C. What is a reasonable explanation for the impermeable layer located at the surface of the Urban model?

Explanation:

Advancements and improvements in remote sensing have enabled the characterization and quantification of impermeable surfaces using techniques such as soil measurement and remote sensing data (Weng, 2012). The latter provide a standardized data collection procedure and enables the analysis of integrated data within a geographic information system (Mwita et al., 2012). This facilitates the generation of information useful to the planning and management of urban spaces; remote sensing data can thus be used to mitigate the floods which are the consequences of unplanned urban processes.

Several approaches to distinguish surface coverage using remote sensing techniques and multispectral data have been suggested (e.g.,Ridd, 1995). Among the various remote sensing techniques, radiometric indices are commonly generated and applied in environmental studies and analyses (Xu, 2010) or in related studies (He et al., 2010; Liu et al., 2013; Zhang and Weng, 2016).

The use of radiometric indices is associated with an increased focus on certain characteristic parameters that they measure; this has been observed often in the wider literature. Yuan and Bauer (2007) indicated heated urban areas by identifying impermeable surface areas using the Normalized Difference Vegetation Index (NDVI). Zhang et al. (2009) characterized the soil surface temperature in relation to impermeable surface area using the NDVI and the Normalized Difference Built‐up Index (NDBI). NDVI is currently the most widespread and best‐known radiometric index that is combined with others to generate new data.

baltic states. baltic states, northeastern region of europe containing the countries of estonia, latvia, and lithuania, on the eastern shores of the baltic sea.

explanation:

d is the logical answer but im not a 100% sure