Measurements are presented that can be used to test theories that predict acoustical characteristics of outdoor surfaces. The specific acoustic impedances of forest soils, grass‐covered surfaces, and bare sandy soils have been measuredinsituusing an inclined track method. Best‐fit effective flow resistivities have also been deduced from the acoustical measurements. For grass‐covered and forest soils the soil stratification has been determined and measurements have been carried out to determine the acoustical significance of the different layers. Physical soil parameters have also been measured, including porosity; water, air, and solid matter content; soil texture; and directly measured air flow resistivity. It is found possible to classify investigated soils as acoustically soft, moderate, or hard, both according to the behavior of the reflection coefficient and impedance with frequency and to the corresponding best‐fit values of effective flow resistivities. Bare sandy soils are found to be acoustically hard surfaces. Forest soils may be classified, in most cases, as acoustically soft. For grass‐covered and forest soils, the real part of the acoustic impedance is relatively independent of frequency, while the imaginary part strongly decreases with frequency. Litter layers do not influence acoustical soil properties. The important role for humus and root layers that has been suggested is not always confirmed by air flow resistivity measurements reported in this paper. A classification of soils based on measured air flow resistivity is possible but is only roughly in agreement with the acoustical classification. Predictions of acoustic impedances, based on the equations of Delany and Bazley [Appl. Acoust.3, 106–116 (1970)] and on directly measured flow resistivities, are not always satisfactory. The predictions are particularly poor for forest floors.