISAT and ICEYE data. Table 4 shows the expected (theoretical) values of the STD, as well as the corresponding measured ones according to the median value of the histograms. In addition, we also show the difference (error) between the expected/measured values of the STD. Table 4 demonstrates that utilizing the proposed sliding window on ICEYE data yields an overall DC behavior that is analogous to that observed in the ENVISAT results in terms of standard deviation. This provides a framework for selecting the pertinent parameters to be employed when applying DCA to ICEYE data. Furthermore, for each DC estimation window, the spectral resolution (SR) and velocity resolution (VR) values are evaluated. As previously stated in Section 3.1, the DC estimation is conducted using sliding windows, which are selected to ensure an optimal balance between spatial resolution and spectral resolution (SR). The latter is given by the ratio  
Figure 5: Histograms of the DC estimate STD of the (**A**) ENVISAT ASAR and (**B**) ICEYE data considering the above-mentioned sliding windows. Red dashed line (1 km \(\times\) 1 km), yellow dashed line (2 km \(\times\) 2 km), and black dashed line (2.5 km \(\times\) 2.5 km). between platform velocity \(v_{sensor}\) and the extent of the area along the azimuth direction, corresponding to the selected sliding window [30], i.e.,  
\[\delta_{SR}=\frac{v_{sensor}}{M_{az}d_{az}} \tag{6}\]  
where \(M_{az}\) and \(d_{az}\) are the number of azimuth samples of the DC estimation window and the azimuth pixel spacing, respectively. In order to obtain radial velocity resolution (VR), it is straightforward to convert \(\delta_{SR}\) as follows:  
\[\delta_{VR}=\frac{\lambda}{2}\delta_{SR}=\frac{\lambda}{2}\frac{v_{sensor}}{M_ {az}d_{az}} \tag{7}\]  
Figure 6 shows the trend of the SR (Figure 6A) and VR (Figure 6B) with respect to the covered ground area along the azimuth direction of the DC estimation window.