A new electronic system for the rectangular midwater trawl (RMT)

This paper describes a modified modern version of the original rectangular midwater trawl (RMT) manufactured by the Institute of Oceanographic Sciences (IOS). The shipboard acoustic transducer and the underwater RMT-monitor were replaced by an electronic interface box was while the data transfer, realized by a single-conductor cable. Using frequency shift keying (FSK) signal transmission, a PC-controlled system onboard handles data acquisition and control as well as real time monitoring of the haul. The volume of water filtered by the net is calculated based on the online readings of a net-angle sensor. The new RMT-system was successfully used in the Antarctic during the European Polarstern Study (EPOS) from October 1988 to March 1989. Fifty-seven tows to a maximum depth of 1000 m in open waters and in ice covered areas were performed.