Spatial Observations and Interpolation

Spatial patterns of hydrological processes are a rich source of variability which in some instances is quite obvious to the observer, as in the case of spatial patterns of a seasonal snow cover; and in other instances is hidden from the eye and very difficult to identify by even the most sophisticated measurement techniques, as is the case with patterns of subsurface preferential flow paths. Part of the richness comes from the diversity in the spatial arrangement of hydrologically relevant variables. It is important to understand this arrangement to design measurement strategies adequately, to interpret the data correctly, to build and/or apply a model of catchment dynamics, and ultimately to use these data in predictions of the hydrological behaviour of catchments. There is a wide spectrum of ‘‘measurement techniques’’ (in a general sense) available for exploring these complex patterns, ranging from traditional stream gauging to remote sensing. Ideally, a measurement technique should be designed to take into account the type of natural variability one would expect to encounter. Depending on the nature of the hydrological variability, certain measurement techniques will be more suitable than others. Measurement techniques that are potentially capable of capturing hydrological patterns differ in terms of their scale and their accuracy. The scale relates to the area and the time that the measurements represent. Point measurements are representative over a small area or volume, such as measurements using Time Domain Reflectometry (TDR), raingauge or infiltrometer measurements. Other measurements average over a larger area or volume, such as runoff data (which averages over a catchment), or remote sensing images where each pixel is representative of a certain area. Many point measurements make up a measured pattern. In fact, most observations of patterns in this book are essentially multiple point measurements. Similarly, in the time domain, measurements can be representative over a very short interval in time (snap shots) such as a single