## 2 UAV Platform Evolution
### UAV Sensors  
Recent advances in sensor miniaturization, onboard processing, and UAV platforms have enabled specialized airborne data capture tailored to the multi-dimensional information needs of climate change assessments in urban environments. UAVs at present carry diverse instrument payloads to map, measure, and monitor the complex factors influencing the resilience, greenhouse gas emissions, adaptation efficacy, and sustainability across the built landscape. This section provides an overview of key UAV sensor types and their importance for climate research.  
High-resolution visible-spectrum cameras have become ubiquitous payloads on UAVs, providing highly detailed aerial images for mapping urban morphology and topography. Miniaturized cameras using CMOS sensors can capture still images or videos at resolutions down to centimeters per pixel from low UAV altitudes [32]. This facilitates precision 3D modeling and digital surface generation to analyze urban form factors correlated with climate impacts, such as heat retention. For example, [PERSON] et al. [68] used UAV-derived orthomosaics at a 2 cm resolution to correlate the urban geometry and heat island intensity by tracking land-surface temperature variations in the urban canyon. High-frequency UAV mapping further enables monitoring incremental changes in the built environment, urban green infrastructure, land use, and urban form relevant to design and evaluate the adaptation strategies.  
Many leading commercial UAV platforms offer high-resolution visual-band camera options tailored to remote sensing and mapping applications. DJI is considered one of the most common and popular UAV platforms that dominates the commercial market of UAVs due to its technical capabilities and diversity. For example, The DJI Phantom 4 Pro has 1-inch CMOS sensors capturing 20-megapixel still images, making them suitable for sub-decimeter GSD mapping from low altitudes [46]. Larger models, including the DJI Inspire 2, leverage Micro Four Thirds cameras to provide an even higher resolution and image quality. Some manufacturers offer modular payloads, such as AgEagle's S.O.D.A. camera line, spanning small to large formats to customize resolution needs [69]. While most UAV cameras use nadir perspectives, adding oblique capabilities provides more immersive urban structural data. Figure 4 compares the most common commercial UAVs, including the sensor's specification, weight, cost, and operation platform. When selecting UAV visible cameras for built environment assessments, the key factors include the intended mapping resolution, area coverage needs, available payload capacity, and processing requirements. Larger sensors typically have a higher resolution but are heavier. Smaller drones may require lower-resolution cameras to stay within the payload limits. The photogrammetric processing time also increases exponentially with higher-resolution imagery. Therefore, the balancing resolution, payload, and area coverage are essential for efficient mapping. Radiometric processing for reflectance data adds a further complexity. Overall, turnkey fixed-camera UAVs offer simplicity, while customizable gimbal and swappable payload options provide greater flexibility to tailor visual data capture to the research needs.