Pedotransfer functions for extended hydraulic models using high resolution soil hydraulic measurements

对土壤-植物-大气系统中水分输送的适当了解对于许多有关环境和农业问题的主题起着重要作用。为了用理查兹方程模拟水的输运，必须知道土壤的水力函数，即保水性和导水性函数。这些函数通常是通过详细的测量以及随后对数据进行适当的模型拟合得出的。如果没有这样的数据并且无法获取，则通常使用Pedotransfer函数（PTF）。这些PTF通过回归方法从通常可用的基本土壤特性（质地，有机碳含量或体积密度）中获得水力函数参数。这对于大尺度环境过程的分布式建模尤其重要，例如集水区尺度的水文建模或气象模型中土壤表面湿度的建模。在过去的几十年里，许多PTF都是为此目的而衍生的。然而，这种PTF的比较表明，一般PTF对当地应用并不精确，因此需要对当地和区域应用进行特殊校准。在我们的建议(i)中，我们假设迄今为止发展的PTF忽略了水力特性的基本特征，如薄膜中的水电导率，从而导致估计参数的系统误差。此外，（ii）这些PTF是基于有限分辨率和湿度范围的数据。由于现代的测量技术，存在大量的高分辨率的水力数据在一个扩大的湿度范围。基于这些数据，开发了新的扩展和一致的水力模型。该项目的目的是将新模型与新数据结合起来，得出新的改进PTF。与经典PTF的比较将显示新开发的PTF是否以及在多大程度上能更好地估计土壤水力特性。

An appropriate knowledge of water transport in the soil-plant atmosphere system plays a major role for many topics regarding environmental and agricultural questions. For modeling water transport with the Richards equation, the soil hydraulic functions, i.e. the water retention and hydraulic conductivity function must be known. These functions are usually derived by elaborate measurements with subsequent fitting of appropriate models to the data. Pedotransfer functions (PTF) are often used if such data are not available and cannot be taken. These PTF derive by means of regression approaches parameters of the hydraulic functions from basic soil properties (texture, organic carbon content or bulk density), which are often available. This is especially important for distributed modeling of environmental processes on large scales, like hydrological modeling at the catchment scale or modeling of the soil surface moisture in meteorological models. In the past decades, many PTF have been derived for such purposes. Yet, comparison of such PTF showed that general PTF are not precise for local applications and therefore a special calibration for local and regional applications was required. In our proposal (i) we hypothesize that the hitherto developed PTF neglect essential features of hydraulic properties, like water conductivity in films, and thus lead to systematic errors in the estimated parameters. Furthermore, (ii) these PTF are based on data with limited resolution and moisture range. Due to modern measurement techniques, there exists a multitude of highly resolved hydraulic data in an extended moisture range. New extended and consistent hydraulic models have been developed based on these data. The aim of the project is to combine the new models with the new data to derive new improved PTF. A comparison with classic PTF will show if, and how much, the newly developed PTF lead to better estimates of soil hydraulic properties.