Underwater Direction Finding Using a Single Hydrophone

By Steven Cohen
Slide 1: Title slide for Underwater Direction Finding Using a Single Hydrophone, presented by Steven Cohen and George Sklivanitis, over a faded background image of an oscilloscope-style waveform trace.

Slide-1

Underwater Direction Finding Using a Single Hydrophone

Steven Cohen, George Sklivanitis PhD.

National Science Foundation: I-SENSE REU 2026

Center for Connected Autonomy and Artificial Intelligence

FAU Department of Electrical Engineering and Computer Science

Slide 2: Traditional Towed Hydrophone Array slide listing its drawbacks, with a diagram of a ship towing three hydrophones, an illustration of a plane wave arriving at a uniform linear array, and a photo of crew handling a large hydrophone cable reel on a boat.

Slide-2

Traditional Towed Hydrophone Array

  • Size
  • Weight
  • Power consumption
  • Cost $$$

Diagram 1: A ship on the water surface tows a cable underwater connected to three hydrophones labeled "Hydrophone C", "Hydrophone B", and "Hydrophone A" (ordered from farthest to nearest the ship), with a submarine shown submerged nearby as the target being tracked.

Diagram 2: An illustration titled with an incoming plane wave signal arriving at an angle theta relative to the "Broadside / Normal direction" of a uniform linear array of 5 elements, numbered 1 through 5, evenly spaced by distance d. Dashed lines show the wavefront reaching each array element at successive time instants t, t+Δt, t+2Δt, t+3Δt, and t+4Δt, illustrating how the time delay between elements is used to estimate the angle of arrival.

Photograph: Two crew members in orange safety gear on a boat deck, winding or handling a large cable reel of hydrophone array cable, with an orange buoy marked "F.D.L." in the foreground.

Slide 3: Diagram of a 3D-printed acoustic metastructure inspired by sea-shell geometry, showing how signals from two unknown directions travel through weak direct, delayed solid, and air cavity reverb paths to reach a central hydrophone.

Slide-3

Inspired by the dynamic, spatial geometry of sea-shells, this plastic (PLA) structure gives signals a low impedance path and uses trapped air as a high impedance resistance.

Diagram description: On the left, a 3D-rendered gray cylindrical structure with an internal spiral chamber and a central hole, representing the physical acoustic metastructure design. On the right, a cross-section of the same structure shows two incoming signals arriving from unknown directions: signal "B" (red) and signal "A" (blue). Each signal travels along three labeled path types through the structure to reach the central hole: A1, a dashed line representing "Weak Direct Path"; A2, a solid line representing "Delayed Solid Path"; and A3, a dotted line representing "Air Cavity Reverb". The diagram shows both signals spiraling through the structure's chamber via these three path types before converging at the central sensor opening.

Citation: A. Bergey, N. Garg, and A. Gadre, "AMULET: Acoustic Metastructure for Direction-of-Arrival Estimation Underwater Using a Single Hydrophone," in Proc. ACM/IEEE Int. Conf. Embedded Artificial Intelligence and Sensing Systems (SenSys '26), Saint Malo, France, May 11-14, 2026, pp. 918-932, doi: 10.1145/3774906.3802750.

Slide 4: Collage of hardware photographs showing the experimental setup, including a stepper motor rig, motor driver electronics on a breadboard, a signal amplifier and DC power supply, networking equipment, and the hydrophone array with the acoustic metastructure submerged in a test tank.

Slide-4

Hardware setup collage, labeled components:

  • Stepper Motor, 3D Printed Mount, 4:1 Gear Ratio, 1 Meter Rod, 3D Printed Bracket — shown in a photo of a motorized rotating arm mechanism used to position the transducer.
  • HR4988 Motor Driver and Teensy 3.2 — shown wired together on a breadboard, powered by a 12 Volt supply (not pictured).
  • GigE Switch and N210 SDRs (software-defined radios) — shown mounted in an equipment rack.
  • VP2000 Amplifier and 120 Volt DC Supply — shown as benchtop lab equipment with connected cables and digital readouts.
  • AS-1 (RX) + Amulet and AS-1 (TX) — shown as two hydrophone transducers, one fitted with the 3D-printed acoustic metastructure ("Amulet"), suspended in a long rectangular water test tank.
Slide 5: Diagram illustrating the direction-of-arrival estimation pipeline, from the acoustic metastructure and directional signature imparted, through impulse response and multipath-resilient signature matching, to a final direction-of-arrival estimation plot.

Slide-5

Heading: The direction of arrival is estimated by matching the saved library of angles to a new signal in a custom processing pipeline.

Pipeline diagram, left to right:

  1. Acoustic Metastructure Design: a photo of the physical device with two incoming signals labeled "B" (red) and "A" (blue) arriving from different directions. An accompanying equation defines the directional signature: s superscript n degrees subscript str of t equals the inverse Fourier transform of the Fourier transform of y(t) divided by the Fourier transform of x(t) times e to the power j2πfτ.
  2. Directional Signature Imparted: a cross-section of the metastructure showing signals A and B spiraling through the internal chamber toward the center, similar to the path diagram on the previous slide.
  3. Impulse Response: a line graph plotting two overlapping noisy waveforms (red and blue) over time, representing the impulse response y(t). Two equations are shown: y(t) = x(t) * h_multipath(t) * s_str^n°(t), and a simplified version y(t) = x(t) * δ(t-τ) * s_str^n°(t).
  4. Calibrated Directional Signatures: a stacked set of small line-graph "cards", each showing a distinct signature waveform, representing a library of pre-calibrated signatures at different angles.
  5. Multipath-Resilient Signature Matching: a line graph titled with y-axis "Matching Score" (0 to 1) and x-axis "Direction-of-arrival (degree)" ranging from 0 to 360. Two curves (red for signal B, blue for signal A) are plotted, each showing a peak at a distinct angle corresponding to the true direction of that signal.
  6. Direction-of-Arrival Estimation: a polar plot with angle labels from 0° to 330° around the circle. Two irregular closed-loop shapes are plotted: a red loop with an arrow pointing toward roughly 120° labeled "B", and a blue loop with an arrow pointing toward roughly 0°/360° labeled "A", representing the estimated directions of the two signals.

Final equation: theta-hat equals the argmax over theta of the maximum over k of the absolute value of rho subscript u, s_theta, at index k.

Slide 6: Results slide reporting a 6.576 dB directional accuracy, with a heatmap comparing known versus unknown angles and a summary table of key performance metrics.

Slide-6

Results

The 6.576 dB directional accuracy shows correct angle matches are about 2.1× stronger than incorrect angle matches.

Heatmap chart: y-axis "Unknown Angles (deg)" ranging from 0 to 360; x-axis "Known Angles (deg)" ranging from 0 to 360. A color scale on the right labeled "Correlation Accuracy" runs from 0.0 (dark purple) to 1.0 (bright yellow). The heatmap shows a bright yellow diagonal band running from the bottom-left (0,0) to the top-right (360,360), indicating strong correlation when unknown and known angles match, with darker, lower-correlation values elsewhere off the diagonal.

Summary table:

Metric Value
Angular Library 400 angles at 0.9°
Direction Accuracy 6.576 dB
Mean Angular Error 2.46°
Median Angular Error 1.80°
Mean Correlation 0.905

Equation: M subscript ij equals the maximum over k of the absolute value of rho subscript u_i, s_j, at index k.

Slide 7: Future Work slide listing next research directions, alongside six 3D-rendered views of the acoustic metastructure design shown from different angles and cross-sections.

Slide-7

Future Work

  • Test other physical geometries to optimize directional sensitivity.
  • Optimize the processing pipeline for moving platforms, changing environments.
  • Experiment with variations to transmit directional underwater acoustic communications.

Image description: Six 3D-rendered gray models of candidate acoustic metastructure designs, arranged in two rows of three. The top row shows: a solid cylinder with a pattern of small holes along its side; a cutaway view revealing an internal spiral chamber with mounting clips; and a similar cutaway from a different angle. The bottom row shows: a semi-transparent rendering revealing internal components and clips; a solid cylinder with a central spiral cavity and mounting clips visible from above; and another angled view of the same spiral cavity design.

Citation: N. Garg, Y. Bai, and N. Roy, "Owlet: Enabling Spatial Information in Ubiquitous Acoustic Devices," in Proc. 19th Annu. Int. Conf. Mobile Systems, Applications, and Services (MobiSys '21), Virtual Event, Wisconsin, USA, Jun. 24-Jul. 2, 2021, pp. 255-268, doi: 10.1145/3458864.3467880.

Slide 8: Closing Thank You slide with a Questions prompt, funding acknowledgment, and NSF and Florida Atlantic University logos on a dark blue background.

Slide-8

Thank you!

Questions?

This work was supported through the NSF REU Site in Sensing and Smart Systems, funded through NSF Award CNS-2447437.

Last slide: Contains plain text stating 'End of presentation. Click the right arrow to return to beginning of slide show.'

End of Presentation

Click the right arrow to return to the beginning of the slide show.

For a downloadable version of this presentation, email: I-SENSE@FAU.