Trawl resistant bottom mounted instrumentation: developments and results to date

This paper briefly describes the characteristics of 4 different types of bottom mounted instrumentation systems developed by the authors and associated others at WHOI. A summary of field experience obtained is presented for each as applicable. One system that included a gimbal mounted 300 kHz RD Instruments ADCP, along with a bottom pressure recording instrument was freefall deployed, twice, in 75 meters of water on Georges Bank as part of the GLOBEC Project. A larger more trawl resistant mount was developed to house a gimbaled 75 KHZ RDI ADCP. Two units of this device were delivered to the US Naval Oceanographic Office, Stennis Space Center, MS and were immediately deployed as part of an ongoing field program. A prototype trawl resistant bottom mount containing a profiling winch is undergoing testing at the time this paper is written. The winch will profile a Video Plankton recording instrument over 70 meters of the water column and is intended for deployment on Georges Bank late in 1996. The fourth design discussed is a simple inexpensive bottom frame system that records bottom pressure measurements. Two have been fabricated and one has been deployed on Georges Bank as part of the GLOBEC project.