Directional, scale-resolved measurement of underwater optical turbulence using multi-beam self-heterodyne detection

We present a self-referenced, frequency-diverse beamlet architecture for characterizing underwater optical turbulence. Multiple mutually coherent, laterally separated beamlets co-propagate through turbulence and are detected on a single-pixel photodetector, generating a set of heterodyne beat tones that uniquely encode beamlet-pair separations. This intrinsic RF channelization enables simultaneous scale-resolved and directional turbulence sensing without scanning, imaging-based beam tracking, or an external local oscillator. Experiments conducted in a Rayleigh-Bénard convection tank demonstrate estimation of turbulence strength, anisotropy, and temporal dynamics across weak-to-strong fluctuation regimes, establishing the approach as a compact and scalable platform for optical turbulence measurements.