Survival time in cold water is measured in minutes. Heavy seas are extraordinarily good at hiding people, but that's the problem DDR was built to solve.
Differential Depolarization Response is a polarimetric LiDAR measurement that distinguishes biological targets from the surrounding ocean by their scattering asymmetry — enabling automated detection of persons in water without requiring an operator to interpret ambiguous returns.
Designed for the hardest detection problem at sea
Search and rescue crews recovering persons in water face a fundamental sensor problem: radar and thermal imaging cannot reliably distinguish a swimmer from the rough sea surface around them, and the difference between a detection and a miss can be measured in minutes.
DDR was developed to solve that specific problem, not by improving existing sensor modalities, but by measuring a physical property that ocean water does not share with biological tissue.
Ocean water depolarizes light isotropically, producing a near-zero DDR signature. Biological tissue such as skin, wetsuit, and life vest material exhibits asymmetric scattering due to its layered, anisotropic structure. Physics-based modeling predicts approximately 20:1 contrast between biological targets and the ocean background; this figure is a design target pending experimental validation in Phase I.
Three addressable markets, one measurement
FMCW Maritime LiDAR
Shipboard and airborne person-in-water detection. Design target: 3-5km range with automated classification, no trained operator required.
Learn moreFMCW Drone Detection
Autonomous aerial target discrimination. DDR asymmetry distinguishes composite drone airframes from birds and background clutter against a near-zero atmospheric background.
Learn morePulsed ToF Radar Augmentation
Polarimetric overlay for existing radar installations. Adds material classification capability to conventional apertures without hardware replacement.
Learn moreThe physics and architecture behind DDR
From photons to classification in a single pipeline
DDR processing runs on dual-wavelength coherent detection at 1550nm with FMCW ranging. Orthogonal polarization states are measured simultaneously through a shared aperture, then compared to produce the depolarization ratio asymmetry that drives classification.
Ocean water exhibits minimal depolarization (DDR ≈ 0), creating a near-zero background. Physics-based modeling predicts approximately 20:1 DDR contrast for biological targets; this is a design target pending Phase I experimental validation. The output is a scalar requiring no image interpretation by the operator.
Full signal architecture
Dual 1D silicon photonic phased arrays
The core sensor uses two orthogonal 256-element silicon photonic phased arrays operating at 1550nm. The 1D architecture provides a manufacturing yield advantage over 2D alternatives, approximately 98.5% per array versus 74% for equivalent 2D dies.
Twenty 1D dies occupy the same wafer area as one equivalent 2D die, driving production unit costs toward $600-$800 at volume versus $50,000-$200,000 for conventional 2D systems.
Hardware architecture detail
What the physics removes from the detection pipeline
The following comparisons reflect physics-based predictions for DDR-enabled sensors. No prototype has been built and no field measurements have been taken. Phase I SBIR funding is being sought to validate these predictions experimentally.
DDR performs material discrimination at the physics layer. Water's near-zero DDR is a property of the medium, not a filter applied after the fact. The ocean surface cancels itself out by measurement. This removes image reconstruction, shape analysis, and trained operator interpretation from the detection pipeline. The scalar output is the classification. The table below shows where that matters and where it does not.
| Axis | DDR | Radar | Thermal |
|---|---|---|---|
| Output type | Scalar classification flag. No image, no shape analysis, no operator interpretation required. | Track with geometry and kinematics. No material information in the return. | Image requiring operator interpretation to distinguish target from background. |
| Sea clutter rejection | Water's symmetric scattering produces near-zero DDR by physics, independent of sea state. Background cancellation is a property of the measurement, not a processing step. | Signal processing problem. Clutter rejection algorithms degrade with increasing sea state. | Thermal contrast between a swimmer and rough ocean surface is unreliable at high sea states. Cold spray and wave action reduce contrast. |
| Operator requirement | Classification is automated. The scalar output drives the detection flag directly. No trained operator required in the loop. | Trained operator required to interpret returns and make classification decisions. Operator latency is a factor in fast-moving SAR scenarios. | Trained operator required. Human judgment determines whether a return is a swimmer, debris, or imaging artifact. |
| Resolution requirement | DDR measures a material property, not a shape. A beam footprint that covers the target is sufficient. High-resolution aperture and image reconstruction are not required. | Resolution sufficient for track initiation. Geometry contributes to classification but does not fully resolve material ambiguity. | Resolution sufficient for shape analysis is required. Distinguishing a swimmer from debris requires recognizable target geometry in the image. |
| Partial submersion | Return amplitude decreases with submersion but signature character does not change. Partial submersion degrades the return but does not defeat classification. | Track continuity degrades as target geometry shrinks. Shape-based clutter rejection becomes less reliable. | Thermal contrast drops sharply as target becomes submerged. Detection becomes unreliable before target is fully submerged. |
DDR does not claim an advantage in detection range, all-weather performance, or system cost at current TRL. These comparisons are limited to axes where the underlying physics favors the DDR measurement approach.
Technology and IP portfolio
The technology page covers the DDR measurement physics, signal architecture, and hardware design in detail. The IP portfolio page lists patent filings and licensing status.