## 2 Materials and Methods
### SAR Data  
In this study, SAR data acquired by the SAOCOM-1 and Sentinel-1 systems are considered. SAOCOM-1 is a two-satellite constellation launched by CONAE, in 2018 and 2020. Sentinel-1 is also a two-platform constellation launched in April 2016 and operated by ESA. The SAR instruments on board these spaceborne platforms work at L-band (\(\lambda\approx 23\) cm) for SAOCOM-1 and C-band (\(\lambda\approx 5.6\) cm) for Sentinel-1. Their use in forestry applications is of great interest due to the way in which microwaves interact with trees [5]. For this study, we selected different temporal series of SAOCOM-1A&B and Sentinel-1B images, covering the period from August to December 2021 in the case of the Corrientes site, and from February to August 2020 in the case of Neuquen site. In the former (Corrientes), a shorter dataset of SAOCOM-1 images with descending orbit was also considered in order to assess the InSAR coherence changes according to the orbit direction, see Section 3.2. Table 1 summarizes the image datasets used in this work, where A and D indicate ascending and descending orbits, respectively, \(\theta^{\circ}\) refers to the approximate mid-range incidence angle. N indicates the number of images of the temporal series, Pol. refers to the polarization, QP for fully-polarimetric data and VV/VH for dual-pol data and, finally, \(B_{\perp,crit}\) is the critical perpendicular baseline. Sections 3.1-3.3 refer to data processed in the Corrientes site, while Section 3.4 makes use of both sites to compare the variation of InSAR coherence according to forest canopy height. Finally, it is worth noting that, since 20 November 2021, the first SAOCOM-1B images started to be acquired over the Corrientes site, allowing us to form 8-day InSAR pairs with the combination with the SAOCOM-1A images. At the moment, the amount of SAOCOM-1B images is not long enough to make a long temporal analysis, but these shorter term orbital L-band interferograms have been included in this work, and are specifically addressed and analyzed in Section 3.3. Figure 2: Study-areas in Corrientes and Neuquén provinces, Argentina. The temporal baseline between the SAOCOM-1A images is 16-day, which is equivalent to the platform's nominal revisit time. This temporal cycle can be reduced to 8 days if images are acquired by the SAOCOM-1A&B constellation. Regarding the C-band dataset, the Sentinel-1B images used for this work are separated by a 12-day temporal baseline. Figure 3a,b depicts the perpendicular spatial and temporal separation between the scenes for the datasets used in the Corrientes and Neuquen sites. The spatial baselines refer to the interferograms created by considering the first images of the series as reference images and the rest as secondary images. As expected, Sentinel-1 spatial baselines tend to be stable since the mission has a narrow orbital tube, which is suitable for instance for Differential SAR Interferometry [49]. On the other hand, SAOCOM-1 does not have control over the orbital tube, and hence the perpendicular spatial baseline shows much more variability. While having larger perpendicular baselines may be better for topography or forest canopy mapping, this is a factor that is not equal between both SAOCOM-1 and Sentinel-1, and will be considered when assessing the temporal decorrelation. As indicated previously, InSAR coherence needs to be estimated from data, see Equation (5), by using a speckle filter. In this work, we will use a 17 \(\times\) 17-pixel multi-look filter. The use of these dimensions is justified to limit the coherence estimation bias at low coherences, especially for C-band data. Additionally, the number of Equivalent Number of Looks (ENL) has been computed on different homogeneous areas, mainly forest sites. For Single Look Complex images, SAOCOM-1 data presents an average of \(ENL=2.24\), whereas Sentinel-1 presents an average of \(ENL=3.32\). These values can be explained as forested areas in the analyzed regions are not totally homogeneous.