towfish to be mounted on a frame and towed at low speeds, as described by 

 Hydromar, Incorporated (1982), and Mazel (1984). These frames can also allow 

 the fish to be moved vertically to provide better images of vertical features, 

 Finally, vertical structures are often topped by roads, providing the poten- 

 tial to deploy the towfish from a truck-mounted crane. 



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