*2.2. Data*

#### 2.2.1. Airborne Imaging Datasets and Their Pre-Processing

Two different airborne image datasets acquired over the Sokolov basin were used in this study. The HyMap image data was acquired in 2010 (August 27) during the HyEUROPE 2010 flight campaign using the HyMap (HyVista Corp., HyVista Corporation Pty Ltd., Baulkham Hills, NSW, Australia) airborne imaging spectrometer. The HyMap sensor records image data in 126 narrow spectral bands covering the entire spectral interval between 0.450 and 2.480 μm of the spectral range with a Full Width Half Maximum (FWHM) of 15 nm and a ground field of view of 4 m. The resulting ground pixel resolution of the image datasets was 5 m. In order to successfully pre-process the hyperspectral data, supportive calibration and validation ground campaigns were organised simultaneously with the HyMap data acquisition. At the selected homogenous targets the ground measurements were acquired by an ASD FieldSpec-3 spectroradiometer to properly calibrate as well as validate the image data and to enable: (i) atmospheric correction of the airborne hyperspectral images and (ii) retrieval of surface reflectance values for further verification. The final atmospheric correction was performed in the ATCOR-4 software package [57] using the MODTRAN 4 physical model of the atmosphere [58]. A detailed description of the HyMap data preprocessing can be found in Adar et al. [59].

The second image dataset was acquired by the Airborne Hyperspectral Scanner (AHS) in collaboration with the Spanish Aerospace Institute (INTA) as a set of day (19 July 2011) and night image data (22 July 2011). The AHS is an imaging 80-band line-scanner radiometer with 63 bands in the visible-near infrared (VNIR) and shortwave infrared (SWIR) regions, seven bands in the mid-wave infrared (MWIR) region and 10 bands in the longwave infrared (LWIR) region [60]. However, due to cloud cover in the daytime image, it was only possible to use the cloud-free night-time LWIR data. These were acquired after a dry day, on a clear night with no precipitation. The flight lines were acquired at an altitude of 2 km above ground level, resulting in a 5-m pixel size (the same pixel size as the HyMap dataset). The temperature and emissivity were derived from the sensor radiance using the approach described in detail by Notesco et al. [42].

Both datasets were geo-corrected using on-board navigation information. After that both datasets were further georeferenced to the very high spatial resolution aerial orthophotos (pixel size = 0.5 m) achieving sub-pixel positional accuracy. To avoid any spatial misalignments, both datasets were resampled to a 10-m spatial resolution using nearest-neighbour resampling.

#### 2.2.2. Ground Verification Data

Various soil/substrate samples were collected in the field in both years (2010 and 2011) and analysed with a Philips X'Pert X-ray Diffractometer (XRD) at the Czech Geological Survey to resolve their mineralogy. The X-ray powder diffraction patterns were obtained using monochromatic (CuK α) radiation and a graphite secondary monochromator. The whole-sample random patterns were collected in the angular range from 2◦ to 70◦ (2θ) with steps of 0.05◦ (2θ). Oriented clay-fraction specimens (fraction < 2 μm) were prepared by a conventional sedimentation method [61]. The oriented clay specimens were analysed after air-drying and after saturation for 10 h with ethylene–glycol vapour at 60 ◦C. Their diffraction data were acquired in the angular range of 2–50◦ (2θ) with steps of 0.05◦ (2θ). Mixed-layered minerals were identified by comparing the analysed XRD patterns of the ethylene-glycolated oriented clay fraction with the modelled XRD patterns obtained by NEWMOD code [61].
