# A New Methodology for Estimating Surface Albedo in Heterogeneous Areas from Satellite Imagery
## 1 Introduction  
The energy transition towards networks based on renewable energies is one of the main measures for climate change mitigation. This transition is regulated by political and economic measures being established worldwide: from national regulations such as the Royal Decree-Law 244/2019 in Spain [1], which rules self-consumption and promotes renewable energies; to international accords such as the Paris Agreement [2]. The final objective of the latter is to reduce the concentration of greenhouse gases through different actions, such as the promotion of renewable energy resources, like the Sun. Currently, emphasis is given to global action plans such as the 2030 Agenda for Sustainable Development [3], whose aim is to promote the Sustainable Development Goal (SDG) number 7, of \"Affordable, Reliable, Sustainable and Modern Energy for all\", among 16 other goals. The generation of affordable, reliable, sustainable, and modern energy implies the use of low-carbon energy resources, among which renewable and nuclear energy can be found. In the case of renewable energies, the use of unlimited natural resources, such as wind and solar radiation, reinforces their contribution to sustainability. Thus, the implementation of improved energy technologies towards reaching SDG 7 is boosted by the technological advances for the capture of more forms of natural resources. Among those mentioned (wind and solar radiation), the latter presents more opportunities for the improvement of its use due to its higher flexibility [4]. Global solar radiation is divided in three components [5]: direct, diffuse, and reflected radiations. The most known and used for energy applications are direct and diffuse radiation. The latter is being increasingly valued, especially in geographic areas where direct solar radiation is not abundant. An example is the region of Galicia, NW Spain, where companies are Spanish leaders in the generation of energy from diffuse solar radiation [6]. Reflected radiation is starting to be used through the installation of bifacial solar panels, although the quantification of reflected solar radiation has not been deeply studied yet [7; 8; 9]. The computation of reflected solar radiation is based on the concept of albedo, as a measure of the index of radiation that an object reflects from the total incoming radiation. For this reason, the study of the albedo is essential for the selection of the optimal photovoltaic material in bifacial panels [7], the ideal ground cover material, and the angle of inclination of the panels since the influence of albedo on solar irradiance increases with the inclination of the panels [10]. Reflected solar energy is not only used at the ground level, as it can also be used in aerial vehicles, where solar radiation reflected by the clouds increases the value of albedo due to the close position of the aerial vehicles to the clouds [11]. In addition to the energy applications, albedo is an essential parameter for different studies, such as Urban Heat Islands (UHI) [12], reduction of which is also required in the energy transition towards the reduction of the consumption of energy for air conditioning [13]. The UHI effect can be reduced thanks to the increase in the value of the surface albedo, also improving air quality within the urban area and the health of the city inhabitants, as well as reducing ambient [14] and air temperature [15]. During the last decade, several preventive measures have been implemented to reduce the UHI effect based on the concept of albedo [16; 17]. Some of these measures are changes in the pavement materials for roads [18], changes in the material of the building envelopes [19], use of vegetation and green materials for roofs [20; 21; 22], and painting roofs and streets in white colour [23; 24]. The objective of these measures is to increase the albedo and reflectivity of the surfaces in order to reduce absorptivity, and consequently, heat storage.