awareness and to feed Naval Oceanographic Office (NAVO) databases to allow better use of the environment in mission planning.

 

Sensors that are capable of measuring turbulent water velocities have been used to carry out oceanographic measurements for decades. These sensors are typically fragile and prone to failure when operated in harsh environments or high-speed conditions for extended periods. Measurements made by these instruments have proven quite valuable for characterizing the physics of ocean turbulence. Similar measurements would enhance the capabilities of U.S. Navy platforms. Navy submarines and Unmanned Undersea Vehicles (UUV) are the primary target platforms for this type of sensor. The size, weight and power requirements are limited to the extent that the sensor is able to fit and operate on a 12 � inch UUV. Permanent installation of these types of sensors enables long- term data collection to fill a NAVO data gap. Examples of existing sensors include the Rockland Scientific shear probe, the Nobska Modular Acoustic Velocity Sensor (MAVS), the Sontek Acoustic Doppler Velocimeter (ADV), Falmouth Scientific Acoustic Current Meters, and electromagnetic (EM) velocity probes. The Rockland Scientific shear probe measures velocity shear by converting lift induced mechanical fluctuations of the probe tip into electrical signals; the acoustic sensors operate by measuring sound travel time or Doppler, while the EM sensor detects fluctuations in the local electromagnetic field.

 

Although typical oceanographic measurements for research purposes generally take place under conditions that are of low risk to the instrument, measurements made from Navy platforms in harsh conditions for extended periods are common. For example, shear probe measurements are generally taking place from a microstructure profiler, a small oceanographic platform that is allowed to freefall through the water column at low speed and under very quiet conditions over short periods (approximately minutes or hours). While measurements taken this way, or on a low- speed platform, are capable of measuring small scale velocities, on the order of 1cm, high-speed platforms introduce increased forcing on the sensor, noise levels, and length scale limitations (due to limited sampling rates). Therefore, current state-of-the-art ocean velocity sensors are generally not suited for Navy vessels.

 

The velocity sensor must be robust and sturdy enough to allow existing naval platforms to measure small-scale turbulent velocities ranging from 1cm to 100m at speeds up to at least 5kn (which equates to a bandwidth of 0.025 � 250 Hz). The software will be sensor-specific and will interface with operating systems that are prevalent on Navy computers, such as Windows and Linux. The software can be either Commercial-Off-The-Shelf (COTS) or custom. For potential software modification purposes, a common programming language, such as C++, will also be used.

The sensor must also be able to survive exposure to harsh environments that involve exposure to seawater for a minimum of 3 months while needing little to no maintenance while at sea. The sensor must also be able to withstand environmental contamination such as bio-fouling and incidental contact with deployment vessels, handling equipment, and submerged or floating oceanic debris. The sensor must be tested in conjunction with similar industry standard oceanographic velocity sensors in a controlled environment such as the tow-tank at the Naval Undersea Warfare Center Division (Newport). After successful laboratory testing, the prototype will be refined and must be tested at sea on an existing Navy platform or on a research vessel (R/V) or unmanned undersea vehicle as necessity and availability dictate. If installed on a submarine, the sensor must meet qualifications regarding electromagnetic interference and shock testing. Validation and testing will take place in a full-scale scenario in locations in which ocean turbulence at the scales of interest can be measured simultaneously with a baseline sensor such as those listed above.

 

PHASE I: Develop a concept for a velocity sensor that meets the requirements above. Demonstrate feasibility through modeling and simulation. Ensure that the concept sensor is rugged enough to withstand the conditions encountered while operating at sea on U.S. Navy platforms at high speed for a minimum of 3 months Develop a Phase II plan. The Phase I Option, if exercised, will include the initial design and capabilities description to build the sensor in Phase II.

 

PHASE II: Develop and deliver a small scale velocity turbulence sensor prototype. Evaluate the prototype based on laboratory measurements, modeling, or at-sea measurements showing that the requirements of the velocity sensor are met by comparing to industry standards for ocean velocity measurements taken by sensors such as a shear probe or MAVS. Deliver the final product to the Navy, including the velocity sensor prototype and the hardware, firmware, and software necessary to test and operate the sensor on an undersea platform. Prepare a Phase III