Angle-Resolved Measurements and Modelling of Diffuse Reflectance and Luminescence

Abstract

This thesis covers angle-resolved spectrophotometric measurements and modelling of diffuse reflectance and luminescence. Most of the work related to diffuse reflectance is performed in view of providing SI-traceability to radiative transfer codes used in Earth observation. The angle-resolved measurements of luminescent surfaces are used to study goniometrical properties of reflectance and luminescence of reference materials used in appearance measurements. Radiative transfer models that simulate the transmission of light through atmosphere and vegetation are used to interpret the measurements of on-orbit sensors. One way of validating these models is using artificial targets that are characterised by SI-traceable measurements of reflectance and shape. The bidirectional reflectance factors of many roughened anodised and non-anodised surfaces were measured, and used to test the suitability of micro-facet scattering functions to present the scattering properties of such surfaces. Based on the results, a grooved and an identical flat target were constructed and characterised for bidirectional reflectance factors. The bidirectional reflectance factors of the flat target were used to parametrise the scattering functions for rough surfaces. The grooved target was measured for its coordinates describing shape, which were used to construct a structural model of the grooved target. The structural model, with its optical properties defined by the parametrised scattering functions, was used to simulate the bidirectional reflectance factors of the grooved target with the tested radiative transfer model. The measured and modelled bidirectional reflectance factors agreed within corresponding expanded uncertainties for most of the measured geometries, but not all. Non-Lambertian emission of luminescence from solid luminescent materials has been established, however, instrumentation for angle-resolved measurements of luminescence have not been readily available. The MIKES-Aalto goniofluorometer was extensively characterised to improve the accuracy of bispectral luminescent radiance factor measurements. In addition, a method for goniometrical measurements of quantum efficiency and quantum yield was validated against interlaboratory measurements. The improved measurement capability was used to describe absorbance dependent reflectance angular profiles in solid amorphous luminescent materials. In addition, a reference material for luminescence measurements was proposed and characterised. The new material showed more Lambertian angular luminescence emission and reflectance profiles than the conventionally used materials.