Reflectance. The daylight directional reflectance of the white paint shall not be less than 84% and not less than 50% for yellow paint of a 15 mils (38I µm) wet film applied to a 2A Leneta Chart or equal. After drying 24 hours, measure the reflectance of the paint over the black portion of the chart using a Colorimeter and test method ASTM E1347 (replaces ASTM E97).
Reflectance. The daylight luminous reflectance of the white material shall be not less than 75% when tested according to A.S.T.M. E1347.
Reflectance. (rho) is the quantitative ratio between reflected light and the incident light on the surface of a flat material. It consists of various portions of "regular reflectance" and "diffuse reflectance".
Reflectance. The maximum reflectance per event, as measured by an OTDR, shall not exceed •40dB.
Reflectance. The reflectance image is currently derived from selected, cloud free Landsat 8 scenes. The absence of clouds is an important requirement for the selection. For London, the reflectance has been calculated for two scenes, July 17, 2013 and October 2, 2015. For Basel, two scenes April 24, 2015 and August 30, 2015 are used. For Heraklion, one scene from November 7, 2015 has been used.
Reflectance. The reflectance is derived from the Landsat 8 radiance images by using ATCOR-2 (Xxxxxxx und Xxxxxxxxx 2015). This atmospheric correction software supports the estimation of aerosols and visibility. Additionally, topographic influences are corrected for by the use of an SRTM DEM. Using these estimations and the correction coefficients provided in the scene metadata, atmospherically corrected reflectance is calculated (BOA reflectance). ATCOR uses the bands 1-7 and 9 (Cirrus) of Landsat. The thermal bands are not considered here. The panchromatic band is corrected separately. In the reflectance images, the bands are sorted after wavelength. The cirrus channel then becomes band 6. Since this band is within the atmospheric water vapour window, it is replaced by an interpolated value between band 5 and 7. The unit of the data is reflectance in %. The original spatial resolution of 30 m is kept. The atmospheric correction of the panchromatic band is carried out with the same aerosol type as the other bands of that acquisition, the mean visibility and a 15 m DEM, resulting in a reflectance image with a spatial resolution of 15 m. The accuracy of the atmospheric correction cannot be expressed in a single figure. The radiometric accuracy depends on the calibration accuracy of the sensor, the quality of geometric co-registration of the spectral bands, the accuracy of the radiative transfer code (MODTRAN 5), the correct choice of atmospheric input parameters, the terrain type (flat or rugged), and the surface cover (Xxxxxxx und Xxxxxxxxx 2015). For flat terrain the accuracy of the retrieved reflectance is between +/- 2 % and +/- 4% (Xxxxxxx und Xxxxxxxxx 2002). For rugged terrain, which is the case for the URBANFLUXES case study areas, the accuracy depends strongly on the quality and matching of the DEM (Xxxxxxx 1998). The accuracy varies with the terrain; the largest errors should be expected in areas with critical geometries, such as mountain ridges. Luckily, such extreme ridges are not present in the URBANFLUXES case study areas.
