A Digital Image Method for Analysis of Soil Pores

Measurements of porosity and pore size distribution provide important data on the physical properties of soils. This paper presents a digital image method for the analysis of soil pores. In the analysis of soil thin sections, the image threshold separating pore space from the surrounding solid, as well as the capillary pore size threshold separating air pores and capillary pores, was obtained by analysis of the thin sections of calibration samples where values of total porosity and capillary porosity were pre-determined by traditional soil physics methods (IM). The total porosity and capillary porosity, as well as percentages of pores of a particular size, of all samples of similar soil type can then be determined by these image thresholds in thin section image analysis. The maximum capillary pore size in soils can also be determined. Because the thresholds for the total porosity and capillary porosity are determined based on physical soil characteristics in this method, the error associated with existing methods (caused by subjective threshold estimates) was overcome. Small variations in results proved that this method has good accuracy and is acceptable. Any personal computer and flatbed scanner, along with any commercial remote sensing software (ENVI, PCI, ERDAS, etc.) and Geographic Information System software (ArcGIS, ArcView, SuperMap, etc.) are sufficient to complete the method. In addition, the method can also be used for analysis of pore shapes and arrangements.