Radiometry of wet surfaces

When an object is wet, in general, as can be observed every day, it becomes darker and more translucent. However, these are only qualitative observations. To try and investigate the optical effects underlying these changes in appearance, and if possible to model, quantify and predict them, a workshop has been organized by the GRD Appamat in June 2021. The presentations in this workshop showed that, actually, the light scattering mechanisms affected by the presence of water depend a lot on the material structure. The optical response is not the same for a moistened porous or powdery material, or for an impermeable diffusing medium covered with a film of water. Moreover, if appearance is related to the human vision, therefore to the visible spectrum of light, the problem can be extended to a wider spectral range, in particular for satellite imaging applications that use the infrared spectral domain and for which the absorption bands of water are important to consider. The cross-view of researchers from these various disciplines and approaches seemed particularly stimulating to us and made us want to share its temporary conclusions through this book.