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In the spectrum measurement experiment, the roughness of the object surface is an essential factor that cannot be ignored. In this experiment, a group of mixed pixel samples with different mixing ratios were designed, and these samples were printed on four kinds of papers with different roughness. The spectral characteristics of mixed pixels with different roughness are quantitatively analyzed by using the measured spectral data. The linear spectral mixture model is used for spectral decomposition, and the effect of roughness on the unmixing precision of mixed pixels was studied. The surface roughness will affect the reflectivity of the mixed pixel. Specifically, the higher the roughness is, the higher the reflectivity of the sample is. This phenomenon is more noticeable when the proportion of white endmember (PWE) is large, and as the white area ratio decreases, the reflectance difference gradually decreases. When the surface roughness of the sample is less than 3.339 μm, the spectral decomposition is performed using a linear spectral mixing model in the visible light band. The average error of the unmixing is less than 0.53%, which is lower than the conventional standard spectral measurement error. In other words, when the surface roughness of the sample is controlled within a specific range, the effect of roughness on the unmixing accuracy of the mixed pixels is small, and this effect can be almost ignored. Multiple scattering within the pixels is the key to model selection and unmixing accuracy, when using the ASD FieldSpec3 spectrometer to perform spectral reflectance measurement and linear spectral unmixing experiments. If the surface roughness of the sample to be measured is less than the maximum wavelength of the spectrometer, the experimental results believe that the photon energy is mainly mirror reflection on the surface of the object and diffuse reflection. At this time, it is still a better choice to use a linear spectral mixing model to decompose the mixed pixels.

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The speci c soil components such as soil organic matter, Fe and Mn oxides exert a signi cant in uence on Cu(II) adsorption in soil. In the present study, clay fraction was separated from an alluvial acid soil, Then the selective chemical extraction method was used to remove the speci c components in the bulk soil and clay fraction. Adsorption experiments showed that the adsorption capacity of the clay fraction of Cu(II) is greater than that of the bulk soil, regardless of whether it is treated by selective chemical extraction or not. Compared with untreated soil samples, after the removal of organic matter by H 2 O 2 , K d decreased by a maximum of 82.8% for the bulk soil and 73.5% for the clay fraction. After the removal of manganese oxides by NH 2 OH•HCl, K d decreased by a maximum of 68.1% for the bulk soil and 73.2% for the clay fraction. However, after the removal of free iron oxides by dithionite-citrate-bicarbonate, K d increased by a maximum of 422% for the bulk soil and 195.5% for the clay fraction. K d increased by 4263.3% when the initial pH increased from 2 to 3.5 and, then, increased to 6. The amount of Cu(II) adsorbed did not change signi cantly. Within a range greater than 6, the increased Cu(II) adsorption may be due to the precipitation of Cu(II). When the concentration of NaNO 3 changes from 0.01 to 0.1 M, the adsorption capacity decreased by a maximum of 36%, K d decreased by a maximum of 84.3%. The presence of foreign ions decreased Cu(II) adsorption; their order of effect on Cu(II) adsorption is Na + < K + < Mg 2+ < Ca 2+ for cations and NO 3 − < SO 4 2− ≈ Cl − for anions. The adsorption of Cu(II) was an endothermic and spontaneous process under the experimental conditions.