## 2 Materials and Methods
### Data Collection and Analysis
#### 2.2.2 Satellite Data  
In this paper, surface reflectance images of Landsat-7, Landsat-8 and Sentinel-2 over the Mediterranean region were used. The Landsat-7 satellite carries the Enhanced Thematic Mapper Plus (ETM+) sensor. It was launched on 15 April 1999, and provided scientific information for 23 years until 6 April 2022 [47]. The USGS Landsat-7 surface reflectance (SR) product was used (Landsat-7 level 2 collection 2); this dataset contains atmospherically corrected and orthorectified surface reflectance [46; 48]. The Landsat-7 SR dataset was developed with the Landsat Ecosystem Disturbance Adaptive Processing System (LEDAPS) algorithm (version 3.4.0) [49]. The Landsat-7 SR data used in this study were archived in GEE as the \"LANDSAT/LE07/C02/T1_L2\" dataset. The Landsat-8 satellite carries two sensors on board, the Operational Land Imager (OLI) and the Thermal Infrared Sensor (TIRS), and it was launched on 11 February 2013 [50; 51]. The USGS Landsat-8 SR dataset (Landsat-8 level 2 collection 2) which contains atmospherically corrected, orthorectified surface reflectance data was used [46]. Landsat-8 SR products are developed with the Land Surface Reflectance Code (LaSRC) [40; 48; 52; 53]. The Landsat-8 SR data used in this study were archived in GEE as the \"LANDSAT/LC08/C02/T1_L2\" dataset. Both Landsat-7 and Landsat-8 have a revisit cycle of 16 days. The Sentinel-2 mission is a constellation of two polar-orbiting satellites that carries Multispectral Instruments (MSI): Sentinel-2A launched on 24 June 2015; Sentinel-2B launched on 7 March 2017 [54]. The combined Sentinel-2 constellation revisit is 5 days. Sentinel-2 MSI surface reflectance data (Sentinel-2, level-2) are generated by the Sen2 Cor software [55; 56; 57]. Figure 1: In red the Mediterranean Basin region boundaries. The study area spanning the area between 10\({}^{\circ}\)W–40\({}^{\circ}\)E and 30\({}^{\circ}\)N–45\({}^{\circ}\)N, in white. SR products were preferred to minimize differences due to atmospheric effects [58]. The Sentinel-2 SR data used in this study were archived in GEE as the \"COPERNII-CUS/S2_SR_HARMONIZED\" dataset. Despite the visually similar appearance of the data collected by the sensors, they differ in terms of the number of bands, band centre, bandwidth, and spatial resolution (Table 1). interpolation due to its ability to yield a smoother surface. To ensure a comprehensive representation of the variability within the study area, we took into careful consideration both the land cover types and the availability of images for each pairwise comparison. The final dataset of sampling points was obtained from uniformly distributed random points across each land cover type using the European Space Agency (ESA) \"World-Cover\" map at 10 m spatial resolution ([[https://esa-worldcover.org/en](https://esa-worldcover.org/en)]([https://esa-worldcover.org/en](https://esa-worldcover.org/en)) (accessed on 2 May 2023)) [61]. The ESA cover map used in this study was archived in GEE as the \"ESA/WorldCover/v200\". To meet the requirement for each pairwise comparison in the studied years, the number of observations was increased to 1500 points. This approach ensures a robust and reliable analysis of the area under investigation. The available ETM+, OLI, and MSI values between 2017 and 2021 were extracted for each of these points. The distinct orbits and swath widths of OLI/ETM+ and MSI sensors facilitate the identification of numerous instances where both satellites capture the same ground locations on the same day. For OLI and ETM+ there are no same-day instances, but instances of 1-day lag were sampled. It is reasonable to assume that there are no significant changes in land surface and atmospheric conditions between the two acquisitions on the same day or adjacent days.