ETH, Switzerland

One of the earliest and most thoroughly documented land streamers was built by the Institute of Geophysics at ETH in Switzerland, as discussed in van der Veen and Green, 1998, and van der Veen et al., 2001. This land streamer is constructed using self-orienting gimbaled geophones weighted with 1 kg housings. The housings are separated by 1 m and mounted on the underside of a rubber sheet. This configuration decouples the geophones from each other, but allows them to dig a small trench to improve contact in softer soil.

The group at ETH first made a thorough comparison of the differences between traditionally planted geophones and their land streamer. This included comparisons on a variety of surface conditions: undisturbed ground, in a shallow trench, on soft soil (meadow), on hard packed gravel and on asphalt. Results were encouraging and suggest that in many conditions, coupling similar to planted geophones can be obtained by increasing the weight on each phone or by tilling a small depression in which the phones can lie.

Equally encouraging were ETH's estimates of labor reduction when using a land streamer. The Institute typically uses 5-6 people for operating a 96 channel survey: one recorder, two on the seismic source, two laying and moving cable and one running an auger for drilling shot holes if an explosive source is used. With the land streamer, they were able to reduce the crew by 30-40% and increase ground coverable by as much as 100%. Further savings could be obtained by using an impulsive or swept surface source that requires no drilling.

Comparisons between planted and unplanted geophones on the surface (left) and planted and unplanted geophones in a shallow trench

Although differences do exist between the planted and dragged geophones, the original character of the data appears well preserved. Shot records on various surfaces reveal only subtle variations. Similarly, van der Veen et al. present a plot of the differences between the land streamer and conventional sections that shows only small values.

The article also recommends that some possibilities exist for either collecting pseudo-3D data by acquiring multiple parallel lines, or even towing multiple parallel streamers for true 3-D acquisition. Although the practical logistics of towing a 3-D array on land would have to be addressed, the cost saving suggested by van der Veen et al.'s 2-D experiments suggest that 3-D land surveying for shallow targets may be practical.

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