DEIMOS was designed and built using off-the-shelf components commonly used in fisheries acoustics research.
A Kongsberg Simrad ER-38DD transducer is the most visible feature of the package. When transmitting, ceramic elements inside the transducer convert electrical energy to mechanical pressure waves. Reflected energy (echoes) at the transducer face are converted from pressure waves back to electrical pulses. Typical transducers are designed to work at depths no greater than 20 meters. The transducer used in DEIMOS is oil-filled, which allows operation at depths up to 1500 meters.
The electronic components from the echosounder are typically housed in a General Purpose Transceiver, or GPT. For DEIMOS, we have modified the components to fit within a Teledyne Benthos glass sphere. A Simrad EK-60 GPT generates the electrical pulses sent to the transducer and senses electrical voltages created by reflected or backscattered pressure waves on the transducer face. GPTs are normally located above the surface of the water, within a boat or mounted on a mooring. For DEIMOS, a 17 inch, borosilicate glass sphere was used to house the echosounder and other electronics. Given the limited space within the sphere, the GPT was re-configured by arranging the electronic boards and power supply in a cross shape, rather than the typical rectangle.
The glass sphere is protected by a thick plastic shell, called a "hardhat". The hardhat can absorb small shocks and prevents direct contact to sensitive parts of the sphere, such as the bulkhead connectors and pressure valve.
The transducer and yellow hardhat are bolted to a custom-designed, galvanized steel "sled". The entire package is ballasted with lead weights to ensure the center of gravity is near the middle of the package. The transducer is negatively buoyant while the glass sphere is positively buoyant.
The instrument package is remotely controlled over an ethernet connection by a computer at the surface. The computer runs the Simrad ER-60 software, which sends commands and collects data from the GPT. The data are stored in the computer's hard drive and later sent, using a server, to our data server in Seattle.