VNIR hyperspectral imaging

Before recording hyperspectral images, soil cores were cut lengthwise, from bottom to top, into two equal halves and then dried at room temperature. For imaging, samples were illuminated with two 150-W halogen lamps. Hyperspectral images were recorded using a Hyspex VNIR-1800 camera (Norsk elektro optikk, Norway) after automatic dark background correction. The sensor was equipped with a 30-cm lens, giving a final field of view of approximately 9 cm for the 1800 detectors (53 × 53 µm2 per pixel). For each pixel, light reflectance intensity was measured for 186 bands in the region 400-990 nm (spectral resolution of 3.17 nm per band).
To account for potential unevenness in illumination and spectral response at different horizontal locations in the core, the spectral intensity (I) of the raw images of the soil cores were normalised to the defined reflectance (R) of calibration target for each wavelength (λ) and pixel (x):