The XMP is the latest addition to our toolbox of turbulence profilers. It features
- Full ocean depth capability (6000 m),
- Two shear probes, pressure sensor, accelerometer, and P25 thermistor,
- Real time data transmission via fibre optic link.
Development of the XMP began in early 2008, in response to requests from our customers who required a low-cost profiler for measurements in the bottom boundary layers in the deep ocean. After several attempts, we finally arrived at a design that satisfies two divergent requirements: High accuracy & Low cost.
Shown on the right is project engineer Brett Prairie deploying a test unit in Georgia Straight. The test, carried out in February 2009, show that the XMP can resolve dissipation rates as low as 5 x 10-10 W/kg.
The XMP consists of a 30 cm long aluminium pressure housing. Two shear probes and an SP25 thermistor protrude forward from the pressuse case. One accelerometer and a pressure transducer are contained inside, along with the electronics and alkaline batteries. The rear section of the XMP is a 100 cm long PVC extender pipe with a brush attachment to provide drag during the profiling. The extender pipe is floods with water after the launch, which increases the XMP's weight and inertia in water. Data are transmitted through an optical fibre to a ship-board laptop computer. Deck spools with up to 12,000 m of optical fibre are available.
Data from test profiles in Georgia Straight, BC, are shown below. The first profile is from a fairly energetic region. The yellow line in the spectrum panel (right) is the raw shear signal. The red line shows the spectrum of the accelerometer. The green line is the shear spectrum after signal content that is coherent with the accelerometer has been removed using our processing scripts. The solid black line is the Nasmyth Emprical Spectrum (NES) for a dissipation rate of ë ~ 2 x 10-7 W/kg. 
The panels below show the data from a quiescent region. The raw and corrected shear spectra agree well with the NES for ë = 5 x 10-10 W/kg.
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