HOMER: Early results from a novel seabed-resident water column profiler

The HOMER deep water vertical profiler (HOMing Environmental Recorder), originally devised at the Proudman Oceanographic Laboratory, has recently been further developed and tested at the Scottish Association for Marine Science (SAMS). The HOMER system comprises a seabed resident winch which repeatedly releases and recovers a buoyant, internally-recording, 0.25m diameter spherical sensor module. The sensor sphere performs CTD (conductivity, temperature, depth) profiles of the water column from the seabed to a pre-programmed altitude. Other sensors will be added in due course, for example current meters and shear micro-structure sensors. In its present configuration the instrument is capable of a total of approximately 200 profiles to a height of 400m above the bed in water depths of up to 4000m. Deployments of up to 2 years duration are possible. Water column profiles are taken at pre-programmed time intervals, and winch control is performed through an embedded microcontroller. The pre-programmed microcontroller instructs a pair of oil filled brushless DC motors; one motor drives the main take-up spool and the other drives a capstan which controls the ascent and decent rate. Power is supplied through a bank of standard lithium D-cells. Sensor sphere and winch are connected via a non-conducting mono-filament line. An infra-red link transfers data from the sensor sphere to the sea-bed frame control sphere between profiles to minimise the risk of data loss. The entire instrument remains on the seabed between profiles, thus minimising problems associated with fishing damage and biofouling.