A number of other methods exist for estimating soil water content such as nuclear magnetic resonance (NMR), which can detect nuclear species that have a magnetic moment or spin. As hydrogen has a nuclear spin of 1/2 the NMR technique can be used to estimate water content in soils. This is a fast and non-destructive method with high accuracy in uniform samples. However the method is costly, not suitable for field use and highly dependent upon sample calibration and is therefore not used in soil studies or in applications related to roads (Veenstra et al., 2005).
Near infrared reflectance spectroscopy (NIRS), seismic methods and thermal properties are all methods that can be used for estimation of soil water content. Although they are in many respects good and accurate methods, they all have some drawbacks making them non-suitable as routine methods to be used in the pavement environment. In the first two methods the calibration process is complex or difficult to perform due to the influence of other factors, and assessing the thermal properties of the soil is costly and needs a long measurement time relative to other methods (Veenstra et al., 2005).
