Abstract
The ABC of the Delany and Bazley [1970] impedance model are given by A = 206.95, B = 9.88, and C = 13.82. Taraldsen [2005] has shown that these coefficients determine a relation between porosity, tortuosity, and flow resistivity such that the law of Darcy [Paris, 1856] gives an impedance model which is very similar to the Delany-Bazley model. This will be explained in more detail, and the models are compared with in situ measurements at 44 sites representing outdoor ground surfaces.