## 4 Critical Literature Review
The inspections carried out by thermography are complemented by terrestrial techniques such as blower door tests to detect infiltration/exfiltration regions and thermal bridges. Energy audits in buildings can be carried out according to two methodologies: with active thermography, i.e., by means of an external stimulus such as an increase in the thermal gradient between the interior and exterior of the building to emphasise the contrast of thermal patterns; and with passive thermography, observing temperature changes in a normal state of the environment without any artificial stimulus [87]. Some authors proposed standardised and detailed procedures for energy inspections of buildings using UAVs [102, 103]. [PERSON] et al. (2013) applied infrared thermography (IRT) to determine energy efficiency and detect defects such as thermal bridges and heat loss in a building. They demonstrated in their research that in addition to temperature, the surface geometry to be examined is a key point for a reliable evaluation of thermal efficiency [104]. It has been demonstrated that the evaluation of the geometry of the building envelope is fundamental for quantifying values such as thermal inertia and energy losses in building facades [58]. Infrared techniques have been widely used in the literature related to the energy efficiency of buildings. [PERSON] et al. (2019) inspected a half-buried building using an infrared camera equipped on an UAV to acquire surface temperature data and complemented it with techniques carried out on land. Both cases proved to be effective in detecting thermal anomalies such as thermal bridges, air leaks, building singularities and humidity [105]. [PERSON] et al. (2018) conducted an aerial inspection to see the potential damage associated with heating, cooling and domestic hot water systems (HVAC) of a public building. They provided a simple and cost effective method to carry out timely inspections of installations confirming that early detection of defects and failures can prolong the life of this equipment [106]. [PERSON] et al. (2020) and [PERSON] et al. (2020) proposed novel methods for detecting faults in photovoltaic panels automatically during a routine inspection providing fast and efficient results [107, 108]. Increasing attention to energy consumption issues is renewing interest in thermal remote sensing applications in urban areas [109]. Thermography can be used to carry out inspections of urban installations and to analyse temperature changes in urban soil. [PERSON] et al. (2019) analysed the domestic hot water (DHW) pipeline leak detection process using remote sensing infrared images together with visible images and geographic information system (GIS) data to support the location of damaged pipes [110]. [PERSON] et al. (2019) evaluated the spatial variability of soil temperatures, according to their use through thermal imaging of the UAVs captured at high resolutions [111]. The analysis of the thermal properties of urban materials is fundamental in determining the microclimate of a city and the energy balance of buildings. Thermography applied in UAVsallows the generation of maps of surface temperature distribution and material properties and can generate urban energy balance models [112]. In particular, the analysis of roof materiality, temperature, albedo and impermeability have proven to be key parameters in the quantification of the urban heat island effect [113; 114]. [PERSON] et al. (2020) examined the micro-meteorological scale in a Lisbon neighbourhood in order to evaluate the radiation balance of roofs, facades and other urban materials and their influence on air temperature. Using an UAV, they recorded the temperatures of these elements and concluded that these were directly due to incident solar radiation. They showed that the air in the streets less exposed to the prevailing wind direction of the city reached higher temperatures than the air in the streets more exposed to the prevailing wind direction [115]. [PERSON] et al.