## 2 UAV Platform Evolution
### Multispectral Sensors  
Multispectral sensors extend optical imaging into non-visible wavelengths, such as near-infrared, capturing unique data for vegetation health, water stress, biomass, and material characteristics unavailable from standard RGB cameras [75]. As UHI mitigation strategies often rely on expanding urban greenery, multispectral UAV data help monitor these heat-regulating plants' growth, canopy size, and condition over time [76]. Near-infrared bands also enhance the differentiation of urban ground surfaces and materials relevant to urban energy modeling. While the resolution is coarser than for visible cameras, multispectral UAV-based mapping provides a rapid wide-area assessment, not requiring extensive processing. Figure 5 compares the different multispectral sensors commonly used in the market, resolution, costs, and compatibility with different UAV platforms. Multispectral UAVs present immense opportunities for assessing and addressing climate vulnerabilities in cities. One of the main applications of UAVs with multispectral sensors in climate change research is monitoring urban vegetation health and its dynamics in cities. Multispectral sensors can capture the data related to chlorophyll content, leaf area index, and vegetation stress, providing insights into the health and vitality of urban vegetation [77; 78]. This information is crucial for assessing the impact of climate change on urban ecosystems, identifying the areas of vulnerability, and developing strategies for urban greening and adaptation. Additionally, high-resolution thermal mapping coupled with meteorological data can significantly assist in modeling urban heat dynamics [79]. Tracking the vegetation NIR reflectance reveals drought-stressed areas needing water conservation and additional-shade trees [80]. Combined thermal and visible imagery facilitates quantifying the cooling provided by green spaces [81]. UAV spectral data also enable the construction of 3D urban models distinguishing rooftop materials to target solar panel deployment [82]. Moreover, repeat multispectral surveys allow the monitoring of the efficacy of resilience strategies, such as cool roofs and stormwater-retention landscaping. Another application of multispectral sensors in climate change research is the analysis of land-cover changes in cities. By capturing the data in different spectral bands, these sensors can differentiate between land-cover types, such as impervious surfaces, vegetation, and water bodies [77; 83]. This information helps monitor urban expansion, changes in land  
Figure 4: Comparison between common commercial UAV platforms and their high-resolution sensor capabilities [70; 71; 72; 73; 74]. use patterns, and the loss of green spaces. These are all critical factors for understanding the urban heat island effect and its contribution to climate change. In addition to vegetation and land-cover analyses, multispectral sensors on UAVs can also contribute to assessing urban heat island effects. By capturing thermal infrared data, these sensors can measure surface temperatures and identify areas of excessive heat in urban environments [84]. This information is crucial for understanding the spatial distribution of heat in cities, identifying heat mitigation strategies, and assessing the effectiveness of urban cooling interventions. Hyperspectral Sensors enable UAVs to capture hundreds of contiguous spectral bands across a wide range of wavelengths [90]. Typical hyperspectral sensors cover wavelengths from 400-2500 nm with a resolution below 10 nm [91]. Thus, they can capture a wide range of light spectrum bands to generate rich datasets that detect the features invisible to sensors with limited bandwidths. The large number of narrow spectral bands enables the identification of specific conditions and characteristics. Sensors with hundreds of bands, especially visible and infrared wavelengths, are increasingly utilized in diverse applications.