A towed geophone system for use in snow-covered terrain

A new type of drag cable has been developed, which was successfully used to collect seismic reflection data on an Antarctic ice shelf. Standard geophone elements were encapsulated in polyurethane to form 25 m long, rectangular sections. Each of the 12 sections incorporated a group of 12 geophones. The resultant towed array resembles a 300 m long flexible ski. The use of a towed cable provided substantial time and manpower savings over the use of planted geophones. In comparison with drag cables utilizing gimbal geophones, the towed array has a much lower coefficient of friction due to its smooth profile, and it is therefore possible to tow an array using snowmobiles. This provides a significant advantage because a system can be deployed by ski-equipped light aircraft to areas that are difficult or impossible to access using large vehicles. The simple construction of the towed array results in a lower cost than when gimbal cables are used. The main disadvantage is that the towed array has poorer wind-noise characteristics than gimbal cables or planted geophones. Use of the array enabled a team of four people 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.