2.1.3. Homogeneous Sites

Three homogeneous sites were selected for this study. First, we studied the impact of the solar zenith angle (SZA) variation through the year over two homogeneous sites. The first site is located on a homogeneous area of dense tropical forest in the Tambopata region of the Peruvian Amazon (12.818S, 69.281W, HLS tile 19LDI) where an albedometer is retrieving continuous measurements [15]. In this work, we have not included the albedo validation of this site, where Franch [14] reported an error of 0.01. This area is located in the southwest Amazon moist forest ecoregion of dense forests with a canopy height between 30 to 50 m high (https://www.worldwildlife.org/ecoregions/nt0173). The second site is located on a homogeneous desert area in Yuma, Arizona (32.499N, 114.498W, HLS tile 11SQS). This area is a lower-elevation section of the Sonoran desert in the southwestern United States and northwest of Mexico. We also analyzed the impact of the view zenith angle (VZA) variation. Because in the tropics the Landsat scan direction is closely aligned with the solar principal plane and the angular effects can be as strong as 20% in reflectance [16], we selected a site located close to the equator on the Brazilian Amazon basin (2.144S, 58.999W, HLS tile 21MTT). This area is located in the Uatuma-Trombetas moist forests ecoregion (Figure 1). The forests are characterized by a dense vegetation with a high number of small-diameter (less than 200 mm) to medium-diameter (200 to 600 mm) stems and a canopy height varying from 20 to 30 m, with emergen<sup>t</sup> trees to 40 m (https://www.worldwildlife.org/ecoregions/nt0173).

**Figure 1.** Harmonized Landsat/Sentinel-2 (HLS) image RGB composite on August 21th of 2016 in the Brazilian Amazon area. The seven dots next to the river show the location and size of the averaged area to analyze the transect covering different VZA (see Section 2.2.3).
