Dye Tracing and Image Analysis for Quantifying Water Infiltration into Frozen Soils

Abstract

New methods are needed to quantify infiltration into frozen soil, an important issue for agricultural management in northern latitude regions. A dye tracer method that uses digital image analysis and fluorescence imaging is presented for visualizing and quantifying flow pathways in frozen soils. The method was applied to three soil columns in a cold chamber. Two of them were packed with sand and the third was an undisturbed soil monolith. After complete freezing to −5°C, the columns were irrigated at above‐freezing temperatures before they were vertically and horizontally sectioned to analyze pictures of the stained profiles and cross‐sections. Image analysis was done for either the visual or fluorescent spectral ranges of three different tracers. Small samples were taken from the profiles to calibrate the dye tracer concentration. This was achieved by means of second‐order polynomials of the R , G , and B values from the corresponding areas of the pictures with coefficients of determination of 0.92 to 0.99. This method results in concentration maps with a high spatial resolution reflecting the infiltration pattern. The experiment confirmed current hypotheses of infiltration mechanisms into frozen soil in that the infiltrability of the initially wet sand was restricted, whereas in the undisturbed soil monolith, the dye solution infiltrated through preferential pathways which were air filled at the time of freezing.