The Geophysical Survey Systems Inc., Subsurface Interface Radar System SIR-3000 (SIR-3000) instrument utilizes impulse radar technology to obtain a continuous, high-resolution profile of the subsurface.  The radar signal transmitted into the subsurface is produced by electrically discharging a pulse of electromagnetic energy from a special antenna.  The transmitted pulse travels through the subsurface until it reaches a soil interface or an embedded object.  Then, depending on the electrical characteristics of the interface or object, a portion of the transmitted pulse is reflected back to the surface where it is picked up by the receiver section of the antenna.  The received signal is processed and a real-time replica of the information is displayed.  Depth of subsurface penetration is directly dependent upon the conductivity of the soil. 

Several types of antennas are available for use with the SIR Ground Penetrating Radar (GPR) system.  The defining characteristic of these antennas is their operating frequency.  Thehigher the antenna’s operating frequency, the smaller the antenna’s size and pulse loop, the greater the data resolution, and the shallower the depth-of-penetration.  An 80 MHz antenna is the practical minimum frequency while 2500 MHz is the practical maximum.