The Department of Defense, specifically the Navy, is seeking innovative solutions for the development of a Lateral Shear and Strain Sensor designed for measuring ocean turbulence. The primary objective is to create a sensor capable of directly measuring lateral velocity gradients over spatial scales of 1-10 meters, addressing the challenges posed by anisotropic turbulence in stratified ocean environments. This technology is crucial for applications such as environmental monitoring, navigation of unmanned underwater vehicles (UUVs), and assessing the impact of offshore structures. Interested parties should note that the solicitation is set to open on January 8, 2025, with proposals due by February 5, 2025. For further details, visit the official source link at https://www.dodsbirsttr.mil/topics-app/.

## Description

Direct measurement of ocean turbulence depends on sampling of quantities at length scales where universal scaling laws hold. These measurements are typically made in the vertical over regimes that are thought to be isotropic (invariant with rotation), homogeneous (invariant in space), and stationary (invariant in time). In the stratified ocean, the assumption of isotropy breaks down when the vertical scale of turbulent overturns is suppressed by the fluid&rsquo;s stabilizing stratification. In contrast, horizontal shear is unrestrained and turbulent eddies persist. This anisotropic turbulence regime resides in between spatial scales dominated by internal gravity waves in the open ocean and the inertial subrange of isotropic turbulence [Ref 1]. It is characterized by what have been termed &lsquo;pancake&rsquo; eddies or vortical motion as turbulent vortices have a &lsquo;flattened&rsquo; aspect ratio in the vertical. Direct measurement of velocity fluctuations over this spatial range are exceedingly rare as most existing Commercial off-the-shelf (COTS) sensors offer either a fixed volume or vertical profile of velocity. The Navy seeks development of a sensor capable of direct measurement of lateral velocity gradients over spatial ranges of order 1-10 meters. The Navy is agnostic to the approach, which may be acoustic [Ref 2], optical [Ref 3], or some alternative platform [Ref 4]. Proposed designs should either sample the lateral velocity vector while resolving differences over the scale of 1 m or measure lateral shear/strain directly on scales of at least 1 meter. The sensor should be capable of 1) resolving gradients of 0.0001 1/s (implying a noise floor below this value) and 2) distinguishing lateral motions from platform tilt either through motion correction or direct sensing. While deployment via a ship is appropriate for the initial design phase, the sensor should ultimately be deployable on autonomous or moored platforms.

## Objective

Develop a sensor to advance our capability of measuring finescale (1-10 m) lateral gradients in ocean velocity for environmental sensing of anisotropic turbulence. The sensor should be capable of direct measurement of lateral gradient fields within this scale range. While deployment via a ship is appropriate for the initial design phase, the design should consider future deployments on autonomous or moored platforms.

## Phase I

Identify a design concept for a sensor along with the hardware components that can meet the stated requirements. Develop a concept for onboard and offline software processing. Develop a detailed power budget for the sensor. A detailed analysis for strengths and weaknesses of the proposed design should be included in Phase I, considerations should include resolution and range tradeoffs, endurance determined by power and storage needs, and physical footprint of the sensor. After assessment of strengths and weaknesses a final design review should be completed.

## Phase II

Develop and test a prototype system. Complete analysis of the performance of the system. Report on results. Perform multi-stage testing, allowing for redesign between tests with initial tests in a surrogate ocean environment (e.g., lake or tank) and final testing in the ocean under controlled conditions (e.g., coastal bay). Both hardware and software systems should be developed and tested during Phase II. Field testing in Phase II will constrain the parameter space under which the system is operationally capable for the Navy.

## Phase III: Dual Use Applications

Support the transition to Navy use. This technology has potential use in DoD and commercial applications that require current velocity information at small scales (1-10 m). Possible applications include monitoring of contaminants shed from wind/wave farms and other offshore structures, monitoring fluxes for marine carbon dioxide removal (mCDR) development, and navigation of UUVs.

Lateral Shear and Strain Sensor for the Ocean Environment

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