An examination of Time Domain Reflectometry (TDR) research, providing information on its use as a robust, reliable and economical production tool. The diverse interest and terminology within the TDR community tends to obscure commonalities and the universal physical principles underlying the terminology. The authors seek to crystallize the basic principles among the seemingly divergent specialties using TDR technology in geomaterials. TDR software and hardware are outlined and the authors compare TDR technology with other commonly-used instruments - lysimeters, Bowen ratio, neuron probes, and...