Instrumentation

Good observations lead to a better understanding of fluid processes, and less guesswork in deciphering their physics. Instruments purchased off-the-shelf can be very useful but often limiting. We have been committed for a long time to finding ways to get more detailed and more quantitative observations of small-scale oceanic flows.

Our workhorse for the past (almost) 20 years is Chameleon. This is a vertically-profiling, freely-falling tethered instrument that is easily deployed from ship. In this photo, a ring protects the sensors at the bottom - we are preparing to crash it into the bottom on purpose. By getting measurements to the seafloor, we gain an appreciation for the frequent thinness of bottom boundary layers (10s of cm at times).

Brushes at the trailing edge break up coherent eddies and help to make Chameleon hydrodynamically quiet, essential for low-noise turbulence measurements.

New sensors are continually being tested on Chameleon's nose.

[Chameleon is described in some detail here]

Our towed body, Marlin, permits observations of turbulence in the deep ocean. We have deployed Marlin to depths of 3300 m and for periods of many days resulting in tows of 100s of km.

[description of Marlin]

One device we have developed to get faster measurements of temperature fluctuations from Marlin and Chameleon is a thermocouple. In fact, we use this to calibrate the frequency response of slower, but hardier sensors so that we can correct measured spectra.
[thermocouple paper]
A new development is , designed to measure temperature microstructure from a mooring. This instrument is attached to a mooring cable and vaned so that the 2 temperature sensors (one at the top, the other at the bottom) face into the flow. A successful test deployment at the TAO mooring at 0 140 W is encouraging. We are extending these measurements to successive equatorial deployments.

deployment tutorial movie (15MB)

Another development is actually pretty straightforward but extremely fruitful. We have taken a few Paroscientific Digiquartz 200 psi pressure sensors, sampled them ourselves, put them in pressure cases and deployed them on landers on the seafloor over the New Jersey shelf as part of the NLIWI / SW06 experiment in summer 2006. (see the white case hose-clamped to the frame at left rear?). These have resolution equivalent to sub-mm surface displacement and permit detection of nonlinear internal waves.

This relatively simple measurement provides a wealth of information about the wave field (see figure 5 in the linked paper below).

[seafloor pressure measurements of nonlinear internal waves]