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György Pillinger, Ahmed Elawad Eltayeb Ahmed, and Peter Kiss
During our previous tests, we determined the change in colour due to moisture content in the case of sandy soil of three colours that can be easily distinguished with the naked eye. To characterize the colour, we used the average of the 600 and 700 nm range of the reflectance curve, because in this range the curves are more linear and the points are better separated, i.e. their resolution is better. Also, this wavelength range corresponds to yellow and red colours, which are better absorbed by water molecules, compared to the 400-600 nm range, which includes violet, blue, green and yellow colours. We found that the parameters characteristic of the colour of the examined sandy soils react more sensitively to the influence of soil moisture up to a moisture content of ~4-5%. The created function used the coordinates of this breaking point to determine the moisture content based on reflectance. In our current article, we continue the further processing of the measurement results, as well as carry out new measurements to clarify the functional relationships. We examine the effect of soil porosity and grain density on the reflectance value. This means that in the future, reflectance is given as a function of saturation. The results predict that reflectance is more highly correlated with saturation than with moisture content alone. Another goal is to determine the effect of the initial colour of the sandy soil on the moisture content. As a reference point, we use a characteristic of the reflectance curve for 0% moisture content. We are looking for an answer, how the water content of wet soil can be determined based on the data of dry soil and the reflectance of wet soil.
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