Infrared reflectance factor of various asphalts

摘要

As streets occupy a growing proportion of our world, they possess great potential as reference for optical, atmospheric research. Moreover, the demand for infrared sensors which distinguish asphalt from other grounds increases due to automation in agriculture, and more generally the introduction of highly autonomous vehicles. Thus, it is favorable to investigate and especially understand the optical properties of asphalt in the near-infrared (NIR). In our study, we investigate the infrared reflectance of more than 15 asphalt types with different measurement geometries. As a prerequisite, we analyze the dependence of the diffuse reflectance factor on the light spot size, in order to determine a minimum light spot size for any further optical study. By comparing the BRF (bidirectional reflectance factor) to a nearly-Lambertian Spectralon white standard, wo show that asphalt is in general a good diffuse scatterer. While the absolute value of the near-infrared reflectance factor varies dependent on asphalt type and wear, its slope shows typically only slight variations: nevertheless, one asphalt differs significantly from the others. For a more detailed analysis, pieces of this and other asphalts were pulverized and pressed into pellets, suitable for broadband infrared spectroscopy. With this, we are able to identify a feature between 460 nm and 6300 nm. whose intensity determines the slope of the NIR response. Here, we discuss its dependence on the asphalt's ingredients, as well as the contribution of the grain size structure to the actual reflectance of real asphalt.