A TOWED GEOPHONE SYSTEM FOR USE IN SNOW-COVERED TERRAIN

A new type of drag cable has been developed, which was successfully us ed to collect seismic reflection data on an Antarctic ice shelf. Stand ard geophone elements were encapsulated in polyurethane to form 25 m l ong, rectangular sections. Each of the 12 sections incorporated a grou p of 12 geophones. The resultant towed array resembles a 300 m long fl exible ski. The use of a towed cable provided substantial time and man power savings over the use of planted geophones. In comparison with dr ag cables utilizing gimbal geophones, the towed array has a much lower coefficient of friction due to its smooth profile, and it is therefor e possible to tow an array using snowmobiles. This provides a signific ant advantage because a system can be deployed by ski-equipped light a ircraft to areas that are difficult or impossible to access using larg e vehicles. The simple construction of the towed array results in a lo wer cost than when gimbal cables are used. The main disadvantage is th at the towed array has poorer wind-noise characteristics than gimbal c ables or planted geophones. Use of the array enabled a team of four pe ople to acquire 158 km of single-fold seismic re flection data on the Ronne Ice Shelf over two field seasons. The data are the first to show sub-seabed structure beneath this major ice shelf.