Laboratory-based spectral data acquisition of roof materials

Roof characteristics such as material type and their properties information are essential to integrating urban agriculture (UA), rainwater harvesting systems (RWHS), and energy systems on roofs. Roof materials can be identified from their spectral signatures. However, this identification requires a priori knowledge of the materials’ spectral characteristics. The main perspective of this work is the future use of spectral data for roof classification. A common practice in mapping materials is the use of spectral libraries. In this regard, this work describes a novel framework for laboratory-based spectral data acquisition. The reflectance data of common, recently introduced (plastics and metals), and representative roof materials from the Mediterranean region were obtained. Data acquisition was conducted in a laboratory under controlled conditions using a high-spatial-resolution (HSR) sensor, which is usually used for airborne surveys. Large variations in the spectral reflectance data were observed due to the composition of the roof material. Flat spectral signatures were found for fibre cement, concrete, gravels and some metals, especially from the near-infrared (NIR) spectral region. Colour and surface finish greatly influence the visible (VIS) spectral range. It was confirmed that the view angle did not modify the spectral shapes. A collection of 39 spectral data of roof materials (ceramics, concrete, fibre cement, metals, plastics, paints, stone, and wood) were compiled into a spectral library that is available online.屋顶材料类型及其属性等屋顶特征，是在屋顶集成都市农业（urban agriculture）、雨水收集系统（rainwater harvesting systems, RWHS）与能源系统的核心前提。可通过光谱特征（spectral signatures）识别屋顶材料，但该识别流程需具备材料光谱特性的先验知识（a priori knowledge）。本研究的核心研究视角在于未来利用光谱数据开展屋顶分类任务。当前材料测绘领域的通用实践是借助光谱库（spectral libraries），据此，本研究提出了一套全新的基于实验室的光谱数据采集（laboratory-based spectral data acquisition）框架。研究采集了地中海地区常见、新近投入使用的（塑料与金属类）典型屋顶材料的反射光谱数据。数据采集于实验室受控环境中完成，使用的是通常用于航空测量（airborne surveys）的高空间分辨率（high-spatial-resolution, HSR）传感器。观测结果显示，屋顶材料的组分差异会导致光谱反射率（spectral reflectance）数据存在显著波动。纤维水泥、混凝土、砾石及部分金属的光谱特征曲线较为平缓，尤其在近红外（near-infrared, NIR）光谱波段区间。颜色与表面光洁度对可见光（visible, VIS）光谱范围的影响极为显著。本研究证实，观测角度（view angle）不会改变光谱形状。本研究共收集39组屋顶材料光谱数据，涵盖陶瓷、混凝土、纤维水泥、金属、塑料、涂料、石材与木材，并将其整合为可在线获取的光谱库（spectral library）。