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Compaction is a major cause of soil degradation. It affects not only the porosity of the soil, but also the soil's hydrostructural stability. Soil that is restored after temporary removal is particularly sensitive to compaction. We investigated the effects of trafficking with a heavy combine harvester on the shrinkage behaviour of a restored soil that had been gently cultivated for several years. We tested the hypothesis that compaction decreases the hydrostructural stability of restored soil by analysing simultaneously measured shrinkage and water retention curves of undisturbed soil samples. Shrinkage strongly depended on clay and organic carbon content. Taking account of this influence and normalizing the shrinkage parameters with respect to these soil properties, we found pronounced effects of trafficking on shrinkage. Ten passes with the combine harvester decreased the structural porosity by about 40% at maximum swelling and by about 30% at the shrinkage limit and increased the bulk density by 8% at maximum swelling and by 10% at the shrinkage limit, but did not significantly affect the porosity of the soil plasma. Moreover, trafficking modified shrinkage, increasing the slopes of the shrinkage curve in the basic and structural shrinkage domains by about 30% and more than 150% after 10 passes, respectively. Evidently the aggregate structure was strongly destabilized. The results indicate that the hydrostructural stability of the soil was still very sensitive to compaction by trafficking even 5 years after restoration. The analysis of shrinkage seemed well suited for the assessment of compaction effects on soil structure.

Today's aircraft noise calculation programs either use simple sound source descriptions with few input parameters or highly sophisticated models with input parameters, which are difficult to obtain. To fill the gap between these two approaches, an aircraft noise emission model based on regression of measured noise with aircraft flight parameters is presented. To find a reasonable compromise between the degree of detail and number of required flight parameters, an extensive data exploration was conducted. The most relevant parameters were incorporated in two multiple linear regression models, one for airframe and one for engine noise sources. An iterative method allowed fitting both regression models to aircraft flyover measurements. In total, aircraft noise emission models for 19 aircraft types were established, which underlines the general applicability of the modeling approach to turbofan-powered aircraft. Example comparisons between measurements and model predictions for two aircraft types revealed that the model accurately reproduces directivity and spectra for different flight configurations. In addition, it is suitable for the assessment and optimization of noise abatement procedures.

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