Geoscience Reference
In-Depth Information
25
Assessing Spatial and Temporal
Soil Water Content
Variation with GPR
Bernd Lennartz, Britta Schmalz, Derk Wachsmuth,
and Heiner Stoffregen
ContentS
25.1 Introduction ......................................................................................................................... 323
25.2 Material and Methods ......................................................................................................... 324
25.2.1 GPR Technique...................................................................................................... 324
25.2.1.1 Migration of Radargrams ...................................................................... 325
25.2.1.2 Normalized Maximum Reflection Amplitude Analysis (NMRA)........ 325
25.2.2 Experimental Setup ............................................................................................... 325
25.2.2.1 Lysimeter Stand ..................................................................................... 326
25.2.2.2 Large Physical Sand Tank ..................................................................... 326
25.2.3 Soil Water Content Profiles ................................................................................... 327
25.3 Results ................................................................................................................................. 327
25.3.1 Water Front Propagation........................................................................................ 327
25.3.2 Seasonal Soil Water Content Changes .................................................................. 328
25.3.3 Spatial Soil Water Content Variations................................................................... 330
25.3.3.1 Dye Experiment..................................................................................... 330
25.3.3.2 Maximum Reflection Amplitude........................................................... 330
25.3.3.3 Simulated Soil Water Content Profiles .................................................. 332
25.4 Conclusions ......................................................................................................................... 333
References ...................................................................................................................................... 334
25.1 IntRodUCtIon
The soil water content is an important variable in soil physics and agricultural production. At small
scales, TDR (time domain reflectometry) probes can measure the water content and especially
changes of water content with very high accuracy (Jacobsen and Schjønning, 1993; Nissen et al.,
1999; Roth et al., 1990). But there is still a lack of methods suitable for larger areas and measure-
ments of heterogeneity of soil water content. Using TDR, a high number of probes have to be
installed, which leads to considerable cost and work. To determine small-scale heterogeneities, the
TDR also has the disadvantage of disturbing the area by installing probes. For these cases, ground-
penetrating radar (GPR) is an alternative measuring device. With respect to water content variabil-
ity analysis, two different procedures based on GPR measurements can be distinguished.
Various authors use tomographic or multi-offset radar methods to determine the velocity
of an electromagnetic wave through the subsurface. The dielectric constant can be calculated
323
