Figure 2. The principle of seismic data acquisition using cellular wireless technology. The remote acquisition unit (RAU) is, in essence, a cellular telephone with a huge memory that is built to withstand harsh weather and rough treatment. The unit also has an accurate internal clock and a precise GPS receiver. An RAU connects directly to a geophone string. The geophone output signal is digitized by the RAU and then is downloaded via radio links to a central data unit, or it is retrieved by a visiting technician, who downloads the data at the geophone station, or the RAU is transported to a data-download station and then returned to the geophone station after emptying its data.