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27 Drydock Avenue
Boston, MA  02210

Organization's Description:


Nortek AS is a scientific instrumentation company that develops and distributes water velocity instruments. Our products are based on the acoustic Doppler principle and span from single point turbulence sensors to long range current profilers. Our customers are scientists, research institutions, and consulting engineers, all with demanding applications requiring state-of-the-art instrumentation that is reliable and easy to use.

NortekUSA is an independent company formed in 1999 to provide sales, technical support, and system integration for the Nortek acoustic Doppler current meters, profilers and velocimeters used to measure currents and waves in the ocean, lake and laboratory.

The NortekUSA office is located in Boston, a center of oceanographic research, technology, and development, and provides customer support and technical services for clients in the western hemisphere, particularly the USA and Canada. It also plays a role in the development of new products, teaming with Nortek-AS. NortekUSA provides technical, scientific, administrative and sales staff in the Boston office and technical sales representatives on the East Coast, West Coast, and Gulf communities as well as in Mexico and Canada.

Nortek AD2CP mounted on Gliders

Autonomous underwater gliders offer a unique sampling platform for ocean measurements with a variety of sensors. A fundamental problem with gliders (and other autonomous underwater vehicles) is locating measurements within the water column with reasonable horizontal and vertical accuracy. Underwater positioning systems, generally based on acoustic travel time, can provide reasonable accuracy but slow update rates because of the acoustic path length. The slow update rate is problematic when dynamic environmental conditions exist such as near the surface. These systems are also unsuited to adaptive sampling strategies or the kilometers long transect lines gliders often fly.

Dead reckoning navigation is an ancient technique relying on estimates of speed and direction to propagate an initial position fix forward in time until a new position fix is obtained. Recent work between iRobot and Nortek has resulted in the integration of a next generation acoustic velocity profiler, the AD2CP-Glider, into the iRobot® 1KA Seaglider™.

The relative velocities measured by the AD2CP-Glider are used to improve dead reckoning position estimates throughout the water column and predict the location of the glider on surfacing based on an initial position fix obtained via GPS at the start of a dive cycle. Error sources, such as surface drift, are identified and corrected for when possible. Data from tests in a large lake are used to assess the validity of the dead reckoning navigation.

Depth averaged velocity estimates derived from the dead reckoned navigation are compared to estimates obtained using a hydrodynamic model to predict glider velocity. The measurement based estimates are expected to perform better in more complex flows where the interaction between the flow and glider is not captured by the hydrodynamic model.

Phone: 617 206 5750
Fax: 617 275 8955