SUOMEN GEODEETTISEN LAITOKSEN JULKAISUJA VERÖFFENTLICHUNGEN DES FINNISCHEN GEODÄTISCHEN INSTITUTES PUBLICATIONS OF THE FINNISH GEODETIC INSTITUTE ════════════════════ N:o 146 ═════════════════════ EMPIRICAL STUDIES ON MULTIANGULAR, HYPERSPECTRAL, AND POLARIMETRIC REFLECTANCE OF NATURAL SURFACES

The reflectance factor is a quantity describing the efficiency of a surface to reflect light and affecting the observed brightness of reflected light. It is a complex property that varies with the view and illumination geometries as well as the wavelength and polarization of the light. The reflectance factor response is a peculiar property of each target surface. In optical remote sensing, the observed reflectance properties of natural surfaces are used directly for, e.g., classifying targets. Also, it is possible to extract target physical properties from observations, but generally this requires an understanding and modeling of the reflectance properties of the target. The most direct way to expand our understanding of the reflectance properties of natural surfaces is through empirical measurements. This thesis presents three original measurement setups for obtaining the reflectance properties of natural surfaces and some of the results acquired using them. The first instrument is the Finnish Geodetic Institute Field Goniospectrometer (FIGIFIGO); an instrument for measuring the view angle dependency of polarized hyperspectral reflectance factor on small targets. The second instrument is an unmanned aerial vehicle (UAV) setup with a consumer camera used for taking measurements. The procedure allows 2D-mapping of the reflectance factor view angle dependency over larger areas. The third instrument is a virtual hyperspectral LiDAR, i.e. a setup for acquiring laser scanner point clouds with 3D-referenced reflectance spectra ([x,y,z,R(λ)]). During the research period 2005–2011, the FIGIFIGO was used to measure the angular reflectance properties of nearly 400 remote sensing targets, making the acquired reflectance library one of the largest of its kind in the world. These data have been exploited in a number of studies, including studies dealing with the vicarious calibration of airborne remote sensing sensors and satellite imagery and the development and characterization of reflectance reference targets for airborne remote sensing sensors, and the reflectance measurements have been published as a means of increasing the general understanding of the scattering of selected targets. The two latter instrument prototypes demonstrate emerging technologies that are being used in a novel way in remote sensing. Both measurement concepts have shown promising results, indicating that, in some cases, it can be beneficial to use such a methodology in place of the traditional remote sensing methods. Thus, the author believes that such measurement concepts will be used more widely in the near future.