High speed georadar data acquisition for groundwater exploration in The Netherlands

Georadar has proved to be a valuable new geophysical technique for non-destructive groundwater exploration in The Netherlands. Under favourable conditions detailed continuous images are obtained to depths of 40 m. To increase the commercial attractiveness of georadar, especially for water supply companies, a high-speed data acquisition system was devised. Sensors & Software Inc. developed a high speed pulseEKKO system and TNO designed and built a polyethylene carrier for the antennas; this carrier is trailed by the "Mule": an All Terrain Vehicle that can move at the required constant low velocities of about 2 km/hour. At this speed a fast portable field computer allows sufficient stacking at common time windows. Continuous georadar data acquisition rates are achieved 10 times higher than conventional manual measurements. The system is distance triggered by pulses produced by an electronic odometer. The carrier is flexible and multi-functional: on loose soil it is dragged, whereas on metalled and rough roads wheels are attached, bringing the antennas at adjustable levels above the ground. The antennas may be rotated 90 degrees, and thus be attuned to the expected strike of geological structures. The carrier can accommodate three antenna-frequencies: 200, 100, and 50 MHz. Prior to the design of the mobile georadar system, tests were run along a profile to examine the influence of antenna elevation and car proximity. This paper shows some of the results of the test surveys, presents the final design of the high speed data acquisition system and illustrates its performance by renewed measurements along the test line. Moreover, some remarkable results recorded by the new system are shown to demonstrate the effectiveness of the high speed georadar system.